U.S. patent application number 15/524895 was filed with the patent office on 2017-12-07 for multipurpose heat treatable aluminum alloys and related processes and uses.
This patent application is currently assigned to Novelis Inc.. The applicant listed for this patent is Novelis Inc.. Invention is credited to Eduardo Adrian Chuc Gamboa, Alok Kumar Gupta.
Application Number | 20170349989 15/524895 |
Document ID | / |
Family ID | 54478965 |
Filed Date | 2017-12-07 |
United States Patent
Application |
20170349989 |
Kind Code |
A1 |
Gupta; Alok Kumar ; et
al. |
December 7, 2017 |
MULTIPURPOSE HEAT TREATABLE ALUMINUM ALLOYS AND RELATED PROCESSES
AND USES
Abstract
This application discloses an aluminum alloy, processes for
preparing the aluminum alloy, processes for fabricating metal
parts, such as automotive panels, comprising the aluminum alloy,
and the automotive parts fabricated from the aluminum alloy.
Inventors: |
Gupta; Alok Kumar;
(Kingston, CA) ; Chuc Gamboa; Eduardo Adrian;
(Kingston, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Novelis Inc. |
Atlanta |
GA |
US |
|
|
Assignee: |
Novelis Inc.
Atlanta
GA
|
Family ID: |
54478965 |
Appl. No.: |
15/524895 |
Filed: |
October 21, 2015 |
PCT Filed: |
October 21, 2015 |
PCT NO: |
PCT/US2015/056720 |
371 Date: |
May 5, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62078027 |
Nov 11, 2014 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 21/08 20130101;
C22F 1/047 20130101; C22C 21/06 20130101; C22F 1/05 20130101 |
International
Class: |
C22F 1/047 20060101
C22F001/047; C22C 21/08 20060101 C22C021/08 |
Claims
1. An aluminum alloy comprising .gtoreq.1.5% Mg by weight produced
by a process comprising heat treatment.
2. The aluminum alloy of claim 1, wherein the process comprises T4
temper.
3. The aluminum alloy of claim 1, wherein the aluminum alloy
further comprises 0.2 to 0.4% Si by weight.
4. The aluminum alloy of claim 1, wherein the aluminum alloy
exhibits age hardening.
5. The aluminum alloy of claim 1, wherein the aluminum alloy is a
sheet aluminum alloy.
6. A stamped sheet form fabricated from the sheet aluminum alloy of
claim 5.
7. The stamped sheet form of claim 6, wherein the stamped sheet
form is an automotive panel.
8. A process for fabricating a sheet aluminum alloy comprising
.gtoreq.1.5% Mg and 0.2 to 0.4% Si by weight, comprising heat
treatment.
9. The process of claim 8, wherein the process comprises T4
temper.
10. The process of claim 8, wherein the sheet aluminum alloy
exhibits age hardening.
11. A process for fabricating a stamped sheet form comprising
stamping the sheet aluminum alloy of claim 5.
12. The process of claim 11, wherein the stamped sheet form is an
automotive panel.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 62/078,027, filed Nov. 11, 2014, which is
incorporated by reference herein in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to the fields of material
science, material chemistry, metallurgy, aluminum alloys, aluminum
fabrication, and related fields.
BACKGROUND
[0003] Aluminum alloys used for various applications must achieve
certain properties. For instance, aluminum alloys are used for
fabrication of inner and outer panels of transportation machinery.
Aluminum alloys are useful for this application due to a
combination of their light weight, which leads to increased fuel
efficiency, strength, and other properties. Among other things, the
aluminum alloys used for fabrication of inner and outer panels of
transportation machinery should possess good formability, paint or
other finish quality, dent resistance and immunity to natural
aging. It is also desirable for the alloys used in the fabrication
of transportation machinery to be recyclable. New and improved
metal alloys with desirable characteristics suitable for
fabrication of transportation machinery panels can expand the range
of alloys available for these applications, lower the material
costs, increase the aluminum recycling rates, decrease the capacity
limits on the production of such alloys, and decrease the
environmental impact of aluminum production and use.
SUMMARY
[0004] The terms "invention," "the invention," "this invention" and
"the present invention" used herein are intended to refer broadly
to all of the subject matter of this patent application and the
claims below. Statements containing these terms should be
understood not to limit the subject matter described herein or to
limit the meaning or scope of the patent claims below. Covered
embodiments of the invention are defined by the claims, not this
summary. This summary is a high-level overview of various aspects
of the invention and introduces some of the concepts that are
further described in the Detailed Description section below. This
summary is not intended to identify key or essential features of
the claimed subject matter, nor is it intended to be used in
isolation to determine the scope of the claimed subject matter. The
subject matter should be understood by reference to appropriate
portions of the entire specification, any or all drawings and each
claim.
