Note: Descriptions are shown in the official language in which they were submitted.
12~34~3~36
1 PC-1090
AN IMPROVED METHOD FOR PRODUCING
DISPERSION STRENGTHENED ALUMINUM ALLOYS
TECHNICAL FIELD
The present inventlon relates to di~pers10n strqngthened
aluminum-base~alloys, and more particularly to a me~hod of producing
forged "mechanically alloyed" aluminum alloy systems having improved
mechanical properties.
BACKGROUND OF THE INVENTION
In recent years there has been an intensive search for hlgh
strength aluminum which wauld ~atisfy the demands of advanced design
ln aircraft, automotive, naval and electrical industries. While high
strength is a key characteristic of the materials sought, to meet the
qualifications for certain advanced tesign applications the alloys
must meet a combination of property requirements such as density,
strength, ductillty, toughness, fatigue and corrosion resistance,
depending on the ultimate end use of the materials. The complexity
of the problem goes far beyond the difflculties of developing
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materials with suitable combinations of properties not achieved
before. Economics also plays a large role in the choice of
materials. The ultimate product forms are often complex shapes, and
the potential savings resulting from possible composition
substitution is only a part of the picture. The new aluminum alloys
would be particularly valuable if they could be shaped into desired
forms using cost effective techniques such as forging while retaining
their preshaped properties and/or if they could be fabricated
economically into the same complex shapes now used with other
materials so as to eliminate the need for retooling for fabrication
of weight saving structures. Moreover, to be commercially useful,
the fabricated parts must have reproducible properties. From a
vantage point of commercial viability, the reproducibility will be
attainable under a practical range of conditions.
The use of powder metallurgy routes to produce high
strength aluminum has been proposed and has been the subject of
considerable research. Powder metallurgy techniques generally offer
a way to produce homogenous materials, to control chemical
composition and to incorporate dispersion strengthening particles
into the alloy. Also, difficult-to-handle alloying elements can at
times be more easily introduced by powder metallurgy than ingot melt
techniques. The preparation of dispersion strengthened powders
having improved properties by a powder metallurgy technique known as
mechanical alloying has been disclosed, e.g., in U.S. Patent No.
3,591,362. Mechanically alloyed materials are characterized by fine
grain structure which is stabilized by uniformly distributed
dispersoid particles such as oxides and/or carbides. U.S. Patent
Nos. 3,740,210 and 3,816,080 pertain particularly to the preparation
of mechanically alloyed dispersion strengthened aluminum. Other
aspects of mechanically alloyed aluminum-base alloys have been
disclosed in U.S. Patent Nos. 4,292,079, 4,297,136 and 4,409,038.
For most uses a powder must be fabricated into a final
product, e.g., by degassing, compaction, consolidation and shaping in
one or more steps. To obtain complex parts the fabrication may take
the form, e.g., of extruding, forging and machining. Usually, the
less machining required to make a part the greater the economy in
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3 PC-1090
material use, labor and time. It will be appreciated that it is an
advantage to be able to make a complex shape by forging rather than
by a route which requires the shaping by manual labor on an
individual basis.
It is academic that composition of an alloy often dictates
the fabrication techniques that can be used to manufacture a
particular product. In general, the target properties which must be
attained in the type aluminum alloys of th~s invention before other
properties will be considered are strength, density and ductility.
One of the marked advantages of mechanically alloyed powders is that
they can be made into materials having the same strength snd
ductility as materials made of similar compositions made by other
routes, but with a lower level of dispersoid. This enables the
production of alloys which can be fabricated more easily without
resorting to age hardening additives. While the mechanical alloying
route produces materials that are easier to fabricate than other
aluminum alloys of comparable composition, the demands for strength
and low density and the additlves used to obtain higher strength
and/or lower densi~y usually decrease workability of the alloy
system. (Workabillty takes into account at least ductility at the
working temperature and the load necessary to form the material.)
The extent of the effect is generally related to the level of
additive in the alloy. The additives not only a~fect the method by
which the material can be fabricated, but also the fabrlcation
techniques affect the properties of the materials.
It has now been found that low density dispersian
strengthened, mechanically alloyed aluminum-lithium-magnesium alloys
can be fabricated into forged parts characterized by improved
strength along with adequate ductility by extruding and forging the
alloys under controlled narrow conditions. It has further been found
that controlling the extrusion of the materials under specific
conditions makes possible a wider range of conditions under which the
materials can be forged. This further enhances the commercial value
of the alloys and improves the reproducibility of the forged parts.
It has also been found that the temperatures at which the alloya
should be forged are in a lower range than would be expected from
normal handbook practice for forging aluminum alloys, e.g., as
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descrlbed in the Metals Handbook, 8th Ed., Vol. 5 (1970) on pp.
127-132.
BRIEF DESCRIPTION OF DRA~INGS
Figure 1 i8 a plan drawing of a "Cruciform"-type forging.
Figure 2 is a plan drawing of a "Hook"~type forging.
SUMMARY OF THE INVENTION
The present invention is directed to a method for obtaining
a forged product composed of a disperslon strengthened, low density
aluminum-base alloy comprised of, aluminum, lithium and magnesium,
said alloy being derived from a powder of said alloy prepared by a
mechanical alloying process, and said method for obtaining the forged
product being comprised of a sequence of steps comprising: degassing
and compacting said powder under vacuum to obtain a compaction billet
having a density sufficiantly high to obtain an extruded billet of
subgtant~ally full density; extruding the resultant compaction billet
at a temperature in the range of above the lncipient extrusion
temperature up to about 400C (750F) said extru~ion being carried
out with lubrication through a conical die to provide an extruded
billet of substantially full density; and forging the resultant
extruded billet ~aid resultant billet being sub~ected to at least a
first forging treatment at a temperature in the range of about 230C
(450F) up to about 400C (750F), with the proviso that for
maximizing strength the forging is carried out at the lower end of
the forging temperature range when the extrusion i6 carried out a~
the higher end of the extruslon temperature range.
Degassing i8 carried out at a temperature higher than any
temperature to be subsequently experienced by the aIloy, and
compaction is carrled out at least to the extent that the poro~ity is
isolated, and preferably to at least about 95% of full density and
higher.
By incipient extrusion temperature is meant the lowest
temperature et which a given alloy can~be extruded on a given
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PC-1090
extrusion press ae a given extrusion ratio. The extrusion ratio is
at least 3:1 and may range, for example, to about 20:1 and higher.
By a conical die is meant a die in whlch the transition
from the extrusion liner to the extruslon die is gradual.
