U.S. patent number 3,642,542 [Application Number 05/014,189] was granted by the patent office on 1972-02-15 for a process for preparing aluminum base alloys.
This patent grant is currently assigned to Olin Corporation. Invention is credited to Damian V. Gullotti, Philip R. Sperry.
United States Patent |
3,642,542 |
Sperry , et al. |
February 15, 1972 |
A PROCESS FOR PREPARING ALUMINUM BASE ALLOYS
Abstract
A process for preparing aluminum base alloys containing silicon
and magnesium comprising the steps of hot working, quenching and
aging and to improved hot-worked aluminum-based alloys having
high-strength and high-impact properties.
Inventors: |
Sperry; Philip R. (North Haven,
CT), Gullotti; Damian V. (West Haven, CT) |
Assignee: |
Olin Corporation (N/A)
|
Family
ID: |
21764025 |
Appl.
No.: |
05/014,189 |
Filed: |
February 25, 1970 |
Current U.S.
Class: |
148/690; 148/694;
148/415 |
Current CPC
Class: |
C22C
21/08 (20130101); C22F 1/05 (20130101) |
Current International
Class: |
C22F
1/05 (20060101); C22C 21/06 (20060101); C22C
21/08 (20060101); C22f 001/04 () |
Field of
Search: |
;75/146,147,141,142
;148/11.5,12.7,159,32,32.5,2 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Dean; Richard O.
Claims
What is claimed is:
1. The process for preparing a material having a combination of
high-strength and high-impact properties which comprises: providing
an aluminum base alloy consisting essentially of from 0.3 to 1.3
percent silicon, 0.3 to 1.5 percent magnesium, 0.03 to 0.4 percent
chromium, 0.03 to 0.2 percent zirconium, balance essentially
aluminum; hot working said alloy at a finishing temperature in
excess of 850.degree. F.; water quenching said alloy to a
temperature of at least 350.degree. F. at a cooling rate of from
1,000.degree. to 10,000.degree. F. per minute; and thermally
artificially aging said alloy at a temperature of from 200.degree.
to 410.degree. F. for 15 minutes to 24 hours.
2. A process according to claim 1 wherein said alloy contains
manganese in an amount from 0.03 to 0.4 percent.
3. A process according to claim 1 wherein said hot working is
extruding at a die exit temperature in excess of 900.degree. F.
4. A process according to claim 1 wherein said hot working is
rolling at a finishing temperature in excess of 900.degree. F.
5. A process according to claim 1 wherein the alloy is homogenized
prior to hot working.
6. A process according to claim 1 wherein after said water
quenching step said alloy is cold worked up to 5 percent.
7. The process for preparing a material having a combination of
high-strength and high-impact properties which comprises: providing
an aluminum base alloy consisting essentially of silicon from 0.3
to 1.3 percent, magnesium from 0.3 to 1.5 percent, chromium from
0.03 to 0.2 percent, zirconium from 0.03 to 0.2 percent, manganese
from 0.03 to 0.2 percent, balance essentially aluminum, wherein the
total chromium plus zirconium plus manganese content is from 0.2 to
0.35 percent; hot working said alloy at a finishing temperature in
excess of 900.degree. F.; air cooling said alloy to a temperature
of at least 350.degree. F. at a cooling rate of from 100.degree. to
1,000.degree. F. per minute; and thermally artificially aging said
alloy at a temperature of from 200.degree. to 410.degree. F. for 15
minutes to 24 hours.
8. A process according to claim 7 wherein said hot working is
extruding at a die exit temperature in excess of 950.degree. F.
9. A process according to claim 7 wherein said hot working is
rolling at a finishing temperature in excess of 950.degree. F.
10. A process according to claim 7 wherein the alloy is homogenized
prior to hot working.
11. A process according to claim 7 wherein after said air cooling
step the alloy is cold worked up to 5 percent.
Description
The present invention relates to a process for obtaining an
aluminum base alloy containing silicon and magnesium. The present
invention also relates to an improved aluminum base alloy
containing silicon and magnesium, wherein said alloy is a
hot-worked alloy and has high-strength and high-impact
properties.