[0005] The present invention provides improved heat treatable
aluminum alloys containing higher amounts of Mg than conventionally
considered suitable for heat treatment and can exhibit age
hardening if solutionized in continuous solution heat treatment
lines. The improved aluminum alloys provided herein can be produced
as sheet alloys and can be more suitable for recycling processes
than conventional alloys. Some embodiments of the present invention
are improved aluminum alloys suitable for fabricating automotive
and other transportation machinery panels. Some other embodiments
of the present invention are innovative new uses and applications
of the aluminum alloys, improved innovative processes for making,
fabricating or manufacturing aluminum alloys, processes for
fabricating aluminum alloy forms, objects and parts, such as
stamped sheet forms, the panels for transportation machinery.
Aluminum alloy objects, parts and forms that are fabricated from
the improved aluminum alloys and/or according to the innovative
processes provided herein are also provided among the embodiments
of the present invention.
[0006] One embodiment of the present invention provided herein is
an aluminum alloy comprising .gtoreq.1.5% Mg by weight produced by
a process comprising heat treatment. The heat treatment process can
comprise T4 temper. The aluminum alloy can further comprise 0.2 to
0.4% Si by weight. The aluminum alloy can undergo age hardening.
The aluminum alloy can be a sheet aluminum alloy. Another
embodiment of the present invention provided herein is a stamped
sheet form fabricated from the above sheet aluminum alloy. The
stamped sheet form can be an automotive panel. One embodiment of
the present invention provided herein is a process for fabricating
a sheet aluminum alloy comprising .gtoreq.1.5% Mg and 0.2 to 0.4%
Si by weight, comprising heat treatment. The process can comprise
T4 temper. The resulting sheet aluminum alloy can exhibit age
hardening. One more embodiment of the present invention described
herein is a process for fabricating a stamped sheet form,
comprising stamping the above sheet aluminum alloys. The stamped
sheet form can be an automotive panel.
BRIEF DESCRIPTION OF THE FIGURES
[0007] FIG. 1 is a schematic diagram illustrating process steps
used for producing sheet aluminum alloys.
[0008] FIG. 2 is a schematic illustration of various sheet
stampings used in automobile production.
[0009] FIG. 3 is a bar graph showing DIN tensile properties of an
alloy in O temper and paint bake.
[0010] FIG. 4 is a bar graph showing tensile properties of an alloy
in the T4, 2% stretch, and 2% stretch followed by 20 min at
185.degree. C.
[0011] FIG. 5 is a bar graph showing tensile properties of an alloy
in the T4 temper and after paint bake simulation (60 min at
180.degree. C.).
[0012] FIG. 6 is a line plot illustrating age hardening of
AA5251-T4 alloy.
DETAILED DESCRIPTION
[0013] In this description, reference is made to alloys identified
by AA numbers and other related designations, such as "series." For
an understanding of the number designation system most commonly
used in naming and identifying aluminum and its alloys, see
"International Alloy Designations and Chemical Composition Limits
for Wrought Aluminum and Wrought Aluminum Alloys," published by The
Aluminum Association. 6xxx series aluminum alloys, such as AA6111,
AA6016 and AA6022, are typically used for producing automotive
outer skin panels.
[0014] In general terms, 6xxx series alloys contain relatively high
levels of Si and low levels of Mg, are heat treatable, and exhibit
age hardening, which confers on these alloys the strength
parameters suitable for fabrication of the outer panels for
transportation machinery, such as automobiles. 5xxx series aluminum
alloys in O temper, such as AA5182-O or AA5754-O, are often
preferred for inner panel fabrication in automotive and related
industries due to their formability properties. 5xxx series
aluminum alloys have very little tolerance to retain Si in solid
solution. If Si is added to 5xxx series aluminum alloys, it tends
to combine with Mg to form coarse Mg.sub.2Si particles during
casting. These particles are difficult to solutionize to produce
super saturated solid solution of Mg and Si during solutionizing
and fast cooling on the continuous annealing lines. For this
reason, 5xxx series aluminum alloys contain relatively low Si
levels and relatively high Mg levels, and are considered to be
non-heat treatable due to their high Mg content. The presence of
coarse Mg.sub.2Si is potentially detrimental to formability.
[0015] Currently, 6xxx and 5xxx aluminum alloys cannot be easily
combined and recycled for fabrication of automotive and related
panels, because the resulting recycled aluminum alloys may contain
undesirably high levels of both Si (as compared to 5xxx series
aluminum alloys) and Mg (as compared to 6xxx series alloys), and
thus be neither suitable for heat treatment, due to high Mg levels,
nor possess the formability of 5xxx series alloys, due to a
combination of relatively high Si and Mg levels. In addition, the
presence of other metals, such as Cu, Mn, Fe or Zn, or combinations
thereof, present in the alloys recycled from the combination of
5xxx and 6xxx alloys can lead to undesirable properties of the
recycled aluminum alloys. For example, an undesirable combination
of properties can leave a recycled aluminum alloy unsuitable for
fabrication of either inner or outer panels for transportation
machinery.