Advantageously the angle of the head of the die with the liner is
less than about 60, and preferably it is about 45.
Alloys of the present invention consist essentially of, by
weight, about 0.5 to about 4% Li, about O.S to about 7% Mg, 0 up to
about 4% Si, a small but effective amount for increased strength,
e.g. about 0.05%, up to about 5% carbon, a small but effective amount
for increased strength and stability up to about 1% oxygen, and the
balance essentially aluminum, and having a dispersoid content of a
small but effective amount for increased strength up to about 10
volume % dispersoid.
In a preferred embodiment of the present process the alloys
contain about 1.5% up to about 2.5% lithium and about 2% up to about
4% magnesium, 0.5% to about 1.2% carbon and up to less than 1%
oxygen, and the ex~rusion is carried out at a temperature in the
range of about 230C (450F) to about 400C (750F). Advantageously
20 the extrusion is carried out below about 370C t700F), preferably in
the range of about 260C (500F) to about 360C (675F), and most
preferably at about 260C (500F). For thls alloy system, the
forging operation (or in a multi~step forging operation the initial
forging step) is carried out at a temperature of about 230C (450F)
25 to about 400C (750F) when extrusion is carried out at about 260C,
and the forging operation (or initial forging step) is carried out at
a narrow range at the lower end of the extrusion temperature range,
e.g. at about 260C (500F) when extrusion is prevlously carried out
at 370C (700F). In accordance with the present invention low
density alloys of such system can be provided which are characterized
by an 0.2% offset yield strength (YS) of at least 410 MPa (60 ksi),
an elongation of at least 3%. In one aspect of the invention the
Al-Li alloys have a density of less than 2.57 g/cm .
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6 PC-1090
DETAILED ASPECTS OF THE INVENTION
_
(A) Composition
The essential components of the matrix of the alloy systems
of the present invention are aluminum, magneslum and lithium. In one
embodiment the alloys contain silicon. The alloys are characterized
in that they are dispersion strengthened and they are formed from
mechanically alloyed powders. In one preferred embodiment they are
prepared as forged articles. The dispersion strengthening agents
comprise carbides and oxides and/or silicides.
Carbon and oxygen along with small amounts of magnesium and
lithium are present as a small weight percentage of the alloy system
in combination as insoluble dispersoids such as oxides andlor
carbides. Other elements may be incorporated in the allo~ so long as
they do not interfere with the desired properties of the alloy for a
particular end use. Also, a minor amount of impurities may be picked
up from the charge materials or in preparing the alloy. Additional
insoluble, stable dispersoids or dispersoid forming agents may be
incorporated in the system, e.g., for strengthening of the alloy at
elevated temperatures, 80 long as they do not otherwise adversely
affect the alloy.
Unless otherwise speclfied, concentration of components is
given in weight %.
The lithium level in the alloys may range, for example,
from about 0.5 to about 4 %, advantageously in an amount of about l
up to about 3%, and preferably from about 1.5 or 1.6 up to about
2.5%. The lithium is introduced into the alloy system as a powder
(elemental or preferably prealloyed with aluminum) thereby avoiding
problems which accompany the melting of lithium in ingot metallurgy
methods. Magnesium may be present, for example, in an amount of
about 0.5% to about 7%. Advantageously, ths magnesium levsl may
range from above 1 up to about 5%, preferably it is about 2 up to
about 4 or 4.5%. Exemplary alloys contain abovs 1.5 up to about 2.5%
lithium and about 2 to about 4.5~ magnssium.
The silicon level may range, for example, from O up to
about 4%. In the silicon-containing alloys the sllicon level may
range from a 3mall but effective amount for strength up to about 4%.
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Advantageously the silicon-containing alloys contain about 0.2 up -to
about 2% and preferably about 0.5% to abou~ 1.5%, and typically
about 0.5 to about 1%.
Carbon is present in the system at a level ranging from a
small but effective amount for increased strength up to about 5%.
Typically the level of carbon ranges from about 0.05 up to about 2%,
advantageously from about 0.2% up to about 1% or 1.5%, preferably
about 0.5 up to about 1.2%. The carbon is generally provided by a
process control agent during the formation of the mechanically
alloyed powders. Preferred process control agents are methanol,
stearic acid, and graphite. In general the carbon present will form
carbides, e.g., with one or more of the components of the system.
Oxygen is usually present in the system, and it is usually
desirable at a very low level. In general, oxygen is present in a
small but efEective amount for increased strength and stability,
e.g., about 0.05% up to 1%, and preferably, it does not exceed about
0.4 or 0.5%. As disclosed in a co-pending application Canadian
Serial No. 460,308 now Canadian Patent 1,230,507 the low oxygen
content is believed to be critical. When the oxygen content is
above 1% the alloy is found to have poor ductility. In a}loys
containing above 1.5% Li, the oxygen content preferably daes not
exceed about 0.5%.
It will be appreciated that the alloys may contain other
elements which when present may enhance certain properties and in
the amounts in whicX they are present do not adversely affect the
alloy of a particular end use.
The dispersoid comprises oxides and carbides present in a
range of a small but effective amount for increased strength up to
about 10 volume % (vol. %) or even higher. Preferably the dispersoid
level is as low as possible consistent with desired strength.
Typically the dispersoid level is about 1.5 to 7 vol. %. Preferably
it is about 2 to 6 vol. %. The dispersoids may be present~ for
example, as an oxide of aluminum, lithium, or magnesium or
combinations thereof. The dispersoid can be formed during the
mechanical alloying step and/or later consolidation and
thermomechanical processing. Possibly they may be added as such to
-~ the powder charge. Other dispersoids may be added or formed in-situ
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so long as they are stable in the aluminum alloy matrix at the
ultimate temperature of service. Examples of dispersoids that may be
present are Al203, ~lOOH, Li20, Li2Al204, LiAlO2, LiAl508 3 Li5Al04
and MgO. The dispersoids may be carbides, e.g., Al4C3.
