Note: Descriptions are shown in the official language in which they were submitted.
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CASTING PROCESS FOR ALUMINIUM ALLOYS
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35USC 119(e) of US
provisional patent
applications 63/110.568 filed November 6, 2020 and 63/262,448 filed October
13, 2021,
the specifications of which are hereby incorporated by reference.
TECHNICAL FIELD
[0002] The present disclosure relates to a casting process for
manufacturing an
aluminum-based alloy sheet from a molten aluminum-based alloy. More
particularly, it
relates to a casting process wherein an aluminum-based alloy strip thinner
than about 10
mm is cast and then can be rolled into an aluminum-based alloy sheet.
BACKGROUND
[0003] Some of the conventional processes for manufacturing an aluminum-based
alloy sheet for use in commercial applications, such as auto panels,
reinforcements,
beverage containers and aerospace applications, employ batch processes which
include
an extensive sequence of separate steps. Typically, a large solid aluminum-
based alloy
is cast to a thickness of up to about 50 centimeters, water-cooled to ambient
temperature,
and then stored for later use. When an aluminum-based alloy ingot is needed
for further
processing, it is first scalped to remove surface defects from the rolling
faces. Then it is
preheated to a specific temperature, requiring a ramp-up hold ramp-down cycle
of 20 to
30 hours, which is termed homogenization. The pre-heated aluminum-based alloy
ingot
is then cooled to a lower temperature for hot rolling. Several passes are
needed to reduce
the thickness of the aluminum-based alloy ingot to the required range for cold
rolling.
Additionally, an intermediate anneal is typically carried out on the coil. The
resulting
aluminum-based alloy strip is then cold-rolled to the desired gauge and coiled
to obtain
the aluminum-based alloy sheet and may be subsequently heated to an elevated
temperature (tempered) to meet a specific mechanical property such as yield
strength,
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tensile elongation, etc. To produce a heat-treatable aluminum-based alloy
sheet that will
meet specific metallurgical requirements, the aluminum-based alloy coiled
sheet may also
be subjected to a separate heat treatment stage, typically in a continuous
heat-treatment
line. This can involve unwinding the coil, solutionizing the aluminum-based
alloy sheet at
a high temperature, quenching and recoiling. The above process, from start to
finish, can
take several weeks for preparing the coil for sale, resulting in large
inventories of work in
progress and final products, in addition to scrap losses at each stage of the
batch process.
[0004] For example, an AA6XXX aluminum-based alloy sheet can be produced via a
Direct Chill casting process which includes rolling of a thick AA6XXX aluminum-
based
alloy ingot and thermo-mechanically processing the AA6XXX aluminum-based alloy
strip
obtained to produce a final AA6)0(X aluminum-based alloy sheet having the
required
gauge. A series of heat-treatment steps are also required to yield a product
in a temper
(T4) that is formable and is an age-hardenable aluminum-based alloy sheet.
Indeed, in
order to produce the desirable aluminum-based alloy sheet, a homogenizing heat
treatment step and a solutionizing heat treatment step are required.
[0005] In operation, and as shown in Prior Art Figure 1, the alum ium-
based alloy is cast
via Direct Chill casting. Water cooling is used to obtain an aluminum-based
alloy ingot
that is solidified over its entire cross-section (i.e., its entire thickness).
The obtained
aluminum-based alloy ingot is typically 2 meters wide, 0.5 meter thick, and 5
meters long.
During the course of the casting process, there is solute redistribution in
the aluminum-
based alloy ingot, which leads to both macrosegregation and microsegregation
of the
elements and intermetallics in the microstructure of the ingot. After the
casting step, the
rolling surface of the aluminum-based alloy ingot is scalped for subsequent
rolling.
However, before rolling can occur, the aluminum-based alloy ingot must be
subjected to
an homogenizing heat treatment step. The ingot is thus introduced into large
furnaces to
decrease or eliminate the microsegregation of its elements and to transform
and/or
change the morphology of some of its intermetallic phases. Typically, the
homogenizing
heat treatment step can be performed at a temperature of about 580 C, and
involves
ramp up time, hold time (typically 8 hours) and cool down time. Thus the
homogenizing
heat treatment step can basically take more than 12 hours. The heat-treated
aluminum-
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based alloy ingot is then subsequently hot-rolled, cold-rolled and coiled to a
gauge
typically in the range of between about 0.5 mm and 2 mm.
[0006] In order to end up into useful parts, the aluminum-based alloy
sheet must be
subsequently subjected to a solutionizing heat treatment step to a T4 temper,
where the
aluminum-based alloy sheet can be heated quickly to a temperature where the
main age-
hardening/strengthening phase, Mg2Si for example, can be put back into solid
solution so
it can be precipitated during the ageing process. This latest heat treatment
step further
strengthens the sheet.
[0007] During the Direct Chill casting process, Mg2Si, for example,
can be present in
the AA6xxx aluminum-based alloy in two forms. One of these two forms comprises
very
finely dispersed Mg2Si clusters. The dispersed Mg2Si clusters are responsible
for the
increased strength during ageing and can be brought back into solution via the
solutionizing heat treatment step. The other of these two forms comprises
Mg2Si
globubles formed during the DC casting operation. Such Mg2Si globubles or
particles do
not redissolve during the solutionizing heat treatment step and do not affect
strengthening
of the aluminum-based alloy sheet during the final ageing step of the process.
[0008] Because of the lengthy processing time in this flow path,
numerous attempts
have been made to shorten it by elimination of certain steps, while
maintaining the desired
properties in the finished aluminum-based alloy sheets. Moreover, because such
heat
treatment steps are energy-consuming and expensive, there is a need for an
improved
process for manufacturing an aluminum-based alloy sheet directly from the
melt, which
would be able to overcome or at least minimize some of the above-discussed
concerns.
The obtained aluminum-based alloy sheets need to have properties comparable to
those
of heat treated sheets, and the overall process needs to be performed in less
process
steps compared to conventional processes, and thus in a shorter period of
time, and
needs to involve less energy.
SUMMARY
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[0009] It is an object of the present disclosure to provide a casting
process for
manufacturing an aluminum-based alloy sheet directly from a molten aluminum-
based
alloy that overcomes or mitigates one or more disadvantages of known
manufacturing
processes, or at least provides useful alternatives.
[0010] It is another object of the present disclosure to provide a
casting process for
manufacturing an aluminum-based alloy sheet directly from a molten aluminum-
based
alloy that includes a limited number of process steps, where the aluminum-
based alloy
sheet produced has at least some properties similar to or exceeding those of
sheets
provided with conventional processes.
[0011] In accordance with a non-limitative embodiment, there is
provided a process for
manufacturing an aluminum-based alloy sheet from a molten aluminum-based
alloy. The
process comprises: continuously casting and simultaneously cooling a
substantially solid
aluminum-based alloy strip thinner than about 10 mm using a belt caster, with
a
compression force on a solidifying aluminum-based alloy strip in a range of
about 2 to
about 3000 pounds per linear inch of alloy strip width.
[0012] In an embodiment, the continuously casting and simultaneous
cooling is carried
out at a cooling rate of between about 100 K/s and about 1500 K/s.
[0013] In accordance with a further non-limitative embodiment, there
is provided a
process for manufacturing an aluminum-based alloy sheet from a molten aluminum-
based alloy. The process comprises, in a belt-cast sequence: continuously
casting and
simultaneously cooling a substantially solid aluminum-based alloy strip
thinner than about
mm and cold-rolling the substantially solid aluminum-based alloy strip,
without carrying
out a quench nor a heat treatment step following the simultaneous casting and
cooling
and prior to the cold-rolling, to obtain the aluminum-based alloy sheet.
[0014] According to another general aspect, there is provided a process for
manufacturing an aluminum-based alloy sheet from a molten aluminum-based
alloy. The
process comprises: continuously casting and simultaneously cooling an aluminum-
based
alloy strip thinner than about 10 mm using a belt caster, with a compression
force on the
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aluminum-based alloy strip, during its solidification, in a range of about 2
to about 3000
pounds per linear inch of alloy strip width to obtain the aluminum-based alloy
strip in a
substantially solid state.
[0015] According to another general aspect, there is provided a process for
manufacturing an aluminum-based alloy sheet from a molten aluminum-based
alloy. The
process comprises: in a continuous in-line sequence: continuously casting and
simultaneously cooling an aluminum-based alloy strip thinner than about 10 mm,
with a
compression force on the aluminum-based alloy strip, during its
solidification, in a range
of about 2 to about 3000 pounds per linear inch of alloy strip width to obtain
the aluminum-
based alloy strip in a substantially solid state.
[0016] The process can further comprise pulse heating the aluminum-
based alloy strip.
The pulse heating can be performed at a temperature range of about 400 C to
about
570 C and for a time period in a range of about 2 seconds to about 10 seconds.
[0017] In an embodiment, the pulse heating comprises pulse
solutionizing, and the
aluminum-based alloy is an age-hardenable aluminum-based alloy, such as a
AA6XXX
aluminum-based alloy and, more particularly, a AA6005 or AA6016 aluminum-based
alloy.
[0018] In an embodiment, the pulse heating comprises pulse annealing,
and the
aluminum-based alloy is a strain hardenable aluminum-based alloy, such as a
AA5XXX
aluminum-based alloy and, more particularly, a AA5182 or AA3104 aluminum-based
alloy.
[0019] According to a general aspect, there is provided a process for
manufacturing an
aluminum-based alloy sheet from a molten aluminum-based alloy. The process
comprises: continuously casting and simultaneously cooling an aluminum-based
alloy
strip thinner than about 10 mm by feeding a belt caster with the molten
aluminum-based
alloy, with a compression force on the aluminum-based alloy strip, during its
solidification,
in a range of about 2 to about 3000 pounds per linear inch of alloy strip
width to obtain
the aluminum-based alloy strip in a substantially solid state.
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[0020] According to another general aspect, there is provided a process for
manufacturing
an aluminum-based alloy sheet from a molten aluminum-based alloy. The process
comprises: in a continuous in-line sequence: continuously casting and
simultaneously
cooling the molten aluminum-based alloy to obtain an aluminum-based alloy
strip thinner
than about 10 mm, while applying a compression force on the aluminum-based
alloy strip,
during its solidification, in a range of about 2 to about 3000 pounds per
linear inch of alloy
strip width to obtain the aluminum-based alloy strip in a substantially solid
state.
[0021] The process can further comprise rolling the substantially solid
aluminum-based
alloy strip following the simultaneous casting and cooling to obtain the
aluminum-based
alloy sheet. For instance, the rolling can be cold-rolling, which can be
performed at a
temperature in a range of about room temperature to about 150 C and, in some
embodiments, at a temperature range of about room temperature to about 100 C.
[0022] In an embodiment, the compression force applied on the solidifying
aluminum-
based alloy strip ranges between about 10 to about 150 pounds per linear inch
of alloy
strip width. In another embodiment, the compression force applied on the
solidifying
aluminum-based alloy strip ranges between about 2 to about 100 pounds per
linear inch
of alloy strip width. In still another embodiment, the compression force
applied on the
solidifying aluminum-based alloy strip ranges between about 10 to about 100
pounds per
linear inch of alloy strip width. In a further embodiment, the compression
force applied on
the solidifying aluminum-based alloy strip ranges between about 10 to about 60
pounds
per linear inch of alloy strip width.
[0023] In an embodiment, the simultaneous casting and cooling is carried out
with a belt
caster.