[0016] The inventors discovered that alloys that contain relatively
high levels of Mg, such as .gtoreq.1.5% Mg, are heat treatable and
exhibit age hardening, if appropriate amounts of Si and/or Cu are
present in such alloy. This property makes aluminum alloys with
relatively high magnesium content, as compared to traditional 6xxx
alloys, unexpectedly and advantageously suitable for applications
where age hardening is desirable. For instance, the inventors
discovered that some aluminum alloys containing higher amounts of
Mg than conventionally considered suitable for heat treatment, but
lower amounts of Mg and higher amounts of Si in comparison to 5xxx
series aluminum alloys traditionally used for inner automotive
panel fabrication, such as AA5754 or AA5182 alloys, can exhibit age
hardening if solutionized in continuous solution heat treatment
lines.
[0017] The inventors' discoveries are embodied in the improved
aluminum alloys described herein. The improved aluminum alloys
described herein can be produced as sheets, in which case they can
be referred to as "sheet aluminum alloys," "aluminum sheets,"
"sheet alloys" or by other related terms, in singular or plural.
The term "aluminum alloy" and similar terms used herein are broader
in scope than "sheet aluminum alloy" and similar terms. In other
words, sheet aluminum alloys are a subset of aluminum alloys. Sheet
aluminum alloys can possess the same or similar composition but, in
some instances, different properties than the same alloy not in a
sheet form. Some of these properties may be conferred by the
manufacturing or fabrication processes used in the production of
sheet aluminum alloys.
[0018] The improved aluminum alloys that embody applicants'
discoveries exhibit age hardening similarly to 6xxx series alloys.
They can also exhibit formability properties similar to those of
5xxx series aluminum alloys. The improved aluminum alloys are heat
treatable. The improved aluminum alloys can be suitable for
fabricating automotive and other transportation machinery panels,
and, more generally, in the applications where high-Mg 5xxx series
alloys are traditionally used. Increased content of Si and/or Cu in
the improved aluminum alloys according to some embodiments of the
present invention is beneficial in the applications where age
hardening is desirable, because Si and/or Cu are capable of
conferring hardening on solutionized alloys due to precipitation of
Mg.sub.2Si and Al.sub.2CuMg particles during natural or artificial
ageing. In addition to Si and/or Cu, some other elements can be
present in the improved aluminum alloys described herein in higher
amounts than in some 5xxx series aluminum alloys conventionally
used for fabrication of automotive panels. The presence of such
elements can confer advantageous properties on the improved
aluminum alloys described herein. For example, increased levels of
Mn may promote formation of dispersoids, which can help to disperse
slip, thus improving formability. The inventors also discovered
that improved aluminum alloys described herein are more suitable
for recycling processes than conventional alloys, because the
improved aluminum alloys are tolerant to relatively higher amounts
of Si, Cu, Fe or Mn, as compared to 5xxx series aluminum alloys
conventionally used for automotive panel manufacturing, such as
AA5754 and AA5182 alloys. Accordingly, improved recycling processes
embody some of the inventors' discoveries.
[0019] In addition to the improved aluminum alloys, the inventors'
discoveries are embodied in innovative new uses and applications of
the aluminum alloys, in improved innovative processes for making,
fabricating or manufacturing aluminum alloys, in the processes for
fabricating aluminum alloy forms, objects and parts, such as
stamped sheet forms, the panels for transportation machinery.
Aluminum alloy objects, parts and forms that are fabricated from
the improved aluminum alloys and/or according to the innovative
processes described herein also embody the inventors'
discoveries.
[0020] Alloys
[0021] The improved aluminum alloys according to the embodiments of
the present invention differ from the conventional alloys used in
automotive applications in that they contain higher levels of one
or more of Si, Cu, Fe, Mn, or Zn and lower levels of Mg, than at
least some of 5xxx series alloys and/or higher levels of Mg than at
least some 6xxx series alloys The composition of the improved
aluminum alloys is illustrated in Table 1, below. The content of
the listed element can fall within the ranges delimited by a lower
range limit and an upper range limit shown in Table 1. A lower
range limit can be delineated by expressions "equal to or more
than" (.gtoreq. sign) or "more than" (> sign), or other related
signs and expression, such as "from . . . ," "higher than" etc. An
upper range limits can be delineated by expressions "equal to or
less than" (.ltoreq. sign), "less than" (< sign) or other
related signs and expressions, such as "to," "less than," etc.