In a preferred alloy system the li-thium content is about
1.5 up to about 2.5%, the magnesium content is about 2 up to about
4~, the carbon content is about 0.5 to about 2%, and the oxygen
content is less than about 0.5%, and the dispersoid level is about 2
or 3 to 6 volume ~. For example, the alloys may be comprised of:
Al-4Mg-1.5Li-1.2C, Al-5Mg-lLi-l.lC, Al-4Mg-1.75Li-l.lC,
Al-2Mg-2Li-l.lC, Al-2Mg-2.5Li-l.lC, Al-4Mg-2.5Li-0.7C and
Al-2Mg-2.5Li-0.7C, Al-4Mg-1.5Li-.5Si-l.lC, Al-4Mg-1.5Li-lSi-l.lC,
Al-2Mg-1.5Li-.5Si-l.lC, Al-2Mg-1.5Li-lSi-l.lC, Al-2Mg-2Li-.5Si-l.lC,
Al-2Mg-2Li-lSi-l.lC, Al-2Mg-1.75Li-lSi-0.7C, Al-4Mg-1.5Li-lSi-0.7C,
Al-4Mg-1.5Li-.5Si-2C.
(B) Alloy Preparation Prior to Fabrication
(13 Mechanical Alloying to Form Powders
Powder compositions treated in accordance with the present
invention are all prepared by a mechanical alloying technique. This
technique is a high energy milling process, which is described in
the aforementioned patents. Briefly, aluminum powder is prepared by
subjecting a powder charge to dry, high energy milling in the
presence of a grinding media, e.g. balls, and a process control
agent, under conditions sufficient to comminute the powder
particles to the charge, and through a combination of comminution and
welding actions caused repeatedly by the milling, to create new,
dense composite particles containing fragments of the initial powder
materials intimately associated and uniformly interdispersed.
Milling is done in a protective atmosphere, e.g. under an argon
or nitrogen blanket, thereby Eacilitating oxygen control since
virtually the only sources of oxygen are the starting powders and
the process control agent. The process control agent is a
weld-controlling amount of a carbon-contributing agent and may be,
for example, graphite or a volatili~able oxygen-containing
hydrocarbon such as organic acids, alcohols, heptanes, aldehydes and
ethers. The formation of dispersion strengthened mechanically
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alloyed aluminum is given in detail in U.S. Patents No. 3,740~210 and
3,816,08Q, mentioned above. Suitably the powder is prepared in an
attritor using a ball-to-powder weight ratio of 15:1 to 60:1. As
indicated above, preferably process control agents are methanol,
stearic acid, and graphite. Carbon from these organic compounds
and/or graphite is incorporated in the powder and contributes to the
dispersoid content.
(2) Degassing and Compaction
Before the dispersion strengthened mechanically alloyed
powder is consolidated it must be degassed and compacted. Degassing
and compacting are effected under vacuum and generally carried out at
a temperature in the range of about 480C (895F) up to ~ust below
incipient liquefication of the alloy. As indicated above, the
degassing temperature should be higher than any subsequently
experienced by the alloy. Degassing is preferably carried out, for
example, at a temperature in the range of from about 480C (900F) up
to 545C (1015F) and more preferably above 500C (930F). Pressing
is carried out at a temperature in the range of about 545C (1015~F)
to about 480C (895F).
In a preferred embodiment the degassing and compaction are
carried out by vacuum hot pressing (VHP). However, other techniques
may be used. For example, the degassed powder may be upset under
vacuum in an extrusion press. To enable the powder to be extruded to
substantially full denslty, eompactlon should be such that the
porosity is isolated, thereby avoiding internal contamination of the
billet by the extrusion lubricant. This is achieved by carrying out
compaction to at least 85% of full density, advantageously above 95%
density, and preferably the material is compacted to over 99% of full
density. Preferably the powders are compacted to 99% of full density
and higher, that is, to substantially full density.
The resultant compaction products formed in the degassing
and compaction step or steps are then consolidated.
(C) Fabrication
(1) Consolidation
Consolidation in the present process is carried out by
extrusion. The extrusion of the material not only is necessary to
insure full density in the alloy, but also to break up surface oxide
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PC-1090
on the particles. The extrusion temperature is critical and wl~hin a
narrow range. The lubrication practice and the conical die-typs
equipment used for extrusion are also important.
The extrusion temperature is chosen so that the maximum
temperature achieved in the extruder is no greater than 10C (50F)
below the solidus temperature. Typically it will be in the range of
about 230C (450F) and about 400C (750F). Advantageously, it
should be carried out below about 370C (700F) and should not exceed
about 345C (650F). Preferably it should be lower than about 330C
(625F). The temperature should be high enough so ehat the alloy can
be pushed through the die at a reasonable pressure. Typically this
will be above about 230C (450F). It has been found that a
eemperature of about 2~0C (500F) for extruslon is highly
advantageous. By carrying out the extrusion at about 260C ~500F),
l~ there is the added advantage of greater flexibility in conditions
which may be used during the forging operation. This flexibility
decreases at the higher end of the extrusion temperature range.
The above given extrusion tamperature ranges which must be
used for the Al-Li-Mg are those whlch will maximize the strength of
the alloy since strength is currently the initial screening test for
the forged parts made from the aluminum-base alloys. It will be
appreciated that when the strength requirements are not as rigorous
the teachings of this invention can be used to trade-off strength
against some other property.
The extrusion ln the present process is carried out in a
conical-faced die as defined above, as opposed to a shear-faced die.
Lubrication is applied to the die or the compaction billet or both of
them. The lubricant~, which aid in the extru~ion operation, must be
compatible with the alloy compaction billet and the extrusion press,
e.g. the liner and die. The lubricant applied to the billet further
protects the billet from the lubricant applied to the extrusion
press.
Properly formulated lubricants for specific metals are well
known in the art. Such lubricants take into account, for example,
requirements to prevent corrosion and to make duration of contact of
the billet with the extrusion press less critical. Examples of
lubrlcants for the billets are kerosene, mineral oil, fat emulsion
1 1 PC- 1 090
and mineral oil containing sulfuri~ed fatty oils. Fillers such as
chalk, sulfur and graphite may be added. An example of a lubricant
for an extrusion press is colloidal graphite carried in oil or water,
molydisulfide, boron sulfide, and boron nitride.
The extruded billets are then in condition to be forged.
If necessary the billets may be machined to remove surface
imperfections.
(2) Forging
In general forged aluminum alloys of the present invention
will benefit from forging temperatures being as low as possible
consistent with the alloy composition and equipment. Forging may be
carried out as a slngle or multi-step operation. In multi-step
forging the temperature control applies to the initial forging or
blocking-type step. As in the extrusion step, it is believed that
for high strength the aluminum alloys of this invention should be
forged at a temperature below one where a decrease in strength will
occur. In the Al-Mg-Li alloyæ system forging should be carried out
below about 400C (750F), and preferably less than 370C) (700F),
e.g. in the range of 230C (450F) to about 345C (650F), typically
20 about 260C (500F). Despite the fact that forgeability may increase
with temperature, the higher forging temperatures have now been found
to have an adverse effect on strength. In a multi-step forging
operation it has been found that it is the initial step that is
critical. In subsequent forging steps of a multi-step operatlon
after the initial forging ætep the temperature range for forging may
be above that recommended for this process.
