U.S. patent application number 14/189179 was filed with the patent office on 2015-08-27 for tailored rolling of high strength aluminum.
The applicant listed for this patent is Ford Global Technologies, LLC. Invention is credited to Michael William DANYO, Nia R. HARRISON, S. George LUCKEY, JR..
Application Number | 20150240339 14/189179 |
Document ID | / |
Family ID | 53881641 |
Filed Date | 2015-08-27 |
United States Patent
Application |
20150240339 |
Kind Code |
A1 |
DANYO; Michael William ; et
al. |
August 27, 2015 |
TAILORED ROLLING OF HIGH STRENGTH ALUMINUM
Abstract
A method of processing high strength aluminum sheet is provided.
The method may comprise uncoiling a coil of O or F-temper 6xxx or
7xxxx series aluminum alloy sheet, tailored rolling the sheet to
form a tailored rolled sheet having at least two different
thicknesses, blanking the tailored rolled sheet to form a tailored
rolled blank (TRB), hot stamping the tailored rolled blank to form
a component, and age hardening the component. The tailored rolling
operation may reduce the thickness of the aluminum sheet by up to
60% in selected regions. The method may include a hot stamping
process for age hardening aluminum alloys that solution heat treats
and quenches the TRB. The method may be used to form lightweight,
high-strength aluminum vehicle components having a controlled
thickness profile to reduce component part weight.
Inventors: |
DANYO; Michael William;
(Trenton, MI) ; HARRISON; Nia R.; (Ann Arbor,
MI) ; LUCKEY, JR.; S. George; (Dearborn, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ford Global Technologies, LLC |
Dearborn |
MI |
US |
|
|
Family ID: |
53881641 |
Appl. No.: |
14/189179 |
Filed: |
February 25, 2014 |
Current U.S.
Class: |
148/693 |
Current CPC
Class: |
C22C 21/10 20130101;
C22C 21/08 20130101; C22F 1/043 20130101; C22F 1/047 20130101; C22F
1/053 20130101; C22F 1/057 20130101; C22F 1/05 20130101 |
International
Class: |
C22F 1/053 20060101
C22F001/053; C22F 1/047 20060101 C22F001/047; C22F 1/043 20060101
C22F001/043; C22F 1/057 20060101 C22F001/057; C22C 21/16 20060101
C22C021/16; C22C 21/08 20060101 C22C021/08; C22C 21/10 20060101
C22C021/10; C22C 21/12 20060101 C22C021/12; C22C 21/14 20060101
C22C021/14; C22F 1/05 20060101 C22F001/05; C22C 21/02 20060101
C22C021/02 |
Claims
1. A method of processing high strength aluminum material
comprising: uncoiling a coil of O or F-temper 6xxx or 7xxxx series
aluminum alloy material; tailored rolling the material to form a
tailored rolled sheet having at least two different thicknesses
along its length; blanking the tailored rolled sheet to form a
tailored rolled blank; hot stamping the tailored rolled blank to
form a component; and age hardening the component.
2. The method of claim 1, wherein the coil is a 7xxx series
aluminum alloy material and the age hardening step includes heat
treating the component to a yield strength of at least 490 MPa.
3. The method of claim 1, wherein the coil is a 6xxx series
aluminum alloy material and the age hardening step includes heat
treating the component to a yield strength of at least 240 MPa.
4. The method of claim 1, wherein the step of tailored rolling
includes reducing a thickness of at least a region of the aluminum
alloy material by up to 60%.
5. The method of claim 1, wherein the 6xxx or 7xxx series aluminum
alloy material has a thickness of 1 to 5 mm and the tailored rolled
sheet has a thickness of 0.5 to 5 mm.
6. The method of claim 1, wherein the hot stamping step includes:
heating the tailored rolled blank to at least its solution
temperature; positioning the tailored rolled blank in a die set;
and closing the die set on the tailored rolled blank to form the
blank into a component and quench the component.
7. The method of claim 1, wherein the age hardening step includes
heat treating the component to a T6 temper.
8. The method of claim 1, wherein the age hardening step includes a
two-step heat treatment of the component, including: a first heat
treatment at 100 to 150.degree. C. for 0.2 to 3 hours; and a second
heat treatment at 150 to 185.degree. C. for 0.5 to 5 hours.
9. The method of claim 1 further comprising re-coiling the tailored
rolled sheet into a coil prior to the blanking step.