[0024] In an embodiment, the process further comprises quenching the
substantially solid
aluminum-based alloy strip following the simultaneous casting and cooling and
prior to
the rolling. The process can be free of heat treatment step following the
simultaneous
casting and cooling and prior to the rolling.
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[0025] In an embodiment, the process is free of quenching and heat treatment
steps
following the simultaneous casting and cooling and prior to the rolling, to
obtain the
aluminum-based alloy sheet.
[0026] In an embodiment, the process further comprises quenching the aluminum-
based
alloy sheet following the rolling. The process can further comprise
artificially ageing the
aluminum-based alloy sheet following the quench.
[0027] In an embodiment, the process further comprises artificially ageing the
alum inum-
based alloy sheet following the rolling.
[0028] In an embodiment, the simultaneously cooling is performed at a cooling
rate of
between about 100 K/s and about 1500 K/s.
[0029] In an embodiment, the process further comprises coiling the aluminum-
based alloy
strip following the simultaneously casting and cooling and uncoiling the
coiled alum inum-
based alloy strip before rolling the aluminum-based alloy strip.
[0030] In an embodiment, the aluminum-based alloy is an age-hardenable
aluminum-
based alloy.
[0031] In an embodiment, the aluminum-based alloy is a AA2XXX aluminum-based
alloy,
a AA4)((X aluminum-based alloy, a AA5X)0( aluminum-based alloy, a AA6)0(X
aluminum-based alloy, or a AA7)00( aluminum-based alloy. For instance, it can
be a
AA6005 aluminum-based alloy, a AA6016 aluminum-based alloy, a AA5182 aluminum-
based alloy, a AlMgSi-based alloy, and the like.
[0032] In an embodiment, the aluminum-based alloy is a AA5XXX aluminum-based
alloy,
the process further comprising heat treating the aluminum-based alloy sheet.
For
instance, the heat treatment can comprise annealing the aluminum-based alloy
sheet.
[0033] In an embodiment, the substantially solid aluminum-based alloy strip
has an as-
cast gauge, and the aluminum-based alloy sheet has an as-rolled gauge being
smaller
than the as-cast gauge, the rolling is performed in continuous in-line
sequence with the
casting and simultaneously cooling and wherein the as-rolled gauge is obtained
in a time
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interval of between about 1 second and about 15 seconds following the
continuously
casting and simultaneous cooling. The as-cast gauge can be between about 2 mm
and
about 5 mm. The as-rolled gauge can be between about 0.15 mm and about 4 mm.
[0034] In an embodiment, the obtained aluminum-based alloy sheet meets
metallurgical
requirements for use in transport applications. In an embodiment, the aluminum-
based
alloy is an AA6016 aluminum-based alloy, and wherein the obtained aluminum-
based
alloy sheet has a Yield Strength (YS) of above or equal to about 260 MPa
and/or an
Ultimate Tensile Strength (UTS) above or equal to about 270 MPa and/or an
elongation
of above or equal to about 6%.
[0035] In an embodiment, the obtained aluminum-based alloy sheet meets
metallurgical
requirements for use in beverage container applications. In an embodiment, the
aluminum-based alloy is an AA5182 aluminum-based alloy, and wherein the
obtained
aluminum-based alloy sheet has an Ultimate Tensile Strength (UTS) above or
equal to
about 440 and/or an elongation above or equal to about 2%.
[0036] In an embodiment, the aluminum-based alloy is a AA6X)0( aluminum-based
alloy
and the metallurgical requirements comprise properties of a T4. In an
embodiment, the
obtained aluminum-based alloy sheet has a Yield Strength (YS) above or equal
to about
300 MPa and/or an Ultimate Tensile Strength (UTS) above or equal to about 310
and/or
an elongation above or equal to about 4%.
[0037] In an embodiment, the aluminum-based alloy is a AA6X)0( aluminum-based
alloy
and the metallurgical requirements comprise properties of an at least
partially solutionized
aluminum-based alloy sheet.
[0038] In an embodiment, the aluminum-based alloy is a AA6014 aluminum-based
alloy,
and wherein the obtained aluminum-based alloy sheet has at least one of a
Yield Strength
(YS) above or equal to about 290 MPa, an Ultimate Tensile Strength (UTS) above
or
equal to about 300, and an elongation above or equal to about 5%.
[0039] In an embodiment, at least about 80 wt% of the substantially solid
aluminum-based
alloy strip is in a solid state following the simultaneous casting and
cooling.
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[0040] In an embodiment, the compression force is between about 2 to about 150
pounds
per linear inch of alloy strip width. In another embodiment, the compression
force is
between about 10 to about 100 pounds per linear inch of alloy strip width.
[0041] In an embodiment, the process further comprises pulse heating the
aluminum-
based alloy strip. Pulse heating can be performed at a temperature range of
about 400
C to about 570 C. Pulse heating can be performed for a time period in a range
of about
2 seconds to about 10 seconds and, in some embodiments, for a time period of
about 5
seconds.
[0042] In an embodiment, pulse heating comprises pulse solutionizing, and the
aluminum-
based alloy is an age-hardenable aluminum-based alloy, such as a AA6XXX
aluminum-
based alloy (e.g. AA6005 or AA6016).
[0043] In an embodiment, pulse heating comprises pulse annealing, and the
aluminum-
based alloy is a strain hardenable aluminum-based alloy, such as a AA5)0(X
alum inum-
based alloy (e.g. AA5182 or AA3104).
[0044] According to another general aspect, there is provided an aluminum-
based alloy
sheet manufactured using the process as described above, having a yield
strength of
between about 200 MPa and about 500 MPa and/or an ultimate tensile strength of
between about 220 MPa and about 520 Mpa and/or an elongation of between about
1 %
and about 12%.
[0045] According to still another general aspect, there is provided an
aluminum-based
alloy sheet manufactured using the process as described above.
[0046] According to a further general aspect, there is provided the use of the
aluminum-
based alloy sheet as described above, for automobile panels, vehicle panels,
reinforcements, beverage containers, or aerospace applications.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0047] Other objects, advantages and features will become more apparent upon
reading the following non-restrictive description of embodiments thereof,
given for the
purpose of exemplification only, with reference to the accompanying drawings
in which:
[0048] Figure 1 shows a flowsheet of a conventional Direct Chill
process for
manufacturing a T4/T4P AA6XXX aluminum-based alloy sheet from a AA6XXX
aluminum-based alloy (Prior Art).
[0049] Figure 2 shows a flowsheet of a process for manufacturing an aluminum-
based
alloy sheet from a molten aluminum-based alloy in accordance with a non-
limitative
embodiment.
[0050] Figure 3 shows a flowsheet of two processes for manufacturing
an aluminum-
based alloy sheet from a molten aluminum-based alloy in accordance with two
non-
lim itative embodiments.
[0051] Figure 4 shows a flowsheet of a process for manufacturing an
aluminum-based
alloy sheet from a molten aluminum-based alloy in accordance with another non-
limitative
embodiment.
[0052] Figure 5 shows an optical micrograph of a cross section of an AA6005
AlMgSi
alloy strip, which is as-cast and etched with 0.5% HF at the indicated
magnification level.
[0053] Figure 6 shows an optical micrograph of a cross section of an AA6005
AlMgSi
alloy strip having a thickness of 2mm, which is as-cast and etched with a
modified
Barker's Reagent that includes boric acid, to show uniformity of cross-section
grain size
at the indicated magnification level.
[0054] Figure 7 shows an optical micrograph showing microstructure at
a surface of an
AA6005 AlMgSi alloy strip having a thickness of 2mm, which is as-cast and
etched with
0.5% HF at the indicated magnification level.
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[0055] Figure 8 shows an optical micrograph showing microstructure at
the centreline
region of an AA6005 AlMgSi alloy strip having a thickness of 2mm, which is as-
cast and
etched with 0.5% HF at the indicated magnification level.
[0056] Figure 9 shows a plot of Ultimate Tensile Strength (UTS in
MPa) vs. a ratio of
Ultimate Tensile Strength to Yield Strength (UTS/YS, which is unitless or
MPa/MPa) for
6 thin strip cast samples of AA6005 aluminum-based alloys.
[0057] Figure 10 shows a plot of Yield Strength (YS) vs. a ratio of
Ultimate Tensile
Strength to Yield Strength (UTS/YS) for 7 thin strip cast samples of AA6005
alum inum-
based alloys.
[0058] Figure 11 shows a plot of Ultimate Tensile Strength (UTS in
MPa) vs. a ratio of
Ultimate Tensile Strength to Yield Strength (UTS/YS) for T4 conditions (T4
referring to
temper, which means the samples have been solutionized and quenched) for 5
thin strip
cast samples of AA6005 aluminum-based alloys.
[0059] Figure 12 shows a plot of Ultimate Tensile Strength (UTS in
MPa) vs. a ratio of
Ultimate Tensile Strength to Yield Strength (UTS/YS) for samples that
underwent ageing.
[0060] Figures 13A to 13D show plots of Ultimate tensile strength
(UTS in MPa) and
yield strength (YS in MPa), on the left Y axis, and Elongation (E in
percentage), on the
right Y axis, vs. elapsed time, in days, for as-cast AA6016 strips at the
following casting
and quenching conditions: 3mm T4P (Figure 13A), 3mm water (Figure 13B), 3 mm
air
(Figure 13C), and 2 mm water (Figure 13D).
[0061] Figures 14A to 14C are optical micrographs of cross sections
of an AA6005
AlMgSi alloy strip having a thickness of 1 mm, which was cast by energy
efficient belt
casting (EEBC), and etched with a modified Barker's Reagent that includes
boric acid, to
show uniformity of cross-section grain size at the indicated magnification
level. In Figure
14A, the AA6005 AlMgSi alloy strip underwent pulse solutionizing at 500 C for
5 seconds.
In Figure 14B, the AA6005 AlMgSi alloy strip underwent pulse solutionizing at
560 C for
seconds. In Figure 14C, the AA6005 AlMgSi alloy strip underwent conventional
solutionizing at 560 C for 60 seconds.
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[0062] Figures 15A and 15B are optical micrographs of cross sections
of an AA5182
AlMg alloy strip having a thickness of 1 mm, which was cast by EEBC, and
etched with a
modified Barkers Reagent that includes boric acid, to show uniformity of cross-
section
grain size at the indicated magnification level. In Figure 15A, the AA5182
AlMg alloy strip
underwent pulse annealing at 510 C for 10 seconds. In Figure 15B, the AA5182
AlMg
alloy strip underwent batch annealing at 380 C for 2 hours.
[0063] DETAILED DESCRIPTION OF EMBODIMENTS
[0064] Definitions
[0065] As used herein, the term "homogenizing heat treatment step"
refers to a
temperature ramp up time (typically with temperature ramp rate of 20 to 100 C
per hour.
In some non-limitative implementations, the ramp up time can be around 12
hours), and
hold time (typically between about 4 to about 12 hours and, in some
implementations,
around 8 hours) at an alloy temperature ranging between about 450 C and about
600 C
(in some implementations around about 560 C). In some non-limitative
implementations,
rolling can be performed directing after homogenization for solid diffusion.
In other non-
limitative implementations, the homogenization is followed by a cool down
time, which
can be, for instance and without being limitative around about 12 hours.
