Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
UN WORKED CONTINUOUSLY CAST HEAT-TREATABLE ALUMINUM ALLOY
PLATES
CROSS-REFERENCE TO RELATED APPLICATION
[001] This patent application claims the benefit of priority of United
States Provisional
Patent Application No. 62/412,554, filed October 25, 2016, entitled "UNWORKED
CONTINUOUSLY CAST HEAT-TREATABLE ALUMINUM ALLOY PLATES", which is
incorporated herein by reference in its entirety.
BACKGROUND
[002] Aluminum alloy plate may be produced by casting an ingot, scalping
and
homogenizing the ingot, hot rolling the ingot to an intermediate or final
gauge, optionally with
cold rolling of the an intermediate gauge to the final gauge. Working of the
product by rolling
generally imparts texture and residual stresses to the final rolled product.
SUMMARY OF THE DISCLOSURE
[003] Broadly, the present patent application relates to methods of
producing heat-
treatable as-cast plate, and products supplied to the customers based on the
same. In one
approach, and referring now to FIG. 1, a method includes the steps of
continuously delivering a
molten aluminum alloy to a delivery tip (2) of a horizontal belt caster (1).
[004] The molten aluminum alloy comprises a sufficient amount of at least
one of zinc
(Zn), magnesium (Mg), silicon (Si), and copper (Cu) to promote formation of
strengthening
precipitates. The horizontal belt caster (1) is used to continuously solidify
the molten
aluminum alloy into an aluminum alloy plate. The aluminum alloy plate is
continuously
discharged from an exit of the horizontal belt caster (1), generally at a
casting rate of from 1
inch to 150 inches per minute (e.g., from 2 to 20 inches per minute). The
discharged aluminum
alloy plate generally has a final gauge of from 0.25 inch to 5.0 inches (e.g.,
from 1.0 to 5.0
inches). The discharged aluminum alloy plate is quenched, via a quenching
apparatus (3),
located proximal the exit of the horizontal belt caster, thereby producing an
as-cast heat-
treatable aluminum alloy plate (4). The quenching comprises contacting outer
surfaces of the
discharged aluminum alloy plate with a quenching media. In the illustrated
embodiment shown
in FIG. 1, air jets are used, but any suitable quenching media can be used,
including any
suitable fluid, such as air, water, a mixture of air and water, or any other
suitable liquid or gas,
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or mixture thereof. The continuously cast heat-treatable plate is then sawed
into applicable
pieces via plate saw (5).
[005] In one embodiment, a method includes artificially aging the as-cast
heat-treatable
aluminum alloy plate, thereby developing strengthening precipitates within the
as-cast heat-
treatable aluminum alloy plate. Since the aluminum alloy plate is quenched at
the exit of the
caster (1), no additional solution heat treatment may be required prior to
artificial aging (i.e.,
the method may be free of a separate / dedicated solution heat treatment
step). Artificial aging
may be accomplished by heating the as-cast heat-treatable aluminum alloy plate
in a suitable
furnace or other heating device for a time sufficient to develop a sufficient
volume (including a
sufficient size and distribution) of the strengthening precipitates. In one
embodiment, the as-
cast heat-treatable aluminum alloy plate is artificially aged at a temperature
of from 275 to
450 F. In one embodiment, the as-cast heat-treatable aluminum alloy plate is
artificially aged
for from 1 to 20 hours. Any number of artificial aging steps may be used to
precipitation
harden the as-cast heat-treatable aluminum alloy plate.
[006] The strengthening precipitates may be developed within the matrix of
the as-cast
heat-treatable aluminum alloy. The strengthening precipitates are generally
coherent (to the
matrix) phases, and the strengthening precipitates generally include at least
one of silicon,
copper, magnesium and/or zinc. The coherent phases generally have an average
size of from
nanometers to 1 micron. In one embodiment, the coherent phases have an average
size of
not greater than 100 nanometer. Due to the composition of the molten aluminum
alloy, the as-
cast heat-treatable aluminum alloy plate comprises a sufficient amount of the
strengthening
precipitates to realize a peak strength (T6) that is at least 5 ksi higher
than the naturally aged
strength (T3). As used herein, "peak strength" means processing to a T6
temper, as per ANSI
H35.1 (2009), and within 1 ksi (+/-) of the highest strength that can be
achieved via artificial
aging. As used herein, naturally aged strength means processing to a T3 temper
as per ANSI
H35.1 (2009). Strength and elongation are measured in accordance with ASTM E8
and B557.