Other types of expressions can also be used to delineate the
ranges, such as "between," "in the range of," etc. When a range is
delineated by only the upper range limit, it is to be understood
that, in some examples, an element in question may not be present,
may not be present in detectable quantities, or may be present in
such low quantities that they are conventionally not recognized as
meaningful in the field of aluminum alloys. It is also to be
understood that some other additives and/or elements can be present
in the aluminum alloys described herein, which are not necessarily
listed in the tables below.
TABLE-US-00001 TABLE 1 Composition of improved aluminum alloys
(element content in wt %) Examples of Examples of Ele- lower range
upper range Range examples ment limit limit Range 1 Range 2 Range 3
Mg 1.5; 1.55; 1.8; 1.85; 1.9 1.6 to 2 1.65 to 1.9 1.6; 1.61; 1.62;
1.63; 1.64; 1.65 Cu 0.3; 0.35; 0.4; .ltoreq.0.8 .ltoreq.0.5
.ltoreq.0.3 0.45; 0.5; 0.55; 0.6; 0.65; 0.7; 0.75; 0.8 Fe 0.35;
0.4; 0.45; .ltoreq.0.5 .ltoreq.0.4 .ltoreq.0.35 0.5 Mn 0.4
.ltoreq.0.4 Si 0.2 0.4 0.2 to 0.4 Zn 0.25; 0.3; 0.35; .ltoreq.0.5
.ltoreq.0.3 .ltoreq.0.25 0.4; 0.45; 0.5 Cr .ltoreq.0.25
.ltoreq.0.20 .ltoreq.0.15
TABLE-US-00002 TABLE 2 Exemplary composition of conventional 5xxx
series alloys used in automotive applications (element content is
expressed in wt %) ELEMENT AA5182 AA5754 Mg 4 to 5 2.6 to 3.6 Cu
.ltoreq.0.15 .ltoreq.0.10 Fe .ltoreq.0.35 .ltoreq.0.40 Mn 0.2 to
0.5 .ltoreq.0.50 Cr .ltoreq.0.10 .ltoreq.0.30 Si .ltoreq.0.20
.ltoreq.0.40 Zn .ltoreq.0.20 .ltoreq.0.20
Properties and Advantages
[0022] Improved aluminum alloys described herein, including sheet
aluminum alloys, possess one or more properties that make them
suitable for the use in automotive applications, such as
fabrication of automotive panels or, more generally, panels for
various types of transportation machinery, or, even more generally,
stamped sheet forms. Some of these properties are formability,
yield strength and age hardening. Improved aluminum alloys also
possess advantageous recycling compatibility with 6xxx series
aluminum alloys, such as AA6111, AA6022 or AA6016. The expression
"recycling compatibility" and related terms are used herein to
describe a notion that improved aluminum alloys according to some
embodiments of the present invention can be combined with 6xxx
series alloys (and, optionally, other alloys or elements) during
metallurgical processes to fabricate commercially and
technologically useful aluminum alloys, which can be characterized
as "recycled."
[0023] Formability and Paint Bake Response
[0024] Formability properties of the aluminum alloys described
herein can be influenced by a number of variables. Formability
properties include, but are not limited to, deep drawability and
stretchability. One variable affecting formability properties is
the composition of an aluminum alloy. For example, formability,
including castability, is influenced by the amounts of Mg, Cu and
Si in an aluminum alloy. High combined amounts of Mg, Si and/or Cu
generally make it more difficult to cast and hot roll an aluminum
alloy. Accordingly, the content of one or more of these elements
can be varied to arrive at the desired formability properties.
Other variables that can affect formability are fabrication process
variations and conditions, such as, but not limited to, aluminum
sheet processing steps and conditions, surface texturing process
steps and conditions and lubrication process steps and conditions.
One or more of the above variables can be adjusted to achieve
desired formability properties. Another important property that can
be varied by one or more of the variables discussed above is paint
bake response of an aluminum alloy, which refers to change in
strength during the paint cure process. Paint bake response is
usually tested in the laboratory by ageing the deformed or
nondeformed material in the T4 temper at elevated temperature. The
exact simulation conditions determine the paint bake response vary
from one car company to the other. For example, the paint bake
response can be defined as change in strength by ageing an aluminum
alloy at 180.degree. C.
[0025] Strength
[0026] The improved aluminum alloys according to the embodiments of
the present invention can exhibit 80 to 160 MPa yield strength
(YS), which can be similar or equivalent to that of AA5754 or
AA5182 in a typical finished and painted part required for
automotive application. In some embodiments, strength of an
improved aluminum alloy is influenced by increasing an amount of Cu
in the aluminum alloy, as compared to Cu content of the alloys
conventionally used for fabrication of panels for automobiles and
other transportation machinery.
