U.S. patent application number 16/266240 was filed with the patent office on 2019-06-06 for optimization of aluminum hot working.
This patent application is currently assigned to Novelis Inc.. The applicant listed for this patent is Novelis Inc.. Invention is credited to Duane E. Bendzinski, Rahul Vilas Kulkarni, Rashmi Ranjan Mohanty.
Application Number | 20190169726 16/266240 |
Document ID | / |
Family ID | 57121545 |
Filed Date | 2019-06-06 |
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United States Patent
Application |
20190169726 |
Kind Code |
A1 |
Mohanty; Rashmi Ranjan ; et
al. |
June 6, 2019 |
OPTIMIZATION OF ALUMINUM HOT WORKING
Abstract
A method of hot forming an aluminum alloy component may include
heating the aluminum alloy component in a heating furnace to a
solutionizing temperature, cooling the aluminum alloy component to
a desired forming temperature, deforming the aluminum alloy
component into a desired shape in a forming device while the
aluminum alloy component is at the desired forming temperature,
maintaining a constant temperature during the deformation of the
aluminum alloy component, and quenching the aluminum alloy
component to a low temperature below a solvus temperature.
Inventors: |
Mohanty; Rashmi Ranjan;
(Roswell, GA) ; Bendzinski; Duane E.; (Woodstock,
GA) ; Kulkarni; Rahul Vilas; (Marietta, GA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Novelis Inc. |
Atlanta |
GA |
US |
|
|
Assignee: |
Novelis Inc.
Atlanta
GA
|
Family ID: |
57121545 |
Appl. No.: |
16/266240 |
Filed: |
February 4, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15276955 |
Sep 27, 2016 |
10266932 |
|
|
16266240 |
|
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62238960 |
Oct 8, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B21B 45/004 20130101;
B21B 3/00 20130101; C22C 21/10 20130101; B21D 22/022 20130101; B21B
2003/001 20130101; C22F 1/053 20130101 |
International
Class: |
C22F 1/053 20060101
C22F001/053; C22C 21/10 20060101 C22C021/10; B21D 22/02 20060101
B21D022/02; B21B 45/00 20060101 B21B045/00; B21B 3/00 20060101
B21B003/00 |
Claims
1. A method of hot forming an aluminum alloy component, the method
comprising: heating the aluminum alloy component in a heating
furnace to a solutionizing temperature; cooling the aluminum alloy
component to a desired forming temperature; transferring the
aluminum alloy component from the heating furnace to a forming
device; deforming the aluminum alloy component into a desired shape
in the forming device while the aluminum alloy component is at the
desired forming temperature; and quenching the aluminum alloy
component to a low temperature below a solvus temperature, wherein
the low temperature is in a range of approximately 0.degree. C. to
approximately 280.degree. C., wherein the heating of the aluminum
alloy component to the solutionizing temperature occurs over a
period of approximately 5 minutes.
2. The method of claim 1, wherein the aluminum alloy component
comprises a 7xxx alloy.
3. The method of claim 2, wherein the aluminum alloy component
comprises a 7075 alloy.
4. The method of claim 1, wherein the desired forming temperature
is in a range of approximately 400.degree. C. to approximately
440.degree. C.
5. The method of claim 1, wherein the solutionizing temperature is
in a range of approximately 400.degree. C. to approximately
600.degree. C.
6. The method of claim 5, wherein the solutionizing temperature is
approximately 480.degree. C.
7. The method of claim 1, further comprising artificially aging the
aluminum alloy component.
8. The method of claim 1, further comprising maintaining a constant
temperature during the deformation of the aluminum alloy component,
wherein the constant temperature is held to within .+-.10.degree.
C.
9. The method of claim 1, wherein: the aluminum alloy component is
an ingot; the forming device is a rolling mill; and the desired
shape is a plate or a sheet.
10. The method of claim 1, wherein the forming device is a forming
press.
11. The method of claim 1, further comprising maintaining the
aluminum alloy component at the solutionizing temperature for a
predetermined time, wherein the predetermined time is up to
approximately 30 minutes.
