Note: Descriptions are shown in the official language in which they were submitted.
WO 2015/021244
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HIGH STRENGTH ALUMINUM ALLOY FIN STOCK FOR HEAT EXCHANGER
CROSS REFERENCE TO RELATED APPLICATIONS
The present application claims the benefit of U.S. provisional patent
application Serial
No. 61/863,572 filed August 8. 2013, and U.S. provisional patent application
Serial No.
611863,568 Fled .August 8, 201.3.
FIELD OF THE INVENTION
[0001] The present
invention relates to the fields of material science, material chemistry,
metallurgy, aluminum alloys, aluminum fabrication, and related fields. '[he
present invention
provides novel aluminum alloys for use in the production of heat exchanger
fins, which are,
in turn, employed in various heat exchanger devices, for example, motor
vehicle radiators,
condensers, evaporators and related devices.
BACKGROUND
[0002] There is a
need for aluminum alloy fin stock material with high strength, for use in
various heat exchanger applications, including radiators for automobiles.
There is also a need
to obtain aluminum alloy fin stock material with strong pre-braze mechanical
properties,
good behavior during brazing, i.e., enhanced brazed material sag resistance,
and reduced lin
erosion, as well as good strength and conductivity characteristics post-braze,
for -usc in high
performance heat exchanger app! ications.
SUMMARY
100031 The present
invention provides an aluminum alloy tin stock material for use in
heat exchanger applications, such as automotive heat exchangers. This aluminum
alloy fin
stock alloy material was made by direct chill (DC) casting. The aluminum alloy
tin stock
material according to the embodiments of the present, invention has one or
more ot the
properties: high strength, desirable post-braze mechanical properties,
desirable sag
resistance, desirable corrosion resistance and desirable conductivity. The
aluminum alloy fin
stock. material according to some embodiments of the present invention
displays larger grain
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dispersoids and improved strength before brazing. Some embodiments of the
aluminum alloy
fin stock material are produced in a desirable pre-braze temper, for example,
H14.
[0004] The improved
aluminum alloy fin stock material can be used in various
applications, for example, heat exchangers. In one embodiment, the aluminum
alloy fin stock
material can be used in automotive heat exchangers, such as radiators,
condensers and
evaporators. In some embodiments, the aluminum alloy fin stock material is
useful for high
performance, light weight automotive heat exchangers. In some other
embodiments,
aluminum alloy fin stock material can be used for other brazed applications,
including, but
not limited to, HVAC applications. Other objects and advantages of the
invention will be
apparent from the following detailed description of the embodiments of the
invention.
DESCRIPTION
[0005] The present
invention provides an aluminum alloy fin stock material. This
aluminum alloy fin stock alloy material was made by direct chill (DC) casting.
Some
embodiments of the aluminum alloy fin stock material have one or more of
improved
strength, improved corrosion resistance or improved sag resistance. In some
embodiments,
the aluminum alloy fin stock material exhibits desirable pre-braze (H14)
temper mechanical
properties and desirable post-braze mechanical properties, sag resistance,
corrosion resistance
and conductivity. In some other embodiments, the aluminum alloy fin stock
material
displays larger grain size after brazing and improved strength pre-brazing.
The aluminum
alloy fin stock material can be used in various applications, for example,
heat exchangers. In
one example, the aluminum alloy fin stock material can be used in automotive
heat
exchangers, such as radiators, condensers and evaporators.
[0006] Compositions
of an aluminum alloy fin stock material fall within the scope of the
present invention. Some exemplary embodiments of the aluminum alloy fin stock
material
compositions are described below. All % values used below and throughout this
document in
reference to the amounts of constituents of the aluminum alloy fin stock
material
compositions are in weight % (wt%).
[0007] In one
embodiment, the aluminum alloy fin stock material comprises about 0.8-
1.4% Si, 0.4-0.8% Fe, 0.05-0.4% Cu, 1.2-1.7% Mn and 1.2-2.3% Zn, remainder
aluminum.
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[0008] In another
embodiment, aluminum alloy fin stock material comprises about 0.9-
1.3% Si, 0.45-0.75% Fe, 0.10-0.30% Cu, 1.3-1.7% Mn and 1.30-2.2% Zn, remainder
aluminum.