As noted above, while it is known in the art that
conditions of for~ing aluminum alloys wlll vary with composition, it
was surpriæing that the forging conditionæ - particularly the
temperature - at which the alloys could be forged iæ related to the
temperature at which the alloy is consolidated, and in particular
extruded.
(3) Age Hardening
A heat treatment may be carried out, if deæired, on alloy
systems susceptible to age hardening. In alloys having age
hardenable components additional strength may be gained, but this may
be with the loss of other properties, e.g. corrosion resistance. It
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is noted that alloys of this invention containing silicon can be age
hardened without significant loss of corrosion resistance. It is a
particular advantage of the present invention that low density
aluminum alloys can be made with high strength, e.g. over 410 MPa
(60 ksi) in the forged condition without having to resort to
precipitation hardening treatments which might result in alloys
which have less attractive properties other than strength.
It is noted that in conversion from F to C, the
temperatures were rounded off, as were the conversion from ksi to
MPa and inches to centimeters. Also alloy compositions are nominal.
With respect to conditions~ for commercial production it is not
practical or realistic to impose or require conditions to the extent
possible in a research laboratory facility. Temperatures may stray,
for example, 50F of the target. Thus, having a wider window for
processing conditions adds to the practical value of the process.
The invention is further described in, but not limited by,
the examples given below. In all the examples the alloys are
prepared from dispersion strengthened alloys comprising aluminum,
magnesium, lithium, carbon and oxygen, prepared by a mechanical
alloying technique. In EXAMPLE 8, silicon is present in the alloy.
EXAMPLE 1
This example illustrates the processing conditions used to
prepare forged Al-Mg-Li dispersion strengthened mechanlcally alloyed
bodies composed of aluminum, magnesium, lithium, carbon and oxygen
25 containing about 1.1~1.2% carbon and less than 1~ oxygen.
Mechanically alloyed powders are prepared having the
nominal magnesium and lithium contents given in TABLE I. The powders
are vacuum hot pressed (~IP) to form 27.9 cm (11 in) diameter
degassed compaction billets.
The compaction billets are then extruded at temperatures of
about 260 and 370~C (500 and 700F) at ram speeds of 45.7 and 25.4 cm
(18 and 10 in), depending on the extrusion temperature. All billets
are sandblasted and coated with Fel-Pro C-300~ ta molybdenum
disulfide air drying product of Fel-Pro Inc.) prior to heat-up for
extrusion, and the extrusion liner coated with resin and swathed
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13 PC-1090
with the lubricant LUBE-A-TUBEIM hot extrusion 230A (a graphite in
heavy oil product of G. Whitfield Richards Co.). All the extrusion
pushed successfully except for some surface tearing at 700aF. Alloy
compositions and extrusion conditions, are given in TABLE I.
TABLE I
Alloy Temp. Ram Speed
Type Mg Li C (F) cm (in.)/min
A 4 1.5 260 (500) 45.7 (18)
B 4 1.75 260 (500) 45.7 (18)
C 2 2 260 (500) 45.7 (18)
D 4 1.5 370 (700) 25.4 (10)
E 4 1.75 370 (700) 25.4 (10)
F 2 2 370 (700) 25.5 (10)
Eight 8.75 cm (3.5 in.) lengths of material from each
extrusion are cut for forging trials. The trial consisted of using
flat dies to upset the preforms parallel to the billet axis.
Forgings are performed at nominal temperatures 260C (500F) and
400C (750F) at ram speeds of 50 cm (20 in.)/min and 5 cm (2
in.)/min to final heights of 5 cm (1 in.) and 2.5 cm (0.5 in.) and
strains of -0.67 and -0.83, respectively. The top and bottom forging
platens are inductlon heated to the same temperatures as the soak
temperatures and were lubricated with White and Bagley 296gM graphite
base lubricant just before upsetting. Extrusion and forging data are
summarized in TABLE II. In general the 260C (500F) extrusions
forged better than the 370C (700F) extrusions, and this is believed
to be due to the better extruded surface quality of the 500F
extrusions. Surface grinding prior to forging should improve
forgeability. The 2Mg-2Li alloy extruded at 370C (700F) had the
poorest forgeability. For all of the other alloys a forging
condition can be found that does not cause edge cracking. In
general, the alloys extruded at 260C (500F) have a higher hardness
than material extruded at 370C (700F). The 4Mg-1.5Li composition
extruded at 260C (500F) did not soften under any of the forging
conditions tried, The 2Mg-2Li alloys soften after forging at about
400C (750F).
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TA8LE II
Forging
Extrusion Final
Soak Ram Sp Soak T Billet Die T Ram Sp Height Forging Har~ness
5Alloy ID T F in/min F T F F in/min in. Appear.* 8
4Mg-1,5Li500 10 As Ext 84
500 -- 500 20 0.95 3 87
2 500 -- 500 20 0.53 2 87
3 500 425 500 2 0.980 2 86
4 500 430 501 2 0.540 2 86
750 680 737 20 1.0 2 85
6 750 -- 734 20 0.520 3 84
7 750 690 735 2 0.960 3 83
8 750 690 747 2 0.525 3 82
4Mg-1.75Li 500 18 As Ext 86
500 440 497 20 0.8 1 88
2 500 440 496 20 0.52 1 87
3 500 -- 497 2 1.0 2 85
4 500 -- 495 2 0.53 3 86
750 680 752 20 0.965 3 85
6 750 680 760 20 0.540 2 86
7 750 680 760 2 0.940 2 84
8 750 670 760 2 0.510 3 84
2Mg-2Li 500 18 As Ext 85
1 500 440 494 20 0.965 3 84
2 500 -- 493 20 0.580 2 85
3 500 440 496 2 1.0 3 82
4 500 -- 49S 2 0.560 2 85
750 680 759 20 0.935 3 80
6 750 -- 759 20 0.510 3 81
7 750 680 752 2 0.960 3 80
8 750 690 755 2 0.50 1 80
4Mg-1.5Li700 10 As Ext 83
500 480 495 20 0.980 2 85
2 500 460 515 20 0.530 2 86
3 500 450 575 2 1.0 2 8g
4 500 450 512 2 0.565 2 87
750 -- 754 20 0.980 3 83
6 750 680 754 20 0.530 2 82
7 750 -- 754 2 1.03 2 82
8 750 670 754 2 0.5 2 82
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TABLE II (CONTINUED)
Forgin~
Extrusion Flnal
Soak Ra~ Sp Soak T Billet Die T Ram Sp Height Forging Har~ness
Alloy ID T F in/min F T F F in/min in. Appear.* B
4Mg-1.75Li 700 10As Ext 80
1 500 -- 51420 1.01 3 83
2 500 460 51320 0.565 1 84
3 500 450 514 2 1.025 3 84
4 500 440 512 2 0.515 1 85
750 700 74920 0.99 3 82
6 750 -- 74220 0.535 2 83
7 750 700 745 2 0.98 3 82
8 750 700 742 2 0.55 1 81
152Mg-2Li 700 10As Ext 80 -
1 500 -- 50620 0.975 2 80
2 500 440 50320 0,575 1 82
3 500 440 506 2 1.025 2 79
4 500 -- 504 2 0.6 2 80
750 690 74220 1.01 2 77
6 750 680 74620 0.42 2 79
7 750 690 749 2 0.93 2 77
8 750 -- 745 2 0,45 1 77
In the ~ABLE: 500F = 260C; 700F = 370C; 1 inch ~ 2.5 cm
*1 = poor 2 - good 3 ~ excellent
EXAMPLE 2
This example concerns the aging respon6e of extruded and
forged alloys described in EXAMPLE l.