[0027] Hardness
[0028] Certain embodiments of the improved aluminum alloys
described herein are heat treatable and exhibit age-related
hardening, while exhibiting formability comparable to typical 5xxx
aluminum alloys conventionally used in automotive applications.
5xxx aluminum alloys were previously not known to be heat treatable
or exhibit age related hardening upon heat treatment. Improved
aluminum alloys according to some embodiments of the present
invention contain higher levels of Mg than the aluminum alloys
conventionally recognized as heat treatable. Some examples of the
improved aluminum alloys of the present invention contain
.gtoreq.1.5% of Mg and are heat treatable. The presence of
appropriate amounts of Si and/or Cu confers heat treatability and
age hardening properties on an improved aluminum alloy containing
.gtoreq.1.5% of Mg. This allows some improved aluminum alloys
according to the embodiments of the present invention to achieve an
unexpectedly advantageous combination of formability (conferred by
higher Mg levels than those conventionally present in
heat-treatable alloys) and age hardening upon heat treatment such
as T4 temper (conferred by higher Si levels than those
conventionally present in 5xxx series alloys).
[0029] In comparison to some of the 5xxx aluminum alloys, such as
those conventionally employed for manufacturing of inner automotive
panels, in some embodiments improved aluminum alloys of the present
invention contain reduced amount of Mg. Reduced levels of Mg can
result in lower cost of the improved aluminum alloys described
herein, as well as in the lower costs of the forms the objects
manufactured from such alloys, since less Mg is required for
production. Reduced levels of Mg in the improved aluminum alloys
described herein can also result in improved solubility of Si in
aluminum during solutionizing, which advantageously affects the
properties of the alloys. Both Si and Cu are capable of improving
hardening of solutionized the improved aluminum alloys described
herein due to precipitation of Mg.sub.2Si and Al.sub.2CuMg or Q
(AlMgSiCu) containing particles during ageing.
[0030] Recyclability
[0031] The improved aluminum alloys of this invention possess a
tolerance for higher amounts of Si than conventional 5xxx series
alloys used for manufacturing of automotive panels. This higher
tolerance for Si and/or the ability of the improved aluminum alloys
described herein to exhibit paint bake response makes them suitable
and compatible with 6xxx alloys for recycling.
[0032] In summary, the improved aluminum alloys of the present
invention have an advantageous combination of properties that
allows these improved alloys to be used in place of conventional
high-Mg aluminum alloys for various applications. The improved
aluminum alloys described herein can expand the range of alloys
available for a variety of applications, one of which is
manufacturing of stamped sheet forms, such as panels for
automobiles and other transportation machinery, increase aluminum
recycling rates, lower the costs of aluminum alloy manufacturing,
and decrease the environmental impact of aluminum production
Fabrication Processes
[0033] The processes for making or fabricating the improved
aluminum alloys are also included within the scope of the present
invention. Improved aluminum described herein can be fabricated by
the processes that include at least some of the technological steps
described below. At least some of these technological steps can
confer advantageous properties on the improved aluminum alloys. It
is therefore important, in some cases, to include process steps
when describing the improved aluminum alloys. For example, one
exemplary embodiment of an improved aluminum alloy described herein
is AA5251 alloy. Prior to the inventors' discovery, AA5251 alloy,
which contains >1.5% Mg, was not known to be suitable for heat
treatment, and to exhibit age hardening, when in the T4 temper.
Accordingly, an exemplary embodiment of improved aluminum alloys
described herein is AA5251 alloy in T4 temper, which can be
referred to as AA5251-T4.
[0034] The processes of making or fabricating the improved aluminum
alloys can involve heat treating in order to alter the physical
and/or chemical properties of the improved aluminum alloys. Heat
treatments involve the use of heating and/or chilling, of an
aluminum alloy to achieve a desired result, such as hardening. An
embodiment of the processes described herein employs T4 or T4P
temper, which involves solution heat treatment and natural aging of
an aluminum alloy to a substantially stable condition. T4P temper
refers to special thermal heat treatment included following
solutionizing. This treatment can be implemented either by
controlled cooling from solutionizing temperature or be reheating
to a temperature ranging from 50 to 110.degree. C. within an hour
of solutionizing. In some other embodiments, T6 and T8 tempers can
also be used.
[0035] It is to be understood that descriptions and illustrations
of the processes described herein are non-limiting. The process
steps described herein can be combined and modified in various ways
and suitably employed for fabricating the improved aluminum alloys
or forms and objects from such alloys. Process steps and conditions
that are not explicitly described herein, yet commonly employed in
the areas of metallurgy and aluminum processing and fabrication,
can also be incorporated into the processes described herein.