[0009] Tn yet
another embodiment, the aluminum alloy fin stock material comprises about
0.9-1.2% Si, 0.50-0.75% Fe, 0.15-0.30% Cu, 1.4-1.6% Mn and 1.4-2.1% Zn,
remainder
aluminum.
[0010] In one
embodiment, the DC fin stock material comprises 0.9-1.1% Si, 0.10-0.25%
Cu, 0.45-0.7% Fe, 1.4-1.6% Mn, and 1.4-1.7% Zn with the remainder Al.
[0011] In yet
another embodiment, the aluminum alloy fin stock material comprises 0.90-
1.0% Si, 0.15-0.25% Cu, 0.5-0.6% Fe, 1.5-1.6% Mn, and 1.5-1.6% Zn, remainder
Al.
[0012] In yet
another embodiment, the aluminum alloy fin stock material comprises 0.9-
1% Si, 0.2% Cu, 0.5-0.6% Fe, 1.5-1.6% Mn, and 1.5-1.6% Zn, remainder Al.
[0013] In yet
another embodiment, the aluminum alloy fin stock material comprises 0.9-
0.95% Si, 0.2% Cu, 0.5-0.6% Fe, 1.5-1.6% Mn, and 1.5-1.6% Zn, remainder Al.
[0014] In another
embodiment, the aluminum alloy fin stock material comprises 0.90-
0.95% Si, 0.15-0.20% Cu, 0.55% Fe, 1.5% Mn, and 1.5% Zn, remainder Al.
[0015] In yet
another embodiment, the aluminum alloy fin stock material comprises
0.95% Si, 0.15% Cu, 0.55% Fe, 1.5% Mn, and 1.5% Zn, remainder Al.
[0016] In yet
another embodiment, the aluminum alloy fin stock material comprises 0.90-
0.95% Si, 0.15-0.20% Cu, 0.5-0.6% Fe, 1.5% Mn and 1.5% Zn, remainder Al.
[0017] In yet
another embodiment, the aluminum alloy fin stock material comprises 1.0-
1.2% Si, 0.2-0.3% Cu, 0.5-0.6% Fe, 1.4-1.55% Mn, and 1.9-2.1% Zn, remainder
Al.
[0018] In yet
another embodiment, the aluminum alloy fin stock material comprises
0.95% 0.05 Si, 0.2% 0.05 Cu, 0.6% 0.1 Fe, 1.45% 0.05 Mn, and 1.55%+0.1 Zn,
remainder
Al.
[0019] In one more
embodiment, the aluminum alloy fin stock material comprises
1.15%+0.05 Si, 0.25%+0.05 Cu, 0.6%+0.1 Fe, 1.5%+0.05 Mn, and 2.0%+0.1 Zn,
remainder
Al.
[0020] Optionally,
Cr and/or Zr or other grain size controlling elements may be present in
the aluminum alloy fin stock material compositions in an amount of up to 0.2%
each, up to
0.15% each, up to 0.1%, each, up to 0.05 % each, or up to 0.03% each. It is to
be understood
that the aluminum alloy fin stock material compositions described herein may
contain other
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minor elements, sometimes referred to as unintentional elements, in an amount
typically
below 0.05%.
[0021] Some
embodiments of the aluminum alloy fin stock materials of the present
invention display a higher solidus temperature, referred to as onset of
melting, leading to
improved core shrinkage, a phenomenon in which brazed aluminum alloy units do
not have
the desired shape. While not wanting to be bound by the following statement,
it is believed,
based on differential scanning calorimetry (DSC) measurements and Thermo-Cale
software
(Stockholm, Sweden) simulations, that lowering the Si content and the Zn
content and
increasing the Mn content in aluminum alloy fin stock material compositions
can lead to
higher onset of melting temperature (solidus), which contributes to core
shrinkage reduction.
In one example, an aluminum alloy fin stock material composition according to
the
embodiments of the present invention displays a solidus temperature above 617
C and a
coarse post braze grain size of about 400 tm. In one more example, limiting
the Si content
of the alloy to 0.9-1% (preferably to 0.9-0.95%) and the Zn content to 1.5-
1.6%, while
maintaining the Mn content relatively high (for example, around 1.5%) raises
the solidus
temperature of the alloy, which, in turn, strengthens the material at the
brazing temperature,
so that it can resist sag or high temperature creep that can result in core
shrinkage.