[0066] As used herein, the term "pulse annealing" of an aluminum
alloy sheet refers to
heating time (typically 3 to 10 seconds) at an alloy temperature ranging
between about
450 C and about 600 C and, in some embodiments, between about 500 C and about
560 C (in some implementations around about 510 C), and quickly cool down. In
some
implementations, the temperature cool down rate can range from about 20 to
about
100 C per hour. In some non-limitative implementations, the cooled down time
can be
around about 60 seconds. When referring to pulse annealing, the primary goal
is to
recrystallize the aluminum alloy sheet to achieve a good balance of strength
and ductility,
and not to solution ize.
[0067] When referring to "solutionizing" for a AA6XXX aluminum-based
alloy, the
primary goal is to solutionize Mg2Si to enable later precipitation to affect
age-hardening
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and thereby strength properties. However, it is appreciated that for other
aluminum-based
alloys, the phase to solutionize can differ. For instance, for AA7)0(X
aluminum-based
alloy and AA2)00( aluminum-based alloy, MnZn and Al2Cu phases are to be
solutionized.
As used herein, the term "pulse solutionizing" refers to heating time
(typically about 3 to
about 10 seconds) at an alloy temperature ranging between about 500 C and
about
570 C and, in some implementations, around about 560 C, i.e. a temperature
generally
higher than those used for annealing, and is cold water quenched for immediate
cool
down. As used herein, the term "conventional solutionizing" refers to a
heating time
between about 30 seconds to about 90 seconds (typically around 60 seconds) at
about
560 C, and is cold water quenched for immediate cool down.
[0068] As used herein, the term "batch annealing" refers to a temperature ramp
up time
for at least 6 hours and, sometimes, for more than 12 hours (typically around
about 10 to
about 12 hours), hold time for about 2 hours to about 8 hours (typically
around 4 hours)
at a temperature ranging between about 300 C to about 450 C (typical around
380 C),
and cool down time that typically totals between about 8 hours to about 20
hours (typically
around 12 hours).
[0069] As used herein, the term "paint bake" refers to an artificial
aging process having
a heating time (typically about 30 minutes to about 60 minutes), at an alloy
temperature
ranging between about 170 C and about 190 C. The goal of aging, or
artificially aging, a
AA6)00( aluminum-based alloy sheet is to precipitate Mg2Si to affect strength
properties.
However, as mentioned above, it is appreciated that for other aluminum-based
alloys, the
phase to precipitate can differ. For instance, for AA7)00( aluminum-based
alloy and
AA2)00( aluminum-based alloy, MnZn and Al2Cu phases are to be precipitated.
[0070] As used herein, the term "P" seen in terms "T6P" and "T4P", refers to a
pre-
aging process having a heating time (typically for about 6 to 12 hours and, in
some non-
limitative implementations, around 8 hours), at an alloy temperature of about
75 C to
about 85 C. The goal of pre-aging an aluminum alloy sheet is to stabilize the
microstructure to prevent brittleness caused by natural aging.
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[0071] As used herein, the term "T4" seen in the term "T4P" refers to
a solutionized
sheet product.
[0072] As used herein, the term "T6" seen in the term "T6P" refers to
an artificially aged
sheet product.
[0073] Embodiments
[0074] A continuous belt-casting process for manufacturing an aluminum-based
alloy
sheet directly from a molten aluminum-based alloy is described. In a
continuous
sequence, and directly from the molten aluminum-based alloy, a substantially
solid and
substantially thin aluminum-based alloy strip is continuously cast and
simultaneously
cooled. The cast and cooled aluminum-based alloy strip has a thickness smaller
than
about 10 mm. It also has a microstructure mostly characterized by equi-axed
grains.
During the simultaneous casting and cooling operation, a compression force (or
rolling
force), which is in a range of about 2 to about 3000 pounds per linear inch of
strip width,
can be applied to a solidifying solid aluminum-based alloy strip following
casting of the
melt and while the alloy strip is being cooled and thereby during its
solidification. The
substantially solid aluminum-based alloy strip can then rapidly be rolled and,
more
particularly, cold-rolled, so as to obtain the aluminum-based alloy sheet.
Indeed, in one
implementation of the process, no additional or intermediate heat treatment
step needs
to be carried out between the simultaneous casting and cooling step, and the
following
cold-rolling step. This continuous casting process is referred to herein as
"energy efficient
belt casting (EEBC)".
[0075] In one scenario, the cooling can be performed at a cooling
rate of between about
100 K/s and about 1500 K/s. In one implementation, the rolling, following the
simultaneous casting and cooling, is cold-rolling which can be performed at an
alloy
temperature (or strip temperature) between room temperature and 250 C. In one
embodiment, cold rolling is performed at a strip temperature lower than about
150 C and,
in some implementations, at a temperature lower than about 80 C. The rolling,
which can
be cold-rolling, can thus be conducted substantially rapidly, in a continuous
and in-line
process, after the simultaneous casting and cooling operation. In an
alternative
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embodiment, the aluminum-based alloy strip can be coiled following the
casting/cooling
step and, eventually, uncoiled to be rolled. Optionally, the produced aluminum-
based
alloy sheet can subsequently be heat treated, annealed for example, to obtain
a final
sheet that meets the requirements of a conventional and at least partially
solutionized
aluminum-based alloy, such as and without being limitative the T4 or the T4P
requirements, without compulsorily carrying out a heat treatment between the
casting/cooling step and the rolling step. In some implementations, no
solutionizing heat
treatment is carried out on the rolled aluminum-based alloy sheet.
[0076] As mentioned above, a compression force is applied on the solid
aluminum-
based alloy strip while it solidifies as it is cooled during the
casting/cooling step.
Compression force is also referred to as "separating force" or "rolling
force", i.e. the load
between the top and bottom belts as the wedge of material solidifies. The
compression
force is applied on the alloy strip from the moment it includes a solid shell
containing
molten alloy until the strip exits the caster in a substantially solid state.
During the EEBC
casting/cooling process, the thickness of the solid shell increases as the
alloy constituting
the strip solidifies. In some embodiments, the alloy strip exiting the caster
is at least 80
wt% solid and, in some embodiments, at least 90 wt%.
[0077] As mentioned above, the compression force results from the load between
the
top and bottom belts as the wedge of material solidifies. It can be measured
using
standard load cells (for instance and without being limitative four load
cells), located
between the top & bottom carriages, i.e. the structure including the pulleys
around which
the casting belts revolve. The compression force can be monitored and can be
controlled
by adjusting the speed of the belt caster. For instance, if increasing
compression forces
(or loads) are monitored, the belt caster speed can be increased to lower the
compression
force applied on the solid aluminum-based alloy strip while it solidifies. The
measured
compression force can be an indirect measurement of the aluminum state (how
much
solid the aluminum is) in the caster mold. More particularly, higher
compression forces
can indicate a more solid aluminum in the caster mold.
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[0078] As described in more details below, even though the process described
herein
includes a limited number of process steps, more particularly between the
simultaneous
casting and cooling step and the rolling step, the aluminum-based alloy sheet
produced
has at least some mechanical properties similar to, or exceeding, those of
aluminum-
based alloy sheets obtained with conventional processes that include
additional heat
treatment steps, such as an homogenizing heat treatment step, between the
casting step
and the cold-rolling step. Indeed, an aluminum-based alloy sheet which meets
metallurgical requirements for use in a variety of applications, including
applications in
the transport industry, the beverage container industry, etc. can be
manufactured. The
aluminum-based alloy sheet having the desired mechanical properties can thus
be
manufactured directly from the melt, and in a more efficient manner (without
additional
heat treatment steps).
[0079] The EEBC process described below thus obviates the need for many of the
process steps that are absolutely needed in a conventional process, with a
reduction in
at least one of processing complexity, material handling and cost. As
mentioned above,
this can be achieved by simultaneously casting and cooling the molten aluminum-
based
alloy to produce the substantially solid and substantially thin aluminum-based
alloy strip,
and by directly and sufficiently quickly or subsequently rolling the
substantially solid and
substantially thin aluminum-based alloy strip to produce the aluminum-based
alloy sheet
so the strengthening phase can be effectively retained in solution. It is
further noted that
the present process allows the as-cast substantially solid aluminum-based
alloy strip to
sustain a relatively important amount of cold reduction (e.g., 90 % or less
and, in some
implementations, 75% or less) to yield a final aluminum-based alloy sheet of
the required
thickness (e.g., 0.2 to 4 mm and, in some implementations, 0.5 to 4mm), as
described
below.
[0080] The EEBC process described herein can thus allow, where the aluminum-
based
alloy is a AA6XXX aluminum-based alloy for example, for the manufacturing of a
AA6XXX
aluminum-based alloy sheet that has at least some of the mechanical properties
of an at
least partially solutionized AA6XXX aluminum-based alloy sheet (i.e., of an
AA6016-T4
sheet), even though no solutionizing heat treating step has been performed on
the
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substantially solid aluminum-based alloy strip after it has been cast, and
before it is cold-
rolled. To achieve this temper using a conventional process, the aluminum-
based alloy
strip is homogenization heat-treated or solution heat-treated following the
casting
operation and the cold-rolling operation, followed by naturally ageing.
According to the
process described herein, the substantially solid AA6)00( aluminum-based alloy
strip can
instead be aged, directly from the melt, and without the need of an additional
or
intermediate heat treatment step, such as an additional solutionizing heat
treatment step
following the rolling step, which can be a cold-rolling step.
[0081] In the present description, the aluminum-based alloy that is
cast can be either
strain-hardenable or age-hardenable and can include, for example, a AA2XXX
aluminum-
based alloy, a AA4)00( aluminum-based alloy, a AA5X)0( aluminum-based alloy, a
AA6)0(X aluminum-based alloy or a AA7X)0( aluminum-based alloy. For instance,
and
without being limitative, the AA2X)0( aluminum-based alloy can include a
AA2008
aluminum-based alloy, the AA5)0(X aluminum-based alloy can include a AA5182
aluminum-based alloy or a AA5754 aluminum-based alloy, the AA6)00( aluminum-
based
alloy can include a AA6005 aluminum-based alloy, a AA6016 aluminum-based
alloy, a
AA6022 or a AA6011 aluminum-based alloy, and the AA7X)0( aluminum-based alloy
can
include a AA7075 aluminum-based alloy.
[0082] The EEBC process is applicable also to new and non-
conventional alloys as it
has a wide operating window both with respect to belt casting and subsequent
rolling,
which can be performed in an in-line processing. In one implementation of the
process,
the aluminum-based alloy to be cast can be an aluminum-based Si-containing
alloy and,
more particularly, an aluminum-based MgSi-containing alloy (i.e., a AlMgSi-
based alloy).
It is noted that other age-hardenable aluminum-based alloy can be used to
produce the
aluminum-based alloy sheet. In other words, the process can involve any
aluminum-
based alloy that requires age hardening, allowing the resulting sheet product
to meet the
metallurgical requirements for use in the transport industry (e.g., automotive
sheets,
aerospace sheets, etc.), the beverage container industry, etc., or to meet the
metallurgical
requirements for manufacturing any other product that involves age-hardenable
aluminum-based alloy sheets.
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[0083] As used herein, the term "solution heat treatment" or
"solutionizing heat
treatment" refers to a metallurgical process in which the aluminum-based alloy
is held at
a high temperature so as to cause the second phase particles of the alloying
elements to
dissolve into solid solution. Temperatures used in solution heat treatment are
generally
higher than those used in annealing, and range up to about 570 C and in some
implementations between about 500 C and about 570 C. This condition is then
maintained by quenching of the metal for the purpose of strengthening the
final product
by controlled precipitation (ageing).