10. A method of processing a coil of high strength aluminum alloy
comprising: uncoiling a coil of O or F-temper 7xxxx series aluminum
alloy; tailored rolling the coil to form a tailored rolled sheet
having at least two different thicknesses along its length;
blanking the tailored rolled sheet to form a tailored rolled blank;
hot stamping the tailored rolled blank to form a component; and age
hardening the component to a yield strength of at least 490
MPa.
11. The method of claim 10, wherein the step of tailored rolling
includes reducing a thickness of at least a region of the aluminum
alloy coil by up to 60%.
12. The method of claim 10, wherein the coil of 7xxx series
aluminum alloy has a thickness of 1 to 5 mm and the tailored rolled
sheet has a thickness of 0.5 to 5 mm.
13. The method of claim 10, wherein the hot stamping step includes:
heating the tailored rolled blank to at least its solution
temperature; positioning the tailored rolled blank in a die set;
and closing the die set on the tailored rolled blank to form the
blank into a component and quench the component.
14. The method of claim 10, wherein the age hardening step includes
heat treating the component to a T6 temper.
15. The method of claim 10, wherein the age hardening step includes
a two-step heat treatment of the component, including: a first heat
treatment at 100 to 150.degree. C. for 0.2 to 3 hours; and a second
heat treatment at 150 to 185.degree. C. for 0.5 to 5 hours.
16. The method of claim 10, wherein the 7xxx series aluminum alloy
is a 7075 aluminum alloy.
17. A method of processing high strength aluminum alloy sheet
comprising: tailored rolling a sheet of 7xxxx series aluminum alloy
to form a tailored rolled sheet having at least two different
thicknesses; blanking the tailored rolled sheet to form a tailored
rolled blank; hot stamping the tailored rolled blank to form a
solution heat treated and quenched component; and hardening the
component to a yield strength of at least 490 MPa, by a first heat
treatment at 100 to 150.degree. C. for 0.2 to 3 hours and a second
heat treatment at 150 to 185.degree. C. for 0.5 to 5 hours.
18. The method of claim 17, wherein the tailored rolling step
includes reducing a thickness of at least a region of the aluminum
alloy sheet by up to 60%.
19. The method of claim 17, wherein the hot stamping step includes:
heating the tailored rolled blank to at least its solution
temperature; positioning the tailored rolled blank in a die set;
and closing the die set on the tailored rolled blank to form the
blank into a component while simultaneously quenching the
component.
20. The method of claim 17, wherein the 7xxx series aluminum alloy
is a 7075 aluminum alloy.
Description
TECHNICAL FIELD
[0001] This disclosure relates to tailored rolling of high strength
aluminum alloys, such as 6xxx and 7xxx series alloys.
BACKGROUND
[0002] Vehicle body panels are known to be made from mild steels.
One method of reducing weight in steel body panels is tailored
rolling the material to create multiple thicknesses throughout the
panel. Aluminum alloy body panels are also being developed to
decrease vehicle weight. Body panels developed for the automotive
and aerospace industries focus primarily on 5xxx and 6xxx series
aluminum alloys, which are aluminum-magnesium and
aluminum-magnesium-silicon alloys, respectively. 5xxx series
aluminum alloys are generally shaped and processed by methods that
are similar to methods used with mild steel sheets.
[0003] 6xxx series aluminum alloys may require an age hardening
treatment for some applications in order to have the required
properties. Aluminum-zinc alloys of the 7xxx series, if age
hardened, may achieve yield strengths similar to those of high
strength steels. 7xxx series alloys may have a variety of tempers,
that may be difficult to process and may require further heat
treatment before the age hardening process. For example, a 7xxx
material received with a T6 temper may be difficult to draw or
stretch at room temperature. The age hardening process for 6xxx and
7xxx series alloys includes a continuous annealing and solution
heat treatment (CASH) process that is limited to sheets having
uniform thickness. Therefore, tailored rolling of high strength
aluminum alloys (e.g., age hardening 6xxx and 7xxx series alloys)
is not possible using current processes.
[0004] This disclosure is directed to solving the above problems,
and other problems as summarized below.
SUMMARY
[0005] According to one aspect of this disclosure, a method is
provided for processing high strength aluminum sheet. The method
comprises uncoiling a coil of O or F-temper 6xxx or 7xxxx series
aluminum alloy sheet. The sheet is tailored rolled to form a
tailored rolled sheet having at least two different thicknesses
along its length. The tailored rolled sheet is cut into blanks to
form a tailored rolled blank. The method may include re-coiling the
tailored rolled sheet into a coil prior to the blanking step. The
method may further include hot stamping the tailored rolled blank
to form a component. The component then undergoes and age
hardening.