[0022] Some
embodiments of the present invention relate to aluminum alloy fin stock
materials having a defined composition and obtained by processes that include
defined
process steps and conditions. A combination of defined composition and
production process
can lead to improved properties of the aluminum alloy fin stock materials. One
example of
such improved properties are improved pre-braze mechanical properties.
Improved pre-braze
mechanical properties (also referred to as properties "in pre-braze
condition") result in
improved fin crush resistance during assembly, while maintaining suitable sag
resistance and
thermal conductivity after brazing (post-brazing).
[0023] The
processes of producing aluminum alloy fin stock materials according to
embodiments of the present invention involve the step of producing an ingot by
a direct chill
(DC) casting process, which is commonly used throughout the aluminum industry,
whereby a
large ingot ¨1.5 m x 0.6 m x 4 m is cast from a large holding furnace which
supplies metal to
a shallow mold or molds supplied with cooling water. The solidifying ingot is
continuously
cooled by the direct impingement of the cooling water and is withdrawn slowly
from the base
of the mold until the full ingot or ingots are completed. Once cooled from the
casting process,
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the ingot rolling surfaces are machined to remove surface segregation and
irregularities. The
machined ingot is preheated for hot rolling. The preheating temperature and
duration are
controlled to low levels to preserve a large grain size and high strength
after the finished fin
stock is brazed. Several ingots (about 8 to 30) are charged to a furnace and
preheated with
gas or electricity to the rolling temperature. The period of maintaining a
temperature
achieved by pre-heating can also be referred to as "soak" or "soaking. In one
embodiment,
the minimum soak time at about 480 C is about 2 hours (in other words, at
least 2 hours). In
another embodiment, the soak time is 4-16 hours at 480 C. Aluminum alloys are
typically
rolled in the range of about 450 C to about 560 C. If the temperature is too
cold, the roll
loads are too high, and if the temperature is too hot, the metal may be too
soft and break up in
the mill.
[0024] The
processes for making some embodiments of the aluminum alloy fin stock
materials, may involve one or more cold rolling steps. Each of the cold
rolling steps may, in
turn, involve multiple cold rolling passes. A cold rolling step characterized
by "% cold
work" or %CW achieved. Generally, % CW can be defined as the degree of cold
rolling
applied to the aluminum alloy fin stock. As used in the present document, %CW
is
calculated as:
intial gauge - final gague
% CW = __________________________________ *100%
intial gauge
[0025] Achieving a
specified range or value of % CW may be desirable in order to attain
the required strength range of the aluminum alloy fin stock material. Some
embodiments of
the of the aluminum alloy fin stock materials are produced by processes that
involve a cold
rolling step achieving 25-35 %CW. In some examples, a cold rolling step
achieving %CW
of 25% or 29% may be employed. In some cases, increasing %CW, for example, to
35%
leads to an increase in pre-braze tensile strength of the aluminum alloy fin
stock material,
which, in turn, beneficially reduces the fin crush during radiator assembly.
In some other
cases, increasing the %CW, however, may be undesirable, as it may lead to
finer post braze
grain size due to an increase in the driving force for recrystallization,
resulting in reduced
sag resistance.
[0026] The
processes for making some embodiments of the aluminum alloy fin stock
materials may also involve an inter-annealing step to attain desired
properties of the
aluminum alloy fin stock material according to the embodiments of the present
invention.
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The term "inter-annealing" or "inter-anneal" (IA) refers to a heat treatment
applied between
cold rolling steps. IA temperature may affect the properties of the aluminum
alloy fin stock
materials according to the embodiments of the present invention. For example,
an
investigation of the IA temperature used in the processes for making certain
embodiments of
the aluminum alloy fin stock materials showed that reducing the IA temperature
from 400 C
to 350 C resulted in coarser post-braze grain size. In some embodiments of the
aluminum
alloy fin stock materials, a combination of %CW and IA temperature employed in
the
production process results in desirable properties. In one example, a
combination of IA
temperature of 350 C and %CW of 35% led to beneficial combination of post-
braze grain
size and sag resistance the aluminum alloy fin stock material. In another
example, a
combination of IA temperature of 300 C and %CW of 25% led to beneficial
combination of
post-braze grain size and sag resistance the aluminum alloy fin stock
material. In another
example, a combination of IA temperature and %CW during processing of the
aluminum
alloy fin stock material in H14 temper resulted in improved fin crush
resistance.