[0036] One exemplary process is schematically illustrated in FIG.
1. It is to be understood that one or more of the process steps
illustrated in FIG. 1 can be incorporated into the processes for
making improved aluminum alloys.
[0037] Another example of a process that incorporates one or more
steps that can be combined in various ways and suitably employed
for fabricating the improved aluminum alloys is described in this
paragraph. An improved sheet aluminum alloy is produced from a
direct chilled (DC) ingot. However, the hot rolling stock may also
be produced from a continuous cast slab. The DC cast ingots are
scalped to remove near surface segregation layer on both sides of
the ingot and homogenized at a temperature between 500 and
575.degree. C. for time periods between 1 to 48 hours before being
subjected to hot and cold rolling to the final gauge. Improved
sheet aluminum alloy can also be subjected to special surface
texturing, such as, but not limited to, electro discharge
texturing, in order to improve formability of the final sheet. The
cold rolled strip is solutionized by heating at >3.degree. C./s
in a continuous annealing line to a temperature between 500 and
575.degree. C., followed by fast cooling and natural ageing to
produce sheet in the T4 temper. Solution heat treatment can
re-dissolve soluble particles, such as Mg.sub.2Si or other
particles back into the matrix, depending on the alloy composition.
Fast quenching is used to produce a super saturated solid solution,
in terms of both solutes and excess vacancies. The fast cooling
from the solutionizing temperature can be carried out in forced
air, water mist, or combination of both water mist and forced air.
Coiling is performed at a temperature between 50 to 110.degree. C.,
followed by coil cooling at a rate .ltoreq.10.degree. C./hour. The
coil can be reheated in the strip form to ensure the coiling
temperature between 50 to 110.degree. C. It is possible to subject
the solutionized sheet alloy to either acidic or alkaline cleaning,
followed by pre-treatment with special chemicals and lubricants,
oils or waxes before coiling at a temperature between 50 and
110.degree. C. The coil can be blanked and used for stamping inner
panels, such as those illustrated in FIG. 2.
[0038] Yet another example of a process that incorporates one or
more steps that can be combined in various ways and suitably
employed for fabricating the improved aluminum alloys is described
in this paragraph. A direct chilled cast alloy ingot is homogenized
above 500.degree. C. for .gtoreq.2 hours, hot rolled to an
intermediate gauge with coiling temperature between 280 to
400.degree. C., cold rolled to the final gauge in one or more
passes with either mill or optimized finished texture and
solutionized in the strip form at temperatures above 480.degree. C.
in a continuous annealing line, fast cooled and coiled between
50.degree. C. and 120.degree. C. The hot coiling step is optional
and is used to improve the paint bake response of the alloy. In
some situations, the solutionized coil may also be cleaned,
pretreated and lubricated prior to stamping.
[0039] The following discussion is included to illustrate the
advantageous properties that fabrication process steps can confer
onto the improved aluminum alloys described herein. Traditionally,
AA5754 or AA5182 alloys are supplied for manufacturing of
automotive panels in the soft O temper, so that a part can be
formed from these alloys and then subjected to paint cure
operation. AA5754 or AA5182 in O temper exhibit softening due to
recovery during paint bake. The improved aluminum alloys according
to some embodiments of the present invention are not subject to
such softening or are not subject to it to the same extent as
AA5754 or AA5182 in O temper. The improved aluminum alloys
described herein can maintain strength closer to AA5754 and AA5182
after forming and paint cure. For example, the strength properties
on the final part manufactured from the improved aluminum alloys of
the present invention can be similar or equivalent to AA5754
alloy.
Uses and Applications
[0040] Uses and applications of the improved aluminum alloys
described herein are included within the scope of the present
invention, as are objects, forms, apparatuses and similar things
fabricated from or comprising the improved alloys described herein.
The processes for fabricating, producing or manufacturing such
objects, forms, apparatuses and similar things are also included
within the scope of the present invention. For example, some
embodiments of the improved aluminum alloys described herein are
suitable for manufacturing of automotive panels. Various automotive
panels, including inner and outer automotive panels, are therefore
included within the scope of the present invention. They are
described, for example, in U.S. Patent Publication No.
2010/0279143, and are also illustrated in FIG. 2.
[0041] It is to be understood, however, that the uses and
applications of the improved aluminum alloys and objects that are
manufactured from such alloys are not limited to automobile panels.
