Note: Descriptions are shown in the official language in which they were submitted.
- -
~S~3~5
The present invention relates to a composite mate-
rial, which comprises aluminum or an aluminum-base alloy con-
taining an alumina fiber or an alumina-silica fiber as a re-
inforcement.
With the recent technical developments ln the aero-
space industries and various other industries, a very strong
demand has developed for construction materials which combine
lightness with superior mechanical strength, stiffness and heat
resistance.
Such materials may be obtained by reinforcing a
metal with a fiber material having a high mechanical strength
and a high tensile modulus, and it has been already tried to
reinforce aluminum, which is a light and conventional metal,
~ith a fiber ma~erial such as boron fiber, carbon fiber,
alumina whisker or the like. Although many efforts have been
made to produce such reinforced aluminum, none have been
successful, bçcause the fibers so far used are not suitable for
reinfsrcing aluminum. Thus, boron fiber has a diameter of more
. . .
than 100 ~ and is inferior in flexibility and fur~her it easily
reacts with aluminum even at a temperature lower than the
melting point of aluminum of the matrix to result in the
deterioration of the properties thereof. Accordingly, lt
is not suitable for producing a composite material. The
carbon fiber ls easily oxidl~ed and reacts with the aluminum of
the matrix, and therefore, the composlte material must be
prepared at a temperature lower than the melting point of aluminum
- in a vacuum or in an atmosphere of an inert gas and further the
ma~rix of the composite material thus obtained is gradually
induced to electrolytical corrosion owing to the electrocon-
ductivity of the fiber. Moreover, the carbon fiber is hardly
wetted with fused aluminum, and th~refore, the production of
-- 2 -
~L~51D305
the aluminum reinforced witl- the fiber is more difficult.
The alumina whisker is also hardly wetted with fused alumlnum,
and therefore, it is difficult to produce the desired composite
material having superior mechanical strength with less defects.
Moreover, the alumina whisker itse:Lf is expensive and it is
very complicated to align the very short alumina whiskers in
the desired direction which results in high cost for producing
the composite material.
It is, therefore, the object of the present ivnention
to overcome some of the above problems and provide a reinforced
aluminum or aluminum-base alloy having superior mechanical
strength and modulus over a wide temperature range, as well as
having excellent fatigue characteristics, creep characteristics
and impact resistance at a high temperature.
According to the present invention, it has b~en
found that certain alumina or alumina-silica fibers, even
without any specific surface treatment, are wetted very easily
with fused aluminum or aluminum-based alloy and strongly
bond to the matrix material, thereby making excellent reinforcing
fibers. The particular fibers used are alumina fibers or
alumina-silica fibers consisting essentially of 72 to 100~ by
weight of alumina and 0 to 28~ by weight of silica and having
substantially no ~-alumina reflection by X-ray diffraction.
Thus, the novel composite material of this invention
comprises aluminum or an aluminum-base alloy reinforced by alumina
fibers or alumina-silica fibers consisting essentially of 72 to 100%
by weight of alumina and 0 to 28% by weight of silica and having
substantially no ~-alumina reflection by X-ray diffraction, the
amount of the alumina fiber or alumina-silica fiber being 5 to 80%
by volume,
A scanning electron microscopic photograph of the
break section of the composite material of the invention shows
the fibers to be closely bonded to the aluminum matrix and
- 3 -
~Qt3~5
further no fiber pull-out is observed, which characteristics
are not observed for the conventional composite material
reinforced wlth carbon fiber or a]umina whisker. These
excellent characteristics of the a~lumina fibers and alumina-
sil~ca fibers of the present invention are very important for
obtaining the desired composite ma~erial, by which many
difficulties encountered with the production of the conventional
fiber-reinforced aluminum or aluminum alloy are overcome and
the desired reinforced aluminum or aluminum-base alloy having
excellent properties can be obtained.
The alumina fiber and alumina-silica fibers which
are used have excellent mechanical properties, such as a
tensile strength of 10 t/cm2 or more and a tensile modulus of
1,500 ~/cm2 or more, excellent oxidation resistance and hea~
resistance and further excellent wettability with a fused
aluminum or aluminum-base alloy. Moreover, they can be
obtained in the form of flexible continuous fibers and therefore
can give the deslred-composite material having excellent mechanical
properties without defects. Besides, the fibers have no electrical
conducti~i~y and there is no problem of electrolytical corrosion,
and therefore, ;the composite materlal produced by using the fibers
is not deteriorated for a long time.
The al~lmina fibers and alumina-silica fibers, which
are fully described in copending application Serial No. 192,993
filed February 19, 1974, may be produced by spinning a solution
of polyaluminoxane or of a mixture of polyaluminoxane and an
appropriate amount of a silicon-containing compound and then
calcining the resulting precursor fiber. The detail of the
production is as follows.
The polyaluminoxane used in the production is a poly-
mer having a structural unit of the formula:
- 4
~OSQ3~5i
-Al-0-
y
wherein Y is one or more kinds of the groups selected from
an alkyl having 1 to ~ carbon atoms (e.g. methyl, ethyl,
propyl, or butyl), an alkoxy hav:ing 1 to 6 carbon atoms
(e.g. ethoxy, propoxy, or butyloxy), an acyloxy having 1 to
6 carbon atoms (e.g. formyloxy, acetoxy, propionyloxy or
butyryloxy), a halogen (e.g. fluorine, or chlorine), hydroxy,
phenoxy which may be substituted by alkyl, such as methyl,
ethyl, propyl, and the like. To be soluble in the organic
solvent it is necessary that not all of the Y groups in the
polyaluminoxane by halogen or hydroxy. In other words, at
least one Y group must represent an alkyl, alkoxy, acyloxy,
phenoxy or substituted phenoxy.
