U.S. patent application number 15/994717 was filed with the patent office on 2019-12-05 for high strength aluminum hot stamping with intermediate quench.
This patent application is currently assigned to Ford Global Technologies, LLC. The applicant listed for this patent is Ford Global Technologies, LLC. Invention is credited to Nia Harrison, Andrey Ilinich, S. George Luckey, JR..
Application Number | 20190368021 15/994717 |
Document ID | / |
Family ID | 68692820 |
Filed Date | 2019-12-05 |
United States Patent
Application |
20190368021 |
Kind Code |
A1 |
Ilinich; Andrey ; et
al. |
December 5, 2019 |
HIGH STRENGTH ALUMINUM HOT STAMPING WITH INTERMEDIATE QUENCH
Abstract
A method of forming an aluminum alloy part is provided for
enhanced formability. The method includes providing a 7xxx series
aluminum alloy blank, heating the blank to at least its solvus
temperature, and performing an intermediate quench on the blank to
a temperature between about 200.degree. C. to about 440.degree. C.
at a rate between about 100.degree. C./s to about 500.degree. C./s.
The blank is transferred to a stamping die where a secondary quench
and forming the blank into a part are carried out, where in one
form, the steps of transferring the blank and performing the
secondary quench and forming are completed within ten seconds or
less. The part may then be optionally artificially aged for
increased strength.
Inventors: |
Ilinich; Andrey; (Novi,
MI) ; Harrison; Nia; (Ann Arbor, MI) ; Luckey,
JR.; S. George; (Dearborn, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ford Global Technologies, LLC |
Dearborn |
MI |
US |
|
|
Assignee: |
Ford Global Technologies,
LLC
Dearborn
MI
|
Family ID: |
68692820 |
Appl. No.: |
15/994717 |
Filed: |
May 31, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22F 1/002 20130101;
C22F 1/053 20130101; B21D 22/022 20130101; C22C 21/10 20130101 |
International
Class: |
C22F 1/053 20060101
C22F001/053; C22F 1/00 20060101 C22F001/00 |
Claims
1. A method of forming an aluminum alloy part comprising the steps
of: providing a 7xxx series aluminum alloy blank; heating the blank
to at least its solvus temperature; performing an intermediate
quench of the blank to a temperature between about 200.degree. C.
to about 440.degree. C. at a rate between about 100.degree. C./s to
about 500.degree. C./s; transferring the blank to a stamping die;
and simultaneously performing a secondary quench on the blank and
forming the blank into a part, wherein the steps of transferring
the blank to the stamping die and performing the secondary quench
and forming are completed within ten seconds or less.
2. The method according to claim 1, wherein the blank is positioned
between flat press plates for the intermediate quench.
3. The method according to claim 1, wherein the secondary quench is
performed to a temperature less than 80.degree. C. in a cooled
die.
4. The method according to claim 3 further comprising a step of
artificial aging.
5. The method according to claim 4, wherein the artificial aging is
a PFHT (post forming heat treatment) at a temperature between about
180.degree. C. and about 205.degree. C. for about 30 minutes.
6. The method according to claim 1, wherein the secondary quench is
performed to a temperature between about 100.degree. C. and about
200.degree. C. in a heated die.
7. The method according to claim 6, wherein the part is transferred
to an elevated temperature enclosure for artificial aging after the
secondary quench.
8. The method according to claim 7, wherein the artificial aging is
a PFHT (post forming heat treatment) at a temperature of about
205.degree. C. for about 30 minutes.
9. A part formed according to the method of claim 1.
10. A vehicle having at least one part formed according to claim
1.
11. A method of forming a part comprising: heating a 7xxx series
aluminum alloy blank; performing an intermediate quench of the
blank to a temperature between about 200.degree. C. to about
440.degree. C.; transferring the blank to a stamping die; and
performing a secondary quench and forming the blank into a
part.
12. The method according to claim 11, wherein the intermediate
quench is performed at a rate between about 100.degree. C./s to
about 500.degree. C./s.
13. The method according to claim 11, wherein the secondary quench
is performed to a temperature less than about 80.degree. C. in a
cooled die.
14. The method according to claim 11, wherein the secondary quench
is performed to a temperature between about 100.degree. C. and
about 200.degree. C.
15. The method according to claim 11 further comprising a step of
artificial aging after the secondary quench.
