U.S. patent application number 12/011495 was filed with the patent office on 2008-08-28 for aluminum automotive structural members.
Invention is credited to Zhong Li, Paul Platek.
Application Number | 20080202646 12/011495 |
Document ID | / |
Family ID | 39714533 |
Filed Date | 2008-08-28 |
United States Patent
Application |
20080202646 |
Kind Code |
A1 |
Li; Zhong ; et al. |
August 28, 2008 |
Aluminum automotive structural members
Abstract
Disclosed is a method for producing aluminum vehicular
structural parts or members such as from molten aluminum alloy
using a continuous caster to cast the alloy into a slab. The method
comprises providing a molten aluminum alloy consisting essentially
of 2.7 to 3.6 wt. % Mg, 0.1 to 0.4 wt. % Mn, 0.02 to 0.2 wt. % Si,
0.05 to 0.30 wt. % Fe, 0.1 wt. % max. Cu, 0.25 wt. % max. Cr, 0.2
wt. % max. Zn, 0.15 wt. % max. Ti, the remainder aluminum,
incidental elements and impurities and providing a continuous
caster such as a belt caster, block caster or roll caster for
continuously casting the molten aluminum alloy. The molten aluminum
alloy is cast into a slab which is rolled into a sheet product and
then annealed. The sheet has an improved distribution of
intermetallic particles (Al--Fe, Al--Fe--Mn or Mg.sub.2Si) and
improved formability. Thereafter, the sheet product is formed into
the vehicular structural part or member with sufficient strength
and formability required by automotive industry.
Inventors: |
Li; Zhong; (Lexington,
KY) ; Platek; Paul; (Massillon, OH) |
Correspondence
Address: |
ANDREW ALEXANDER & ASSOCIATES
3124 KIPP AVENUE, P.O. BOX 2038
LOWER BURRELL
PA
15068
US
|
Family ID: |
39714533 |
Appl. No.: |
12/011495 |
Filed: |
January 28, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10926704 |
Aug 27, 2004 |
|
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12011495 |
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Current U.S.
Class: |
148/551 |
Current CPC
Class: |
C22C 21/08 20130101;
B22D 11/0605 20130101; B22D 11/003 20130101 |
Class at
Publication: |
148/551 |
International
Class: |
C22F 1/04 20060101
C22F001/04 |
Claims
1. In the production of an aluminum automotive structural part or
member from a molten aluminum alloy using a continuous caster to
cast the alloy into a slab, the method comprising: (a) providing a
molten aluminum alloy consisting essentially of 2.7 to 3.6 wt. %
Mg, 0.1 to 0.4 wt. % Mn, 0.02 to 0.2 wt. % Si, 0.05 to 0.30 wt. %
Fe, 0.1 wt. % max. Cu, 0.25 wt. % max. Cr, 0.2 wt. % max. Zn, 0.15
wt. % max. Ti, the remainder aluminum, incidental elements and
impurities; (b) providing a continuous caster for continuously
casting said molten aluminum alloy; (c) casting said molten
aluminum alloy into a slab having Al--Fe, Al--Fe--Mn or Mg.sub.2Si
intermetallic particles; (d) rolling said slab into a sheet
product; (e) annealing said sheet product to an O-temper condition,
said sheet having substantially uniform distribution or minimized
striations of said intermetallic particles and have an average
grain size in the range of about 15 to 20 .mu.m; and (f) forming
said sheet in said O-temper into said structural part or member by
stamping at room temperature.
2. In the production of the aluminum structural member in
accordance with claim 1 wherein manganese is maintained in the
range of 0.1 to 0.35 wt. %.
3. In the production of the aluminum structural part or member in
accordance with claim 1 wherein magnesium is maintained in the
range of 2.8 to 3.5 wt. %.
4. In the production of the aluminum structural part or member in
accordance with claim 1 wherein iron is maintained in the range of
0.5 to 0.25 wt. %.
5. In the production of the aluminum structural part or member in
accordance with claim 1 wherein said continuous caster is a belt
caster, a block caster or a roll caster.
6. In the production of the aluminum structural part or member in
accordance with claim 1 including annealing said sheet product in a
temperature range of 650.degree. to 950.degree. F.
7. In the production of the aluminum structural part or member in
accordance with claim 1 including annealing said sheet product in a
temperature range of 700.degree. to 900.degree. F.
8. In the production of the aluminum structural part or member in
accordance with claim 7 including annealing for about 2 to 10
hours.
9. In the production of the aluminum structural part or member in
accordance with claim 1 including continuously annealing said sheet
product.
10. In a method for the production of an aluminum automotive
structural part or member from molten aluminum alloy using a
continuous caster to cast the alloy into a slab, the method
comprising: (a) providing a molten aluminum alloy consisting
essentially of 2.7 to 3.6 wt. % Mg, 0.1 to 0.4 wt. % Mn, 0.02 to
0.2 wt. % Si, 0.05 to 0.30 wt. % Fe, 0.1 wt. % max. Cu, 0.25 wt. %
max. Cr, 0.2 wt. % max. Zn, 0.15 wt. % max. Ti, the remainder
aluminum, incidental elements and impurities; (b) providing a
continuous caster for continuously casting said molten aluminum
alloy; (c) casting said molten aluminum alloy into a slab having a
thickness in the range of 0.2 inch to 2 inch and having Al--Fe,
Al--Fe--Mn or Mg.sub.2Si intermetallic particles; (d) hot rolling
said slab into a hot rolled sheet product, said hot rolling
starting in a temperature range of 750.degree. to 1000.degree. F.
and ending in a temperature of 400.degree. to 825.degree. F.; (e)
annealing said hot rolled sheet product to an O-temper condition,
said hot rolled sheet product in said condition having a tensile
strength in the range of 28 to 35 ksi, a yield strength in the
range of 12 to 17.5 ksi, and an elongation greater than 19% and
having substantially uniform distribution or minimized striations
of said intermetallic particles and have an average grain size in
the range of about 15 to 20 .mu.m; and (f) forming said sheet
product in said 0-temper condition into said structural part or
member by stamping at room temperature.