Other objects can be suitably manufactured from the improved
aluminum alloys described herein. One example is the panels
generally incorporated into various transportation vehicles and
other moving machinery, which can be termed "transportation panels"
or "machinery panels." For instance, the panels used for transport
trucks can be advantageously manufactured from the improved
aluminum alloys described herein. Transport trucks with aluminum
cabs are traditionally produced from AA5052 alloy. This alloy has a
tendency to exhibit stretch bands or yield point elongation during
forming, causing objectionable surface appearance. Improved
aluminum alloys according to some embodiments of the present
invention do not exhibit yield point elongation and can be used to
advantageously replace AA5052 alloy for manufacturing of panels
used in transport trucks.
[0042] More generally, some embodiments of the improved aluminum
alloys described herein, in comparison to conventional 5xxx alloys,
show less tendency to display Liiders bands, also known as "slip
bands" or "stretcher-strain marks," which are localized bands of
plastic deformation in metals experiencing tensile stresses.
Accordingly, the improved aluminum alloys described herein can be
advantageously employed in the manufacturing of parts or objects
where Liiders bands are objectionable, such as outer panels for
automobiles and other transportation vehicles and moving
machinery.
[0043] Some embodiments of the alloys described herein are suitable
for complex electronic applications. One example of such
application is aluminum TV frames. More generally, various sheet
stamping, stamped sheet forms, stamped panels, or related objects
fabricated from the improved aluminum alloys described herein are
included within the scope of the embodiments of the present
invention.
[0044] The following examples will serve to further illustrate the
present invention without, at the same time, however, constituting
any limitation thereof. On the contrary, it is to be clearly
understood that resort may be had to various embodiments,
modifications and equivalents thereof which, after reading the
description herein, may suggest themselves to those skilled in the
art without departing from the spirit of the invention. During the
studies described in the following examples, conventional
procedures were followed, unless otherwise stated. Some of the
procedures are described below for illustrative purpose.
Example 1
Testing of Tensile Properties of AA5251 Alloy in O Temper
[0045] An aluminum ingot containing 1.85% Mg, 0.3% Fe, 0.28% Mn and
0.29% Si was homogenized at 540.degree. C. for >5 hours, hot
rolled to 3.2 mm gauge, cold rolled to the final 1.3 mm gauge and
batch annealed for 1 hour at 340.degree. C. to obtain O temper. The
transverse tensile properties of the annealed sheets were
determined using DIN specimens. FIG. 3 shows the DIN tensile
properties of the alloy in both O and paint bake (5% stretch plus
20 min at 185.degree. C.). The alloy exhibited 70 MPa yield
strength (YS), 164 MPa Ultimate Tensile Strength (UTS) and 23%
total elongation in the O temper and showed no hardening after
ageing for 20 min at 185.degree. C. The higher YS in the paint bake
temper (5% stretch plus 20 minutes at 185.degree. C.) is the net
result of work hardening due to stretching and recovery due to
ageing.
Example 2
The Effect of Solutionizing on the Tensile Properties of AA5251
Aluminum Alloy
[0046] This example shows the effects of solutionizing on the
tensile properties of an aluminum alloy. An aluminum ingot
containing 1.85% Mg, 0.3% Fe, 0.28% Mn and 0.29% Si was homogenized
at 540.degree. C. for >5 hours, hot rolled to 3.2 mm gauge and
cold rolled to the final 1.3 mm gauge. The cold rolled 1.3 mm gauge
sheets were solutionized for 2 min at 560.degree. C., cooled and
immediately pre-aged for 8 h at 85.degree. C. The transverse ASTM
properties of the solutionized alloy were determined after 24 hours
of natural ageing. FIG. 4 shows comparative tensile properties of
the alloy in the T4 temper, 2% stretch and 2% stretch plus 20 min
at 185.degree. C. tempers. The aluminum alloy in the T4 temper was
stronger in comparison to its O temper counterpart, as illustrated
by the comparison of FIGS. 3 and 4. The aluminum alloy in T4 temper
exhibited a significant increase in YS due to 2% stretch and after
subjecting the stretch sample to ageing at 185.degree. C. for 20
min. The tensile properties of the aluminum alloy in the T4 temper
were close to the conventional AA5754 alloy. The yield strength of
the aluminum alloy was close to the expected strength of AA5182 or
AA5754 alloy, after subjecting it to similar paint bake
treatment.
Example 3
The Role of Cu Addition to an Alloy
[0047] An aluminum ingot containing 1.75% Mg, 0.78% Cu, 0.23% Fe,
0.11% Mn and 0.38% Si was homogenized at 560.degree. C. for >18
hours, then hot rolled and cold rolled to the final 1.6 mm gauge
and solutionized in a continuous annealing line at 540.degree. C.,
cooled and pre-aged. The transverse tensile properties of the 1.6
mm gauge sheets were determined using ASTM specimens.