Accordingly, the processes of producing aluminum alloy fin stock materials
employing
specified IA temperature and %CW, which lead, in some examples, to higher pre-
braze
tensile strength and improved fin crush resistance during assembly, are
included within the
embodiments of the present invention.
[0027] Once
preheated, the ingot is hot rolled to form a coil which is then cold rolled.
The cold rolling process takes place in several steps, and a step of inter-
annealing is
employed between cold-rolling steps to reciystallize the material prior to the
final cold rolling
step. IA temperature in the range of about 275-400 C, 300-400 C, 300-450 C,
340-460 C,
or 325-375 C may be employed. For example, IA temperature of about 300 C, 350
C or
400 C may be employed in the processes of producing aluminum alloy fin stock
materials
according to embodiments of the present invention. After inter-annealing, the
aluminum
alloy fin stock material is cold rolled in the final cold rolling step to
obtain the desired final
gauge or thickness. After the final cold rolling step, the aluminum alloy fin
stock material
can be slit into narrow strips suitable for the manufacture of radiators and
other automotive
heat exchangers. In some embodiments the processes of producing aluminum alloy
fin stock
materials according to embodiments of the present invention, %CW employed in
the final
cold rolling step is 20-35% or 25-35%, for example, about 25% or 29%.
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[0028] Various
combinations of production parameters may be beneficially employed in
the processes for processes of producing aluminum alloy fin stock materials
according to
embodiments of the present invention. In one example, %CW in the range 25-35%
is
employed in the final rolling step, resulting in improved pre-braze yield
strength and tensile
strength of the aluminum alloy fin stock materials, which, in turn, leads to
reduction in the fin
crush occurrence during assembly. In another example, selecting IA temperature
of about
350 C results in larger post-braze grain size. In one more example, using %CW
of about
29% during the final cold rolling step further increases post-braze grain
size. In yet another
example, inter-annealing at 350 C for 4 hours is employed in combination with
29% CW in
the final cold rolling step, which results in a material with desirable
characteristics of good
pre-braze strength and large post-braze grain size, high thermal conductivity
and good sag
behavior. In yet another example, inter-annealing at 400 C for an average of
about 3 hours is
employed, followed by applying % cold work (CW) of about 29% to achieve final
gauge. In
yet another example, soaking at about 480 C for an average of 4 hours is
employed during
the hot-rolling step, in combination with interannealing at about 300-400 C
and % CW in the
final cold-rolling step of about 25-35% to final gauge. In yet another
example, soaking at
480 C for 4-16 hours in hot rolling step is employed in combination with
interannealing at
350 C and %CW of 29% in the final rolling step. In yet another example,
soaking at 480 C
for 4-16 hours in hot rolling step is employed in combination with
interannealing at 400 C
and %CW of 29% in the final rolling step. In one more example, soaking at 480
C for an
average of 4 hours in hot rolling step is employed in combination with
interannealing at of
350 C and %CW of 35% in the final rolling step. In one more example, inter-
annealing at
325-375 C and 20-35% CW, such as interannealing at 300 C and CW 25% in the
final cold
rolling step is employed.