11. The method in accordance with claim 10 wherein magnesium is
maintained in the range of 2.8 to 3.5 wt. %.
12. The method in accordance with claim 10 wherein iron is
maintained in the range of 0.05 to 0.25 wt. %.
13. The method in accordance with claim 10 including annealing said
hot rolled sheet in a temperature range of 650.degree. to
950.degree. F.
14. The method in accordance with claim 10 including annealing said
hot rolled sheet in a temperature range of 700.degree. to
900.degree. F.
15. The method in accordance with claim 13 including annealing for
about 2 to 10 hours.
16. The method in accordance with claim 10 including continuously
annealing said sheet product.
17. A method for producing aluminum vehicular part or member from
molten aluminum alloy using a continuous caster to cast the alloy
into a slab, the method comprising: (a) providing a molten aluminum
alloy consisting essentially of 2.7 to 3.6 wt. % Mg, 0.1 to 0.4 wt.
% Mn, 0.02 to 0.2 Wt. % Si, 0.05 to 0.30 wt. % Fe, 0.1 wt. % max.
Cu, 0.25 wt. % max. Cr, 0.2 wt. % max. Zn, 0.15 wt. % max. Ti, the
remainder aluminum, incidental elements and impurities; (b)
providing a continuous caster for continuously casting said molten
aluminum alloy into a slab having a thickness in the range of 0.2
inch to 2 inch; (c) rolling said slab into a sheet product having a
thickness in the range of 0.01 inch to 0.2 inch; (d) annealing said
rolled sheet product to provide a rolled and annealed sheet product
having a tensile strength in the range of 28 to 35 ksi, a yield
strength in the range of 12 to 17.5 ksi and an elongation greater
than 19%, said rolled and annealed sheet product having a
substantially uniform distribution or minimized striations of said
intermetallic particles and have an average grain size in the range
of about 15 to 20 .mu.m; and (e) forming said rolled and annealed
sheet into a vehicular structural part or member by stamping at
room temperature.
18. The method in accordance with claim 17 wherein said rolled
sheet product has Al--Fe, Al--Fe--Mn or Mg.sub.2Si intermetallic
particles formed during solidification in a size range of 0.05 to
10 .mu.m.
19. A process for producing plural panel automotive members having
inner and outer panels connected to form said members, said inner
panels having threaded fasteners securely crimped into said inner
panels to provide means for bolting accessories to said automotive
member, said inner panel formed by the process comprising: (a)
providing a molten aluminum alloy consisting essentially of 2.7 to
3.6 wt. % Mg, 0.1 to 0.4 wt. % Mn, 0.02 to 0.2 wt. % Si, 0.1 to
0.25 wt. % Fe, 0.1 wt. % max. Cu, 0.25 wt. % max. Cr, 0.2 wt. %
max. Zn, 0.15 wt. % max. Ti, the remainder aluminum, incidental
elements and impurities; (b) providing a continuous caster for
continuously casting said molten aluminum alloy; (c) casting said
molten aluminum alloy into a slab having Al--Fe, Al--Fe--Mn or
Mg.sub.2Si intermetallic particles; (d) rolling said slab into a
sheet product; (e) annealing said sheet product to an O-temper
condition, said sheet having substantially uniform distribution or
minimized striations of said intermetallic particles and have an
average grain size in the range of about 15 to 20 m; (f) forming a
portion of said sheet product in said O-temper into said inner
panels by stamping at room temperature to provide inner panels
having raised portions and recessed portions to provide stiffeners
to said inner panels; (g) crimping at least one threaded fastener
to said inner panel; (h) providing an outer panel for joining to
said inner panel; and (i) connecting said outer panel to said inner
panels to provide said plural panel automotive member having
threaded fasteners joined thereto.
20. A process for producing plural panel automotive members having
inner and outer panels connected to form said members, said inner
panels having threaded fasteners securely crimped into said inner
panels to provide means for bolting accessories to said automotive
member, said inner panel formed by the process comprising: (a)
providing a molten aluminum alloy consisting essentially of 2.7 to
3.6 wt. % Mg, 0.1 to 0.4 wt. % Mn, 0.02 to 0.2 wt. % Si, 0.05 to
0.25 wt. % Fe, 0.1 wt. % max. Cu, 0.25 wt. % max. Cr, 0.2 wt. %
max. Zn, 0.15 wt. % max. Ti, the remainder aluminum, incidental
elements and impurities; (b) providing a continuous caster for
continuously casting said molten aluminum alloy; (c) casting said
molten aluminum alloy into a slab having a thickness in the range
of 0.2 inch to 2 inch and having Al--Fe, Al--Fe--Mn or Mg.sub.2Si
intermetallic particles; (d) hot rolling said slab into a hot
rolled sheet product, said hot rolling starting in a temperature
range of 750.degree. to 1000.degree. F. and ending in a temperature
of 4000 to 825.degree. F.; (e) annealing said hot rolled sheet
product to an O-temper condition, said hot rolled sheet product in
said condition having a tensile strength in the range of 28 to 35
ksi, a yield strength in the range of 12 to 17.5 ksi, and an
elongation greater than 19% and having substantially uniform
distribution or minimized striations of said intermetallic
particles and have an average grain size in the range of about 15
to 20 .mu.m; (f) forming a portion of said sheet product in said
O-temper into said inner panels by stamping at room temperature to
provide inner panels having raised portions and recessed portions
to provide stiffeners to said inner panels; (g) crimping at least
one threaded fastener to said inner panel; (h) providing an outer
panel for joining to said inner panel; and (i) connecting said
outer panel to said inner panels to provide said plural panel
automotive member having threaded fasteners joined thereto.