In one embodiment, the as-cast heat-treatable aluminum alloy plate comprises a
sufficient
amount of the strengthening precipitates to realize a peak strength (T6) that
is at least 7.5 ksi
higher than the naturally aged strength (T3). In another embodiment, the as-
cast heat-treatable
aluminum alloy plate comprises a sufficient amount of the strengthening
precipitates to realize
a peak strength (T6) that is at least 10 ksi higher than the naturally aged
strength (T3). In yet
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another embodiment, the as-cast heat-treatable aluminum alloy plate comprises
a sufficient
amount of the strengthening precipitates to realize a peak strength (T6) that
is at least 12.5 ksi
higher than the naturally aged strength (T3). In yet another embodiment, the
as-cast heat-
treatable aluminum alloy plate comprises a sufficient amount of the
strengthening precipitates
to realize a peak strength (T6) that is at least 15 ksi higher than the
naturally aged strength (T3),
or higher.
[007] The as-cast heat-treatable aluminum alloy plate also generally
comprises good
ductility for a thick, as-cast product. In one embodiment, the as-cast heat-
treatable aluminum
alloy plate realizes an elongation of at least 0.5%. In another embodiment,
the as-cast heat-
treatable aluminum alloy plate realizes an elongation of at least 1%. In
another embodiment,
the as-cast heat-treatable aluminum alloy plate realizes an elongation of at
least 2%. In another
embodiment, the as-cast heat-treatable aluminum alloy plate realizes an
elongation of at least
3%. In another embodiment, the as-cast heat-treatable aluminum alloy plate
realizes an
elongation of at least 4%, or higher.
[008] As shown in FIG. 1, the as-cast heat-treatable aluminum alloy plate
is generally not
worked after casting. Thus, in one embodiment, a method includes maintaining
the as-cast
grain structure of the as-cast heat-treatable aluminum alloy plate.
Development of
strengthening precipitates does not materially affect the as-cast grain
structure of the as-cast
heat-treatable aluminum alloy plate. Thus, after any artificial aging step,
the heat-treatable
aluminum alloy plate generally comprises the as-cast grain structure with the
strengthening
precipitates. In one embodiment, a method includes providing the as-cast heat-
treatable
aluminum alloy plate to a customer, wherein the as-cast heat-treatable
aluminum alloy plate has
the as-cast grain structure with the strengthening precipitates. In one
embodiment, the
maintaining the as-cast grain structure step comprises forgoing hot or cold
working of the as-
cast heat-treatable aluminum alloy plate after the continuously casting step.
[009] In one approach, an as-cast aluminum alloy plate has a thickness of
from 0.25 inch
to 5.0 inches, and the as-cast aluminum alloy plate comprises at least 0.5 wt.
% of at least one
of zinc (Zn), magnesium (Mg), silicon (Si), and copper (Cu). In one
embodiment, an as-cast
plate has a dendritic microstructure. In one embodiment, an as-cast aluminum
alloy plate has a
secondary dendritic arm spacing of from 30 to 150 microns in all of the
longitudinal (L), the
long-transverse (LT) and the short-transverse (ST) directions of the as-cast
aluminum alloy
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plate. In one embodiment, an as-cast aluminum alloy plate has equiaxed grains
and is generally
free of elongated grains.
[0010] As used herein, "dendritic microstructure" means a branching
microstructure
formed during solidification wherein the branches form from an initial
solidified nucleus, and
maintain generally the same crystallographic orientation as the nucleus from
which they are
formed.
[0011] As used herein, "secondary dendritic arm spacing" means the spacing
between the
centers of the branches in a dendritic microstructure.
[0012] As used herein, "equiaxed grains" means grains having a grain aspect
ratio of < 2:1
in all of the L, LT and ST directions, as measured using the linear intercept
method on
representative micrographs of the as-cast aluminum alloy plate.
[0013] As used herein, "elongated grains" means any grains that are not
equiaxed grains.
[0014] As used herein, "free of elongated grains" means an as-cast aluminum
alloy plate
comprises not greater than 5 vol. % of elongated grains.
[0015] The feedstock used to produce the aluminum alloy may be any suitable
feedstock
for producing an aluminum alloy, such as any conventional feedstock used to
produce a 2xxx,
6xxx, 7xxx, or Sxxx(HT) aluminum alloy. Thus, in one embodiment, the feedstock
is a
conventional 2xxx, 6xxx, 7xxx, or 8xxx(HT) feedstock.
[0016] Further, it has been uniquely found that the molten aluminum alloy
used to produce
the as-cast heat-treatable aluminum alloy plate can be produced from aluminum
alloy scrap.
Thus, in one aspect, the method includes melting an aluminum alloy scrap
feedstock, thereby
producing a molten aluminum alloy for the horizontal belt caster, where the
aluminum alloy
scrap feedstock comprises a combination of at least two different aluminum
alloy materials.