Hot-worked aluminum base alloys containing magnesium and silicon
find wide application in a wide variety of uses, for example, they
may be readily used as extrusions, forgings or rolled products.
There are many applications where it is highly desirable to develop
a hot-worked product having a combination of high-strength and
high-impact properties. For example, there are certain applications
for aluminum alloy extrusions where high impact strength is one of
the major requirements. A highway bridge railing or median barrier
of extruded aluminum must absorb a considerable amount of energy
from a vehicle crashing into it before it fails.
Accordingly, it is a principal object of the present invention to
provide new and improved hot-worked aluminum base alloys.
It is a further object of the present invention to provide a
process for obtaining improved hot-worked aluminum base alloys.
It is a still further object of the present invention to provide
improved hot-worked aluminum base alloys having a combination of
high-strength and high-impact properties.
Further objects and advantages of the present invention will appear
hereinafter.
In accordance with the present invention it has now been found that
the foregoing objects and advantages may be readily obtained.
The improved hot-worked alloy of the present invention consists
essentially of silicon from 0.3 to 1.3 percent, magnesium from 0.3
to 1.5 percent, chromium from 0.03 to 0.40 percent and zirconium
from 0.03 to 0.20 percent. Preferably, the alloy of the present
invention also contains manganese in an amount from 0.03 to 0.4
percent.
The improved alloy of the present invention is a hot-worked product
and has a surprising combination of high-strength and high-impact
properties. The microstructure of the alloy of the present
invention is characterized by a substantially unrecrystallized
grain structure. It is surprising that the combination of
ingredients of the alloy of the present invention achieves such
excellent properties and it is further surprising that the
substantially unrecrystallized grain structure results in improved
impact properties.
The process of the present invention comprises: hot working the
alloys at a finishing temperature in excess of 850.degree. F.;
water quenching the alloys down to a temperature of 350.degree. F.
or below at a cooling rate of from 1,000.degree. to 10,000.degree.
F. per minute; and thermally artificially aging the alloys at a
temperature from 200.degree. to 410.degree. F. for from 15 minutes
to 24 hours.
As stated hereinabove, the alloys of the present invention are
characterized by a surprising combination of high-strength and
high-impact toughness. For example, generally the minimum
properties obtained in accordance with the foregoing process are as
follows: tensile strength at least 38,000 p.s.i.; yield strength at
0.2 percent offset at least 35,000 p.s.i. and elongation at least 8
percent.
The minimum impact toughness of the alloys of the present invention
is for a 1/8-inch-thick specimen, the Charpy Notch impact test
yields at least 15 foot-pounds. One would obtain at least 20
foot-pounds for a 0.394-inch-thick specimen, and typically 30 to 40
foot-pounds.
In addition to the foregoing the alloy of the present invention has
numerous other highly desirable characteristics, for example, it is
easily extruded and has good corrosion resistance.
The alloy of the present invention contains from 0.3 to 1.3 percent
silicon and preferably from 0.4 to 0.9 percent silicon. Silicon in
the preferred range has been found to give particularly
advantageous results. The alloy of the present invention contains
magnesium in an amount from 0.3 to 1.5 percent and preferably from
0.4 to 1.0 percent. The chromium content may vary from 0.03 to 0.40
percent and preferably from 0.05 to 0.35 percent. The zirconium may
vary from 0.03 to 0.20 percent and preferably from 0.05 to 0.15
percent.
As stated hereinabove, it has been found to be particularly
advantageous to include manganese in an amount from 0.03 to 0.4
percent and preferably in an amount from 0.05 to 0.3 percent.
Other especially advantageous additives are titanium up to 0.10
percent and vanadium up to 0.15 percent.
Naturally, the present invention contemplates conventional
impurities common for alloys of this type. This is important since
it indicates that the improved properties of the alloys of the
present invention are obtainable with normal commercial purity
materials. For example, normal impurities include 0.60 percent
maximum iron; 0.30 percent maximum copper; 0.50 percent maximum
zinc; up to 0.008 percent boron; 0.10 percent maximum each of other
elements the total of which is a maximum of 0.50 percent.