To 6treamline the aging study two forgings from each alloy
of EXAMP~E 1 are selected. One of each type is forged at 260C
(500F) at 50.8 cm (20 in)/min to 2.54 cm (l in.) final height, and
the other is forged at 400C (750F) at 5.08 cm (2 in)lmin to 1.27 cm
(0.5 in) final height. These are the two extreme forging conditions.
The compositions 4Mg-l.75Li and 2Mg-2Li show hardness increases at
about 125C (255F) after solution treating at about 480C (900F),
and from the hardness data it can be predicted that both these alloys
can be aged to achieve the desired target YS in the forged condition
of about 410 to 450 MPa (60-65 ksi). The "as-extruded" alloys appear
to age slower than the forged stock. It i~ assumed that the
additlonnl working of forging speeds the aging kinetics.
, ~ ,
.
,
`
~2a4~6
16 PC-1090
EX~MPLE 3
This example illustrates forgeability of alloys in a
cruciform forging test. Cruciform forging trials are performed on
extruded billets of the type shown in Example 1, all alloys being
extruded with lubrication through a 3.875 in. dia. conical die in an
8:1 extrusion ratio.
The "cruciform"-type forging is shown in plan view in
Figure 1. The center portion of the forging is a cruciform formed
from two perpendicular raised ribs. The rib portion of the forging
is thicker than the base portion. The forging in the tests is made
in a two-step operation: (1) blocking extrusion preform on flat
dies; (2) forging blocker into raised rib "cruciform", the blocking
extrusion corresponding to an initial forging step in a forging
operation. The 5 in. x 3.675 in. dia. extruded preforms are blocked
in the extrusion direction to 2.5 in. high. The blockers are
"squared-up" by repeatedly pressing perpendicular to the extrusion
direction forming an octahedron approximately 2.5 in. high with a
5.25 in. diagonal. The flat dies are held at about 315C (600F +
25DF) and no lubricant is used. Extruded surface roughness produced
cracking during the blocker operations. Preforms with gross surface
surface defects had been ground prior to blocking and had less
tendency to crack than did as-extruded surfaces. Blocker cracking
also occurred due to high forging speeds, necessitating blocking
speed to be lowered from 50.8-63.5 cm (20-25 in)/min to 12.7 cm (5
in)/min.
All cruciforms are final forged at 370C (700F), at a
constant die temperature of 315C (600F), press rate of 12.7 cm (5
in)/min, utilizing full press tonnage of 1500 tons. The die was
lubricated with a l to 3 mixture of Withrow-A-Paste~M (a lubricant of
a graphite type produce of Arthur C. Withrow Co.) and mineral oil.
Cruciforms of acceptable appearance were forged of each material.
Most problems :Ln blocker cracking appear to be due to surface
imperfections. Some cracking in the cruciform was related to slight
cracking in the blocker. Recorded in TAB~E III are extrusion
temperature, blocker temperature, forging temperature and "as-forged'
hardness for varlous aluminum alloys of this invention.
~:8~ 3~
17 PC-1090
TABLE III
Ext. Block Forged
Temp. Temp. Temp. Aæ-Forged
Alloy Type F F F Hardness, RB
4Mg-1.5Li 500 500 700 79
500 700 700 79
4Mg-1.5Li 700 500 700 80
700 700 700 77
4Mg-1.75Li 500 500 700 80
500 700 700 81
2Mg-2Li 500 500 700 80
5~0 700 700 78
4Mg-1,75Li 700 500 700 79
7~0 700 700 80
2Mg-2Li 700 700 700 71
All of the 4Mg-1.5Li alloys have "as-forged" ~ardnesses
greater than 78 RB except for the alloy extruded, blocked and forged
at 370C (700F) and it was ascertained that in these forgings a
hardness of 78 RB or better correlates to a YS of 410 MPa (60 ksi) or
better. Accordingly, the inference can be made that alloys extruded
at 370C (700F) and blocked at 260C (500F) would meet tbe target
forged YS requirement of 410 MPa (60 ksi).
The "as-forged" hardness of compositlons 4Mg-1.75Li and
2Mg-2Li can be improved by aging treatments. The 2Mg-2Li ~ges slower
than the 4Mg-1.75Li alloy.
EXAMPLE 4
This example lllustrates the tensile proper~ies of various
Al-Mg-Li alloys of this invention in the extruded, blocked, forged
and/or aged condltions of cruciform-type forgings tested at two
different sites.
Tensile propertles oE various Al-Mg-Li alloys, essentially
of the type descrlbed in EXAMPLE 1, in the extruded, blocked, forged
and/or aged conditions are given in TABLE IV. The blocked and forged
cond1tions, viz. "Block Temp" and "Forge Temp", respectively, refer
.. ,
'
~L28~8~36
18 PC-1090
to the temperatures of the two steps given in EXAMPLE 3 for forming
the cruciform-type forging. All tests are carried out in the rib
portion of the cruciform. The key to the temper of the tensile
sample (TPR) is: 1 = as-extruded, 2 = as-blocked, 3 = "as-forged",
4 - forged and solution treated at 480C (900F) for 2 hours and
water quenched (WQ) then aged at 125C (255F) for 2 hours, and 5 =
solution treated as in TPR 4 but aged at 150C (300F) for 24 hours;
Mod s Young's Modulus. Tensile properties obtained on different test
equipment for a duplicate set of forged cruciform forgings on either
the base (B) or rib (R) portion in various tempers and orientations
are given in TABLE V.