[0006] The coil may be a 7xxx series aluminum alloy sheet and the
age hardening step may include heat treating the component to a
yield strength of at least 490 MPa. The coil may also be a 6xxx
series aluminum alloy sheet and the age hardening step may include
heat treating the component to a yield strength of at least 240
MPa. The tailored rolling step may include reducing a thickness of
at least a region of the aluminum alloy sheet by up to 60%. The
6xxx or 7xxx series aluminum alloy sheet may have a thickness of 1
to 5 mm and the tailored rolled sheet may have a thickness of 0.5
to 5 mm.
[0007] The hot stamping step may include heating the tailored
rolled blank to at least its solution temperature, positioning the
tailored rolled blank in a die set and closing the die set on the
tailored rolled blank to form the blank into a component and quench
the component. The age hardening step may include heat treating the
component to a T6 temper. The age hardening step may include a
two-step heat treatment of the component, which may include a first
heat treatment at 100 to 150.degree. C. for 0.2 to 3 hours and a
second heat treatment at 150 to 185.degree. C. for 0.5 to 5
hours.
[0008] According to another aspect of this disclosure, a method of
processing high strength aluminum sheet is provided that includes
uncoiling a coil of O or F-temper 7xxxx series aluminum alloy
sheet, tailored rolling the sheet to form a tailored rolled sheet
having at least two different thicknesses along its length, and
blanking the tailored rolled sheet to form a tailored rolled blank.
The method further includes hot stamping the tailored rolled blank
to form a component and subsequently age hardening the component to
a yield strength of at least 490 MPa. The age hardening step may
include heat treating the component to a T6 temper.
[0009] The tailored rolling step may include reducing a thickness
of at least a region of the aluminum alloy sheet by up to 60%. The
7xxx series aluminum alloy sheet may have a thickness of 1 to 5 mm
and the tailored rolled sheet may have a thickness of 0.5 to 5 mm.
The 7xxx series aluminum alloy sheet may be a 7075 aluminum alloy.
The hot stamping step may include heating the tailored rolled blank
to at least its solution temperature, positioning the tailored
rolled blank in a die set, and closing the die set on the tailored
rolled blank to form the blank into a component and quench the
component. The age hardening step may include a two-step heat
treatment of the component, which may include a first heat
treatment at 100 to 150.degree. C. for 0.2 to 3 hours and a second
heat treatment at 150 to 185.degree. C. for 0.5 to 5 hours.
[0010] According to a further aspect of this disclosure, a method
of processing high strength aluminum sheet is provided including
tailored rolling a sheet of 7xxxx series aluminum alloy (e.g.,
7075) to form a tailored rolled sheet having at least two different
thicknesses along its length and blanking the tailored rolled sheet
to form a tailored rolled blank. The tailored rolled blank is hot
stamped to form a solution heat treated and quenched component that
is then age hardened to a yield strength of at least 490 MPa. The
age hardening may include a first heat treatment at 100 to
150.degree. C. for 0.2 to 3 hours and a second heat treatment at
150 to 185.degree. C. for 0.5 to 5 hours.
[0011] The tailored rolling step may include reducing a thickness
of at least a region of the aluminum alloy sheet by up to 60%. The
hot stamping step may include heating the tailored rolled blank to
at least its solution temperature and positioning the tailored
rolled blank in a die set. The die set is then closed on the
tailored rolled blank to form the blank into a component and quench
the component.
[0012] The above aspects of this disclosure and other aspects will
be described below in greater detail with reference to the attached
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic view of a tailored rolling
apparatus;
[0014] FIG. 2 is a schematic view of an aluminum hot stamping
apparatus; and
[0015] FIG. 3 is a flowchart showing a method for tailored rolling
of age hardening aluminum alloys.
DETAILED DESCRIPTION
[0016] The illustrated embodiments are disclosed with reference to
the drawings. However, it is to be understood that the disclosed
embodiments are intended to be merely examples that may be embodied
in various and alternative forms. The figures are not necessarily
to scale and some features may be exaggerated or minimized to show
details of particular components. The specific structural and
functional details disclosed are not to be interpreted as limiting,
but as a representative basis for teaching one skilled in the art
how to practice the disclosed concepts.
[0017] Aluminum alloys are generally identified by a four-digit
number, with the first digit generally identifying the major
alloying element. The major alloying element in 7xxx series
aluminum is zinc while the major alloying element of 5xxx series is
magnesium and for 6xxx series is magnesium and silicon. Additional
numbers represented by the letter "x" in the series designation
define the exact aluminum alloy. For example, a 7075 aluminum alloy
may be used that has a composition of 5.1-6.1% zinc, 2.1-2.9%
magnesium, 1.2-2.0% copper, and less than half a percent of
silicon, iron, manganese, titanium, chromium, and other metals.