The manner of melting and casting the alloy is not especially
critical and conventional methods of melting and casting may be
conveniently employed. It is desirable to uniformly distribute the
silicon and magnesium throughout the matrix of the alloy before the
process of the present invention is performed, such as by a
homogenization heat treatment subsequent to the casting operation.
Before or during hot working some high temperature precipitate
should be formed due to Cr, Zr and Mn, as this is the mechanism by
which recrystallization is inhibited. However, this can be
accomplished by reheating for hot working as well as by
homogenization.
After casting the alloy is hot worked at a finishing temperature in
excess of 850.degree. F. and preferably in excess of 900.degree.
F., for example, forging, rolling or extruding. By "finishing
temperature" it is meant the final temperature at which significant
deformation is obtained in the hot-working operation. When the
alloy is extruded, the die exit temperature should be in excess of
850.degree. F. It is preferable that the actual temperature be high
enough to dissolve substantially all Mg and Si which is available
for maximum strengthening.
Following the hot working operation it is important to rapidly
quench the material to a temperature of at least 350.degree. F. at
a cooling rate of 1,000.degree. to 10,000.degree. F. per minute.
The rapid quenching is normally obtained by plunging the material
in water or by passing the material through a water spray
quench.
Optionally, the material may then be cold worked up to 5 percent,
e.g., rolling, stretching, etc.
The material should be then artificially aged at a temperature of
200.degree. to 410.degree. F. for 15 minutes to 24 hours.
The alloys of the present invention are quench sensitive. It is a
particularly surprising finding of the present invention that this
quench sensitivity can be controlled with respect to a particularly
preferred composition. This is accomplished by a critical
adjustment of the quantities of chromium, zirconium and manganese
present in the alloy so that each of these materials are present in
an amount of 0.03 to 0.2 percent, and the total chromium plus
zirconium plus manganese content is from 0.2 to 0.35 percent. It
has been found that when the composition has been controlled in
this manner, the alloy can be air cooled at a cooling rate from
100.degree. to 1,000.degree. F. per minute; otherwise, the alloy
must be water quenched at the more rapid rate specified
hereinabove.
The air cooling is normally achieved by using appropriately placed
fans.
In this particularly preferred composition, the hot working step
should be performed at a finishing temperature in excess of
900.degree. F. and preferably in excess of 950.degree. F.
As stated hereinabove, the alloy of the present invention is a
hot-worked product with a surprising combination of high-strength
and high-impact properties and with a microstructure characterized
by a substantially unrecrystallized grain structure.
The process of the present invention and improvements resulting
therefrom will be more readily apparent from a consideration of the
following illustrative examples.
EXAMPLE I
Ingots were prepared by direct chill (DC) casting in a conventional
manner summarized as follows. Melting and alloying was carried out
in a gas-fired, open hearth furnace. After alloying the melt was
degassed by gaseous chlorine fluxing for 20 minutes. The average
pouring temperature was 1,370.degree. F. The average casting speed
was 41/2 inches per minute and the metal head was maintained
between 21/2 and 3 inches. The composition of the alloys prepared
are given in Table I below.
---------------------------------------------------------------------------
TABLE I
Alloy A silicon 0.78 magnesium 0.47 iron 0.14 titanium 0.01
chromium 0.050 zirconium 0.056 manganese 0.054 copper 0.00 zinc
0.04 aluminum Balance Alloy B silicon 0.81 magnesium 0.53 iron 0.14
titanium 0.01 chromium 0.107 zirconium 0.108 manganese 0.108 copper
0.00 zinc 0.03 aluminum Balance
__________________________________________________________________________
EXAMPLE II
The alloys prepared in Example I were processed in the following
manner. The ingots were given a homogenization heat treatment of
about 1,025.degree. F. for about 10 hours followed by cooling in
air. The billets were sawed to length and reheated for extrusion in
a gas-fired, control temperature set at 1,000.degree. F. Measured
surface temperatures ranged between 975.degree. and 1,025.degree.
F. before entering the press. Three extrusion dies were used to
produce section thicknesses of one-eighth, one-fourth, and one-half
inch. Exit temperatures ranged from 980.degree. to 1,000.degree. F.