[0084] As also used herein, the term "substantially solid aluminum-
based strip" refers
to the aluminum-based alloy in the substantially thin strip form. The
substantially solid
aluminum-based strip of the present disclosure can be produced by any number
of
apparatus for continuously casting a substantially solid and substantially
thin aluminum-
based alloy strip from a molten aluminum-based alloy, that are well known to
those skilled
in the art. One apparatus for forming the substantially solid and
substantially thin
aluminum-based alloy strip is described in U.S. Patent Publication No.
2018/0290204
assigned to Hazelett Strip Casting Corp, which is incorporated by reference
herein. For
example, the continuously-cast aluminum-based alloy strip can have a thickness
smaller
than 10 mm and, in some embodiments, the continuously-cast aluminum-based
alloy strip
can range from about 2 to about 5 mm in thickness. It is also noted that at
least 80 wt%
of the substantially solid aluminum-based alloy strip can be in a solid state
just
downstream of the simultaneous casting and cooling step. In some
implementations, at
least 95 wt% of the aluminum-based alloy strip is in the solid state just
downstream of the
simultaneous casting and cooling step. The substantially solid aluminum-based
strip can
be produced using a belt caster (such as a twin-belt caster) or alternatively,
a roll caster.
In one scenario, the caster is operated with a compression force in a range of
about 2 to
about 3000 pounds per linear inch of strip width applied to a continuously
cast alloy strip
while it solidifies so that the produced strip can have a microstructure
comprised of equi-
axed grains, as described below. In some implementations, the compression
force is
higher than about 2 pounds per linear inch of strip width and lower than about
1000
pounds per linear inch of strip width. In some embodiments, it is lower than
about 500
pounds per linear inch of strip width, in some embodiments, lower than about
150 pounds
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per linear inch of strip width and, in still other embodiments, less than
about 100 pounds
per linear inch of strip width. In other embodiments, the compression force is
between
about 2 to about 100 pounds per linear inch of strip width. In still other
embodiments, the
compression force is between about 10 to about 100 pounds per linear inch of
strip width
and, in further embodiments, the compression force is between about 10 to
about 60
pounds per linear inch of strip width.
[0085] When the simultaneous casting and cooling process is performed with a
belt
caster, molten metal is injected between two counter-rotating belts, i.e.
between an upper
belt and a lower belt. More particularly, the molten metal is injected thru a
rigid refractory
(nonreactive to the melt) injector (also referred to as a 'nosepiece' or
'snout') into the
parallel and straight section between the belts as a means of delivering
liquid metal to the
externally cooled belt surfaces. The parallel and straight section between the
two belts
defines a mold for the metal solidification. The belts are wrapped around two
pulleys and
supported by back up rolls in the straight section on the back side of the
belts, as
illustrated in Figure 1 of US patent application no. 2018/0290204, which is
incorporated
herein by reference.
[0086] In conventional belt-casting, the molten metal first contacts
the belt past a pulley
tangent point where the belt is not yet supported by back up rolls. The
unsupported belt
is thus subject to thermal shock from molten metal and a belt take-off. Belt
take-off refers
to the natural tendency of a tensioned belt to come away from its radiused or
planar guide
surface when subject to a bending moment. It has been observed that such
conditions
make the belt very unstable where the initial solidification occurs, as
illustrated in Figure
2 of US patent application no. 2018/0290204. Thus, the compression force
applied by
the belts on the molten and solidifying metal is minimal since the molten
metal solidifies
at the same thickness as the mold opening defined by the gap between two
parallel belts.
[0087] It has been observed that, molten metal can be fed on the
curved region of the
belt, upstream of the beginning of the parallel and straight section, as
illustrated in Figure
3 of US patent application no. 2018/0290204. As shown, the belts are supported
by
curved mold support sections where molten metal first meets the belt. As
detailed in the
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description of US patent application no. 2018/0290204, the large radius
portion of the
mold defined by the belt supports eliminates or significantly reduces the
possibility of belt
take-off at the tangent of the comparatively small, fixed radius nip roll
where the belt
transitions from a curved to planar path. As a result, the mold entry region
becomes very
stable, allowing casting thinner strips.
[0088] Since the molten metal first contacts the belt in the curved
region where the
belts are converging, a strip thickness can be larger than a spacing height in
the parallel
and straight section (also referred to as mold opening). Once entering the
parallel and
straight section, the belts exert a compression force on the alloy strip 18
while it solidifies.
It has been observed that even a small compression force (about 2 pounds per
linear inch
of strip) would be conducive to the extended contact between belts and metal
strip and
benefit solidification.
[0089] Depending on the metal feeding point (feeding nozzle setback)
and speed of
casting, the compression force can vary significantly. For example, if the
molten metal is
fed very close to the beginning of the parallel section in the mold and the
belts travel at a
high speed, the metal strip could be not fully solidified when entering the
nip (the smallest
clearance in the mold), therefore the rolling force could be very small.
[0090] The term "homogenization" or "homogenization heat treatment
step" is also
used herein. Homogenization of an alloy is done to provide sufficient time at
a specific
temperature for the microsegregation, which occurs during the Direct Chill
casting step,
to be "leveled" by diffusion of elements within the microstructure. That is,
during the
solidification process alloys that contain appreciable solute microsegregation
(termed
'coring') occurs across the dendrite/cells. In conventional processing, unless
homogenized, such materials cannot be successfully rolled without fracturing
in the rolling
mill due to the extent of coring. This behaviour is known to happen in alloy
families such
as AA2XXX, AA4XXX, AA5XXX, AA6XXX and AA7XXX. By providing sufficient time at
a
specific temperature for the nonequilibrium solute levels in the cast ingot to
level, the
material can subsequently be rolled without cracking. For aluminum alloys in
conventional
processsing, homogenization is typically performed in the range of about 450 C
to about
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600 C, a range of temperature over which other metallurgical processes may
also
simultaneously occur, via recrystallization, solutionizing, intermetallic
phase
transformation, etc.
[0091] As also used herein, the term "anneal" refers to a heating
process that causes
recrystallization of the metal to occur, producing uniform formability and
assisting in
earing control. Typical temperatures used in annealing aluminum alloys range
from about
315 to 490 C for longer than a few minutes. The annealing heat treatment step
is used to
reduce or remove residual stresses in the alloy, by reducing its stored
energy, without
significantly lowering its tensile strength. In aluminum metallurgy, the
annealing heat
treatment can be comprised of three steps, namely, recovery, recrystallization
and grain
growth. Reducing the stored energy has the effect of eliminating atomic level
defects,
primarily dislocations, due to atomic level lattice mismatch, in the alloy.
During the early
stages of annealing, the alloy experiences recovery, at temperatures up to
about 300 C,
and, thereafter, recrystallization. Depending upon the alloy composition, it
is possible to
transform insoluble intermetallic species and to age the alloy during
annealing.
[0092] Recovery is the metallurgical process of reducing the stored
energy by the
elimination or reduction of defects in the crystal lattice and precedes
recrystallization.
Often, there is only a very slight decrease in the strength of the material
from a recovery
heat treatment. Recovery heat treatments are performed below about 300 C.
[0093] On the other hand, recrystallization is a metallurgical
process wherein a worked
material, when heated above its recovery temperature, forms domains (i.e.,
grains) of
atoms that have, within them, a similar atomic lattice orientation. The
formation of grains
leads to a large decrease in tensile strength of the material. For aluminum
alloys,
recrystallization commences around about 300 C for most alloys.
[0094] Finally, grain growth occurs subsequent to the
recrystallization process at
temperatures above about 300 C and involves the growth of larger, more
energetically
favoured crystallographic orientations, at the expense of smaller higher
energy grains.
The tensile strength of aluminum decreases with increased grain size.
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[0095] It is also noted that age hardening is a metallurgical process
wherein an alloy
with a supersaturated solid solution can be suitably heat treated to form
stable
precipitates in a solid that are of the correct size and distribution to
impede and/or pin
dislocation movement, which is required for plastic deformation. Alloy systems
such as
AA2XXX, AA6XXX and AA7XXX systems rely on age hardening for a significant
proportion of their high strength performance. Age hardening is a particularly
potent
means of strengthening aluminum alloys.
[0096] It is further noted that aluminum has limited solid solubility
with most other
alloying elements. Notable exceptions are with Mg (AA5XXX) and Li (AA8XXX)
alloys.
Solid solution strengthening relies on atoms with sizes similar to that of
aluminum being
substantially positioned in the crystal lattice. The presence of slightly "off-
size" atoms
impedes the movement of dislocations during deformation and strengthens the
material.
Solid solution strengthening typically only provides a modest increase to the
yield/ultimate
tensile strength of aluminum alloys. However, it has a large effect upon the
work
hardening rate. Indeed, when aluminum is plastically deformed, it generates
dislocations
that increases aluminum resistance to further deformation. The presence of
more
substitutional atoms in the crystal lattice (e.g., Mg and Li) increases the
rate of dislocation
generation (i.e., the tensile strength) of the alloy at a higher rate than for
solute that is not
substitutional in the crystal lattice. The rate of strength increases with
increasing
deformation (strain) is referred to as its work hardening rate.
[0097] Typically, the grain structure obtained following the
casting/cooling step is a
grain structure consistent with two opposing solidification fronts. In some
implementations, the grain structure comprises equi-axed grains, i.e. grains
of an alloy
that show no directionality and tend to be similarly-sized in all directions,
as shown in
Figure 6.
[0098] Referring now to the drawings and more particularly to the non-
limitative
embodiment of Figure 2, there is shown a process 10 for manufacturing an
aluminum-
based alloy sheet 12 directly from a molten aluminum-based alloy 14 (i.e.,
directly from
the melt 16). Sequentially, and directly from the molten aluminum-based alloy
14, a
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substantially solid and substantially thin aluminum-based alloy strip 18 is
continuously
cast and simultaneously cooled, in a continuous casting and cooling system 20.
In one
implementation, the substantially solid aluminum-based alloy strip 18 can
simultaneously
be cast and cooled in a belt caster, in the belt caster as well described in
U.S. Patent
Publication No. 2018/0290204 assigned to Hazelett Strip Casting Corp, for
example.
However, in another implementation, the substantially solid aluminum-based
alloy strip
18 can simultaneously be cast and cooled in a roll caster. It is noted that
any casting
device producing a substantially solid and substantially thin aluminum-based
alloy strip
18 while applying a compression force thereto during casting in a range of
about 2 to
about 3000 pounds per linear inch of strip width can be used, as mentioned
above. As
mentioned above, the compression force is applied on the solidifying aluminum-
based
alloy strip 18, i.e. as the melt solidifies inside a solid alloy shell, by the
two belts (upper
and lower belts) which are located on each side of the aluminum-based alloy
strip 18
during the simultaneous casting and cooling step. In some embodiments, the
compression force applied to the melt and on the resulting strip during the
casting/cooling
step is higher than about 2 pounds per linear inch of strip width and lower
than about
1000 pounds per linear inch of strip width and lower than about 150 pounds per
linear
inch of strip width. In other embodiments, the compression force is between
about 2 to
about 100 pounds per linear inch of strip width. In still other embodiments,
the
compression force is between about 10 to about 100 pounds per linear inch of
strip width
and, in further embodiments, the compression force is between about 10 to
about 60
pounds per linear inch of strip width. The thin aluminum-based alloy strip 18
has a grain
structure consistent with two opposing solidification fronts and which can
comprise equi-
axed grains. The thin aluminum-based alloy strip 18 has a thickness smaller
than about
mm, in some embodiments, thinner than about 6 mm, and still other embodiments,
thinner than about 4 mm. In some embodiments, the aluminum-based alloy strip
18 is
thicker than about 2 mm.