12. The method of claim 1, wherein the quenching comprises die
quenching with water flowing internally through a die such that the
aluminum alloy component is cooled at a rate between approximately
50.degree. C./second and approximately 500.degree. C./second.
13. A method of hot forming an aluminum alloy component, the method
comprising: heating the aluminum alloy component in a heating
furnace to a solutionizing temperature; cooling the aluminum alloy
component to a desired forming temperature in a range of
approximately 380.degree. C. to approximately 470.degree. C.;
deforming the aluminum alloy component into a desired shape in a
forming device while the aluminum alloy component is at the desired
forming temperature; and quenching the aluminum alloy component to
a low temperature below a solvus temperature, wherein the low
temperature is in a range of approximately 0.degree. C. to
approximately 280.degree. C., wherein heating the aluminum alloy
component in the heating furnace results in an approximate grain
size of 10-35 microns for the aluminum alloy component.
14. The method of claim 13, wherein the desired forming temperature
is in a range of approximately 400.degree. C. to approximately
440.degree. C.
15. The method of claim 13, wherein the heating of the aluminum
alloy component to the solutionizing temperature occurs in a range
of approximately 10 seconds to 15 minutes.
16. The method of claim 15 wherein the heating of the aluminum
alloy component to the solutionizing temperature occurs in
approximately 5 minutes.
17. The method of claim 13, further comprising maintaining a
constant temperature during the deformation of the aluminum alloy
component, wherein the constant temperature is held to within
.+-.10.degree. C.
18. The method of claim 13, wherein: the aluminum alloy component
is an ingot; the forming device is a rolling mill; and the desired
shape is a plate or a sheet.
19. The method of claim 13, wherein the forming device is a forming
press.
20. A method of hot forming an aluminum alloy component, the method
comprising: heating the aluminum alloy component in a heating
furnace to a solutionizing temperature, wherein the heating is
performed at a rate such that (i) the aluminum alloy component
reaches the solutionizing temperature after a period of at least 5
minutes and (ii) the aluminum alloy component comprises an
approximate grain size of at least 10 microns; cooling the aluminum
alloy component to a desired forming temperature in a range of
approximately 380.degree. C. to approximately 470.degree. C.;
deforming the aluminum alloy component into a desired shape in a
forming device while the aluminum alloy component is at the desired
forming temperature; and quenching the aluminum alloy component to
a low temperature below a solvus temperature, wherein the low
temperature is in a range of approximately 0.degree. C. to
approximately 280.degree. C.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation application of U.S.
patent application Ser. No. 15/276,955, filed Sep. 27, 2016,
entitled OPTIMIZATION OF ALUMINUM HOT WORKING, which claims
priority benefits from U.S. Provisional Application Ser. No.
62/238,960 ("the '960 application"), filed on Oct. 8, 2015,
entitled OPTIMIZATION OF ALUMINUM HOT WORKING, which are each
incorporated herein by reference in their entirety.
FIELD
[0002] This invention relates to processes for hot working or hot
forming aluminum and optimizing manufacturing variables.
BACKGROUND
[0003] Aluminum alloys can be grouped into two categories:
heat-treatable alloys and non-heat-treatable alloys. Heat-treatable
alloys are capable of being strengthened and/or hardened during an
appropriate thermal treatment whereas no significant strengthening
can be achieved by heating and cooling non-heat-treatable alloys.
Alloys in the 2xxx, 6xxx, and 7xxx series (and some 8xxx alloys)
are heat-treatable. Alloys in the 1xxx, 3xxx, 4xxx, and 5xxx series
(and some 8xxx alloys) are non-heat-treatable. Hot working is
plastic deformation of metal at such temperature and rate that
strain hardening (i.e., cold working) does not occur.
[0004] A heat-treatable aluminum alloy component ("component") may
undergo solution heat treating. Solution heat treating may include
three stages: (1) solution heating, which may include both heating
and soaking (at a given temperature) of the component; (2)
quenching; and (3) aging. The heating and soaking step dissolves
large particles and disperses the particles as smaller precipitates
or dissolved atoms (acting as soluble hardening elements) to
strengthen the component. Quenching, or rapid cooling, effectively
freezes or locks the dissolved elements in place (i.e., still
dispersed) to produce a solid solution with more alloying elements
in solution at room temperature than would otherwise occur with a
slow cool down.