21. A process for producing plural panel automotive members having
inner and outer panels connected to form said members, said inner
panels having threaded fasteners securely crimped into said inner
panels to provide means for bolting accessories to said automotive
member, said inner panel formed by the process comprising: (a)
providing a molten aluminum alloy consisting essentially of 2.7 to
3.6 wt. % Mg, 0.1 to 0.4 wt. % Mn, 0.02 to 0.2 wt. % Si, 0.05 to
0.25 wt. % Fe, 0.1 wt. % max. Cu, 0.25 wt. % max. Cr, 0.2 wt. %
max. Zn, 0.15 wt. % max. Ti, the remainder aluminum, incidental
elements and impurities; (b) providing a continuous caster for
continuously casting said molten aluminum alloy; (c) casting said
molten aluminum alloy into a slab having a thickness in the range
of 0.2 to 2 inches thick, said slab containing Al--Fe, Al--Fe--Mn
or Mg.sub.2Si intermetallic particles; (d) hot rolling said slab
into a hot rolled sheet product; (e) cold rolling said hot rolled
sheet product to a thickness in the range of 0.01 inch to 0.2 inch
to provide a cold rolled sheet product; (f) annealing said cold
rolled sheet product to provide an annealed sheet product, said
annealed sheet product having a tensile strength in the range of 28
to 35 ksi, a yield strength in the range of 12 to 17.5 ksi and an
elongation greater than 19%, said annealed sheet product having a
substantially uniform distribution or minimized striations of said
intermetallic particles and have an average grain size in the range
of about 15 to 20 .mu.m; (g) crimping at least one threaded
fastener to said inner panel; (h) providing an outer panel for
joining to said inner panel; and (i) connecting said outer panel to
said inner panels to provide said plural panel automotive member
having threaded fasteners joined thereto.
22. A process for producing plural panel automotive members having
inner and outer panels connected to form said members, said inner
panels having threaded fasteners securely crimped into said inner
panels to provide means for bolting accessories to said automotive
member, said inner panel formed by the process comprising: (a)
providing a molten aluminum alloy consisting essentially of 2.7 to
3.6 wt. % Mg, 0.1 to 0.4 wt. % Mn, 0.02 to 0.2 wt. % Si, 0.05 to
0.25 wt. % Fe, 0.1 wt. % max. Cu, 0.25 wt. % max. Cr, 0.2 wt. %
max. Zn, 0.15 wt. % max. Ti, the remainder aluminum, incidental
elements and impurities; (b) providing a continuous caster for
continuously casting said molten aluminum alloy; (c) casting said
molten aluminum alloy into a slab having a thickness in the range
of 0.2 to 2 inches, said slab containing Al--Fe, Al--Fe--Mn or
Mg.sub.2Si intermetallic particles; (d) hot rolling said slab into
a hot rolled sheet product, said hot rolling starting in a
temperature range of 750.degree. F. to 1000.degree. F. and ending
in a temperature range of 450.degree. to 800.degree. F.; (e)
annealing said hot rolled sheet product to provide an annealed
sheet product; (f) cold rolling said annealed sheet product to a
thickness in the range of 0.01 inch to 0.2 inch; (g) annealing said
cold rolled sheet product to provide a cold rolled and annealed
sheet product having a tensile strength in the range of 28 to 35
ksi, a yield strength in the range of 12 to 17.5 ksi and an
elongation greater than 19%, said cold rolled and annealed sheet
product having a substantially uniform distribution or minimized
striations of said intermetallic particles and have an average
grain size in the range of about 15 to 20 .mu.m; (h) forming the
said annealed sheet at room temperature into said inner panel; (i)
crimping at least one threaded fastener to said inner panel; (j)
providing an outer panel for joining to said inner panel; and (k)
connecting said outer panel to said inner panels to provide said
plural panel automotive member having threaded fasteners joined
thereto.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of U.S. Ser. No.
10/926,704, filed Aug. 27, 2004, incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] This invention relates to aluminum alloy vehicular
structural parts or members and more particularly, it relates to a
method of casting aluminum alloy into sheet having good forming
characteristics and to forming the sheet into vehicular structural
parts or members such as dash panel, floor panel, door panel,
window trim, radio bracket, reinforcements for panels, etc.
[0003] In many instances, continuous casting of molten aluminum
into slab utilizing twin belt, twin roll or block casters is
favored over DC casting because continuous casting can result in
substantial energy savings and total conversion cost savings
compared to the DC cast method. In the continuous casting process,
molten metal is continuously introduced to an advancing mold and a
slab is produced which may be continuously formed into a sheet
product which is collected or wound into a coil. However, the
continuous casting is not without problems. For example, it has
been discovered that the alloy composition and the processing steps
must be carefully controlled in order to have the formability level
to avoid cracking during forming and yet have the requisite
strength properties in the final product. That is, the alloy and
the processing thereof must be carefully controlled to provide
sheet having the formability suited to the fabricating steps
necessary to form the final product or vehicular structural parts.
If the alloy and processing steps are not controlled, then in the
forming steps, fracture can occur and the formed parts have to be
scrapped. Thus, there is a great need for selection of an aluminum
alloy, continuous casting thereof, and thermal mechanical
processing methods which provide a sheet product having forming
characteristics and strength properties which permit forming
operations such as bending, stamping, deep drawing, stretching or
crimping to hold fasteners during production of vehicular
structural parts or members while avoiding problems of fracturing
or cracking, for example.
[0004] The continuous casting of molten aluminum and rolling slab
produced therefrom into a sheet product is disclosed in various
patents. For example, U.S. Pat. No. 5,976,279 discloses a process
for continuously casting aluminum alloys and improved aluminum
alloy compositions. The process includes the steps of continuously
annealing the cold rolled strip in an intermediate anneal using an
induction heater and/or continuously annealing the hot rolled strip
in an induction heater. The alloy composition has mechanical
properties that can be varied selectively by varying the time and
temperature of a stabilizing anneal.