[0018] The 7xxx series and certain 6xxx series alloys require an
age hardening process (also known as precipitation hardening) to
achieve a high yield strength (YS). For example, age hardening can
create a YS of over 400 MPa for a 7xxx series alloy. Heat treating
6xxx series alloys (e.g., 6061 and 6111) and the 7xxx series alloys
(e.g., 7075) requires a solutionizing treatment, a quench, and a
subsequent age hardening process. The solution heat treatment
process may distort a part originally stamped from a 6xxx or 7xxx
alloy.
[0019] In 7xxx series alloys the major alloying elements are added
to introduce specific properties such as strength and toughness
through precipitation hardening. The minor alloying elements
indirectly affect properties as grain refiners/pinners. The major
alloying elements in 7xxx series are Zn, Mg, and Cu, which have
solid solubility for solution heat treatment. The major alloying
elements in 6xxx series are Mg, Si, and Cu, which have solid
solubility for solution heat treatment. These major alloying
elements support strength, toughness, and ductility. The minor
alloys elements have low solid solubility, and thus support grain
refinement during solution heat treatment and quench.
[0020] Age hardening is preceded by a solution heat treatment (or
solutionizing) and quench of the aluminum alloy material. Solution
heat treatment generally includes heating the alloy to at least
above its solvus temperature and maintaining it at the elevated
temperature until the alloy forms a homogeneous solid solution or a
single solid phase. The temperature that the alloy is held during
solutionizing is known as the solution temperature. For example,
the solution temperature for a 7xxx series aluminum alloy may be
approximately 460.degree. C. to 490.degree. C. and the solution
heat treatment may last from about 5 to 45 minutes. For a 6xxx
series aluminum alloy, the solution temperature may be
approximately 510.degree. C. to 580.degree. C. and the solution
treatment may last from about 1 minute to two hours. The solution
temperature and/or time is determined based upon the composition of
a given aluminum alloy. The solution temperature may be the
temperature at which a substance is readily miscible. Miscibility
is the property of materials to mix in all proportions, forming a
homogeneous solution. Miscibility may be possible in all phases;
solid, liquid and gas.
[0021] Following the solution treatment, a quenching step is
performed in which the alloy is rapidly cooled to below the solvus
temperature to form a supersaturated solid solution. Due to the
rapid cooling, the atoms in the alloy do not have sufficient time
to diffuse long enough distances to form two or more phases in the
alloy. The alloy is therefore in a non-equilibrium state. The
quench rate may be any suitable rate to form a supersaturated
solution in the quenched alloy. The quench rate may be determined
in a certain temperature range, for example from 400.degree. C. to
290.degree. C. In at least one embodiment, the quench rate is at
least 100.degree. C./sec. The quench may be performed until the
alloy is at a cool enough temperature that the alloy stays in a
supersaturated state (e.g., diffusion is significantly slowed),
such as about 290.degree. C. The alloy may then be air cooled or
otherwise cooled at a rate slower than the quench rate until a
desired temperature is reached. Alternatively, the quench may be
performed to a lower temperature, such as below 100.degree. C. or
down to about room temperature.
[0022] The solution heat treatment of 6xxx and 7xxx series sheet is
conventionally performed using a continuous annealing and solution
heat treatment (CASH) furnace. The quenching is generally done by
immersing the sheet in a quenching medium, such as water or oil, or
otherwise applying the quenching medium (e.g., spraying). Furnaces
that perform the CASH process are configured and setup to treat a
sheet having a uniform thickness. Settings such as temperature,
speed of the conveyor, length of conveyor, treatment time, and
others are tailored to the thickness of the sheet being treated in
order to ensure that the correct solution heat treatment is
achieved in the sheet. Similarly, the quenching process is tailored
to the sheet thickness in order to ensure that the correct quench
is achieved in the sheet (e.g., quenching medium, quench time,
quench rate, and others).
[0023] A solution treated and quenched 7xxx series aluminum alloy
must be age hardened (or precipitation hardened) to achieve a YS of
at least 400 MPa or more, while an age hardened 6xx series alloy
may achieve a YS of at least 200 MPa. Age hardening includes
heating and maintaining the alloy at an elevated temperature at
which there are two or more phases at equilibrium. The
supersaturated alloy forms fine, dispersed precipitates throughout
as a result of diffusion within the alloy. The precipitates begin
as clusters of atoms, which then grow to form GP zones, which are
on the order of a few nanometers in size and are generally
crystallographically coherent with the surrounding metal matrix. As
the GP zones grow in size, they become precipitates, which
strengthen the alloy by impeding dislocation movement. Since the
precipitates are very finely dispersed within the alloy,
dislocations cannot move easily and must either go around or cut
through the precipitates in order to propagate.