Reference to TABLE IV sho~s:
The non-heat treatable Al-4Mg-1.5Li alloy extruded at 260C
(500F), blocked at 260C (500F) and forged at 370C (700F), has a
15 444 MPa (64.4 ksl) YS, 518 MPa (75.2 ksi) UTS (ultimate tensile
strength) and 11% El (elongation to failure). The "as-extruded", YS
477 MPa (69.3 ksi), is higher than the forged material, w~ile the
"as-extruded" ductility, 7% El, is lower. The strengths of the 260C
(500F) blocker are less than the forged strengths. The 4Mg-1.5Li
20 alloy extruded at 370C (700F), blocked at 260C (500F) and forged
at 370C (700F~, has a YS = 424 MPa (61.5 ksi~.
For all conditions tested the 4Mg-1.75Li alloy extruded at
260C (500F) has a YS of greater than 410 MPa (60 ksi)~ Solution
treatlng and aging raises the YS to approxlmately 572 MPa (83 ksi)
with ~ust a slight decrease ln ductility from the "as-forged"
conditlon. The 370C (700F) extrusion blocked at 260C (500F) can
also be aged (TPR = 4) to 551 MPa(80 ksl) yleld strength. For the
same aglng treatment the 370C (700F) extrusion blocked at 370C
(700F) has a 537 MPa (78 ksi) YS.
The 2Mg-2Li alloy extruded at either 260C ~500F) or 370C
(700F) produce forgings that have lower as-forged strength than the
alloys containing 4~ magneslum. Aglng at (TPR ~ 5) increases the YS
to 530 MPa (77 ksl) and 502 MPa (73 ksl), respectively, for the 260C
(500F) and 370C (700F) extruslons blocked at 370C (700F).
The tests demonstrate the importance of extrusion
temperature in processing mechanically alloyed Al-Mg-Li alloys to
maximize strength in the final forging. Blocker temperature has a
.,,
~2~ 6
19 PC-1090
secondary effect on forged strength with the lower blocker
temperature leading to high strengths. Final forging temperature
appears to be of less importance as long as the material has been
extruded and blocked at relatively low temperatures.
A comparison of data for "as-forged" longitudinal samples
in TABLES IV and V shows the consistency of results in different
testing equipment.
TABLE IV
Ext. Blocker Forge Tensile Properties
10 Temp. Temp. Temp. YS UTS El. RA Mgd
F F F TPR Orient. ksi ksi % ~ 10 psi
Al-4Mg-1.5Li
500 -- -- 1 L 69.3 74.8 7 12.5 10.9
500 -- -- 1 T 67.9 78.7 0 1 14.0
500 500 -- 2 L 61.7 73.7 3.5 8.5 11.2
500 500 700 3 L 64.4 75.2 11 22 10.9
500 700 -- 2 L 59.9 72.2 7.5 12 10.8
500 700 700 3 L 58.8 71.8 -- 19 11.1
Al-4Mg-1.5Li
700 -- -- 1 L 65.9 73.1 6 11 11.5
700 -- -- 1 T 61.9 73.2 2 4.5 11.2
700 500 -- 2 L 57.7 75.3 3.5 9.5 10.2
700 500 700 3 L 61.5 74.6 -- 9.5 10.0
700 700 -- 2 L 55.1 71.4 7.5 12.5 10.9
700 700 700 3 L 55.6 70.7 -- 17.0 10.5
Al-4Mg-1.75Li
500 -- -- 1 L 75.9 96 0.5 1.0 11.4
500 -- -- 1 T 65.9 79.3 0 0.5 11.2
500 500 -- 2 L 62.5 80.2 0 1.5 10.7
500 500 700 3 L 63.5 74.4 -- 9.0 11.1
500 500 700 4 L 82.7 87.4 -- 8.25 10.5
500 700 -- 2 L 58.2 73.8 2.0 7.0 10.0
500 700 700 3 L 61.7 75.5 4.5 4.0 11.6
500 700 700 4 L 82.6 88.1 3.5 11 10.5
~ 2~ 39~
PC-lO9O
TABLE IV (CONTINVED)
Ext. Blocker Forge Tensile Properties
Temp. Temp. Temp. YS UTS El. RA Mgd
F F F TPR Orient. ksi ksi % % 10 psi
Al-2Mg-2Li
500 -- -- 1 L 73.5 91.1 0.5 2.5 11.6
500 -- -- 1 T 60.1 71.1 0 1.0 11.7
500 500 -- 2 L 53.8 67.5 0 1.5 10.4
500 500 700 3 L 56.6 69.5 4.5 11.0 9.8
10 500 500 700 5 L -- -- -- -- --
500 700 -- 1 L 53.8 67.5 0 1.5 10.4
500 700 700 3 L 56.6 69.5 4.5 11.0 9.8
500 700 700 5 L 77.3 84.5 2 4.3 10.6
Al-4Mg-1.75Li
15 700 -- -- 1 L 63.8 70.2 2.0 4.0 11.1
700 ~ 1 T 61.9 72.9 1.0 0.5 11.3
700 500 -- 2 L 55.9 72.4 2.0 9.5 10.4
700 500 700 3 L 58.3 72.3 6.5 11.0 10.7
700 500 700 4 L 80 85.7 3.510 10.4
20 700 700 700 3 L 53.1 73 6.5 lO.5 10.8
700 700 700 3 L 56.1 71.3 6.5 10.0 11.2
700 700 700 4 L 78 85 3.5 9 10.3
700 700 700 4 L 75.5 84.3 7.0 10.1 11.2
Al-2Mg-2Li
25 700 -- -- 1 L 65.7 76.4 1 4.5 11.6
700 -- -- 1 T 56.6 68.5 1 0.5 11.3
700 500 -- 2 L 48.3 64.2 2 7.0 9.2
700 500 700 3 - -- -- ~- __ __
700 500 700 3 - -- -- -- __ __
30 700 700 -- 2 L 48.7 64.3 2 4.5 9.2
700 700 700 3 L 48.2 63.6 9 15 11.3
700 700 700 5 L 73 80.1 3.54.0 11.1
TABLE V
Alloy
35 (Extrusion ~ Blocker Test YS UTS
Conditions) Orient. Temper* ksi ksi % El
Al-4Mg-1.5Li T R F 64.7 75.2 6.7
(500F Extrusion) T R ST + A 65.7 75.2 8.1
(500F Blocker) T BST + A 66.8 76.0 9.5
T B ST 65.0 76.8 8.1
L RST ~ A 69.2 77.6 12.3
L RST + A 68.8 78 10.9
L R F 69.2 78.1 8.1
L R F 70.4 77.7 8.1
T BST + A 64.8 74.0 10.2
i.~`,'~
.