[0005] U.S. Pat. No. 6,264,765 discloses a method and apparatus for
casting, hot rolling and annealing non-heat treatment aluminum
alloys. The method and apparatus comprises continuous casting, hot
rolling and in-line inductively heating the aluminum sheet to
obtain the mechanical properties within the specification tolerance
of the hot rolled product.
[0006] U.S. Pat. No. 5,985,058 discloses a process for continuously
casting aluminum alloys and improved aluminum alloy compositions.
The process includes the step of heating the cast strip before,
during or after hot rolling to a temperature in excess of the
output temperature of the cast strip from the chill blocks. The
alloy composition has a relatively low magnesium content yet
possesses superior strength properties.
[0007] U.S. Pat. No. 5,993,573 discloses a process for continuously
casting aluminum alloys and improved aluminum alloy compositions.
The process includes the steps of (a) heating the cast strip
before, during or after hot rolling to a temperature in excess of
the output temperature of the cast strip from the chill blocks and
(b) stabilization or back annealing in an induction heater of cold
rolled strip produced from the cast strip.
[0008] U.S. Pat. No. 5,833,775 discloses an aluminum alloy sheet
and a method for producing an aluminum alloy sheet. The aluminum
alloy sheet is useful for forming into drawn and ironed container
bodies. The sheet preferably has an after-bake yield strength of at
least about 37 ksi and an elongation of at least about 2 percent.
Preferably the sheet also has earing of less than about 2
percent.
[0009] U.S. Pat. No. 6,086,690 discloses a process of producing an
aluminum alloy sheet article of high yield strength and ductility
suitable, in particular, for use in manufacturing automotive
panels. The process comprises casting a non heat-treatable aluminum
alloy to form a cast slab, and subjecting said cast slab to a
series of rolling steps to produce a sheet article of final gauge,
preferably followed by annealing to cause recrystallization. The
rolling steps involve hot and warm rolling the slab to form an
intermediate sheet article of intermediate gauge, cooling the
intermediate sheet article, and then warm and cold rolling the
cooled intermediate sheet to final gauge at a temperature in the
range of ambient temperature to 340.degree. C. to form said sheet
article. The series of rolling steps is carried out continuously
without intermediate coiling or full annealing of the intermediate
sheet article. The invention also relates to the alloy sheet
article produced by the process.
[0010] U.S. Pat. No. 5,244,516 discloses an aluminum alloy plate
for discs superior in Ni--P platability and adhesionability of
plated layer and having a high surface smoothness with a minimum of
nodules and micropits, said aluminum alloy plate comprising an
aluminum alloy containing as essential elements Mg in an amount
more than 3% and equal to or less than 6%, Cu in an amount equal to
or more than 0.03% and less than 0.3%, and Zn in an amount equal to
or more than 0.03% and equal to or less than 0.4%, and as
impurities Fe in an amount equal to or less than 0.07% and Si in an
amount equal to or less than 0.06% in the case of semi-continuous
casting, or Fe in an amount equal to or less than 0.1% and Si in an
amount equal to or less than 0.1% in the case of strip casting, and
also containing Al--Fe phase intermetallic compounds, with the
maximum size being smaller than 10 .mu.m and the number of
particles larger than 5 .mu.m being less than 5 per 0.2 mm.sup.2,
and Mg--Si phase intermetallic compounds, with the maximum size
being smaller than 8 .mu.m and the number of particles larger than
5 .mu.m being less than 5 per 0.2 mm.sup.2.
[0011] U.S. Pat. No. 5,514,228 discloses a method for manufacturing
aluminum sheet stock which includes hot rolling an aluminum alloy
sheet stock, annealing and solution heat treating it without
substantial intermediate cooling and rapid quenching.
[0012] In spite of these disclosures, there is a great need for
selection of aluminum alloy and method for producing vehicular
parts or members utilizing a continuous caster, optimized thermal
mechanical processing, to provide good strength and levels of
formability which permit ease of forming into intricate parts
without cracking.
[0013] The term "formability" when used herein is used to describe
the ease with which a sheet of metal can be shaped through plastic
deformation. Formability of a metal can be evaluated by measuring
strength, ductility, and the amount of deformation to cause
failure.
[0014] The term "aluminum" when used herein is meant to include
aluminum and its alloys.
[0015] The term "automotive" as used herein is meant to include
automobile and other vehicular parts or members as described herein
and other transport parts or members having similar
construction.
SUMMARY OF THE INVENTION
[0016] It is an object of the invention to provide an improved, low
cost process including continuous casting and rolling to
continuously produce aluminum sheet product having consistent
levels of formability.
[0017] It is another object of the invention to provide a process
including continuously casting a slab and rolling the slab into a
sheet product suitable for use in producing vehicular parts.
[0018] It is still another object of the invention to provide a
process employing continuous casting of molten aluminum into slab
and rolling the slab into sheet product for meeting the forming
requirements, such as bending, stamping, stretching or deep drawing
of vehicle structural parts or members.
[0019] And yet it is another object of the invention to provide an
improved process for producing aluminum sheet product employing a
continuous caster to produce slab, continuously rolling the slab to
produce a sheet product and annealing the sheet product for forming
into vehicular structural parts or panel members having fasteners
such as threaded fasteners attached thereto by crimping the sheet
product around the fastener.
[0020] It is yet another object of the invention to provide a
process for producing vehicular members such as shallow or deep
formed panel members which includes continuously casting an
aluminum alloy into a slab, rolling the slab to a sheet product and
annealing the sheet product having good levels of formability,
forming the sheet product into a panel having threaded fasteners
attached thereto by crimping to provide a formed vehicular member
for mechanically fastening to support members, for example.
[0021] And yet it is another object of the invention to provide a
process for casting a molten alloy comprising 2.7 to 3.6 wt. % Mg,
0.1 to 0.4 wt. % Mn, 0.02 to 0.2 wt. % Si, 0.05 to 0.30 wt. % Fe,
0.1 wt. % max. Cu, 0.25 wt. % max. Cr, 0.2 wt. % max. Zn, 0.15 wt.