16. The method according to claim 11, wherein the steps of
transferring the blank and performing the secondary quench and
forming are completed within ten seconds or less
17. A method of forming an aluminum alloy part comprising the steps
of: providing a 7xxx series aluminum alloy blank; heating the blank
to at least its solvus temperature; performing an intermediate
quench of the blank to a temperature between about 200.degree. C.
to about 440.degree. C. at a rate between about 100.degree. C./s to
about 500.degree. C./s; transferring the blank to a stamping die;
simultaneously performing a secondary quench on the blank and
forming the blank into a part, wherein the steps of transferring
the blank to the stamping die and performing the secondary quench
and forming are completed within ten seconds or less; and
artificially aging the part.
18. The method according to claim 17, wherein the artificial aging
is a PFHT (post forming heat treatment) at a temperature between
about 180.degree. C. and about 205.degree. C. for about 30
minutes.
19. The method according to claim 17, wherein the secondary quench
is performed to a temperature less than about 80.degree. C. in a
cooled die.
20. The method according to claim 17, wherein the secondary quench
is performed to a temperature between about 100.degree. C. and
about 200.degree. C. in a heated die.
Description
FIELD
[0001] The present disclosure relates to metal forming, and more
specifically to forming parts made from high-strength aluminum
alloys such as 7000 series aluminum alloys.
BACKGROUND
[0002] The statements in this section merely provide background
information related to the present disclosure and may not
constitute prior art.
[0003] Commercially successful vehicle body panels have
traditionally been made from steel. In recent decades, due to an
increasing demand to reduce the weight of vehicle structures while
meeting various strength and safety requirements, aluminum body
panels have gained interest. The automotive and aerospace
industries have predominantly focused on aluminum magnesium (5xxx
series) alloys and aluminum-magnesium-silicon (6xxx series) alloys.
The 5xxx and 6xxx series aluminum alloys are generally processed by
traditional mild steel methods.
[0004] Typical 6xxx series aluminum alloys provide a substantial
weight savings compared to steel and, with a T6 temper, have a
yield stress around or below 350 MPa. However, aluminum-zinc alloys
of the 7xxx series can deliver an additional 20-40% potential
weight reduction compared to steel. The additional potential weight
reduction weight is due to the higher T6 yield strengths, which can
exceed 500 MPa. Unfortunately, 7xxx series aluminum alloys does not
have a stable T4 temper and generally cannot be stamped at room
temperature due to their changing formability.
[0005] One economical method of forming 7xxx series aluminum alloys
is hot stamping. During the hot stamping process, aluminum sheet is
heated, and then simultaneously stamped and quenched in a
water-cooled die. This process has been successfully demonstrated
and is described in U.S. Pat. No. 8,496,764, which is commonly
owned with the present application and incorporated herein by
reference in its entirety. However, the formability of 7xxx series
aluminum alloys may not be optimal at elevated temperatures.
[0006] The present disclosure addresses the issues of forming 7xxx
series aluminum alloys at lower temperatures, among other issues
related to hot forming 7xxx series aluminum alloys.
SUMMARY
[0007] In one form of the present disclosure, a method of forming
an aluminum alloy part is provided. The method comprises the steps
of providing a 7xxx series aluminum alloy blank, heating the blank
to at least its solvus temperature, and performing an intermediate
quench of the blank to a temperature between about 200.degree. C.
to about 440.degree. C. at a cooling rate between about 100.degree.
C./s to about 500.degree. C./s, where the cooling rate is
determined from 400.degree. C. to 290.degree. C. Then, the blank is
transferred to a stamping die, where a secondary quench and forming
the blank into a part are simultaneously performed. Transferring
the blank to the stamping die and performing the secondary quench
and forming are completed within ten seconds or less.
[0008] In variations of this method, the blank is positioned
between flat press plates for the intermediate quench, and the
secondary quench is performed to a temperature less than 80.degree.
C. in a cooled die.
[0009] In another variation, the method further comprises a step of
artificial aging, wherein the artificial aging may be a PFHT (post
forming heat treatment) at a temperature between about 180.degree.
C. and about 205.degree. C. for about 30 minutes.
[0010] In another variation, the secondary quench is performed to a
temperature approximately between 100.degree. C. and 200.degree. C.
in a heated die. In a variation of this form, the part is
transferred to an elevated temperature enclosure for artificial
aging after the secondary quench, wherein the artificial aging may
be a PFHT (post forming heat treatment) at a temperature of about
205.degree. C. for about 30 minutes.
[0011] The present disclosure also includes parts formed according
to the various methods disclosed herein, in addition to vehicles
having at least one such part.