[0024] Five basic temper designations may be used for aluminum
alloys which are; F--as fabricated, O--annealed, H--strain
hardened, T--thermally treated, and W--as quenched (between
solution heat treatment and artificial or natural aging). The
as-received raw material for the disclosed solutionizing and age
hardening processes may initially have any of the above temper
designations. The temper designation may be followed by a single or
double digit number for further delineation. An aluminum alloy with
a T6 temper designation is an alloy that has been solution heat
treated and artificially aged, but not cold worked after the
solution heat treatment. T6 may represent the point of peak age
yield strength along the yield strength vs. time and temperature
profile for the material. A T7x temper may designate that a
solution heat treatment has occurred, and that the material was
artificially aged beyond the peak age yield strength (over-aged)
along the yield strength vs. time and temperature profile. A T7x
temper material may have a lower yield strength than a T6 temper
material, but the T7x temper generally provides increased corrosion
performance compared to the T6 temper. In one embodiment, a 7xxx
series aluminum alloy part with a T6 temper is formed with a YS of
490 MPa or greater (e.g., at least 500 MPa). In another embodiment,
a T7x temper is formed, such as a T73 or T76 temper. A T7x temper
material may have a YS of at least 435 MPa. A 6xxx series aluminum
alloy may be age hardened to a T6 temper having a YS of 240 MPa or
greater (e.g., at least 260 MPa) or a T7 temper having a YS of at
least 200 MPa. For example, 6061 at a T6 temper may have a yield
strength of about 275 MPa and 6111 at a T6 temper may have a yield
strength of about 300 MPa.
[0025] In the automotive industry, replacing steel vehicle
components with aluminum components may allow for a reduction in
weight of the components and, therefore, the vehicle as a whole.
Another approach to reducing weight in steel vehicle components is
to tailor the thickness of the components in multiple regions such
that the steel component has relatively thick regions (e.g., high
load regions) and relatively thin regions (e.g., low load regions).
Tailoring the thickness of steel components may allow the thickness
to be reduced in portions of the component that were previously
thicker than they needed to be. Tailored thickness of steel
components may be accomplished using a process called tailored
rolling.
[0026] Referring to FIG. 1, a tailored rolling apparatus 10 is
shown with a coil of metal 12 being uncoiled and passed through two
sets of rollers 14 and 16. As illustrated in FIG. 1, each set of
rollers includes two rollers. However, there may only be a single
roller above and below the sheet or there may be three or more
rollers above and below the sheet, or any combination thereof
(e.g., two rollers above and one below). A gap 18 between the two
sets of rollers 14 and 16 controls the thickness 20 of the sheet 12
after passing through the rollers. The size of the gap 18, and
therefore the thickness 20 of the sheet 12, may be adjusted by
moving the sets of rollers 14 and 16 vertically relative to each
other. If the rollers 14 and 16 are moved towards each other, the
gap 18 becomes smaller and if the rollers 14 and 16 are moved away
from each other, the gap 18 becomes larger. To change the size of
the gap 18, the rollers 14 and 16 may both be moved relative to
each other. Alternatively, either one of the sets of rollers 14 or
16 may be moved relative to the other, with one set of rollers 14
or 16 remaining stationary. The thickness 20 of the sheet 12 may be
increased or decreased along a length of the sheet 12 by adjusting
the size of the gap 18 as the sheet 12 is passed through the
rollers 14 and 16. The apparatus 10 may produce uniform transition
areas. Movement of the rollers 14 and/or 16 may be controlled by
computer software that is programmed to produce a certain thickness
profile or contour in the sheet 12 or may have saved algorithms for
producing various thickness profiles in the sheet 12.
[0027] The sheet 12 may be cut into blanks 24 downstream of the
rollers 14 and 16. As shown in FIG. 1, opposing blades 22 may
perform the cutting. However, any suitable method may be used to
cut the sheet 12 into blanks 24, such as a punch and die. In some
embodiments, rather than cutting the sheet 12 into blanks 24, the
sheet 12 having varying thicknesses along its length may be rolled
into a coil 26 for later processing.