[0005] The aging step allows the alloying elements dissolved in the
solid solution to migrate through cool metal (even at room
temperature) but not as fast or as far as they could at high
temperatures. Accordingly, atoms of dissolved alloying elements may
slowly gather to form small precipitates with relatively short
distances between them, but not large, widely-spaced particles. The
quantity and high density of small dislocation-pinning precipitates
gives the alloy its strength and hardness because the precipitates
have a different elastic modulus compared to that of the primary
element (aluminum) and thus inhibit movement of the dislocations,
which are often the most significant carriers of plasticity. The
aging may be natural or artificial. Some alloys reach virtually
maximum strength by "natural aging" in a short time (i.e., a few
days or weeks). However, at room temperature, some alloys will
strengthen appreciably for years. To accelerate precipitation,
these alloys undergo "artificial aging," which includes maintaining
the component for a limited time at a moderately raised
temperature, which increases the mobility of dissolved elements and
allows them to precipitate more rapidly than at room
temperature.
[0006] Conventionally, because some alloys have poor formability
(i.e., the ability to undergo plastic deformation without being
damaged) at room temperature, to shape components of these alloys
into desired geometric shapes, these components may undergo hot
working (or hot forming) after solution heating and before
quenching at temperatures at or near the solutionizing temperature.
For example, see U.S. Patent Application Publication 2012/0152416
(the '416 Publication), which describes that the transfer between
the heating station to the forming press should be as fast as
possible to avoid heat loss from the aluminum (see paragraph [0035]
and FIG. 1). Hot working or hot forming processes may include, for
example, drawing, extrusion, forging, hot metal gas forming, and/or
rolling.
[0007] There is a known problem with hot working some aluminum
alloys (in particular, 7xxx alloys) where components exhibit
unsatisfactory deformability. For example, see N. M. Doroshenko et
al., Effect Of Admixtures Of Iron And Silicon on the Structure and
Cracking of Near-Edge Volumes in Rolling of Large Flat Ingots from
Alloy 7075, Metal Science and Heat Treatment, Vol. 47, Nos. 1-2,
2005 at 30 ("Doroshenko"). Doroshenko focuses on hot rolling of
7xxx and the resultant cracks. To address this problem, Doroshenko
describes analysis and proposed guidelines for the particular
chemical composition of 7xxx alloys.
[0008] There is a need for improving the deformability of aluminum
alloys (particularly 7xxx alloys) during hot forming processes
without exhaustive analysis and modification of the chemical
composition of the alloy.
SUMMARY
[0009] The terms "invention," "the invention," "this invention" and
"the present invention" used in this patent are intended to refer
broadly to all of the subject matter of this patent and the patent
claims below. Statements containing these terms should be
understood not to limit the subject matter described herein or to
limit the meaning or scope of the patent claims below. Embodiments
of the invention covered by this patent are defined by the claims
below, not this summary. This summary is a high-level overview of
various aspects of the invention and introduces some of the
concepts that are further described in the Detailed Description
section below. This summary is not intended to identify key or
essential features of the claimed subject matter, nor is it
intended to be used in isolation to determine the scope of the
claimed subject matter. The subject matter should be understood by
reference to appropriate portions of the entire specification of
this patent, any or all drawings and each claim.
[0010] According to certain examples of the present invention, a
method of hot forming an aluminum alloy component comprises:
heating the aluminum alloy component in a heating furnace to a
solutionizing temperature; cooling the aluminum alloy component to
a desired forming temperature in a range of approximately
380.degree. C. to approximately 470.degree. C.; deforming the
aluminum alloy component into a desired shape in a forming device
while the aluminum alloy component is at the desired forming
temperature; and quenching the aluminum alloy component to a low
temperature below a solvus temperature wherein the low temperature
is in a range of approximately 0.degree. C. to approximately
280.degree. C.
[0011] In some examples, the aluminum alloy component comprises a
7xxx alloy. In certain examples, the aluminum alloy component
comprises a 7075 alloy.