[0012] In another form of the present disclosure, a method of
forming a part is provided that comprises heating a 7xxx series
aluminum alloy blank, performing an intermediate quench on the
blank to a temperature between about 200.degree. C. to about
440.degree. C., transferring the blank to a stamping die, and
performing a secondary quench and forming the blank into a part. In
one form, the steps of transferring the blank and performing the
secondary quench and forming are completed within ten seconds or
less.
[0013] In variations of this method, the intermediate quench is
performed at a rate between about 100.degree. C./s to about
500.degree. C./s, the secondary quench is performed to a
temperature less than 80.degree. C. in a cooled die, the secondary
quench is performed to a temperature between about 100.degree. C.
and about 200.degree. C. in a heated die, and an additional step of
artificial aging after the secondary quench is performed.
[0014] In yet another form of the present disclosure, a method of
forming an aluminum alloy part is provided that comprises the steps
of providing a 7xxx series aluminum alloy blank, heating the blank
to at least its solvus temperature, performing an intermediate
quench on the blank to a temperature between about 200.degree. C.
to about 440.degree. C. at a rate between about 100.degree. C./s to
about 500.degree. C./s, transferring the blank to a stamping die,
simultaneously performing both a secondary quench on the blank and
forming the blank into a part, and artificially aging the part.
Transferring the blank to the stamping die and performing the
secondary quench and forming are completed within ten seconds or
less in one form of the present disclosure.
[0015] Further areas of applicability will become apparent from the
description provided herein. It should be understood that the
description and specific examples are intended for purposes of
illustration only and are not intended to limit the scope of the
present disclosure.
DRAWINGS
[0016] In order that the disclosure may be well understood, there
will now be described various forms thereof, given by way of
example, reference being made to the accompanying drawings, in
which:
[0017] FIG. 1 is a binary phase diagram for an aluminum-zinc alloy
system to which the teachings of the present disclosure are
applied;
[0018] FIG. 2 is an isothermal transformation diagram of various
aluminum alloys;
[0019] FIG. 3 is a graph of numerous isothermal fracture strain
versus lode parameter at a 0.1/s strain rate, according to the
teachings of the present disclosure; and
[0020] FIG. 4 is a flow diagram for a method for hot stamping 7xxx
series aluminum alloys according to the teachings of the present
disclosure.
[0021] The drawings described herein are for illustration purposes
only and are not intended to limit the scope of the present
disclosure in any way.
DETAILED DESCRIPTION
[0022] The following description is merely exemplary in nature and
is not intended to limit the present disclosure, application, or
uses. It should be understood that throughout the drawings,
corresponding reference numerals indicate like or corresponding
parts and features.
[0023] While investigating 7xxx series aluminum alloy in-situ
material characteristics and properties, the inventors discovered
that 7xxx series aluminum alloy formability is not optimal above
440.degree. C. Therefore, to address issues related to hot forming
aluminum blanks, the present disclosure provides innovative methods
that have been demonstrated to successfully hot form 7xxx series
aluminum alloys at or below 440.degree. C. while maintaining high
strength, high fracture toughness, and good corrosion
resistance.
[0024] Referring to FIG. 1, a binary phase diagram for the
aluminum-zinc system is shown. The aluminum alpha phase is present
across a range of temperatures and compositions. The solid solution
region below the Al--Zn eutectic and bounded by the aluminum solvus
and zinc solvus is generally more difficult to process than the
alpha-phase (a) of aluminum.
[0025] Now referring to FIG. 2, an isothermal transformation
diagram for various aluminum alloys is shown. An isothermal
transformation diagram is only valid for one specific composition
of material, and only if the temperature is held constant during
the transformation, and strictly with rapid cooling to that
temperature. Isothermal transformation diagrams are commonly
referred to as Time-Temperature-Transformation (TTT) plots, with
lines for various phases referred to as TTT-curves. In this
diagram, TTT-curve 42 is for 7075 aluminum, which is being used as
illustrative of an entire 7xxx series of aluminum alloys. TTT-curve
42 has a desired process window 44, within which a 7075 aluminum is
in an easier to process alpha-phase. (Process window 44 is
represented by points A, B, E, and F). If the 7xxx series alloy
cools at a rate that avoids intersecting the nose of the TTT curve,
then the response of the material to artificial aging is improved
and susceptibility to corrosion reduced.
[0026] Furthermore, aging an alloy that has been cooled at a rate
that avoids intersecting the nose of the TTT curve enables the
"peak yield strength" of the alloy. The lower the aging temperature
increases the time of the aging process.