.,
~L28~96
2] PC-1090
TABIE V (CONTINUED)
Alloy
(Extrusion & Blocker TestYS UTS
Conditions) Orient. Temper* ksi ksi ~ El
Al-4Mg-1.5Li T R F 60.8 72.8 9.5
(500F Fxtrusion) T R ST + A 64.8 74.0 9.5
(700F Blocker)T B ST ~ A 61.2 72.8 12.3
T B ST 62.8 73.2 12.3
L R ST + A 62.4 72.8 15.1
L R ST + A 60.4 72.8 12.3
L R F 60.0 72.4 lO.9
L R F 60.0 71.6 10.9
T B ST + A 60.8 72.4 10.2
Al-4Mg-1.5Li T R F 60.4 74.9 8.1
(700F Extrusion) T R ST + A 61.2 74.4 6.7
(500F Blocker)T B ST + A 61.2 74.4 8.1
T B ST 60.4 73.6 8.1
L R ST + A 63.2 74.8 10.9
L R ST + A 63.3 75.2 12.3
L R F 63.6 75.2 6.7
L R F 63.2 74.8 8.1
T B ST + A 60.8 73.2 6.7
Al-4Mg-1.5Li T R F 58.8 72.8 9.5
(700F Extrusion) T R ST + A 62.8 75.2 12.3
(700F Blocker)T B ST + A 61.2 74.0 9.5
T B ST 60.8 73.2 8.1
L R ST + A 62.0 74.8 11.6
L R ST ~ A 60~0 73.6 9.5
L R F 59.2 73.2 8.1
L R F 58.8 73.6 10.9
T B ST + A 60.0 73.5 12.3
Al-4Mg-1.75Li T R F 61.6 75.2 6.7
(500F Extrusion) T R ST + A 86.8 90.8 5.3
(500F Blocker)T B ST + A ô8.8 92.06.7
T B ST 69.4 77.9 6.7
L R ST + A 90.5 93.7 6.7
L R ST + A 90.8 94.0 5.3
L R F 67.2 75.6 3.9
L R F 68.4 79.2 3.9
T B ST + A 86.8 89.2 5.3
: .
: ~ . : . .
.
~2~ 396
22 PC-1090
TABLE V (CONTINUED)
Alloy
(Extrusion ~ Blockar Test YS UTS
Conditions) Orient. Temper* ksi ksi % El
Al-4Mg-1.75Li T R F 65.2 75.6 5.3
(500F Extrusion) T R ST + A88.4 93.2 3.9
(700F Blocker) T BST + A 86.8 91.6 3.9
T B ST 65.6 76.0 8.1
L RST + A 89.2 92.8 6.7
L RST + A 88.1 91.4 5.3
L R F 63.2 76.4 6.7
L R F 63.2 69.2 3.2
T BST + A 85.4 88.7 2.5
Al-4Mg-1.75Li T R F 60.0 72.8 8.1
(700F Extrusion) T R ST + A83.6 88.4 3.9
(500F Bloc~er) T BST + A 85.2 89.7 5.3
T B ST 63.6 76.0 10.9
L RST + A 85.2 89.2 5.3
L RST ~ A 85.2 89.2 3.9
L R F 61.6 72.8 8.1
Al-4Mg-1.75Li T R F 60.4 72.8 3.9
(700F Extrusion) T R ST + A83.2 89.2 6.7
(700F Blocker) T BST + A 81.9 86.7 3.9
T B ST 61.2 74.0 10.9
L RST + A 83.2 88.0 6.0
L RST + A 82.8 86.8 6.7
L R F 58.8 74.0 9.5
L R F 58.8 74.4 9.5
T BST + A 84.0 87.2 3.9
Al-2Mg-2Li T R F 59.6 74.0 5.3
(500F Extrusion) T R ST + A81.6 88.8 3.9
(500F Blocker) T BST + A -- 76.6 --
T B ST 58.1 68.2 2.5
L RST + A 84.4 90.8 3.9
L RST + A 82.0 89.2 2.5
L R F 60.0 72.8 3.2
L R F 58.0 72.8 2.5
T BST + A 82.8 88.8 2.5
89~;
23 PC-1090
TABLE V (CONTINUED)
Alloy
(Extrusion ~ Blocker Test YS UTS
Conditions) Orient. Temper* ksi ksi ~ El
Al-2Mg-2Li T R F58.0 70.8 3.9
(500F Extrusion) T RST + A80.5 86.5 1.8
~700F Blocker) T BST + A-- 81.2 --
T B ST 58.0 69.6 3.9
L RST + A 82.4 87.2 6.7
L RST + A 80.0 86.4 2.5
L R F 54.0 67.2 3.8
L R F 53.6 68.8 2.5
T BST ~ A 80.0 84.0 2.5
Al-2Mg-2Ll T R F 50.4 65.2 8.1
(700~F Extrusion) T R ST + A 75.2 80.4 6.7
(700F Blocker) T BST ~ A 74.4 81.2 5.3
T B ST 51.6 65.0 8.1
L RST + A 76.4 81.2 3.2
L RST ~ A 73.2 79.2 5.3
L R F 50.0 64.8 10.9
L R F 49.6 64.0 6.7
T BST + A 74.8 79.2 3.9
*Tempers: F ~ As-Forged - 370C (700F)
ST ~ Solutlon Treated - 495C (925F)/lhr/WQ
A = Aged - 125C (255F~/10hr/AC
EXAMPLE 5
This example illustrates the tensile properties of the
dlspersion strengthened alloys of this invention in "Hook"-type
forglng samples. All materials were prepared as extruded billets
essentlally as shown in EXAMPLE 1
The "Hook" forging die set used in the test~ consists of a
high deformation 1st blocker die, a 2nd blocker die which raises the
ribs of the forging and a finish die which produces minimal
deformation but achieves flnal tolerances in the part. For this test
to avoid the time and expense of using the finish die, evaluation of
the forgings was made after the 2nd blocker, l.e. at an intermediate
forging step.