[0012] In some cases, the desired forming temperature range may be
approximately 390.degree. C. to approximately 460.degree. C. or in
a range of approximately 400.degree. C. to approximately
440.degree. C. In some cases, the desired forming temperature is
approximately 425.degree. C.
[0013] The solutionizing temperature, in certain examples, is in a
range of approximately 400.degree. C. to approximately 600.degree.
C. In some examples, the solutionizing temperature is in a range of
approximately 420.degree. C. to approximately 590.degree. C. or
approximately 460.degree. C. to approximately 520.degree. C. In
some examples, the solutionizing temperature has a minimum value of
480.degree. C. and in some cases is equal to approximately
480.degree. C.
[0014] In certain examples, the method of hot forming an aluminum
alloy component includes artificially aging the aluminum alloy
component.
[0015] The method of hot forming an aluminum alloy component, in
some examples, includes maintaining a constant temperature during
the deformation of the aluminum alloy component wherein the
constant temperature is held .+-.10.degree. C.
[0016] In some examples, the aluminum alloy component comprises an
ingot, the forming device comprises a rolling mill, and the desired
shape comprises a plate or a sheet. In some cases, the forming
device is a forming press.
[0017] The method of hot forming an aluminum alloy component, in
some examples, includes maintaining the aluminum alloy component at
the solutionizing temperature for a predetermined time.
[0018] In certain examples, the method of hot forming an aluminum
alloy component includes transferring the aluminum alloy component
from the heating furnace to the forming device through an insulated
enclosure.
[0019] In some examples, the quenching comprises die quenching with
water flowing internally through a die such that the aluminum alloy
component is cooled at a minimum rate of approximately 50.degree.
C./second. The cooling rate may be between approximately 50.degree.
C./second and approximately 500.degree. C./second, and, in some
examples, may be between 300.degree. C./second and approximately
350.degree. C./second.
[0020] According to certain examples, a method of hot forming an
aluminum alloy component comprises: heating the aluminum alloy
component in a heating furnace to a solutionizing temperature of
approximately 480.degree. C.; cooling the aluminum alloy component
to a desired forming temperature in a range of approximately
400.degree. C. to approximately 440.degree. C.; deforming the
aluminum alloy component into a desired shape in a forming device
while the aluminum alloy component is at the desired forming
temperature; maintaining a constant temperature during the
deformation of the aluminum alloy component, wherein the constant
temperature is held .+-.10.degree. C.; and quenching the aluminum
alloy component to a low temperature below a solvus temperature,
wherein the low temperature is approximately 23.degree. C.
[0021] In some examples, the aluminum alloy component comprises a
7xxx alloy. In certain embodiments, the aluminum alloy component
comprises a 7075 alloy.
[0022] In certain examples, the method of hot forming an aluminum
alloy component includes artificially aging the aluminum alloy
component.
[0023] In some examples, the aluminum alloy component comprises an
ingot, the forming device comprises a rolling mill, and the desired
shape comprises a plate or a sheet.
[0024] The forming device, in certain examples, comprises a forming
press.
[0025] The method of hot forming an aluminum alloy component, in
some examples, includes maintaining the aluminum alloy component at
the solutionizing temperature for a predetermined time.
[0026] In certain examples, the method of hot forming an aluminum
alloy component includes transferring the aluminum alloy component
from the heating furnace to the forming device through an insulated
enclosure.
[0027] In some examples, the quenching comprises die quenching with
water flowing internally through a die such that the aluminum alloy
component is cooled at a rate between approximately 50.degree.
C./second and approximately 500.degree. C./second.
[0028] The methods described herein may prevent edge cracking on
ingots during hot rolling processes for aluminum alloys, including
7xxx alloys, such as but not limited to 7075 alloy. In addition,
the disclosed processes may be used to optimize joining processes
and other forming processes such as hot gas forming, drawing,
extrusion, and forging. These optimizations can increase production
efficiency, improve yields, reduce energy expenditures, reduce
scrap, and improve overall productivity. These improvements to hot
forming of 7xxx alloys may have significant implications for
numerous industries where high strength-to-weight ratio materials
are desired such as, for example, the transportation and aerospace
industries, particularly the manufacture of motor vehicles such as
automobiles and trucks.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Illustrative, but non-limiting, embodiments of the present
invention are described in detail below with reference to the
following drawing figures.