[0099] The casting apparatus is operated at a casting speed that can
be varied in
accordance with the thickness of the cast strip. In some implementations, a
product of the
casting speed (in meter per minute) and the thickness of the strip 18 (in mm)
ranges
between 120 and 200, depending on a length of the cooling zone in the casting
apparatus.
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For instance, for casting a 4 mm thick aluminium-based strip, the casting
speed can range
between 30 m/min and 50 m/min. For casting a 2 mm thick aluminium-based strip,
the
casting speed can range between 60 m/min and 100 m/min.
[0100] As mentioned above, the aluminum-based alloy strip 18 is
simultaneously
cooled as it is cast. Cooling rate was determined using dendrite arm spacing
as described
in Miki etal. (Japanese Institute of Light Metals, vol. 25, issue 1, p. 1-9
(1975)) and in
Spear and Gardner (Trans. AFS, vol 71, p. 209 (1963)). In one scenario, the
cooling can
be performed at a cooling rate of between about 100 K/s and about 1500 K/s
and, in
another scenario, the cooling can be performed at a cooling rate of between
about 500
K/s and about 1200 K/s. Once again, the cooling rate can vary in accordance
with the
thickness of the cast strip. Typically, the thicker the cast strip 18 is then
the slower the
cooling rate. In some implementations, for a 10 mm thick cast strip, the
cooling rate is
between about 100 K/s to about 400 K/s while, for a 2 mm thick cast strip, the
cooling rate
is between about 1200 K/s to about 1500 K/s
[0101] In some implementations, the substantially solid aluminum-
based alloy strip 18
can then be rolled, substantially rapidly, in a continuous in-line process
with the
simultaneous casting/cooling step, and, more particularly, in some
implementations, cold-
rolled substantially rapidly, by passing through a rolling system 22 including
one or more
roll(s), so as to obtain the aluminum-based alloy sheet 12.
[0102] In other implementations, the substantially solid aluminum-
based alloy strip 18
can be stored for a period of time before being rolled. For instance, it can
be coiled into a
roll and, then unrolled, before being rolled. For instance, the storage period
between the
simultaneous casting/cooling step and the following rolling step can be
between 1 day
and up to about 60 days. In one implementation, it can be between about 5 days
and
about 60 days.
[0103] As mentioned above, the rolling stage can be cold rolling
wherein the cast strip
18 has a temperature below 250 C. It can also be warm rolling, wherein the
cast strip has
a temperature between about 150 C and about 250 C, or even hot rolling
(temperature
above about 2500C).
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[0104] In some implementations wherein the substantially solid
aluminum-based alloy
strip 18 is cold-rolled, substantially rapidly, in a continuous in-line
process with the
simultaneous casting/cooling step, the temperature of the substantially solid
alum inum-
based alloy strip 18 is maintained below 250 C following the simultaneous
casting/cooling
step and before the cold-rolling step.
[0105] For example, the substantially solid aluminum-based alloy
strip 18 can
simultaneously be cast and cooled so that it has an as-cast gauge of below
about 10 mm
and, in some implementations, between about 2 mm and about 5 mm. On the other
hand,
the substantially solid aluminum-based alloy strip 18 can be rolled, for
instance and
without being !imitative, cold-rolled so that the aluminum-based alloy sheet
12 obtained
has an as-rolled gauge of between about 0.5 mm and about 4 mm. In a system
wherein
the process is carried-out continuously and in-line, benefiting from the
substantially high
cooling rate provided by the casting and cooling system 20, the as-rolled
gauge of the
aluminum-based alloy sheet 12 can be obtained in a substantially short time
interval. For
example, the desired as-rolled gauge of the aluminum-based alloy sheet 12 can
be
obtained after less than about 25 seconds, and in some embodiments, only
between
about 1 second and about 25 seconds.
[0106] For example, the substantially solid aluminum-based alloy
strip 18 can be rolled
at a temperature lower than its solutionizing temperature, for example, at a
strip
temperature lower than about 300 C (i.e., temperature of the strip just
before entering
the rolling system 22). As mentioned above, in one implementation of the
process, no
additional or intermediate heat treatment step, no additional or intermediate
homogenization heat treatment step for example, needs to be carried out
between the
casting and cooling system 20 and the rolling system 22. In some
implementations of the
process described herein, the substantially solid aluminum-based alloy strip
18 that has
been cast is thus directly and rapidly rolled and, more particularly, directly
and rapidly
cold rolled, without re-heating the substantially solid aluminum-based alloy
strip 18
between the casting and cooling system 20 and the rolling system 22.
Therefore, the
substantially solid aluminum-based alloy strip 18 can enter the rolling system
22 at a strip
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temperature lower than about 300 C and, in other implementations at a strip
temperature
lower than about 150 C.
[0107] In other implementations of the process described herein, as
shown for instance
in Figure 3, the substantially solid aluminum-based alloy strip 18 that has
been cast is
stored before being rolled. For instance, it can be coiled for storage
purposes. The
substantially solid aluminum-based alloy strip 18 can optionally be quenched
28 before it
is rapidly coiled. Quenching can be performed to further diminish the rate of
any incipient
ageing that may occur prior to the rolled sheet reaching its storage/shipping
temperature.
Then, following storage and shipment, if any, it can be uncoiled, if required,
and
subsequently, rolled, for instance cold-rolled. If required, it can be re-
heated before being
rolled in the rolling system 22. In these implementations, the substantially
solid aluminum-
based alloy strip 18 is heated before the rolling stage to enter the rolling
system 22 at a
strip temperature lower than about 250 C and, in other implementations at a
strip
temperature lower than about 150 C.
[0108] Referring now more particularly to the non-limitative
embodiments of Figures 3
and 4, it is noted that the produced aluminum-based alloy sheet 12, after it
has been
rolled, can further be heat treated. This subsequent heat treatment can be
performed in
a continuous in-line sequence with the rolling stage. For example, the
produced
aluminum-based alloy sheet 12 can be subjected to a solution heat treatment
stage 24
and solutionized (see left side of Figure 3), or alternatively, subjected to
an annealing
device 26 to be annealed. In other words, additional heat treatment stages can
be
involved in the process 10, after the cold-rolling of the substantially solid
aluminum-based
alloy strip 18. These additional heat treatments are thus performed on the
obtained
aluminum-based sheet 12. For example, large furnaces or ovens can be used for
the
solutionizing heat treatment step and/or the annealing heat treatment step.
After the
solutionizing heat treatment step or the annealing heat treatment step, the
aluminum-
based alloy sheet 12 can optionally be quenched 28 (e.g., air or water
quenched), coiled
30 and pre-aged 32. The ageing / pre-ageing step can be an artificial ageing
step. In
some implementations, an artificial ageing step can be performed without any
solutionizing heat treatment step between the rolling step and the artificial
ageing step. In
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other implementations, an anneal and quench was performed following the
rolling step to
allow for formability. Following forming, an artificial ageing step was
performed to
strengthen the newly formed part. For instance, for artificial ageing, the
aluminium-based
alloy sheet 12 can be maintained in an environment between about 150 C and
about
250 C for about 15 minutes to about 8 hours and, in some implementations, for
about 5
hours to about 8 hours. Artificial ageing can also occur during paint baking.
It can also
include a pre-ageing step wherein the aluminium-based alloy sheet 12 can be
maintained
in an environment between about 50 C and about 100 C for about 5 hours to
about 8
hours. Still referring to the non-limitative embodiment of Figure 2, the
substantially solid
aluminum-based alloy strip 18 can optionally be quenched before it is rapidly
coiled and,
subsequently, rolled. Quenching can be performed to further diminish the rate
of any
incipient ageing that may occur prior to the rolled sheet reaching its
shipping temperature.
[0109] In operation, the substantially solid aluminum-based alloy
strip 18 can be
directly rolled and, more particularly, cold-rolled, to its as-rolled gauge
and then, be
artificially aged. Indeed, by casting an aluminum-based Mg2Si-containing
alloy, for
example, at a sufficiently high cooling rate, it is possible to put more of
the Mg2Si into
solution and suppress the formation of Mg2Si globules and/or eliminate its
interdendritic
form entirely. The aluminum-based alloy sheet 12 obtained can thus have a
similar
strength (i.e., at least one of Yield Strength (YS), Ultimate Tensile Strength
(UTS) and
Elongation) to that of an aluminum-based alloy sheet resulting from a
conventional Direct
Chill process having the same chemical composition. However, since the
aluminum-
based alloy sheet 12 resulting from the present process 10 has more cold work
therein,
the resulting sheet 12 can also have a lower elongation to failure than that
of an
aluminum-based alloy sheet resulting from the conventional Direct Chill
process.
[0110] In an embodiment, the EEBC continuous belt-casting process
described above
further comprises a pulse heating step, which will be referred to hereinafter
as
"EEBC + Pulse". The pulse alloy heating is carried out following the
simultaneous casting
and cooling step and the subsequent cold-rolling step.
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[0111] Due to its effect on the aluminum alloy, pulse heating may be
referred to herein
as pulse solutionizing when describing pulse heating of age-hardenable
aluminum alloys
(i.e., 6xxx series). Similarly, pulse heating may be referred to herein as
pulse annealing
when describing pulse heating of strain hardenable aluminum alloys (i.e., 5xxx
series).
[0112] As used herein, the term "pulse solutionizing" refers to an
increase of the alloy
temperature, typically, at an alloy temperature ranging between about 500 C
and about
570 C and, in some implementations, around about 560 C, for a relative short
heating
time (typically about 3 to about 10 seconds), followed by a quench.
Furthermore, the rapid
temperature increase is quickly followed by a quench for immediate cool down.
In some
implementations, the quench is a cold-water quench.
[0113] VVhen referring to pulse annealing, the primary goal is to
recrystallize the
aluminum alloy sheet to achieve a good balance of strength and ductility, and
not to
solutionize. As used herein, the term "pulse annealing" of an aluminum alloy
sheet refers
to an increase of the alloy temperature, typically, at an alloy temperature
ranging between
about 450 C and about 600 C and, in some embodiments, between about 500 C and
about 560 C (in some implementations around about 510 C), for a relative short
heating
time (typically 3 to 10 seconds) followed by a cool down immediately after the
temperature
increase. In some implementations, the temperature cool down rate can range
from about
20 to about 100 C per hour. In some non-limitative implementations, the
cooled down
duration can be around about 60 seconds.
[0114] In an embodiment, the pulse heating step carried out in
combination with the
above-described EEBC removes the need for conventional solutionizing. More
particularly and surprisingly, the EEBC + Pulse process can remove the need
for
conventional solutionizing of age-hardenable (i.e., 6xxx series) aluminum
alloys.
Additionally, it can reduce the need for annealing of strain hardenable (i.e.,
5xxx series)
aluminum alloys. In this way, it can potentially reduce an aluminum casting
facility
footprint and, more particularly, an aluminium sheet production facility
footprint (i.e. allows
for a reduced length of processing line).
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[0115] In an embodiment, to quickly heat the aluminum-based alloy
sheet 12 to perform
pulse solutionizing or pulse annealing thereon, infrared heater(s) can be
used. In an
embodiment, during the quick temperature increase substantially the entire
aluminum-
based alloy sheet 12 will reach the target temperature, even in a center
thereof.
[0116] In addition, the aluminum alloy sheets that are obtain via the
EEBC + Pulse
process can exhibit equivalent or improved strength and ductility when
compared to
aluminum alloy sheets that were processed using conventional solutionizing, as
will be
described in more details below in reference to the results shown in Table 4.