With the proper mixture of aluminum alloy scrap, a heat-treatable as-cast
aluminum alloy plate
may be produced. Further, since scrap materials are used, in many instances,
no additional
additives may be required to produce the as-cast heat-treatable aluminum alloy
plate.
[0017] In one approach, the scrap feedstock comprises at least two
different classes of
aluminum alloys. For instance, the at least two different classes of aluminum
alloys may be
selected from the following aluminum alloy series: 1 xxx, 2xxx, 3xxx, 4xxx,
5xxx, 6xxx, 7xxx,
and 8xxx aluminum alloys. In one embodiment, the at least two different
classes of aluminum
alloys are selected from the following aluminum alloy series: 3xxx, 4xxx,
5xxx, 6xxx, and
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7xxx aluminum alloys. In one embodiment, the aluminum alloy scrap comprises at
least two of
3xxx, 4xxx, and a 6xxx aluminum alloy scrap, optionally with 5xxx aluminum
alloy scrap. In
one embodiment, at least 50 wt. % of the scrap is a non-heat-treatable alloy,
such as at least 50
wt. % of 3xxx, 4xxx and/or 5xxx aluminum alloy scrap, the remainder being heat-
treatable
alloy scrap, such as one or more of 6xxx and/or 7xxx aluminum alloy scrap.
Several different
ones of any class of aluminum alloy may be used to make-up the scrap feedstock
(e.g., multiple
different 3xxx, multiple different 4xxx, multiple different 5xxx, and/or
multiple different 6xxx
aluminum alloys may be used to create the feedstock).
[0018] In one embodiment, the scrap feedstock comprises (or consist of) at
least two
different aluminum alloys from the same class. For instance, a scrap feedstock
may include at
least two different 6xxx aluminum alloys. In another embodiment, a scrap
feedstock may
include at least two different 7xxx aluminum alloys. In yet another
embodiment, a scrap
feedstock may include at least two different 2xxx aluminum alloys. In another
embodiment, a
scrap feedstock may include at least two different 8xxx aluminum alloys,
wherein at least one
of the 8xxx aluminum alloys is a heat-treatable aluminum alloy. Other scrap
feedstock
combinations may be used.
[0019] The 1 xxx, 2xxx, 3xxx, 4xxx, 5xxx, 6xxx, 7xxx, and 8xxx aluminum
alloys are
defined by the Aluminum Association document "International Alloy Designations
and
Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys"
(2015)
(a.k.a., the "Teal Sheets"), incorporated herein by reference in its entirety.
1 xx, 2xx, 3xx, 4xx,
5xx, 7xx, 8xx and 9xx aluminum casting and ingot alloys are defined by the
Aluminum
Association document "Designations and Chemical Composition Limits for
Aluminum Alloys
in the Form of Castings and Ingot" (2009) (a.k.a., "the Pink Sheets"),
incorporated herein by
reference in its entirety.
[0020] As used herein, a "1 xxx aluminum alloy" is an aluminum alloy
comprising at least
99.00 wt. % Al, as defined by the Teal Sheets. The "1 xxx aluminum alloy"
compositions
include the lxx alloy compositions of the Pink Sheets.
[0021] A 2xxx aluminum alloy is an aluminum alloy comprising copper (Cu) as
the
predominate alloying ingredient, except for aluminum. The 2xxx aluminum alloy
compositions
include the 2xx alloy compositions of the Pink Sheets.
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[0022] A 3xxx aluminum alloy is an aluminum alloy comprising manganese (Mn)
as the
predominate alloying ingredient, except for aluminum.
[0023] A 4xxx aluminum alloy is an aluminum alloy comprising silicon (Si)
as the
predominate alloying ingredient, except for aluminum. The 4xxx aluminum alloy
compositions
include the 3xx alloy compositions and the 4xx alloy compositions of the Pink
Sheets.
[0024] A 5xxx aluminum alloy is an aluminum alloy comprising magnesium (Mg)
as the
predominate alloying ingredient, except for aluminum. The 5xxx aluminum alloy
compositions
include the 5xx alloy compositions of the Pink Sheets.
[0025] A 6xxx aluminum alloy is an aluminum alloy comprising both silicon
and
magnesium, and in amounts sufficient to form the precipitate Mg2Si.
[0026] A 7xxx aluminum alloy is an aluminum alloy comprising zinc (Zn) as
the
predominate alloying ingredient, except for aluminum. The 7xxx aluminum alloy
compositions
include the 7xx alloy compositions of the Pink Sheets.