[0030] FIG. 1 is a schematic view of an exemplary method of hot
forming an aluminum alloy component.
[0031] FIG. 2 is a temperature plot of the method of FIG. 1.
[0032] FIG. 3 is a stress-strain plot for aluminum alloy components
tested in compression for various temperatures.
[0033] FIG. 4 shows aluminum alloy tensile test samples for various
temperatures.
[0034] FIG. 5 is a stress-strain plot for aluminum alloy components
tested in tension for various temperatures.
[0035] FIG. 6A is a stress-strain plot for aluminum alloy
components tested in tension for various temperatures.
[0036] FIG. 6B is a stress-strain plot for aluminum alloy
components tested in tension for various temperatures.
[0037] FIG. 6C is a stress-strain plot for aluminum alloy
components tested in tension for various temperatures.
[0038] FIG. 7A is a magnified view showing grain structures of an
aluminum alloy component.
[0039] FIG. 7B is a magnified view showing grain structures of an
aluminum alloy component.
[0040] FIG. 7C is a magnified view showing grain structures of an
aluminum alloy component.
[0041] FIG. 8A is a stress-strain plot for aluminum alloy
components tested in tension after being heated at various
rates.
[0042] FIG. 8B is a stress-strain plot for aluminum alloy
components tested in tension after being heated at various
rates.
[0043] FIG. 9A is a magnified view showing grain structures of an
aluminum alloy component that was heated to solutionizing
temperature in approximately 10 seconds.
[0044] FIG. 9B is a magnified view showing grain structures of an
aluminum alloy component that was heated to solutionizing
temperature in approximately 5 minutes.
DETAILED DESCRIPTION
[0045] This section describes non-limiting examples of processes
for hot forming aluminum alloys and does not limit the scope of the
claimed subject matter. The claimed subject matter may be embodied
in other ways, may include different elements or other attributes,
and may be used in conjunction with other existing or future
technologies. This description should not be interpreted as
requiring any particular order or arrangement among or between
various elements.
[0046] In this description, reference is made to alloys identified
by AA numbers and other related designations, such as "series." For
an understanding of the number designation system most commonly
used in naming and identifying aluminum and its alloys, see
"International Alloy Designations and Chemical Composition Limits
for Wrought Aluminum and Wrought Aluminum Alloys" or "Registration
Record of Aluminum Association Alloy Designations and Chemical
Compositions Limits for Aluminum Alloys in the Form of Castings and
Ingot," both published by The Aluminum Association.
[0047] FIGS. 1-9B illustrate examples of hot working aluminum alloy
components. As shown in FIGS. 1 and 2, a method of hot forming an
aluminum alloy component (e.g., component 50) may include removing
the component 50 from a supply of alloy blanks 104, heating the
component 50 in a heating furnace 103 to a solutionizing
temperature Y, cooling the component 50 to a desired forming
temperature T.sub.F, deforming the component 50 into a desired
shape in a forming device 102 while the component 50 is at the
desired forming temperature T.sub.F, quenching the component 50 to
a low temperature below a solvus temperature X, and artificially
aging the component 50.
[0048] To effectively hot form a 7xxx aluminum alloy component, the
component must be heated to increase ductility (i.e., a measure of
the degree to which a material may be deformed without breaking)
and to eliminate strain hardening. In general, the ductility of
aluminum increases with increasing temperature. However,
experiments have been conducted for both tensile and compressive
tests for 7xxx alloys, which contradict this characteristic. For
example, FIG. 4 shows four "dog bone" tensile test specimens for
7075 alloy. The first specimen 401 is from a tensile test completed
at 425.degree. C. The three remaining test specimens are from
higher temperature tests (25.degree. C. increments) where 402 is
from a 450.degree. C. tensile test, 403 is from a 475.degree. C.
tensile test, and 404 is from a 500.degree. C. tensile test. As
shown in FIG. 4, the samples from the experiments conducted at
475.degree. C. and 500.degree. C., 403 and 404, respectively,
exhibit significantly less ductility compared to the 425.degree. C.