% max. Ti, the remainder aluminum, incidental elements and
impurities, casting the alloy into a slab which is hot rolled and
annealed to provide a sheet product suitable for forming into a
vehicular structural part or frame member where good formability is
necessary.
[0022] In accordance with these objects, there is provided a
process for producing aluminum vehicular structural parts or
members from molten aluminum alloy using a continuous caster to
cast the alloy into a slab. The method comprises providing a molten
aluminum alloy consisting essentially of 2.7 to 3.6 wt. % Mg, 0.1
to 0.4 wt. % Mn, 0.02 to 0.2 wt. % Si, 0.05 to 0.25 wt. % Fe, 0.1
wt. % max. Cu, 0.25 wt. % max. Cr, 0.2 wt. % max. Zn, 0.15 wt. %
max. Ti, the remainder aluminum, incidental elements and impurities
and providing a continuous caster such as a belt caster for
continuously casting the molten aluminum alloy. The molten aluminum
alloy is cast into a slab having Al--Fe, Al--Fe--Mn or Mg.sub.2Si
containing intermetallic particles. The slab is rolled into a sheet
product which is then annealed to provide a sheet product having a
substantially uniform distribution or less striations of
intermetallic particles for improved formability. Thereafter, the
sheet product is formed into a vehicular structural part or member
such as a panel member for a door or hood, for example, having
fasteners crimped thereto.
[0023] Alternatively, the hot rolled sheet may be cold rolled after
hot rolling, and then annealed prior to the forming steps. In yet
another embodiment, the hot rolled sheet may be annealed or even
homogenized and then cold rolled to a cold rolled sheet product.
The cold rolled product can be annealed to provide a product suited
to the various forming steps.
[0024] These and other objects will become apparent from a reading
of the specification and claims appended hereto.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a schematic of a continuous caster, hot rolling
mill and rolls of sheet material.
[0026] FIG. 2 is a flow chart showing steps in the invention.
[0027] FIG. 3 is a micrograph showing microstructure of D.C. cast
material.
[0028] FIG. 4 is a micrograph showing microstructure of sheet
material formed by continuous casting (CC) and rolling in
accordance with the invention.
[0029] FIG. 5 is a schematic of a vehicular rear hatch door or lift
gate.
[0030] FIG. 6 is a side view of a vehicle showing rear door
open.
[0031] FIG. 7 is a perspective view showing structural members of a
rear hatch door separated.
[0032] FIG. 8 is a cross-sectional view showing structural members
hemmed together.
[0033] FIG. 9 is a cross-section of a threaded fastener crimped
into the metal.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0034] The vehicular structural parts or members, for example, of
the invention are comprised of an aluminum base alloy containing
controlled amounts of magnesium, iron, silicon and manganese for
the required strength and formability in the sheet product produced
by the casting and thermomechanical process. The total amounts of
the alloying elements are required to be controlled to meet the
strength requirement without causing casting difficulty in the
process. Further, the amount of alloying elements also is required
to be controlled to meet the formability requirements, especially
the amount of iron, manganese and silicon. Al--Fe, Al--Fe--Mn or
Mg.sub.2Si intermetallic particles form during solidification. That
is, the distribution, size and amount of such intermetallic
particles after rolling of continuous cast slab can drastically
influence the formability of the sheet material.
[0035] The Al--Fe, Al--Fe--Mn or Mg.sub.2Si containing
intermetallic particles form during solidification. The
distribution of such intermetallic particles after rolling of
continuous belt cast aluminum slab can be severely striated or
lined causing forming problems. By comparison, direct chill (D.C.)
ingot cast material has a more uniform distribution of
intermetallic particles providing good formability. Striations of
intermetallic particle structure causes stress concentration during
plastic deformation which deteriorate formability of the sheet
product. Thus, it is desired that the rolled sheet of the invention
has a substantially uniform distribution or less striations of
intermetallic particles to provide for improved formability.
[0036] Accordingly, the aluminum base alloy consists essentially of
2.7 to 3.5 wt. % Mg, 0.1 to 0.4 wt. % Mn, 0.02 to 0.2 wt. % Si,
0.05 to 0.3 wt. % Fe, 0.1 wt. % max. Cu, 0.25 wt. % max. Cr, 0.2
wt. % max. Zn, 0.15 wt. % max. Ti, the remainder aluminum,
incidental elements and impurities. Preferably, magnesium is
maintained in the range of 2.8 to 3.3 or 3.5 wt. % and manganese is
preferably maintained in the range of 0.1 to 0.25 or 0.35 wt. %.
Further, preferably iron is maintained in the range of 0.05 or 0.10
to 0.25 wt. %, typically 0.05 to 0.2 wt. % and silicon is
maintained in the range of 0.05 to 0.15 wt. %. Impurities are
preferably limited to not more than 0.05 wt. % each and the
combination of impurities should not be greater than 0.15 wt. %
total.
[0037] Thus, it will be understood that to use an alloy of the
above composition in the process of the invention to form
automotive members having the requisite properties requires careful
control of the alloying elements in the alloy and the casting
thereof to avoid forming intermetallic particle structures adverse
to the forming operation. That is, it will be appreciated that in
the present process, there is great difficulty in balancing all the
constituents in the alloy for strength and procedural steps
necessary to forming a sheet product having desirable properties
for forming into the final product while avoiding undesirable
properties which leads to fracture or cracking, for example, during
the forming process. Further, it should be understood that high
magnesium contents can result in edge cracking during casting and
formation of hot rolling holes during processing. Thus, it is
important to keep the magnesium content lower, for example, in the
range of 2.7 to 3.45. With respect to manganese, iron and silicon,
these elements tend to form intermetallic particles during
solidification. Thus, in continuous casting and rolling, heavy
striations of intermetallic particles will be formed if the
manganese, iron and silicon are not carefully controlled. It is
important to avoid these particles in order to have high
formability stamping at room temperature. In other alloys, high
manganese is needed to prevent grain growth when such alloys are
formed at high temperatures.