[0027] In their investigations of hot forming 7xxx series aluminum
sheets, the inventors tested, among other relationships, the
isothermal relationship between the equivalent plastic strain to
failure and a lode parameter within the bounds of process window
44. The isothermal failure strain versus lode parameter curves at a
0.1/s (0.1 s.sup.-1) strain rate are plotted in FIG. 3, with T200
representing 200.degree. C., T280 representing 280.degree. C., et
al., which are tabulated in Table 1 below:
TABLE-US-00001 TABLE 1 Isothermal strain versus load parameter at:
FIG. 4 indicia 200.degree. C. T200 280.degree. C. T280 360.degree.
C. T360 400.degree. C. T400 440.degree. C. T440 480.degree. C.
T480
[0028] As shown in FIG. 3, the unexpected results of the present
disclosure include an improved formability at elevated temperatures
of an equivalent plastic strain to failure above about 1 at a
strain rate of 0.1/s both at a lode parameter of about 0 and a lode
parameter of about -0.25.
[0029] Unexpectedly, T480 strain to failure was lower than T440 but
higher than at T200. The T480 strain to failure reduced the bounds
of process window 44 to those of process window 44'. (Process
window 44' is bounded by points C, D, H, and G).
[0030] Based on these findings, the inventors have discovered that
an intermediate quench, followed by a secondary quench that is
carried out simultaneously with forming a blank, provides an
improvement in forming 7xxx series aluminum at lower temperatures.
The intermediate quench quickly cools a blank to an improved
forming temperature between about 200.degree. C. and about
440.degree. C., and is further enabled by an intermediate quench
rate between about 100.degree. C./s to about 500.degree. C./s,
wherein the blank is transferred to a stamping die and the
secondary quench is completed within ten (10) seconds or less.
[0031] Referring to FIG. 4, this general form of a method for hot
stamping a 7xxx series aluminum alloy is illustrated and generally
indicated by reference numeral 50. In this method 50, a 7xxx series
aluminum alloy blank is provided in step 52. This blank may be from
a cold-rolled coil in one form of the present disclosure. In step
54, the blank is heated to at least its solvus temperature, which
in this form is about 480.degree. C. In the next step 56, an
intermediate quench is performed at a temperature between about
200.degree. C. to about 440.degree. C. In this intermediate quench
step 56, the blank may be positioned between flat press plates.
Further, the intermediate quench is performed at a rate between
about 100.degree. C./s to about 500.degree. C./s in one form of the
present disclosure.
[0032] In step 58, the warm blank is transferred to a stamping die,
which in one form is a cooled die at less than or equal to about
80.degree. C. Alternately, as set forth below, the stamping die is
heated to a temperature between about 100.degree. C. and about
200.degree. C. Then, in this step 58, the blank is formed into a
part while simultaneously performing a secondary quench on the
blank. The secondary quench may thus be performed in a cooled die
or a heated die as set forth above. In one form, the steps of
transferring the blank to a stamping die and performing the
secondary quench and forming are completed within ten seconds or
less.
[0033] As further shown, the method 50 may also include an optional
step of artificial aging of the formed blank in step 60. This
optional step of artificial aging is provided after the
intermediate and secondary quenches for improved mechanical
properties, such as improved tensile strength. When the secondary
quench is carried out in a heated die, the time for artificial may
be reduced as the secondary quench begins the aging process.
Accordingly, the secondary quench temperature ranges from about
100.degree. C. to about 200.degree. C. in the heated die, depending
on desired aging characteristics.
[0034] In one form, the artificial aging is a PFHT (post form heat
treatment) at a temperature between about 180.degree. C. to about
205.degree. C. for 30 minutes. The formed part may be transferred
to an elevated temperature enclosure for artificial aging after the
secondary quench.
[0035] The combination of quenching temperatures, quenching rates,
and transfer times provide the desired material properties, such as
by way of example, corrosion resistance, fracture toughness, and
yield strength. Overall, the present disclosure provides a method
in which the formability of 7xxx series aluminum alloys is improved
and artificial aging time may be reduced.
[0036] Numerous methods of the present disclosure, the form parts
and the parts are often incorporated into vehicles.
[0037] Unless otherwise expressly indicated herein, all numerical
values indicating mechanical/thermal properties, compositional
percentages, dimensions and/or tolerances, or other characteristics
are to be understood as modified by the word "about" or
"approximately" in describing the scope of the present disclosure.
This modification is desired for various reasons including
industrial practice, manufacturing technology, and testing
capability.
[0038] The description of the disclosure is merely exemplary in
nature and, thus, variations that do not depart from the substance
of the disclosure are intended to be within the scope of the
disclosure. Such variations are not to be regarded as a departure
from the spirit and scope of the disclosure.
* * * * *