sample 401. In other words, the 500.degree. C. specimen 404
deformed significantly less (i.e., plastically deformed by
stretching in the longitudinal direction) than the 425.degree. C.
sample 401. The 425.degree. C. sample 401 and the 450.degree. C.
sample 402 show significantly more necking before failure. The
results of these tensile tests support a conclusion that 7xxx
aluminum (particularly, 7075 aluminum) does not show continuously
increasing ductility with increasing temperature. In particular, as
shown in FIG. 4, 7075 aluminum exhibits a decrease in ductility
with increasing temperature after exceeding a threshold
temperature. The threshold temperature appears to be between
400.degree. C. and 450.degree. C. Furthermore, the decrease in
ductility at these elevated temperatures has been verified in
laboratory trials of hot rolling 7075 ingots that exhibit edge
cracking.
[0049] Detailed examination of the fracture surfaces (of samples
such as those shown in FIG. 4) revealed distinct cup-and-cone
dimple fractures consistent with ductile fracture for the
425.degree. C. sample 401 while the surfaces of the 475.degree. C.
sample 403 revealed intergranular fractures consistent with brittle
fractures. In some examples, detailed examination occurred by
viewing magnified images of the samples, such as via SEM
micrograph.
[0050] Compression tests were conducted using a Gleeble 3800
thermomechanical simulator (manufactured by Dynamic Systems Inc. in
Poestenkill, N.Y.) for various temperatures with 7xxx samples. The
compression tests were conducted for 7075 samples at a constant
strain rate of 10 s.sup.-1 up to a strain of 0.5. FIG. 3
illustrates stress-strain curves for compression testing at
temperatures from 400.degree. C. to 480.degree. C. in 20.degree. C.
increments. The curves in FIG. 3 show an initial (approximately
linear) elastic deformation region 301 and a plastic deformation
region 302. The 460.degree. C. and 480.degree. C. samples each
failed under compression loading and exhibited cracks. The
480.degree. C. sample completely failed (cracked) during the test.
As shown in FIG. 3, the flow stress (i.e., the instantaneous value
of stress required to continue plastically deforming the material)
decreases with increasing temperature.
[0051] In addition to the compression tests, results of tensile
tests are shown in FIG. 5. FIG. 5 shows stress-strain curves for
tensile testing at temperatures of 390.degree. C., 400.degree. C.,
410.degree. C., 420.degree. C., 425.degree. C., 430.degree. C.,
440.degree. C., 450.degree. C., and 475.degree. C. The results show
a drop in flow stress when the temperature is increased (similar to
the compression results in FIG. 3). The results further show a
decrease in the true strain before failure with increasing forming
temperature. Samples formed at temperatures less than or
approximately 425.degree. C. (e.g., approximately 390.degree. C.,
approximately 400.degree. C., approximately 410.degree. C.,
approximately 420.degree. C., and approximately 425.degree. C.)
show true strain percentage greater than approximately 0.44% before
failure. Samples formed at temperatures greater than approximately
425.degree. C. (e.g., approximately 430.degree. C., approximately
440.degree. C., approximately 450.degree. C., and approximately
475.degree. C.) show significantly reduced true strain before
failure. As shown in FIG. 5, the alloy strength is decreased with
increasing forming temperature.
[0052] Based on the aforementioned experiments and subsequent
conclusions, a new method for hot working 7xxx aluminum alloy
components is described herein.
[0053] As shown in FIG. 1, the component 50 is removed from the
supply of alloy blanks 104 and inserted into the heating furnace
103. FIG. 2 illustrates the changes in temperature of the component
50. After entering the heating furnace 103, the temperature
increases (see 201 in FIG. 2) above the solvus temperature X (i.e.,
the limit of solid solubility). Once the component 50 reaches the
target solutionizing temperature Y, the component 50 is maintained
at the solutionizing temperature Y for a predetermined time 202.