[0038] Not only is it important to have alloying elements and
impurities in the controlled amounts as herein described, but the
slab produced by continuous casting, the sheet formed from the slab
and automotive member fabricated from the sheet must be prepared in
accordance with specific method steps in order to produce sheet and
automotive structural parts or members therefrom having the
desirable characteristics. That is, the process must be controlled
in order to produce product having near formability properties of
DC ingot fabricated material without the cost penalties of the DC
ingot process.
[0039] Thus, referring now to FIG. 1, there is shown a schematic
illustration of a belt caster 2 and rolling mill for producing
sheet suitable for forming into vehicular structural parts or
members in accordance with the invention.
[0040] In FIG. 1, molten aluminum 10 is provided in a furnace or
reservoir 12. Molten aluminum from reservoir 12 is directed along
line 14 to a tundish 16 from where it is metered through a nozzle
18 into an advancing mold created by revolving belts 20 and 22 and
side dam blocks (not shown). Belts 20 and 22 are turned by means of
rolls 24. Molten metal, e.g., molten aluminum, is solidified to
form a continuous slab 15 between belts 20 and 22 which are chilled
using coolant spray 26. Belt caster 2 is described in U.S. Pat.
Nos. 3,864,973; 3,921,697; 4,648,438; 4,940,076 and 4,972,900,
incorporated herein by reference as if specifically set forth.
Improved nozzles for a belt caster are set forth in U.S. Pat. No.
5,452,827, incorporated herein by reference.
[0041] Another casting apparatus that may be used in the present
invention is a block caster wherein the blocks are connected to
form belts and is included herein as a belt caster. As described
with respect to belt caster 2, a tundish and nozzle are provided to
transfer molten metal to the block belts of the block caster
wherein solidification occurs to provide a solidified slab 15 and
the blocks are chilled to aid in solidification of the molten
metal.
[0042] Yet another apparatus that may be utilized to cast a
continuous strip or slab 15 is a roll caster which includes two
rolls which rotate to provide the continuously advancing mold. As
in the belt caster, a tundish and nozzle are used to transfer
molten aluminum to the mold defined by the two rolls. Again, the
rolls are normally chilled to aid in solidification of the molten
metal into a strip or slab. The different casters are described in
U.S. Pat. No. 5,452,827. By the use of the term "continuous caster"
is meant to include all these casters.
[0043] Molten aluminum alloy of the invention is introduced to the
caster in a temperature range of about 1220.degree. to 1320.degree.
F., typically 1250.degree. to 1285.degree. F., and exits the caster
at a temperature in the range of 750.degree. to 1150.degree. F.,
typically 860.degree. to 950.degree. F. In addition, typically the
continuous slab exiting the belt caster has a thickness in the
range of 0.2 to 2 inches, for example, 0.2 to 1 inch. A typical
slab thickness for the belt caster is about 0.6 to 0.875 inch. Belt
casting speed can range from 10 to 40 ft/min, depending on the
thickness of the slab. It is important to adhere to these casting
conditions in order to obtain microstructures with less striations
or lines of intermetallics such as Al--Fe, Al--Fe--Mn or Mg.sub.2Si
for purposes of formability and corrosion resistance. It should be
noted that DC cast material normally has good or substantially
uniform distribution of intermetallic particles. But, as noted
earlier, DC cast material has the penalty of higher conversion
costs than the subject continuous cast slab. Thus, the present
invention provides continuous cast slab for forming into sheet
material with near DC cast properties to obtain the cost savings
and yet retain the desirable properties such as formability.
[0044] After exiting the caster, the slab 15 is directed to rolling
mill 30 where it is rolled to form a rolled strip or flat product
34 using preferably a hot mill. Hot mill 30 is comprised of one or
more pairs of oppositely opposed rolls 32 which reduces the
thickness of the slab a controlled amount as it passes between each
stand of rolls. Three sets of hot stands or rolls are illustrated
in FIG. 1. For example, slab 15 having a thickness of about 0.2 to
1 inch would be reduced to a sheet product having a thickness of
about 0.01 to 0.25 inch. Typically, for vehicular structural parts
or plural panel members the sheet product would have a thickness in
the range of 0.02 to 0.1 or 0.2 inch, for example, depending on the
application. The temperature of the slab entering hot mill 30 would
typically be in the range of about 700.degree. to 1100.degree. F.,
if no heat is added. Typically, temperature of sheet product
exiting mill 30 would be in the range of 350.degree. to 700.degree.
F. In another aspect of the invention, the slab from caster 3 may
be heated prior to hot rolling (not shown in FIG. 1) to a
temperature of 800.degree. to 1100.degree. F. to increase the
rolling temperature prior to hot rolling. Thus, slab entering the
hot mill can have temperatures of about 800.degree. to 1100.degree.
F.
[0045] Hot mill 30 can reduce the thickness of the slab about 60 to
95% of its original thickness, with typical reduction being 75 to
95%. Depending on the end use of the sheet product, heat may be
applied to the strip or slab between hot stands in addition to or
instead of heating prior to the hot mill.
[0046] The temperature of the aluminum alloy sheet exiting the hot
mill can be in the range of about 400.degree. to 825.degree. F.,
depending on whether there was heat input before or during hot
rolling.
[0047] After hot rolling, hot rolled strip 34 can have a
deformation texture and deformed grain structure. The hot rolled
strip can have a partially or fully recrystallized grain structure
with an optimum texture depending on previous heat input and
rolling reduction. If the structure remains deformed and a
recrystallized grain structure is necessary for the end product,
then annealing of the hot rolled strip 34 can be applied to promote
recrystallization of the deformed structures. For example, it is
important for automotive application using the aluminum alloy of
the invention to have a fine, fully recrystallized grain structure
with random texture for the purpose of forming automotive parts in
accordance with the invention. Thus, in the present invention, it
is preferred that the hot rolled sheet be fully annealed to
O-temper in annealer 40. Hot rolled sheet in the fully annealed
condition can have a tensile strength in the range of 28 to 35 ksi,
a yield strength in the range of 12 or 13 to 17.5 ksi and an
elongation greater than 19%, e.g., 19-30%.