One extrusion of each thickness was fan cooled as it exited from
the press at a cooling rate in the range of the process of the
present invention; another was water quenched by passing it through
an open ended trough fed by an upward flow of water at both ends at
a cooling rate in the range of the process of the present
invention. All extrusions were aged at room temperature for about
24 hours, followed by artificial aging at 350.degree. F. for 5
hours. Tensile test specimens and Charpy impact specimens were
taken from the extrusions. The 1/8- and 1/4-inch-thick extrusions
were tested with reduced width from the standard 0.394 inch and the
impact test value was corrected for reduced area.
The results are shown in Table II below and clearly show a
combination of high strength and high impact properties.
The excellent improved impact toughness was due to the retention of
an unrecrystallized grain structure in the alloys. There were
shallow layers of recrystallized grains at the extrusion surfaces.
These shallow layers were shallower for Alloy B than for Alloy A.
##SPC1##
EXAMPLE III
Ingots were prepared in a conventional manner from two kilogram
melts cast by the tilt mold (Durville) process. The resultant
compositions are indicated in Table III below.
---------------------------------------------------------------------------
TABLE III
Alloy C silicon 0.71% magnesium 0.56% iron 0.16% copper <0.01%
titanium 0.02% zirconium 0.16% aluminum Balance
Alloy D silicon 0.83% magnesium 0.58% iron 0.20% copper <0.01%
titanium 0.01% chromium 0.31% aluminum Balance
Alloy E silicon 0.71% magnesium 0.57% iron 0.16% copper <0.01%
titanium 0.02% chromium 0.22% zirconium 0.10% aluminum Balance
Alloy F silicon 0.78% magnesium 0.58% iron 0.17% copper <0.01%
titanium 0.02% chromium 0.10% manganese 0.09% zirconium 0.11%
aluminum Balance
__________________________________________________________________________
EXAMPLE IV
The alloys prepared in Example III were processed in the following
manner. The ingots were homogenized at 1,025.degree. F. for 12
hours. The ingots were hot rolled from 1,000.degree. F., 80 percent
in one pass. The materials were quenched by plunging into water at
room temperature, thus providing a cooling rate in the range of the
process of the present invention. The materials were age hardened 5
hours at 350.degree. F. The materials were then tested for tensile
properties and Charpy impact properties using 1/8-inch specimens.
The results are shown in Table IV below. The results clearly show
that the alloy of the present invention namely Alloys E and F gave
surprising improved properties over comparative Alloys C and D. It
is noted that Alloy C does not contain the chromium addition and
Alloy D does not contain the zirconium addition. ##SPC2##
EXAMPLE V
Ingots were prepared in a manner after Example I to have the
composition indicated in Table V below.
---------------------------------------------------------------------------
TABLE V
Alloy G silicon 0.84% magnesium 0.50% iron 0.20% copper 0.003%
titanium 0.023% boron 0.004%
Alloy H silicon 0.81% magnesium 0.58% iron 0.19% copper 0.004%
titanium 0.023% chromium 0.25% zirconium 0.082% boron 0.004%
Alloy I (Commercial Alloy AA 6351) silicon 1.08% magnesium 0.65%
iron 0.19% copper 0.004% titanium 0.024% manganese 0.66% boron
0.004%
Alloy J (Commercial Alloy 6061) silicon 0.64% magnesium 1.10% iron
0.25% copper 0.25% titanium 0.017% chromium 0.18% manganese 0.053%
__________________________________________________________________________
EXAMPLE VI
The materials from Example V were processed in a manner after
Example IV except that the materials were hot rolled 50 percent in
one pass rather than 80 percent and Alloys I and J were aged for 8
hours at 350.degree. F. The results are given in Table VI below and
clearly show the surprising properties of Alloy H which represents
the alloy of the present invention. It should be noted that the
Charpy impact test utilized standard 0.394 inch specimens.
##SPC3##
This invention may be embodied in other forms or carried out in
other ways without departing from the spirit or essential
characteristics thereof. The present embodiment is therefore to be
considered as in all respects illustrative and not restrictive, the
scope of the invention being indicated by the appended claims. and
all changes which come within the meaning and range of equivalency
are intended to be embraced therein.
* * * * *