The solutionizing temperature Y is between approximately
400.degree. C. and approximately 600.degree. C. In some cases, the
solutionizing temperature is in a range of approximately
420.degree. C. to approximately 590.degree. C. or in a range of
approximately 460.degree. C. to approximately 520.degree. C. In
some examples, the solutionizing temperature Y has a minimum value
of 480.degree. C. and in some cases is equal to approximately
480.degree. C. The predetermined time for maintaining the component
50 at the solutionizing temperature Y depends on the particular
component 50 for solution heating and may be up to 30 minutes.
[0054] After the solution heating is complete, the component 50 is
intentionally cooled (see 203 in FIG. 2) to a desired forming
temperature T.sub.F (see 204 in FIG. 2). This cooling step 203
before forming contradicts the '416 Publication, which explicitly
discloses immediate forming and requires minimal heat loss before
forming in an attempt to form at temperatures close to if not equal
to the heat treatment temperature.
[0055] In some examples, the cooling step 203 occurs during the
transfer from the heating furnace 103 to the forming device 102. As
shown in FIG. 1, the component 50 may be transferred via an
insulated enclosure 101. The transfer between the heating furnace
103 and the forming device 102 occurs in a predetermined time. This
predetermined time may be several minutes, such as, for example, 1,
2, or 3 minutes. In some non-limiting examples, this predetermined
time may be less than 60 seconds and, in particular, may be
approximately 20 seconds.
[0056] Once the component 50 reaches the desired forming
temperature T.sub.F, the forming process 204 (FIG. 2) occurs in the
forming device 102 (FIG. 1). As shown in FIG. 2, the temperature of
the component 50 may be held approximately constant at the desired
forming temperature T.sub.F during the forming process. The forming
temperature T.sub.F may be any temperature in the range of
approximately 380.degree. C. to approximately 470.degree. C., for
example in the range of approximately 390.degree. C. to
approximately 460.degree. C. or in the range of approximately
400.degree. C. to approximately 440.degree. C. The temperature of
the component 50, for example, may be held constant at the desired
forming temperature T.sub.F.+-.10.degree. C., may be held constant
at the desired forming temperature T.sub.F.+-.5.degree. C., or may
be held constant at the desired forming temperature
T.sub.F.+-.1.degree. C. In some examples, heat may be applied to
the component 50 during the forming process in the forming device
102 to ensure the component 50 is maintained at the desired forming
temperature T.sub.F.
[0057] The effect of heating rate to the solutionizing temperature
Y for the component 50 was also evaluated, and both ductility and
microstructure were characterized. Component 50 samples were heated
to the solutionizing temperature Y (approximately 480.degree. C.)
over the following approximate time periods: 10 seconds, 5 minutes
and 15 minutes. FIG. 8A shows the tensile characteristics of the
component 50 when cooled to and maintained at 425.degree. C. after
solutionizing heat treatment. When heated quickly (approximately 10
seconds), the component 50 exhibited significantly reduced
ductility, as well as smaller grain size (see FIG. 9A). In
particular, as shown in FIG. 8A, failure for the 10 second heated
sample occurred at less than 0.35% strain, compared to failure at
greater than 0.5% for other illustrated rates. Heating the
component 50 to the solutionizing temperature Y at lower rates
(i.e., longer times) allowed higher ductility and a corresponding
larger grain size (see FIG. 9B, which shows a magnified view of the
5 minute heated sample having larger grain sizes than the 10 second
heated sample shown in FIG. 9A). FIG. 8B shows the high temperature
tensile characteristics of the component 50 when cooled to and
maintained at 450.degree. C. after solutionizing heat treatment.
The ductility of the component 50 is reduced significantly from the
samples tested at 425.degree. C. Furthermore, as shown in FIG. 8B,
failure for the 10 second heated sample occurred at approximately
0.2% strain, compared to failure at approximately 0.3% for other
illustrated rates.
[0058] The reduction in ductility at temperatures above about
420.degree. C. was evaluated according to the microstructure of the
component 50. FIG. 6A demonstrates an approximate 60% decrease in
ductility for a sample tested at approximately 450.degree. C.
(tensile conditions) compared to a sample at approximately
425.degree. C. The microstructure for this alloy is shown in FIG.