[0048] Referring to FIG. 1, it will be seen in the embodiment
illustrated that the hot rolled sheet product is directed to a
continuous annealer 40, using a heater such as an infrared,
solenoidal or transverse flux induction heater. While any
continuous heater may be used, an induction heater is preferred.
Continuous anneal may also be required if cold rolling (not shown
in FIG. 1) of the hot rolled strip is necessary. Thus, the hot or
cold rolled strip may be continuously annealed in annealer 40 in a
temperature range of 600.degree. to 1100.degree. F. in time periods
from 0.5 to 60 seconds in order to effect fully recrystallized
sheet having fine grains and highly desired formability properties.
However, care is required that the sheet product is not over
annealed to the point where secondary recrystallization occurs.
Secondary recrystallization is the growth of fine grains into
undesirable coarse grains which are detrimental to formability.
[0049] Instead of continuous annealing, the hot rolled sheet may be
batch annealed. That is, hot rolled sheet 42 is wound into coils 48
or 49. These coils are then placed in a furnace and soaked in a
temperature range of 600.degree. to 1000.degree. F. for 2 to 10
hours to provide the rolled sheet in a fully annealed or O-temper
condition. If the slab has been hot rolled to a gauge suitable for
forming, then no further thermal mechanical processing is necessary
and the sheet is in condition for the forming steps. If the slab
has been hot rolled to an intermediate gauge, then after annealing,
the annealed material is subjected to cold rolling followed by
further annealing to provide sheet in the O-temper for forming
operations.
[0050] After hot rolling, the hot rolled sheet or flat product may
be allowed to cool prior to other operations. For example, after
hot rolling, with or without annealing and cooling, the resulting
strip 42 may be cold rolled (not shown in FIG. 1) to a sheet
product having a final gauge. The cold rolling may be performed by
passing strip 42 through several pairs or stands comprising a cold
mill to provide the cold rolling required to produce the final
gauge. Cold rolling can reduce the thickness of strip 42 by 20% to
80% or 90%. Final gauge can range from 0.02 to 0.09 or even 0.2
inch, typically 0.03 to 0.12 inch, for automotive applications. It
will be appreciated that the cold rolling, which is rolling at
lower than 300.degree. F., can be performed in a cold rolling line
separate from the subject continuous casting and rolling line.
[0051] After cold rolling to final gauge, the sheet product is
subject to further anneal to ensure the required crystallographic
texture and grain structure necessary for forming into the final
automotive product.
[0052] After hot rolling or annealing sheet 42 may be subject to a
continuous rapid quenching such as cold water quench 50 prior to
further operations. Quench 50, if used and shown after anneal, can
be located at different locations in the process.
[0053] Referring to FIG. 2, it will be seen that in an alternate
process annealed hot rolled sheet may subject cold rolling followed
by further annealing prior to forming. In a further embodiment or
alternate process, after hot rolling, the sheet may be directly
cold rolled followed by annealing of the cold rolled sheet prior to
being formed into a vehicular structural part or member. The cold
rolled and annealed sheet, along the rolling direction, can have a
tensile strength in the range of 28 to 35 ksi, a yield strength in
the range of 12 to 17.5 ksi and an elongation greater than 19%.
Further, the finish gage coils may go through one or combination of
steps before the forming process, such as tension leveling,
slitting, surface pretreatment, lubrication or cut-to-length.
[0054] As an example of the desirable microstructures which have
good forming characteristics of continuously cast (CC) aluminum
sheet, reference is made to FIGS. 3 and 4. FIG. 4 shows the
microstructure of CC 5754 alloy with controlled chemistry while
FIG. 3 shows that of the commercially used DC 5754 alloy sheet.
Both sheets are 0.060 inch in thickness and are in the O-temper
condition. SEM inspection of the particles which were formed during
solidification shows that they are comprised of Al--Fe, Al--Fe--Mn
and Mg.sub.2Si. The particle structure of CC sheet is substantially
uniformly distributed with only minimal striations or lines while
the intermetallic particles of DC sheet are uniformly distributed.
The intermetallic particle size of CC material ranges from about
0.1 to 7 .mu.m while that of DC material ranges from about 0.5 to
10 .mu.m. The area fraction of intermetallic particles is 0.43% for
CC material while the area fraction is 0.56% for DC material. Also,
with the optimum-processing route, CC sheet has a finer grain
structure than DC sheet. The measurement of the grain size shows
that CC material has an average grain size of 16.6 .mu.m while DC
material has an average grain size of 17.8 .mu.m. Grain size for CC
material can have a range of 15 to 17 .mu.m. Thus, it will be seen
that with control of chemistry and optimization of processing, the
continuous cast technology can produce microstructures which are
similar to those produced by the DC cast technology and thus
provides formability properties required by automotive industry,
for example.
[0055] Referring now to FIG. 5 there is illustrated an automotive
lift gate 100 provided as part of a sports utility vehicle (SUV).
The lift gate is comprised of a bottom metal portion 102 and a
window frame portion 104 covered with glass. Lift gate 100 is
mounted to roof 108 of the SUV using hinges 106 and is closed or
secured to the vehicle using handle 110. Generally, sides 112,
bumper 114 and roof 108 define the opening closed by the lift gate.
In FIG. 6, lift gate 100 is shown partially open and supported by
strut 116. Compared to steel, a lift gate fabricated from an
aluminum alloy of the invention can result in substantial weight
savings which can be as much as 20 pounds, depending on the
vehicle. Further, lighter and less costly struts can be used to
open and support the lift gate, adding to the weight savings. It
will be noted that strut 116 is fastened to lift gate 100 at 118
which requires the aluminum alloy to have good forming
characteristics to hold a threaded fastener.