[0028] The tailored rolling of aluminum sheet has previously been
limited to materials that may only require annealing prior to a
subsequent forming process. For example, 5xxx series aluminum
alloys may be batch annealed after tailored rolling and then
stamped. However, as discussed above, 6xxx and 7xxx series aluminum
alloys require a solution heat treatment and quench before they can
be processed into high strength components. In industries that
require high volume throughputs at acceptable costs, such as the
automotive industry, solution heat treatment for age hardening
aluminum alloys is carried out using continuous annealing and
solution heat treatment furnaces (e.g., CASH) and subsequent
quenching. This approach cannot be used with tailored rolling,
however, because CASH cannot accommodate the change in sheet
thickness that is present in a tailored rolled blank (TRB). The
furnaces used in the CASH process are configured to run at a
certain temperature, time, and/or speed for a predetermined sheet
thickness. Therefore, the CASH process may not be able to
accommodate the changes in sheet thickness that are generated
during the TRB process. Portions of the TRB that are thicker
compared to the furnace's target settings may receive insufficient
heat treatment and portions that are thinner may receive too much
heat treatment. Either over or under heat treating may result in
unacceptable microstructure or properties in the sheet. Therefore,
it is not possible using conventional methods to perform tailored
rolling on high strength aluminum alloys (e.g., 6xxx and 7xxx
series) with high volume throughput. In addition, coils of 6xxx and
7xxx series aluminum are typically purchased with at least some age
hardening already performed (e.g., a T4 or T6 temper). Age hardened
coils cannot be used with the tailored rolling process.
[0029] A novel method for hot stamping age hardening aluminum
alloys was recently developed and described in commonly assigned
U.S. Pat. No. 8,496,764, the disclosure of which is incorporated by
reference in its entirety. FIG. 1 of U.S. Pat. No. 8,496,764 is
reproduced as FIG. 2 in the present application, with revised
element numbering. With reference to FIG. 2, a system 50 for
forming a blank 52 is shown. The system 50 may include a heating
apparatus 54, a transfer mechanism 56, and a die set 58. In at
least one embodiment, the blank 52 is an O or F-temper 6xxx or 7xxx
series aluminum alloy blank 52.
[0030] The heating apparatus 54 is provided to heat the blank 52.
The heating apparatus 54 may be an industrial furnace or oven
capable of producing internal temperatures high enough to heat
blanks 52 placed in the heating apparatus 54 to a predetermined
temperature, such as a solution, solvus, or solidus temperature of
the blank 52. The heating apparatus 54 does not heat the blank 52
past its liquidus (melting) temperature. The blank 52 may be heated
to at least its solvus or solidus temperature but less than its
liquidus temperature, to provide a blank 52 that is substantially
solid to facilitate handling and transport but that is more readily
formable due to its near liquid or partial liquid phase.
[0031] The transfer mechanism 56 is configured to move and position
the blank 52. The illustrated transfer mechanism 56 may be a
manipulator, such as a robot. The transfer mechanism 56 may be
configured to quickly transfer the blank 52 from the heating
apparatus 54 to the die set 58 to reduce heat loss from the blank
52. For example, the system 50 and transfer mechanism 56 may be
configured such that the temperature of the blank 52 does not
decrease to or below its critical quench temperature. The critical
quench temperature is the temperature at which quenching must begin
to achieve a proper quench of the material. For example, the
critical quench temperature for most 7xxx series aluminum alloys is
approximately 400.degree. C.
[0032] A die set 58 is provided to form the blank 52 into a part
having a predetermined shape. The die set 58 may include a first
die 60, a second die 62, at least one actuator 64, and a staging
apparatus 66. The first and/or second dies 60, 62 are configured to
form the blank 52 into the part having a predetermined shape. An
actuator 64 may move the first die 60 and/or the second die 62
toward or away from each other and provide force to form the blank
52. The actuator 64 may be of any suitable type, such as hydraulic,
pneumatic, mechanical, electromechanical, or combinations thereof.
The die set 58 and actuator 64 combination may also be referred to
as a machine press, stamping press, or quenching press.
[0033] A staging apparatus 66 is provided for positioning the blank
52 between and spaced apart from the first and second dies 60, 62.
As such, the staging apparatus 66 may inhibit conductive heat
transfer between the blank 52 and the die set 58, thereby helping
to maintain the blank 52 at or above its critical quench
temperature. The staging apparatus 66 receives the blank 52 from
the transfer mechanism 56 and releases the blank 52 as the first
die 60 and/or the second die 62 are closed and engage the blank 52.