[0117] Thus, the EEBC + Pulse processing can enable casting of
solutionized
aluminum alloy sheet with less than 10 seconds of heating, typically only
about 5 seconds
of heating. When compared to about 60 seconds of heating that is needed in a
conventional solutionizing process, the EEBC + Pulse can further allow for a
reduction in
energy consumption, and ultimately, operation costs. In a non-limitative
embodiment, it
can be estimated that the EEBC + Pulse process can consume about 75% less
energy
and can create a significant amount (possibly as high as 90%) less waste
compared to
the conventional ingot processing method. Additionally, in some
implementations, the
footprint of the EEBC + Pulse line can be smaller than the one of conventional
processing
lines for producing aluminum sheets (e.g., aluminum automotive body sheets).
In a non-
limitative embodiment, an EEBC + Pulse processing line can convert liquid
aluminum to
a 10 ton coil of 2 mm sheet in about 70 meters and about 20 minutes. To
produce the
same quantity of aluminum sheet, the footprint of a conventional solutionizing
line can
require an order of magnitude larger footprint in terms of the square area
coverage.
Furthermore, the time required to convert liquid aluminum to 2 mm sheet via
the
conventional DC ingot method can typically take 20 or more days. In comparison
with a
conventional processing line, the EEBC + Pulse line can have low capital and
operating
costs, with a small plant footprint and can provide at least equivalent
aluminum sheets
using short processing times to final product. Accordingly, the EEBC + Pulse
process
can provide at least one of an economic advantage and an environmental
advantage over
existing technologies.
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[0118]
Therefore, the present process allows to, directly from a molten
aluminum-
based alloy 14, simultaneously cast and cool a substantially solid aluminum-
based alloy
strip 18 of a substantially thin as-cast gauge (thinner than about 10 mm),
using for
example, a belt caster. Since the substantially solid aluminum-based alloy
strip 18 can be
cooled at a sufficiently high cooling rate, the produced aluminum-based strip
18 can be
directly processed to an aluminum-based alloy sheet having at least some
mechanical
properties similar to a solutionized 14 (age-hardenable) temper, without the
need for an
intermediate homogenization heat treating step between the casting and cooling
system
20 and the rolling system 22 and, more particularly, without the need of an
homogenization heat treatment step between the simultaneous casting and
cooling step
and the cold-rolling step. Furthermore, the process described herein can
further include
heat treating the rolled aluminum-based alloy sheet 12 (i.e., after the cold-
rolling step) to
reduce the amount of hardening via working of the alloy that may be due to an
inline pinch
roll (for gauge and profile control), and subsequent rolling steps. A
separate, or
alternatively, in-line, recovery step can thus be performed. The aluminum-
based alloy
sheet 12 obtained is fairly uniform in cross-section, and exhibits slight
coarsening towards
the cast centreline.
[0119]
The process described herein, that allows cooling from the melt to a
rollable
thin strip, has many benefits over the prior art processes. First, by
simultaneoulsy casting
and cooling the substantially solid aluminum-based alloy at a substantilly
high cooling rate
(i.e., at a cooling rate of about 1,500K/s to about 100 K/s vs. 10K/s for
conventional
processes), more alloy elements are put into solid solution. Increased amounts
of certain
phases in solid solution (e.g., Mg2Si in AA6XXX series alloys) makes the alloy
more
effectively age-hardenable. Second, by being able to put sufficient amounts of
the age-
hardening (i.e., strengthening) phase into the as-cast substantially solid
aluminum-based
alloy strip, the strip can be successfully aged, without any additional or
intermediate heat
treatment stages that are usually necessary in conventional sheet processing
routes.
[0120] As mentioned above, the resulting aluminum-based alloy sheet can thus
end up
with characteristics that meet at least partially the metallurgical
requirements for use in
transport applications, for example. Indeed, a common alloy used in the
manufacture of
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transportation aluminum-based products is the AA6016 aluminum-based alloy.
Typical
mechanical properties for a conventionally produced, solution heat treated and
aged
AA6016 in the T6 temper can be as follow: Yield Strength (YS) 210 MPa,
Ultimate
Tensile Strength (UTS) 240 MPa, Elongation 12%. On the other hand, mechanical
properties for a produced AA6016 sheet resulting from the present process
(simultaneous
casting and cooling, followed by cold-rolling and ageing) can range as follow:
YS:
between about 250 and about 260 MPa; UTS: between about 260 and about 280 MPa;
and between about elongation is between about 7 % and about 8 %.
[0121] Moreover, the resulting aluminum-based alloy sheet can end up with
characteristics that meet at least partially metallurgical requirements for
use in beverage
container applications, for example. Indeed, a common alloy used in the
manufacture of
beverage container aluminum-based products is the AA5182 aluminum-based alloy,
which can form, for example, the top of a can. It is critical that the
supplied alum inum-
based sheets have suitable mechanical properties in the fully hard and stoved
condition.
Stoving is the process where, after the container has been filled, it is
heated for a period
of time above the boiling point of water to pasteurize the liquid being
contained therein.
Typical mechanical properties for a conventionally stoved AA5182 sheet can be
as
follows: Yield Strength (UTS): 340-395 MPa, Elongation
5%. On the other hand,
mechanical properties for a produced AA5182 sheet resulting from the present
process
(simultaneous casting and cooling, and cold-rolling from an as-cast gauge of 2
mm to an
as-rolled gauge of 0.208mm) can range as follows: YS: between about 420 and
about
450 MPa, UTS: between about 440 and about 470 MPa, and Elongation: between
about
2 % and about 5 %. Mechanical properties following a subsequent stoving can
range as
follow: YS: between about 350 and about 370MPa and elongation is between about
7 %
and about 10%.
[0122]
It is noted that, in general, the aluminum-based alloy sheet 12
manufactured
using the process as described above can have a Yield Strength (YS) of between
about
200 MPa and about 500 MPa, depending on the nature of the alloy, the thickness
of the
sheet, etc. Moreover, the resulting aluminum-based alloy sheet 12 can have an
Ultimate
Tensile Strength (UTS) of between about 220 and about 520, depending on the
nature of
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the alloy, the thickness of the sheet, etc. Finally, the resulting aluminum-
based alloy sheet
12 can have an elongation of between about 1 % and about 12%, depending on the
nature of the alloy, the thickness of the sheet, etc. Non-limitative examples
are detailed
in Table 1.
Table 1. Alloy Sheet Tensile Property Range for four different aluminum-based
alloys.
AA5182 AA6005 AA6016 AA6014
UTS (MPa) 440-470 310-340 270-300
300-330
YS (MPa) 420-450 300-330 260-290
290-320
Elongation
2-5 4-7 6-7 5-6
(%)
Properties Properties Properties
Properties
obtained obtained obtained obtained
under the under the under the under the
Remarks state of 0.208 state of 1 mm state of 1 mm state of 1
mm
mm as rolled as rolled after as rolled after
as rolled after
after 90% cold 50% cold 50% cold
67% cold
reduction. reduction. reduction. reduction.
[0123] EXPERIMENTS AND RESULTS
[0124] The following working examples and experiments further illustrate the
above-
described casting process and are not intended to be limiting in any respect.
[0125] A number of experiments were conducted to assess operating parameters
and
performance of the process for manufacturing an aluminum-based alloy sheet
directly
from a molten aluminum-based alloy, by simultaneously casting and cooling a
substantially solid and substantially thin aluminum-based alloy strip, and by
rolling the
substantially solid and substantially thin aluminum-based alloy strip to
produce the
aluminum-based alloy sheet, without carrying out any heat treatment step, such
as
homogenization, between the simultaneous casting and cooling operation and the
rolling
operation.
[0126] A number of experiments were also conducted to assess the mechanical
properties of the produced aluminum-based alloy sheets, depending on the
nature of the
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aluminum-based alloy, the operating parameters of the process, the as-cast
thickness of
the strips, the as-rolled thickness of the sheets, etc.
[0127] First off, Figure 5 shows an optical micrograph of a cross
section of an AA6005
AlMgSi alloy strip, which is as-cast and etched with 0.5% HF at the indicated
magnification
level. Figure 6 shows an optical micrograph of a cross section of an AA6005
AlMgSi alloy
strip having a thickness of 2mm, which is as-cast and etched with a modified
Barker's
Reagent that includes boric acid to show uniformity of cross-section grain
size at the
indicated magnification level. Figure 7 shows an optical micrograph showing
microstructure at a surface of an AA6005 AlMgSi alloy strip having a thickness
of 2mm,
which is as-cast and etched with 0.5% HF at the indicated magnification level.
Figure 8
shows an optical micrograph showing microstructure at the centreline region of
an
AA6005 AlMgSi alloy strip having a thickness of 2mm, which is as-cast and
etched with
0.5% HF at the indicated magnification level. Unlike other thin strips
resulting from
conventional casting processes, such as the Direct Chill casting process,
benefiting from
the substantially high cooling rate and substantially low compression force
applied to the
strip, the microstructure of the substantially solid aluminum-based alloy
strip resulting of
the present process is fairly uniform in cross-section, exhibiting slight
coarsening towards
the cast centreline.
[0128] Also, Figure 9 shows a plot of the Ultimate Tensile Strength
(UTS in MPa) vs. a
ratio of the Ultimate Tensile Strength to the Yield Strength (UTS/YS, which is
unitless or
MPa/MPa) for 6 thin strip cast samples of AA6005 aluminum-based alloys.
Indeed, the
thin strip cast samples (i.e., the substantially solid aluminum-based alloy
strips) were
simultaneously cast and cooled to an as-cast gauge of 2mm, cold-rolled to
obtain an
aluminum-based alloy sheet having an as-rolled gauge of 1mm and then, tensile
tested
(cooling rate was 500-1200 K/second; time interval was 5-60 days; rolling
force was 10-
30 lbs per inch of cast strip width). For comparison, the plot of Figure 9
also shows the
UTS vs. the UTS/YS for aluminum-based alloy sheets obtained via a conventional
Direct
Chill process. The dotted lines show the results for the as-rolled AA6005
sheets (DC-AR,
i.e. Direct Chill and As-Rolled) resulting from the Direct Chill process. The
strips were cast
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to an as-cast gauge of 75mm, homogenized for 6 hours at 560 C, hot rolled to
an as-
rolled gauge of 4mm, cold-rolled for an as-rolled gauge of 1mm, and tensile
tested.
[0129] Figure 10 shows a plot of the Yield Strength (YS) vs. a ratio
of the Ultimate
Tensile Strength to Yield Strength (UTS/YS) for 7 thin strip cast samples of
AA6005
aluminum-based alloys. The thin strip cast samples were simultaneously cast
and cooled
to an as-cast gauge of 2mm, cold-rolled to an as-rolled gauge of 1mm, and
tensile tested.
Depending on the sample, the cooling rate was between about 500 K/s and about
1200
K/s; the time interval between the casting/cooling and the cold-rolling was
between 5 and
60 days; and the rolling force was between about 2 and about 30 lbs per inch
of cast strip
width. For comparison, the plot of Figure 10 also shows the YS vs. the UTS/YS
for
aluminum-based alloy sheets obtained via a conventional Direct Chill process.
The dotted
lines show the results for the as-rolled AA6005 sheets (DC-AR) resulting from
the Direct
Chill process. The strips were cast to an as-cast gauge of 75mm, homogenized
for 6h at
560 C, hot-rolled to an as-rolled gauge of 4mm, cold-rolled to an as-rolled
gauge of 1mm,
and tensile tested.