Figure 2 shows a plan drawing of the finished "Hook"-type
forging. Tensile specimens were heat treated in sets of two,
representing the longitudinal (L) and the short transverse (ST)
orientations.
':
~L~Z~89~i
24 PC-1090
TABLE VI shows propertles in two direc~ions for forgings in
two conditlons: F (as-forged) and T4 (solution ~reated and naturally
aged) for an alloy system containing 4Mg-1.5Li. The data show no
significant difference in results between the F and T4 conditions.
The best properties exhibited in TABLE VI are for the alloy of tast
1, i.e. in the as-forged condition processed at 260C (500F)
extrusion and first blocker temperatures. The data confirm that
strength is primarily controlled by extrusion temperature and
secondarily by blocker temperature.
TABLE VI
1st 2nd
Ext. Blocker Blocker
Temp. Temp. Temp. YS UTS El RA
(F) (F) (F) Orient. Temper (k3i) (ksi) % %
500 500 610 L F 67.0 76.2 13 25
500 500 610 ST F 62.4 71.7 11 15
500 500 610 L T4 66.4 76.0 14 23
500 500 610 ST T4 62.0 71.7 7 11
500 675 610 L F 65.6 74.0 14 26
500 675 610 ST F 58.8 71.1 10 20
500 675 610 L T4 64.2 74.2 13 23
500 675 610 ST T4 60.2 71.7 11 21
700 500 610 L F 59.6 72.8 12 18
700 500 610 ST F 59.0 71.8 9 12
700 500 610 L T4 59.4 72.6 13 20
700 500 610 ST T4 59.8 71.5 7 14
700 675 610 L F 59.8 70.0 14 23
700 675 610 ST F 54.4 68.3 11 18
700 675 610 L T4 56.4 70.2 14 22
700 675 610 ST T4 53.4 67.1 12 21
Similar tests carried out on alloys containing 4Mg-1.75Li
and 2Mg-2Li in blocked forgings showed that the Li level affected
both the strength and age hardening aspects of the alloy~ markedly.
A comparison with results on "cruciform" forgings shows
that there is essentially the same trend in the alloy properties
resultlng from the processing conditions.
- ' ' `~' ' .
. .: . . .
~ 2~896
PC-1090
EXAMPLE 6
This example illustrates the effect of normal forging
practice on the tensile properties of a forged sample of an alloy of
the type Al-4Mg-1.5Li. An extruded billet is prepared from a vacuum
hot pressed compaction billet as described ln EXAMPLE 1. The
compaction billet was extruded from 27.9 cm (ll in~ to 9.53 cm (3-3/4
in) diameter rod at temperatures of 650-700F through a shear-faced
die at an extrusion ram speed of 0.1 in/sec. and a breakthrough
pressure of 1100-1600 tons. The extrusion liner was lubricated but
not the billets. A "Hook" forging was made At a temperature of 420C
(788F) in the first blocker and 488C (838F) in the second blocker.
Tensile tests on various locations on the specimen showed it to have
in the as-forged condition the average properties: YS of 368 MPA
(52.7 ksi), UTS of 470 MPa (68.3 ksi), El of 14.5% and RA of 19.7%.
In the solution treated condition of l hour at 480C (900F)/glycol
quench condition the average properties are: YS of 352 MPa (51.5
ksi), UTS of 466 MPa (67.6 ksi), El of 14% and the RA of 19.9%. The
method of this example is not effective for achieving the maximum
strength potential of the alloy.
EXA~PLE 7
This example lllustrates the effect of normal forging
practice on the tensile properties of a cruciform forging. An
extruded billet of an alloy of the 4Mg-l.SLi-type is prepared as
described in EXAMPLE 6. The first blocker temperature of the
cruciform forging is carried out at 370C (700F). A lubricant, a
Withrow A Paste-mineral oil mixture, is used in the finish forging
which is carried out at various temperatures. Finlsh forging
temperatures and tenslle properties of the finish cruciform forgings
in the longitudinal and transverse directions are shown in TABLE VII.
The method of this sxample is not effective for achieving ~aximum
strength potential of the alloy.
: , ~ , ................................. .
~ , '
~ 2~ S96
26 PC-1090
TABLE VII
Forging
Temp. YS UTS El RA
Direc~ion(F) (ksi) (ksi) (~) (%)
Longitudinal 600 52.668.212 15
600 51~1 65.212 20
650 52.4 67.811 16
650 51.7 67.411 18
700 52.3 66.712 17
700 52.0 65.911 19
750 51.8 66.411 16
750 51.6 66.613 16
800 51.3 66.413 17
800 50.9 66.211 16
15 Short 600 49.9 62.7 5 6
Transverse600 51.3 65.3 5 3
600 50.3 57.7 2 5
600 53.1 62.6 2 7
700 49.9 65.111 13
750 4g.9 63.9 6 10
800 49.8 65.811 11
EXAMPLE 8
This example illustrates dispersion strengthened low
density alloys of this invention composed of aluminum, lithium,
magnesium, siliconj carbon and oxygen, and containing about 1.1 to
1.2~ carbon and less than 1~ oxygen.
Mechanically alloyed powders are prepared having the
nominal magneslum, lithium and silicon contents given in TABLE VIII.
The powders are vacuum hot pressed to compaction billets and extruded
essentially as described in EXAMPLE l, except that all extruded
blllets are prepared at 260C (500F) and at ram speeds of 25.4 cm
(10 in)/min. Extruded billets are forged at 260C (500F) to form
"Hook"-type forgings essentially as described in EXAMPLE 5. An age
hardening treatment i8 applied to the forged product consisting of a
35 solution treatment at a temperature of about 520C (970F), water
quenching, and aging at about 145 to 175C (300 to 340F) for up to
18 hours.
. .
~, . .
.
. .
' '
848~6
27 PC-1090
The alloys of this invention in the forged, age hardened
condltion have high strength, with advantageous preservation of
corrosion resistant properties in the alloy. It is believed that the
increased strength i9 due to the precipitation of a silicide such as
Mg2Si and/or lithium silicide.
TABLE VIII
Alloy Type Mg Li Si
G 4 1.5.5
H 4 1.51.0
I 2 1.5.5
J 2 1.51.0
K 2 2 .5
L 2 2 1.0
Although the present invention has been described in conjunction
with preferred embodiments, it is to be understood that modifications
and variations may be resorted to without departing from the spirit
and scope of the invention, as those skilled in the art will readily
understand. Such modifications and variations are considered to be
within the purview and scope of tne invention and appended claLms.