In addition, the system 50 may be configured to minimize heat loss
from the blank 52 between removal from the heating apparatus 54 and
closing of the die set 58. The temperature of the blank 52 may
decrease by less than 10.degree. C. However, the blank 52 could
experience a greater temperature loss, for example, the blank 52
could lose up to a 75.degree. C. assuming that the blank 52 is
heated to 490.degree. C. and the critical quench temperature is
415.degree. C.
[0034] The die set 58 may include piping 68 that facilitates
cooling of the first and/or second dies 60, 62 and quenching of the
part formed from the blank 52. The piping 68 may include voids or
channels formed in the die set 58, and may include a combination of
externally connected piping and channels. The piping 68 may be
connected to a cooling source and may receive a heat transfer
medium, such as a fluid, from the cooling source for cooling the
die set 58 to a desired temperature. The heat transfer medium may
be any fluid medium capable of cooling the die set 58 to a
predetermined temperature range, such as from 1.degree. C. to
30.degree. C. The die set 58 may be cooled in a manner that
inhibits formation of condensation on one or more surfaces of the
die set 58. In a mass production setting, the temperature of the
die set 58 may be cooled to the predetermined temperature range
before forming and quenching a blank 52 to remove heat that may
have been transferred from a blank 52 to the die set 58 during
forming of a previous part.
[0035] Forming the heated blank 52 into a part may occur
simultaneously with quenching of the part. The quench rate affects
the final temper strength and corrosion performance of the
material. In some embodiments, the quench rate for the aluminum
alloy, as it passes from 400.degree. C. to 290.degree. C., may be
equal to or greater than 150.degree. C./second. The part may be
further cooled to a final temperature from 200.degree. C. to
25.degree. C. before removal of the part from the die set 58 to
provide dimensional stability during subsequent processing.
[0036] The system 50 may be designed to operate continuously with a
number of blanks 52 being heated in series or parallel by one or
more heating apparatuses 54 and then transferred to at least one
die set 58 for forming and quenching. At least one die set may
become hotter than 30.degree. C. during, or after, the forming of
the blank 52 and/or simultaneous quenching of the part, and as such
more than one die set 58 may be used to provide faster production
speeds.
[0037] The part may be removed from the die set 58 by the transfer
mechanism 56, another transferring device, or by hand. The part
then progresses on to subsequent processing which may include
flanging, trimming, and a natural and/or artificial aging to bring
the aluminum alloy part to a high strength temper such as T6 or
T7x.
[0038] Referring to FIG. 3, a method 100 of tailored rolling age
hardening aluminum alloys is illustrated by a flowchart. The alloy
is a 6xxx or 7xxx series alloy, for example, a 7075 alloy. At 102,
the method begins by providing a coil of 6xxx or 7xxx series
aluminum alloy sheet. The coil may be of O or F-temper aluminum
alloy (annealed or "as fabricated," respectively). As discussed
above, commercially available coils of high strength aluminum alloy
are typically partially age hardened. Coils of F-temper 7xxx
aluminum alloy are not generally commercially available.
[0039] At 104, the coil may be unrolled according to methods known
in the art. At 106, the unrolled sheet may be tailored rolled, for
example, using an apparatus described with respect to FIG. 1. The
tailored rolled sheet may have at least two regions of different
thicknesses and, for example, may have two, three, four, five, or
more regions of different thicknesses. The thickness of the
unrolled sheet may be reduced in some regions by up to about 30,
40, 50, or 60%. However, the sheet thickness may be reduced by a
lesser amount (e.g., 5, 10, or 20%) or not at all in some regions.
A thickness profile or contour of the sheet may be predetermined
based on the desired properties or characteristics (e.g., loading,
weight, safety, or others) of the component to be produced. The
unrolled sheet may have any suitable thickness before the tailored
rolling process, for example, a thickness of 1 to 5 mm. The
tailored rolled sheet may have regions with any thickness from
about 40% of the pre-rolled thickness up to 100% of the pre-rolled
thickness. For example, regions of the tailored rolled sheet may
have thicknesses ranging from 0.5 to 5 mm or any range contained
therein. For example, a sheet having a pre-rolled thickness of 3 mm
may be tailored rolled to have regions with thicknesses of 2.0 mm,
2.5 mm, and 3.0 mm.