[0029] The aluminum
alloy fin stock materials produced according to some embodiments
of the present invention are produced as sheets varying in gauge (thickness)
between 45 p.m
and 80 p.m. The aluminum alloy fin stock material according to the embodiments
of the
present invention has one or more of the following properties: minimum
ultimate tensile
strength (UTS) of 130 MPa (in other words, 130 MPa or more, or at least 130
MPa) measured
post-brazing (for example, 134 or 137 MPa); average conductivity value of
about 43%, about
41.5%, about 42.7% or about 43.3% (International Annealed Copper Standard
(IACS)); an
open circuit potential corrosion value vs. Standard Calomel Electrode (SCE) of
-680mV or
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less, -700 mV or less or -740 or less (for example, -710mv, -720 my, -724 my, -
725 my, -743
my, -740mV or -758 mV); a sag value between 7 mm, where the final gauge was
47.5 gm,
and 5 mm, where the final gauge was 50 gm, with a cantilevered length of 35
mm. The
above properties of aluminum alloy fin stock material sheets are measured
after applying a
faster braze cycle, whereby the material is heated to a temperature of 605 C
and cooled to
room temperature in a period of about 20 minutes, to simulate the temperature
time profile of
a commercial brazing process. The aluminum alloy fin stock material according
to the
embodiments of the present invention can have UTS pre-brazing in the range of
180-220
IVIPa (for example, 185 or 190 MPa). The aluminum alloy fin stock material
according to the
embodiments of the present invention can also have grain size >200 gm for
example, 200 or
400 gm
[0030] The
following examples will serve to further illustrate the present invention
without, at the same time, however, constituting any limitation thereof. On
the contrary, it is
to be clearly understood that resort may be had to various embodiments,
modifications and
equivalents thereof which, after reading the description herein, may suggest
themselves to
those skilled in the art without departing from the spirit of the invention.
Example 1
[0031] An aluminum
alloy fin stock material was made by a process that involved DC
casting, preheating the ingot to 480 C for about 8 hours, followed by hot
rolling to about 2.5
mm, cold rolling, and inter-annealing at 350 C for about 2 hours prior to
final cold rolling
step. The composition range of the aluminum alloy fin stock material was
within the
following specification: 1.1 0.1% Si, 0.6 0.1% Fe, 0.2 0.05% Cu, 1.4 0.1% Mn
and
1.50 0.1% Zn, with the remainder Al. The aluminum alloy fin stock material
produced
varied in gauge between 49 and 83 gm. The aluminum alloy fin stock material
had a
minimum ultimate tensile strength of ¨130MPa. The aluminum alloy fin stock
material had
an average conductivity after brazing of ¨43 IACS and an open circuit
potential corrosion
value vs. SCE of -741 mV. These values were measured after applying a
simulated brazing
cycle, whereby the sample was heated to a temperature of 605 C and cooled to
room
temperature in a period of about 20 minutes to simulate the temperature time
profile of a
commercial brazing process.
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Example 2
100321 Two samples of
aluminum alloy fin stock material were made by a process that
involved DC casting, followed by hot rolling with pre-beating at 480 C for 4-
16 hours, cold
rolling, and inter-annealing at 350 C for the first sample and at 400 C for
the second sample,
prior to thud cold rolling to 29% %CW . The composition of the first sample
was: 0.95% Si,
0.6% Fe, 0.2% Cu, 1.45% Mn and 1.5.5% Zn, with the remainder Al. The
composition of the
second sample was: 1.15% Si, 0.6% Fe, 0.25% Cu, 1,5% Mn and 2% Zit, with the
remainder
Al. The aluminum alloy fin stock material had a post-braze ultimate tensile
strength of ¨134
-MPa for the first sample and ¨137 MPa for the second sample. The aluminum
alloy fin stock
material had an average conductivity after brazing of ¨42.7 1ACS for the first
sample and
¨43.3 IACS for the second sample. The aluminum alloy fin stock material had an
open
circuit potential corrosion -value vs. SCE of -710 niV for the first sample
and -743mV for the
second sample. The aluminum alloy fin stock material had a grain size of 400
um for the
first sample and 200 pm for the second sample. The aluminum alloy fin stock
material
exhibited pre-braze UTS of 1X5MPa for the firm sample and 190 M.Pa for the
second sample.
The comparison between the two samples revealed that both samples produced
attractive
mechanical properties, but the open circuit potential corrosion value of the
first sample was
lower, indicating that increase in Zn content may be desirable. The second
sample had
advantageously lower open circuit potential corrosion value.
100331
Various embodiments of the invention
have been described in fulfillment of the various objectives of the invention.
It should be
recognized that these embodiments are merely illustrative of the principles of
the present
invention. Numerous modifications and adaptations thereof will be readily
apparent to those
of skill in the art without departing from the spirit and scope of the
invention as defined in the
following claims.
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