[0130] Figure 11 shows a plot of the Ultimate Tensile Strength (UTS
in MPa) vs. a ratio
of the Ultimate Tensile Strength to Yield Strength (UTS/YS) for T4 conditions
(T4 referring
to temper, which means the samples have been solutionized and quenched) for 5
thin
strip cast samples of AA6005 aluminum-based alloys. The thin strip cast
samples were
cold-rolled to produce sheets having an as-rolled gauge of 1mm, solutionized
for 30s at
560 C and tensile tested. Depending on the sample, the cooling rate was
between about
500 K/s and about 1200 K/s; the time interval between the casting/cooling and
the cold-
rolling was between 5 and 60 days; and the rolling force was between about 2
and about
30 lbs per inch of cast strip width. For comparison, the plot of Figure 11
also shows the
UTS vs. the UTS/YS for aluminum-based alloy sheets obtained via a conventional
Direct
Chill processes, under T4 conditions. The strips were cast to an as-cast gauge
of 75mm,
homogenized for 6h at 560 C, hot-rolled to an as-rolled gauge of 4mm, cold-
rolled to an
as-rolled gauge of 1mm, solutionized at 560 C, and tensile tested. As shown,
the
strengths exhibited by the thin strip cast T4 samples resulting from the
present process
were similar to those obtained for the samples resulting from the conventional
process.
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That is, although no heat treatment (i.e., homogenization) was required to
obtain those
results, the physical properties of all samples were similar.
[0131] Figure 12 shows a plot of the Ultimate Tensile Strength (UTS
in MPa) vs. a ratio
of the Ultimate Tensile Strength to Yield Strength (UTS/YS) for samples that
underwent
ageing. Thin strip cast samples of AA6005 were simultaneously cast and cooled
to an as-
cast gauge of 2mm, cold-rolled to an as-rolled gauge of 1mm, aged 5 hours at
180 C and
tensile tested. Depending on the sample, the cooling rate was between about
500 and
about 1200 K/second; the time interval between the casting/cooling and the
cold-rolling
was between 5 and 60 days; and the rolling force was between about 2 and about
30 lbs
per inch of cast strip width. For comparison, the plot of Figure 12 also shows
the YS vs.
the UTS/YS for aluminum-based alloy sheets obtained via a conventional Direct
Chill
process. The dotted lines show the results for the as-rolled AA6005 sheets (DC-
AR)
resulting from the Direct Chill process. The strips were cast to an as-cast
gauge of 75mm,
homogenized at 560 C for 6 hours, hot-rolled to an as-rolled gauge of 4mm,
cold-rolled
to an as-rolled gauge of 1mm, solutionized at 560 C for 30 seconds, aged 5
hours at
180 C and tensile tested.
[0132] In brief, the aluminum-based alloy sheets resulting from the
process described
herein have similar mechanical properties to those of sheets of the same
composition
resulting from conventional processes, even though the present process
provides no re-
heating of the cast strip between the simultaneous casting and cooling
operation and the
cold-rolling operation. The sheets obtained via the present process can
therefore reach
the high metallurgical requirements of a plurality of industries, namely, of
the transport
industry, beverage container industry and the like, with a process that is
saves time,
energy and money.
[0133] Table 2 and Figures 13A to 13D show results of experiments with AA6016
alloy.
Specifically, as-cast AA6016 strips of 5.25 inches width and designated
thickness, were
placed vertically in a furnace already at 515 C. The strips were rapidly
heated for 15
minutes until reaching 500 C. They were then removed and hot rolled (at about
500 C)
to obtain an approximate 1 mm target thickness. When the strips came out of
the hot mill,
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they were quenched per temper requirements. Figure 13a, labelled "3mm water",
shows
results from 3mm samples (cast 3.298) of AA6016 wherein sample strips were hot
rolled
at about 500 C to about 1.1 mm and immediately quenched in water. Figure 13b,
labelled
"3mm T4P", shows results from 3 mm samples (cast 3.298) of AA6016 wherein
sample
strips were hot rolled at about 500 C to about 1.1 mm and rapidly quenched in
water.
They were pre-aged by soaking at 85 C in a furnace for 8 hours. The furnace
was then
cooled naturally to room temperature in about 4 hours. Figure 13c, labelled
"3mm Air",
shows results from 3 mm sample strips of AA6016 (cast 3.298) that were hot
rolled at
about 500 C to about 1.1 mm thickness and subsequently left to cool to room
temperature
in air. It was estimated that it took about 10 minutes for the thin and narrow
strips to cool
to room temperature. Finally, Figure 13d, labelled "2mm Water", shows results
from 2 mm
samples of AA6016 (cast 3.271) wherein sample strips were hot rolled at about
500 C to
about 1.0 mm and immediately quenched in water. Results are detailed in Table
2.
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Table 2. Average Mechanical Properties for AA6016 samples
Tensile Yield Elongation
Days after (MPa) (MPa) (%)
rolling
3 3mm T4P 242.0 202.1
14.1
3mm Water 243.3 207.5 11.8
3mm Air 217.6 187.8 11.1
2mm Water 264.4 217.6 16.8
4 3mm T4P 238.9 200.2
13.3
3mm Water 239.3 200.2 14.7
3mm Air 232.6 209.0 7.8
2mm Water 262.9 217.0 14.3
6 3mm T4P 240.3 203.1
12.5
3mm Water 236.3 196.0 15.4
3mm Air 223.9 193.6 9.7
2mm Water 268.0 219.0 14.9
9 3mm T4P 240.8 199.6
16.3
3mm Water 239.0 200.2 13.8
3mm Air 220.7 193.3 8.9
2mm Water 268.7 219.6 14.3
14 3mm T4P 238.5 194.0
16.7
3mm Water 243.5 204.2 13.8
3mm Air 223.5 196.6 8.2
2mm Water 268.1 219.5 15.4
[0134] Different tests were carried out with two different compositions of
6xxx series heat-
treatable aluminum alloys as shown in Table 3. More particularly, aluminium-
based
sheets were manufactured with these two aluminum alloy compositions using two
different casting processes: Direct casting (DC) and EEBC (see Table 3). The
results,
shown in Table 4, are mean results taken from 3 tests (n=3).
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Table 3. Chemical composition of AA6xxx alloys
Alloy Casting Method Weight %
Si Fe Cu Mn Mg
AA6005 DC
0.70 0.15 0.05 0.05 0.48
AA6005 EEBC
0.62 0.19 0.07 0.08 0.57
AA6016 EEBC
1.3 0.19 0.09 0.12 0.5
Table 4. Longitudinal T4P tensile properties of 1 mm AA6xxx (n=3)
Details of Tensile Yield
Alloy, Casting Method,
Elongation
Heat Strength Strength
Temper Heat Treatment (T)
Treatment (MPa) (MPa)
Typical as-delivered specifications >200 <130 >25
AA6005,
DC, Full solutionizing 560 C for
213 103
25
T4P 60 s
AA6005, EEBC, Full
560 C for 246 133
26
T4P solutionizing
60 s
EEBC, Pulse
AA6005, 560 C for
solutionizing 246 133
28
T4P 5 s
"EEBC+pulse"
EEBC, Pulse
AA6005, 500 C for
solutionizing 208 105
24
T4P 5 s
"EEBC+pulse"
EEBC, Pulse
AA6016, 500 C for
T4P
solutionizing 250 126
28
5s
"EEBC+pulse"
[0135] Experiment 1: DC Casting followed by conventional solutionizing
(Control sample
¨Row 1 of Table 4)
[0136] A heat-treatable alloy, series AA6005, was Direct Chill (DC) cast as 75
mm thick
slab, homogenized at 560 C for 6 hours, hot rolled to 4 mm and subsequently
cold rolled
to 1 mm.
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Table 5. Longitudinal T6P tensile properties of 1 mm AA6016 after a paint-
baking
simulation
Casting
Details of Tensile Yield
Method,
Elongation
Alloy Heat Temper Strength Strength
Heat
(96 )
Treatment (MPa) (MPa)
Treatment
Typical paint-baked specifications T6x/T8x >240 <200
>18
500 C for
EEBC, Pulse
AA6016 solutionizing secs T6P 302 231
20
(Paint-
("EEBC+pulse")
baked)
[0137] Experiment 2: EEBC Casting followed by conventional solutionizing (Row
2 of
Table 4)
[0138] Heat-treatable strips of AA6005 were produced via the
continuous casting
EEBC process, as described herein. Each strip was cast to 2mm at a speed of 90
m/m in.
For AA6005, a compression force of about 50 pounds per linear inch width was
applied.
Each strip was immediately quenched by water inline to a room temperature in
order to
avoid precipitation of Mg2Si out of solid solution. After each strip was
cooled to ambient
temperature, it was laboratory cold rolled from 2 mm to lmm at room
temperature with
the strip reaching a temperature not exceeding 60 C. All materials at 1 mm
were
subjected to a conventional solutionizing treatment with a heating time of
about 60
seconds at a temperature of about 560 C).
Table 6. Chemical composition of EEBC produced AA5182 strip
Alloy Casting Method Weight %
Si Fe Cu Mn Mg
AA5182 EEBC 0.13 0.09 0.01 0.34 4.05
[0139] Experiment 3: EEBC Casting followed by pulse solutionizing
("EEBC + Pulse")
(Row 3 of Table 4)
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[0140] Heat-treatable strips of AA6005 were produced via the continuous
casting EEBC
process, as described herein with a compression force of about 50 pounds per
linear inch
width. Each strip was cast to 2mm at a speed of 90 m/min. Each strip was
immediately
quenched by water inline to a room temperature in order to avoid precipitation
of Mg2Si
out of solid solution. After the strip was cooled, it was cold rolled to 1mm.
All materials at
1 mm were subjected to a pulse solutionizing treatment with a heating time of
about 3 to
about 10 seconds at a temperature of about 560 C.
[0141] Experiment 4: EEBC Casting followed by lower temperature pulse
solutionizing
("EEBC + Pulse") (Row 4 of Table 4)
[0142] Heat-treatable strips of AA6005 were produced via the continuous
casting EEBC
process, as described herein with a compression force of about 50 pounds per
linear inch
width. Each strip was cast to 2mm at a speed of 90 m/min. Each strip was
immediately
quenched by water inline to a room temperature in order to avoid precipitation
of Mg2Si
out of solid solution. After the strip was cooled, it was cold rolled to 1mm.
All materials at
1 mm were subjected to a pulse solutionizing treatment with a heating time of
about 3 to
about 10 seconds at a temperature of about 500 C.
[0143] Experiment 5: EEBC Casting followed by lower pulse solutionizing
("EEBC + Pulse") (Row 5 of Table 4)
[0144] Heat-treatable strips of AA6016 were produced via the continuous
casting EEBC
process, as described herein with a compression force of about 60 pounds per
linear inch
width. Each strip was cast to 2mm at a speed of 90 m/min. Each strip was
immediately
quenched by water inline to a room temperature in order to avoid precipitation
of Mg2Si
out of solid solution. After the strip was cooled, it was cold rolled to 1mm.
All materials at
1 mm were subjected to a pulse solutionizing treatment with a heating time of
about 3 to
about 10 seconds at a temperature of about 500 C.