[0048] FIG. 5 shows the tensile properties of the alloy in both T4
and paint bake (60 min at 180.degree. C.). This alloy, which
contains higher levels of copper than AA5251 alloy discussed in
Examples 1 and 2, was significantly stronger in comparison to the
AA5251 alloy. The alloy tested in this example exhibited 143 MPa
YS, 284 MPa UTS and 28% total elongation in the T4 temper, and
showed significant hardening after ageing for 60 min at 180.degree.
C. due to precipitation of CuMgAl.sub.2 and Mg.sub.2Si
particles.
Example 4
Comparative Testing of AA5754 in O Temper and AA5251 in O and T
Tempers
[0049] The aluminum ingots of AA5754 and AA5251 alloy having the
composition shown in Table 3 were homogenized at 540.degree. C. for
>5 hours, hot rolled and cold rolled to the final 1 and 1.3 mm
gauges, respectively, in separate trials. Coils of AA5754 and
AA5251 were solutionized on the continuous annealing line at 500
and 560.degree. C., respectively.
[0050] The tensile test results from the trial coils are shown in
Table 4. It can be seen that the yield strength and ultimate
tensile strength of the conventional AA5754 sheet in O temper in
the 0.degree., 45.degree. and 90.degree. with respect to the
rolling direction is close to 100 MPa and within the 219 to 231 MPa
range, respectively. AA5251 alloy in O temper exhibits lower values
compared to the AA5754, except for the strain hardening exponent
(n) value. AA5251 alloy in T temper exhibits significant
improvement in strength properties, such as yield strength and
ultimate tensile strength, compared to AA5251 O temper alloy. In
terms of strength, AA5251 T temper alloy falls between AA5754 and
AA5251-O temper. AA5251 T temper alloy exhibits paint bake response
typically not observed in the AA5251 and AA5754-O temper alloys.
The detected improvements in AA5251 T temper alloy offer a
possibility of using it as a substitute for AA5754 and possibly
AA5182 alloys. Marginally inferior forming characteristics of
AA5251 T temper alloy, indicated by lower elongation, UTS and n
values can be compensated by variety of techniques including
optimizing alloy and process composition, using preferred sheet
surface texture, or choice of lubricant during forming.
TABLE-US-00003 TABLE 3 Aluminum alloy composition Composition wt %
Alloy Cu Fe Mg Mn Si Cr Ti AA5754 0.02 0.20 3.10 0.22 0.06 0.05
AA5251 0.01 0.30 1.83 0.30 0.29 0.03 0.01
TABLE-US-00004 TABLE 4 Comparative testing results of AA5754 in O
temper and AA5251 in O and T tempers Yield Tensile Gauge Strength
Strength Total Temper Dir mm ksi MPa ksi MPa Elongation % n R CASH
Annealed AA5754 Coil#2271809 O 0 1.0 14.6 101 33.4 230 26 0.30 0.87
45 14.5 100 32.3 223 26 0.31 0.57 90 14.4 99 31.9 220 24 0.31 0.64
Batch Annealed AA5251 Coil#L55203R1 O 0 1.3 9.7 67 24.9 172 23 0.34
0.67 45 9.6 66 24.2 166 26 0.32 0.59 90 9.6 66 23.7 163 21 0.32
0.55 CASH Solutionizd AA5251 Coil#L55203R2 T4 0 14.1 97 28.4 196 26
0.26 0.81 45 13.9 96 27.8 192 26 0.26 0.55 90 13.8 95 27.4 189 24
0.26 0.61 2% + 20 min @ 0 20.1 139 31.5 217 21 0.21 0.83
185.degree. C. 45 20.0 138 31.0 214 20 0.21 0.52 90 19.8 137 30.5
210 20 0.21 0.60
Example 5
Age Hardening of AA5251 T4 Temper Alloy at 185.degree. C.
[0051] Age hardening studies of AA5251 T4 temper alloy were
performed by placing tensile samples of the alloy in a furnace set
at 180.degree. C. The samples were taken out of the furnace after
different ageing times. FIG. 6 shows the ageing hardening behavior
of the alloy at 180.degree. C. The alloy exhibited about 70% and
20% increase in YS and UTS, respectively, after about 8 h of
ageing. The results illustrated in FIG. 6 support a conclusion that
the alloy underwent age hardening.
[0052] All patents, publications and abstracts cited above are
incorporated herein by reference in their entirety. Different
arrangements and combinations of the elements and the features
described herein are possible. Similarly, some features and
subcombinations are useful and may be employed without reference to
other features and subcombinations. Various embodiments of the
invention have been described in fulfillment of the various
objectives of the invention. It should be recognized that these
embodiments are merely illustrative of the principles of the
present invention. Numerous modifications and adaptations thereof
will be readily apparent to those skilled in the art without
departing from the spirit and scope of the present invention.
* * * * *