[0040] At 108, the tailored rolled sheet may either be rolled back
into a coil or it may be cut into blanks. At 110, tailored rolled
blanks (TRBs), either received directly from the tailored rolling
process or later cut from a coil, are stamped. The stamping
operation may be a hot stamping process, for example, using an
apparatus described with respect to FIG. 2. The blanks may be, for
example, TRBs of an O, W, or F-temper 7xxx series aluminum alloy
(e.g., 7075). However, the TRBs may also be a different aluminum
alloy, such as a 6xxx series alloy. The hot stamping process may
include heating each TRB to at least a solution, solvus, or solidus
temperature, positioning the TRB in a die set, and closing the die
set on the TRB to form the TRB into a component while also
quenching the component. The stamping may also be a W-temper
stamping process, in which a W-temper TRB (solution heat treated,
but not artificially aged) is stamped. The stamping may be
performed before the TRB naturally ages to a different temper
designation. For example, a 6xxx alloy may have a T4 temper after
naturally aging for 96 hours or more. Therefore, stamping may be
performed on the W-temper TRB prior to the TRB naturally aging for
96 hours.
[0041] At 112, the TRBs are age hardened in order to increase their
strength. The TRBs may be age hardened to one of the well-known
tempering designations, such as T4, T6, or T7x. For example, the
TRBs may be formed of a 7xxx series alloy and age hardened to a T6
temper. The industry established standard age hardening heat
treatments for 7xxx alloys comprises holding the alloy at a
temperature of about 110-130.degree. C. for over 20 hours,
generally about 24 hours. For example, the standard age hardening
heat treatment for 7075 aluminum is 115-126.degree. C. for 24 hours
to achieve a T6 temper. Suitable age hardening heat treatments for
the other known tempering designations are also known in the art.
Alternatively, a novel two-step age hardening treatment for 7xxx
series alloys may be performed, which is described in commonly
assigned, co-pending U.S. application Ser. No. 14/055,476, the
disclosure of which is incorporated by reference in its entirety.
The two-step age hardening treatment may include, for example, a
first heat treatment step at 100 to 150.degree. C. for about 0.2 to
3 hours and a second heat treatment step at 150 to 185.degree. C.
for about 0.5 to 5 hours.
[0042] The standard age hardening heat treatment to achieve a T6
temper in a 6xxx alloy may be at a temperature of about 160.degree.
C. to 180.degree. C. for 8 to 18 hours (generally, if the
temperature is near the top of the range then the time is towards
the bottom of the range, and vice versa). However, there is no
industry standard for tempering a 6xxx alloy to a T7 or T8 temper
(a T8 temper is artificially aging after the material has been cold
worked). As an alternative to the standard age hardening heat
treatment for 6xxx series alloys, a novel age hardening treatment
may be performed to form a T7 or T8 temper 6xxx series aluminum
alloy, which is described in commonly assigned, co-pending U.S.
application Ser. No. 14/189,050, the disclosure of which is
incorporated by reference in its entirety. The age hardening
treatment may include, for example, heat treating the alloy at a
temperature of 215.degree. C. to 245.degree. C. for 15 minutes to 8
hours.
[0043] According to the methods disclosed above, tailored rolling
of age hardening 6xxx and 7xxx series aluminum alloys may be
performed. Previously, the solution heat treatment (e.g., CASH) and
quenching required for age hardening of these alloys prevented the
use of tailored rolling. O or F-temper coils of 6xxx and 7xxx
series alloys may be directly utilized in the disclosed methods,
which is highly unusual. The aluminum hot stamping process allows
the solution treatment and quenching steps to be performed quickly
and effectively after the tailored rolling process. With steel
TRBs, processing is essentially complete following a stamping
process that forms martensite. Age hardening aluminum TRBs requires
the further step of age hardening after hot stamping. Age hardening
may be performed by aging for a standard time period (e.g., 24
hours), however, the standard age hardening process may not provide
adequate volume throughput for high-volume industries (e.g.,
automotive). The novel two-step age hardening process allows for
greatly increased throughput by reducing the age hardening time to
less than about 8 hours.
[0044] By tailored rolling high-strength aluminum alloys, even
greater reduction in weight may be possible in vehicle components
compared to just replacing steel components with aluminum. Many
vehicle components may benefit from the inclusion of tailored
rolled high-strength aluminum, for example, rocker panels, roof
rails, bumper structures, A, B, or C pillars, and others. In
addition to weight, the function, cost, and/or complexity of the
high-strength aluminum components can be improved.
[0045] While exemplary embodiments are described above, it is not
intended that these embodiments describe all possible forms of the
disclosure. The words used in the specification are words of
description rather than limitation. Changes may be made to the
illustrated embodiments without departing from the spirit and scope
of the disclosure as claimed. The features of the illustrated
embodiments may be combined to form further embodiments of the
disclosed concepts.
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