7A, where the approximate grain size (or approximate diameter) is
about 10 microns. FIG. 6B demonstrates an approximate 50% decrease
in ductility for a sample tested at approximately 450.degree. C.
(tensile conditions) compared to a sample at approximately
425.degree. C. The microstructure for this alloy is shown in FIG.
7B, where the approximate grain size (or approximate diameter) is
about 25 microns. In some embodiments, the grain size is
approximately 15-35 microns. FIG. 6C demonstrates an approximate 7%
decrease in ductility for a sample tested at approximately
450.degree. C. (tensile conditions) compared to a sample at
approximately 425.degree. C. The microstructure for this alloy is
shown in FIG. 7C, where the approximate grain size (or approximate
diameter) is about 75 microns. In some embodiments, the grain size
is approximately 65-85 microns. High temperature formability of
7xxx aluminum alloys appears to be dependent on grain size based on
these experiments. For example, as shown in FIGS. 6A and 6C, when
comparing an approximate grain size of 75 microns and 10 microns,
the larger grain size produces greater ductility at 425.degree. C.
(failure at approximately 0.55% strain compared to approximately
0.5% strain). In addition, as shown in FIGS. 6A and 6C, when
comparing an approximate grain size of 75 microns and 10 microns,
the larger grain size produces significantly greater ductility at
450.degree. C. (failure at approximately 0.5% strain compared to
approximately 0.2% strain).
[0059] Based on the experiments described above, it has been
determined that the desired forming temperature T.sub.F is in a
range of approximately 380.degree. C. to approximately 470.degree.
C., for example in the range of approximately 390.degree. C. to
approximately 460.degree. C. or in the range of approximately
400.degree. C. to approximately 440.degree. C. In some cases, the
desired forming temperature T.sub.F is approximately 425.degree. C.
The component 50 must be hot enough to ensure sufficient
formability; however, as shown in FIG. 4, at elevated temperatures,
the 7075 aluminum alloy components become less ductile and
increasingly brittle with increasing temperature (particularly at
temperatures of 450.degree. C.-475.degree. C. and higher).
[0060] The forming process 204 occurs in the forming device 102,
which may be a forming press (i.e., including a die), a rolling
mill, or any other suitable forming device. In some examples, the
forming process 204 lasts a few seconds (e.g., less than 10
seconds).
[0061] After the forming process is complete, the component 50 is
quenched to a low temperature at 205 in FIG. 2. The low temperature
may be approximately 0.degree. C. to approximately 280.degree. C.,
or may be approximately 5.degree. C. to approximately 40.degree.
C., or may be approximately 23.degree. C. in certain embodiments.
In some cases, the quenching occurs in a closed die with internal
water cooling such that cooling water flows through internal
passages in the die. The component 50 may be cooled at a minimum
rate of approximately 50.degree. C./second. The cooling or quench
rate may be between approximately 50.degree. C./second and
approximately 500.degree. C./second or may be between 300.degree.
C./second and approximately 350.degree. C./second. In some
instances, more advantageous material properties are observed for
higher quench rates such as more than 300.degree. C./second.
[0062] As shown in FIG. 2, after the quenching process 205 is
complete, the component 50 may undergo an artificial aging
treatment 206. In particular, the artificial aging treatment 206
may include heat treatment at a temperature of approximately
100.degree. C. to 150.degree. C. (in some cases, approximately
125.degree. C.) for approximately 24 hours. In some cases, the
component 50 may undergo a double aging treatment that includes
heat treatment at a temperature of approximately 100.degree. C. to
150.degree. C. (in some cases, approximately 125.degree. C.) for
1-24 hours followed by heat treatment at approximately 180.degree.
C. for approximately 20-30 minutes.
[0063] Different arrangements of the objects depicted in the
drawings or described above, as well as features and steps not
shown or described are possible. Similarly, some features and
sub-combinations are useful and may be employed without reference
to other features and sub-combinations. Embodiments of the
invention have been described for illustrative and not restrictive
purposes, and alternative embodiments will become apparent to
readers of this patent. Accordingly, the present invention is not
limited to the embodiments described above or depicted in the
drawings, and various embodiments and modifications may be made
without departing from the scope of the claims below.
* * * * *