[0145] Pulse solutionizing was conducted by immersing a strip in a molten salt-
bath for
various short soaking durations, typically about 1 to about 10 seconds. During
this time,
samples were rapidly heated to a target temperature in the range of 500 C to
560 C.
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Once this temperature range was reached, samples were immediately removed from
the
salt bath and quenched in cold water. The strip temperature during immersion
in the
molten salt-bath was measured by a thermocouple embedded in the strip and the
recorded data were data logged.
[0146] Immediately after quenching, all samples underwent a T4P treatment at
85 C for
a total soak of 8 hours. Samples treated in this way are considered to have a
T4P temper.
This heat-treatment is a recognized laboratory practice meant to simulate a
pre-age. The
aim of pre-ageing is to stabilize microstructure (e.g., clusters and zones)
such that
strength loss is reduced, or even eliminated, during subsequent natural
ageing. The T4P
treatment should not produce any significant increase in the initial strength,
which is
important for the formability needed for automotive body-panel applications.
[0147] Finally, tensile samples were machined and tested in the rolling
direction after a
minimum of 7 days of natural ageing. Results are shown in Table 4 and
explained below.
[0148] First, a comparison was conducted between Direct Chill conventional
casting
versus EEBC casting for AA6005 sheets, as shown in row 1 versus row 2. The
EEBC
casted sheet exhibited higher T4P strength values compared to the Direct Chill
cast alloy,
which could be the result of the retention of higher amounts of Mg2Si in solid
solution after
solutionization.
[0149] A comparison was also conducted between EEBC casts of AA6005 that were
conventionally solutionized (i.e, 60 seconds at 560 C) versus EEBC + Pulse
casts (i.e.,
the casting process was EEBC and the solutionizing was performed by a pulse
heating
step (i.e, 5 seconds at 560 C)), as shown in row 2 versus row 3 of Table 4.
Mechanical
properties, including strength and ductility, were equivalent for the
conventionally
solutionized EEBC samples as for the EEBC + Pulse samples, with EEBC + Pulse
requiring a lower energy consumption and thus being . Thus, Equivalent
mechanical
properties of these samples was demonstrated even though there is a
significant
difference between the energy efficiency and thus lower processing/operating
costs.
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[0150] The effect of the temperature of solutionization was also investigated
for the
EEBC + Pulse treatment of AA6005, as shown in row 1, row 3, and row 4 of Table
4. For
a lower temperature, a temperature of about 500 C was selected. As expected,
lower
mechanical properties were obtained for a temperature of solutionization of
500 C (row
4) versus a temperature of solutionization of 560 C (row 3). However, the
mechanical
properties of the AA6005 solutionizing by pulse solutionizing at 500 C (row 4)
are
equivalent to those of the conventionally cast Direct Chill samples of AA6005
with a
conventional solutionizing of 560 C shown in row 1 of Table 4, which is a
surprising result
since the lower solutionizing temperature (i.e, 500 C) would not be used for
conventional
solutionizing. More particularly, conventional solutionizing at 500 C would be
expected to
produce an AA6005 product that falls significantly short of these values.
Notably, the
equivalent mechanical properties for these two test results demonstrate the
value of the
EEBC + Pulse process for providing substantially equivalent products, in term
of
mechanical properties, from less energy consumption and thus lower
processing/operating costs.
[0151] The effect of the composition of the aluminum alloy was also
investigated, as
shown in rows 4 vs 5 of Table 4, for the EEBC + Pulse treatment (5 seconds at
500 C).
More particularly, the mechanical properties of the AA6016 alloy following the
EEBC + Pulse treatment (row 5) were compared to those of the AA6005 alloy (row
4).
AA6016 alloy is characterized by a higher concentration of Mg and Si than
AA6005 alloy.
As shown in rows 4 and 5, the yield strength and elongation of both aluminum
alloys after
the low-temperature pulse treatment were sufficient to satisfy the industry
standards.
Thus, the results showed in Table 4 demonstrate that the cast and rolled
aluminum alloys
treated with the EEBC + Pulse process were fully solutionized using the above-
described
cost effective, low-temperature and shorter-duration practice, and met the T4
specifications.
[0152] The samples produced via the above-detailed examples were additionally
examined for grain size. More particularly, Figures 14A, 14B, and 14C show
optical
micrographs of cross sections of AA6005 AlMgSi alloy strip having a thickness
of 1 mm,
which respectively underwent pulse solutionizing at 500 C for 5 seconds (Table
3, row
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4), pulse solutionizing at 560 C for 5 seconds (Table 3, row 3), and
conventional
solutionizing at 560 C for 60 seconds (Table 3, row 1). The EEBC + Pulse
processing
(5 sec 500 C and 560 C) produced fully recrystallized grains in the range of
about 20 pm
to about 30 pm. A simulation of the conventional solutionizing heat treatment
(60 seconds
at 560 C) produced grains in the range of about 40 pm to about 50. It is
known that a
finer grain size increases the material's ductility and is beneficial, if not
critical, to the
forming of an auto-body panel. Thus, the optical micrographs of Figures 14a
and 14b
demonstrate that the EEBC + Pulse process produced aluminum alloy strips with
superior
mechanical properties in comparison with the aluminum alloy strips processed.
[0153] After an automotive closure part (e.g., body panel) is formed, it is
typically
subjected to thermal treatments as the paints and lacquers are cured. To
simulate this
'paint-baking' processes in the laboratory, samples were placed in an air-
circulating
muffle furnace held at 180 C for 30 minutes. After this treatment, samples
were
considered to be in the artificially age-hardened T6 temper. As can be seen
from Table
5, the T6 paint-baked or age-hardened properties of the EEBC + Pulse AA6016
alloy (5
sec, 500 C), exceeded properties attained for conventional processed AA6016.
It will be
appreciated that these improved properties of ultimate tensile strength, yield
strength and
elongation of the strip reached by the EEBC + Pulse processing produced an
aluminum
alloy sheet that was superior to the aluminum alloy sheet produced from
previously known
methods.
[0154] Experiment 2: Testing of non-heat treatable alloy
[0155] In the following example, a non-heat treatable alloy AA5182, with the
chemical
composition given in Table 6, was produced via the EECB process, as described
herein.
The strip was cast at 2 mm with a compression force of about 75 pounds per
linear inch
width, cold rolled from 2mm to 1 mm and then pulse annealed at 510 C for 10
seconds
in a molten salt bath as described above to produce an 0-tempered material.
The cold
rolling was perfomed in laboratory at room temperature with the strip reaching
a
temperature not exceeding 80 C. As a comparison, a 1 mm AA5182 sheet cold
rolled
from 2mm EECB strip was subject to a simulation of a conventional batch
annealing
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process at 380 C for 2 hours in an air-circulating muffle furnace. Samples
were then
prepared for longitudinal tensile testing and the results are shown in Table
7. The samples
were also metallographically examined for grain size determination.
Table 7. Tensile properties of 1mm AA5182 sheet under various processing
Tensile Yield
Casting Heat
Elongation
Alloy Temper Strength Strength
Method Treatment
(%)
(MPa) (MPa)
Batch
annealing:
AA5182 EEBC 380 C for 2 289 139
25.0
hours
Pulse
AA5182 EEBC annealing: 286 130
26.1
510 C for 10
seconds
[0156] As shown in Figure 15A, the grain structure of 1 mm AA5182 cold rolled
sheet was
fully recrystallized after pulse annealing at 510 C. Pulse annealing produced
uniform
and equiaxed grains, with a mean grain size of around 20 pm. In comparison,
and as
shown in Figure 15B, the grains of the AA5182 strip produced via conventional
batch
annealing were significantly coarser, not nearly as uniform, and had a mean
grain size of
about 40 pm. The uniformity and small grain size is an extremely desirable
property for
0-temper automotive structural applications. Structural panels of a monocoque
auto-
body have fairly modest requirements in terms of strength (most designs
utilize relatively
thick gauges to provide sufficient stiffness), but require a high degree of
formability
(elongation) in order to produce the complex shapes required. As shown in
Table 7,
tensile properties of 1 mm AA5182 sheet after pulse annealing are comparable
to those
produced via batch annealing. Pulse annealing at 510 C for 10 seconds
generated slightly
higher elongation, which can be partly attributed to the significantly finer
grains observed
in the microstructure. Notably, the combination of EECB processing followed by
pulse
annealing (EEBC + Pulse) gave superior elongation values, and more uniform and
finer
grain structure when compared with the previously known methods, including
conventional batch annealing.
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[0157] Although the present invention has been described hereinabove by way of
specific embodiments thereof, it can be modified, without departing from the
spirit and
nature of the subject invention defined in the appended claims.
[0158] In the present description, the same numerical references
refer to similar
elements. Furthermore, for the sake of simplicity and clarity, namely so as to
not unduly
burden the figures with several reference numbers, not all figures contain
references to
all the components and features, and references to some components and
features may
be found in only one figure, and components and features of the present
disclosure which
are illustrated in other figures can be easily inferred therefrom. The
embodiments,
geometrical configurations, materials mentioned and/or dimensions shown in the
figures
or described in the present disclosure are embodiments only, given solely for
exemplification purposes.
[0159] Moreover, steps of the process(es) described herein could be
modified,
simplified, altered, omitted and/or interchanged, without departing from the
scope of the
present disclosure, depending on the particular applications which the present
process is
intended for, and the desired end results, as briefly exemplified herein and
as also
apparent to a person skilled in the art.
[0160] Although various features of the invention may be described in
the context of a
single embodiment, the features may also be provided separately or in any
suitable
combination. Conversely, although the invention may be described herein in the
context
of separate embodiments for clarity, the invention may also be implemented in
a single
embodiment.
[0161] Reference in the specification to "some embodiments", "an
embodiment", "one
embodiment" or "other embodiments" means that a particular feature, structure,
or
characteristic described in connection with the embodiments is included in at
least some
embodiments, but not necessarily all embodiments, of the inventionsit is to be
understood that the terms "including", "comprising", "consisting" and
grammatical variants
thereof do not preclude the addition of one or more components, features,
steps, or
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integers or groups thereof and that the terms are to be construed as
specifying
components, features, steps or integers.
[0162] It is to be understood that where the claims or specification
refer to "a" or "an"
element, such reference is not be construed that there is only one of that
element. It is to
be understood that where the specification states that a component, feature,
structure, or
characteristic "may", "might", "can" or "could" be included, that particular
component,
feature, structure, or characteristic is not required to be included.
[0163] The descriptions, examples, methods and materials presented in
the claims and
the specification are not to be construed as limiting but rather as
illustrative only. The
present invention may be implemented in the testing or practice with methods
and
materials equivalent or similar to those described herein.
[0164] In the following description, the term "about" means within an
acceptable error
range for the particular value as determined by one of ordinary skill in the
art, which will
depend in part on how the value is measured or determined, i.e. the
limitations of the
measurement system. It is commonly accepted that a 10% precision measure is
acceptable and encompasses the term "about".
[0165] Several alternative embodiments and examples have been described and
illustrated herein. The embodiments of the invention described above are
intended to
be exemplary only. A person of ordinary skill in the art would appreciate the
features of
the individual embodiments, and the possible combinations and variations of
the
components. A person of ordinary skill in the art would further appreciate
that any of the
embodiments could be provided in any combination with the other embodiments
disclosed herein. It is understood that the invention may be embodied in other
specific
forms without departing from the central characteristics thereof. The present
examples
and embodiments, therefore, are to be considered in all respects as
illustrative and not
restrictive, and the invention is not to be limited to the details given
herein. Accordingly,
while the specific embodiments have been illustrated and described, numerous
modifications come to mind. The scope of the invention is therefore intended
to be limited
solely by the scope of the appended claims.
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