[0027] The 8xxx aluminum alloy compositions include the 8xx alloy
compositions and the
9xx alloy compositions of the Pink Sheets.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a schematic representation of a system for continuously
casting heat-
treatable aluminum alloy plate via a horizontal belt caster (1) and a
quenching apparatus (3)
located proximal the exit of the horizontal belt caster (1).
[0029] FIG. 2 is a graph showing testing results of Example 1.
[0030] FIG. 3 is a graph showing testing results of Example 2.
DETAILED DESCRIPTION
Example 1 - Lab Scale Trials
[0031] A horizontal belt caster was used to produce a 4.4 inch (11.18 cm)
6xxx aluminum
alloy as-cast plate from a mixture of scrap. After casting, lab-scale sections
of as-cast plate
were solutionized at 980 F for 5 minutes in a lab-scale furnace, and then
quenched using three
different methods: (a) still air, (b) forced air jets and (c) cold water
quenching. The materials
were then artificially aged at 365 F for 18 hours. Material properties of the
as-cast and
artificially aged plate were then determined in accordance with ASTM B557, the
results of
which are shown in Table 1, below. As shown, heat-treatable alloys were
produced from the
mixture of scrap, the artificially aged products being substantially stronger
than the naturally
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aged products. The full artificial aging curves (shown in FIG. 2) show that
the scrap-based
alloy, when properly solutionized and quenched, exhibits the potential for age
hardening.
Table 1: Example 1 Results (ksi and MPa)
Specimen Quench Aging Yield Tensile
Yield Tensile Elongation
Number Method Method Strength Strength Strength Strength 4D or 4W
(ksi) (ksi) (MPa) (MPa)
(yo)
Natural
Still Air
1 Age 11.9 20.7 82 143 6.5
Forced- Natural
2 Air Age 13.0 22.3 90 154 5.3
Natural
CWQ
3 Age 19.5 30.2 134 208 6.2
Forced- Artif.
4 Air Age 15.3 24.4 106 169 5.8
Artif.
CWQ
Age 39.7 40.7 274 281 1.6
Example 2 ¨ Industrial-Scale Quenching and Aging
[0032]
A horizontal belt caster was used to produce a 2.225 inch (5.65 cm) as-cast
plate
from a mixture of 3xxx, 4xxx, 5xxx and 6xxx aluminum alloys. Upon exiting the
horizontal
belt caster, the as-cast plate was quenched using air knives, supplied by a
high volume blower,
which directed a continuous blast of ambient air onto the upper and lower
surfaces of the as-
cast plate. As the plate moved continuously from the caster to the flying saw
(FIG. 1), the
surface temperature was measured at fixed positions from the caster exit.
Using these
temperature readings and the casting speed, the plate surface temperature was
plotted against
time, the results of which are given in Table 2, below, and shown in FIG. 3.
Samples from
each condition were subsequently artificially aged at 365 F for 8 hours.
Material properties
were then measured, the results of which are given in Table 3, below. As
shown, increased
yield strength is realized using forced air cooling (imposed immediately upon
exiting the
continuous caster) and the surface temperature of the plate is reduced.
Table 2: Example 2 Cooling Rate Results
Specimen Blower Time (1) Temp. (1) Time (2)
Temp. (2) Time (3) Temp. (3)
Rate
Number (RPM) (min) (T) (min) ( F) (min) (T)
1 0 1.2 900 6.5 865 8.8 832
2 1125 1.1 818 5.8 613 7.9 613
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Blower
Specimen Rate Time (1) Temp. (1) Time (2)
Temp. (2) Time (3) Temp. (3)
Number (RPM) (min) (0F) (min) (4) (min) (
F)
3 1125 1.2 802 6.7 620 9.1 580
4 1125 1.3 751 7.1 575 9.7 525
1700 1.3 762 7.1 510 9.7 446
6 2250 1.3 724 6.9 482 9.4 440
Table 3: Example 2 Results (ksi and MPa)
Blower Yield Tensile Yield Tensile
Specimen
Elongation
Rate Strength Strength Strength Strength
Number (%)
(RPM) (ksi) (ksi) (MPa) (MPa)
1 0 18.1 25.1 125 173 2.6
3 1125 25.5 30.5 176 210 2.0
4 1125 25.8 28.5 178 196 1.3
5 1700 35.3 36.0 243 248 1.0
6 2250 33.1 35.5 228 245 1.5
[0033] While various embodiments of the new technology described herein
have been
described in detail, it is apparent that modifications and adaptations of
those embodiments will
occur to those skilled in the art. However, it is to be expressly understood
that such
modifications and adaptations are within the spirit and scope of the presently
disclosed
technology.
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