[0056] FIG. 7 shows an exploded view of an automotive lift gate
structure comprised of an outer panel 120 and an inner panel 122
which are peripherally joined to provide a dual panel lift gate
structure. It will be appreciated that doors, hoods, fenders and
the like can employ the same type of construction, i.e., inner and
outer panels. Further, it will be seen from FIGS. 7 and 8 that
outer panel 120 employs a generally curved, smooth shape. Also from
FIG. 7 it will be seen that outer panel 120 configuration shows
window frame 104 as an integral part of bottom portion 102.
Referring further to FIG. 7, it will be noted that inner panel 122
uses a more complicated design which includes dished portions 124
and can have raised channels and open portions (not shown),
particularly when used for doors or hoods. The inner panel with its
dished portions and raised portions serves to increase the flexural
strength of the lift gate. Further, the inner panel or outer panel
can be shaped from a single sheet using stamping between mating
dies to provide the structural features necessary to the lift gate
assembly. While the outer panel is relatively smooth and curved, as
noted, the inner panel will usually be shaped to form a channel 126
(FIG. 8) to provide increased strength to the window frame portion.
It should be noted that outer panel 120 can be formed of steel or,
for example, aluminum alloys AA6111 or AA5083, the composition of
which is provided in the Aluminum Association publication entitled
"International Alloy Designations and Chemical Composition Limits
for Wrought Aluminum and Wrought Aluminum Alloys", dated January
2001, all of which is incorporated herein by reference as if
specifically set forth.
[0057] FIG. 8 shows a cross section of a lift gate employing outer
panel 120 hemmed or seamed to inner panel 122. Thus, outer panel
120 is relatively smooth and inner panel 122 has recessed areas and
employs a channel around the window frame 104 for increased
strength. The lift gate derives its strength from the dual or
plural structure of the two formed panels.
[0058] Formed panels can include doors, hoods, trunk lids, fenders,
floors, wheels and bumper backup bars and can be formed from flat
sheets of aluminum alloy formed between mating dies to provide a
three-dimensional structure. The dual or plural structure as
depicted employs peripheral seaming or hemming to provide the
vehicular structural member; however, other means of joining can
include welding, riveting, adhesive bonding and thus the inner and
outer panels can be joined by any of these methods and such is
contemplated. The seaming or hemming referred to is shown in FIG. 8
where outer panel 120 is hemmed around inner panel 122. Thus, outer
panel 120 should be capable of forming or bending 180.degree.
without cracking where the radius of the bend is about half the
thickness of the metal.
[0059] In some instances, the structural member may include a
combination of steel and aluminum alloy, but such structure would
not provide the same weight savings.
[0060] The alloy of the invention is required to have good
formability for yet another reason. That is, hinges 106 and struts
116, for example, are preferred to be joined to steel threaded
fasteners. Thus, at 118 where strut 116 is connected to lift gate
100, it is preferred to use a metal fastener such as a steel
fastener. Accordingly, a threaded fastener 130 is crimped into the
sheet metal of the inner panel as shown in FIG. 9. The crimping
must be of a severity to pull the sheet metal around shoulder 132
of the threaded fastener without forming cracks in the sheet metal.
The locking of the threaded fastener in the sheet metal must be
sufficiently tight to permit screwing a bolt through an eye in the
strut into the fastener. Crimping in this manner obviates welding
and readily permits joining of aluminum to a steel threaded
fastener for ease of fabrication. Crimping is alloy sensitive and
if the iron is too high, the metal can crack during the crimping
operation. Thus, for purposes of crimping, it is preferred to keep
iron less than 0.25 wt. % and preferably in the range of 0.05 or
0.1 to 0.2 wt. %.
[0061] Thus, aluminum alloy vehicular parts or members produced in
accordance with the foregoing practices provide material having the
strength and formability for use as vehicular or automotive sheet
which can be formed into many different automotive structural
members.
[0062] All ranges provided herein are meant to include all the
numbers within the range as if specifically set forth, e.g., 1 to 5
would include 1.1, 1.2, 1.3, etc., or e.g., 2, 3, 4.
[0063] The following example is further illustrative of the
invention.
EXAMPLE
[0064] An aluminum base alloy containing 3.267 wt. % Mg, 0.201 wt.
% of Mn, 0.080 wt. % Si, 0.164 wt. % Fe, 0.020 wt. % Cu, 0.004 wt.
% Cr and 0.024 wt. % Zn, was fed to a twin belt caster at a
temperature of 1260.degree. F. and solidified to produce a 0.875
inch thick slab existing the caster at a temperature of 900.degree.
F. The slab was directly fed into a three stand hot rolling mills
and rolled to final gauge of 0.100 inch. The temperature of
introducing the slab to the hot rolling mill was at about
820.degree. F. and the temperature of exiting the mill was at about
520.degree. F. The hot rolled sheet was wound into a coil. The coil
was annealed in an anneal furnace at a temperature of 730.degree.
F. for 4 hours. The annealed coil was tension leveled and slit into
the required width and then the coil was given a surface
pretreatment and lubricated. The material had properties in the
rolling direction before forming into automotive parts of: ultimate
tensile strength of 32.8 ksi, yield strength of 15.5 ksi,
elongation of 21.4%. All these properties met the requirement
identified by Aluminum for Automotive Body Sheet Panels, published
by The Aluminum Association. The material was formed into inner
structural panels, and threaded fasteners were crimped into the
sheet with satisfied quality inspection. Thus, the alloy can be
cast in a twin belt caster, rolled into a sheet product, stamped or
shaped into an automotive structural part or member with sufficient
strength and formability.
[0065] It will be seen that the continuous caster can be used to
produce a slab which can be thermomechanically treated to form a
sheet product having the properties for forming into vehicular
parts or members.
[0066] Having described the presently preferred embodiments, it is
to be understood that the invention may be otherwise embodied
within the scope of the appended claims.
* * * * *