The useful polyaluminoxane may have an alumina
content of 10% or more, preferably of 20% or more by weight.
The alumina content means the numeral calculated by the
following expression:
(51/molecular weight of the structural unit) X 100 (%)
and when Y is two or more kinds of the groups~ the molecular
weight means the average thereof. When a polyaluminoxane
having an alumina content of less than 10% is used, it is
very difficult to obtain a practically useful alumina f-ber
or alumina-silica fiber having excellent strength, even though
it is not impossible.
The most preferred group Y may be an alkyl, alkoxy
and acyloxy having each not more than 4 carbon atoms since a
polyaluminoxane having these groups has high alumina content
and the precursor fiber made thereof may be easily hydroly~ed
as described later.
~ _ 5 _
~ ~05(~3~15
There is no specific limitation to the degree of
polymerization of the polyaluminoxane and two or more degree
of polymerization is enough. However, in view of ease of
polymerization reaction, the compound having the degree of
polymerization of not more than 1,000 may be preferable one.
The more preferable one may be the one having a degree of
polymerization of from 10 to 200.
- Sa -
~5~3~t~
The polyaluminoxane generally dissolve~ in an organic
solvent such a~ ethyl ether, tetrahydrofuran, dioxane, benzene
or toluene to give a viscous solution having large spinnability
ln an appropriate concentration. The relation between the con-
centration and the spinnability of the solution may vary in ac-
cordance with the kind of the polyaluminoxan-e, the degree of
polymerization thereof, the kind o~ the solvent and the kind
and amount o~ the silicon-containing compound to be mixed with,
but it may be preferable to use a solution having a viscosity
of from 1 to 5,000 poises at room temperature for the pur~ose
o~ spinning thereo~. Accordingly, the spinning solution must
be prepared so that the viscosity thereo~ becomes within the
range as mentioned above. Besides 9 the polyaluminoxane con-
taining 1 to 20 ~o by mol, preferably 1 to 10 ~o by mol of the
re~idue Y selected from palmitoyloxy and/or stearoyloxy is
particularly preferable in view of its excellent spinna-
bility.
As the silicon-containing compound to be mixed with~
there may be preferably used a polyorganosiloxane having a
structural unit of the formula:
,. Rl
--S i--O--
wherein Rl and R2 are the same or different and represent
~ydrogen, an alkyl ~roup having 1 to 6 carbon atoms (e.g. methyl
ethyl, propyl, and butyl)~ an alkenyl group having 1 to 6 carbon
atoms (e.g. vinyl), an alkoxy group h~ving 1 to 6 carbon atoms
(e.g. ethoxy), phenyl group, chlorine or the like1 and a poly-
8ilicic acid ester having a structural unit of the foxmula:
3 0 oR3
--si--o--
~ 4
3~5
wherein R3 and R4 are the same or different and represent
hydrogen, an alkyl ~roup having 1 to 6 carbon atoms (e.g. methyl
ethyl, propyl, and butyl)~ an alkenyl group havin~ 1 to 6 carbon
atoms ~e.g. vinyl), phenyl group, chlorine or the like, but
may be used an organosilane of the formula: R5Si(oR6)4 n wherein
R5 and R6 are the same or different and represent hydrogen, an
alkyl group having 1 to 6 carbon atoms (e.g. methyl and ethyl),
an alkenyl group having 1 to 6 carbon atoms (e.g. vinyl~, phenyl
group, chlorine or the like, and n is an integer of 1 to 4; a
- silicic acid ester of the formula: Si(oR7)4 wherein R7 is
- 13 hydrogen, an alkyl group h~ving 1 to 6 carbon atoms, phenyl
group or the like; and any other silicon-containing compound.
The silicon-containing compound to be mixed with
may be pre~erably dissolved homogeneously into a solution of
the polyaluminoxane, but may be dispersed therein without dis-
solving. Furthermore, the silicon~containing compound may be
preferable to give a solution having spinnability when it is
dissolved in the solution of the polyaluminoxane, but it is
... .
not essential.
20- ~urther-, to the spinnin~ solution there may be pre-
ferably added a small amount of one or more kinds of the com-
pounds containing an element such as lithium, beryllium, boron,
~odium, magnesium, phosphorus, potassium, calcium, titanium,
~hromium, manganese~ yttrium, zirconium, barium, lanthanum,
or tungsten, by whlch the various characteristics of the alumina
flber or alumina-silica fiber are improved.
When a solution of polyaluminoxane or of mixture of
poiyaluminoxane and silicon-containing compound is spun, it
may be conveniently carried out by dry-spinning method, but
there may be also used any other conventional methods such
as centri~ugal pot spinning or blow spinning.
~OS~30$
When the spinning is carried out in air, the poly-
aluminoxane ~orming the precursor fiber may be gradually hydro
ly~ed by moi~ture contained in air and thereby the organic
component may be gradually 105t, by which the content of alumina
in the precur~or fiber may be increased and further the mecha-
nical properties of the alumina fiber or alumina silica fiber
obtained by calcining thereof may be preferably improved. Ac-
cordingly, the silicon-containing compound to be mixed with
may ~e preferably the one being easily hydrolyzed, such as
polysilicic acid ester. Furthermore, it may be preferable
to contact positively the precursor fiber with a steam atmos~
phere or an acidic aqueous solution to promote the hydrolysis
mentioned abo~e~
~ he precursor fiber produced by the present process
may usually have an average diameter of 1 to 600 ~ but not
limited thereto. The alumina or alumina-silica precursor fiber
i~ composed in a homogeneous and continuous state wherein the
alumina or silica forming materials are contained in a high
concentration, and therefore it is very ef~ective for improv-
ing the various characteristics of the final product. alumina
fiber or alumina-silica fiber.
The alumina or alumina-silica precursor fiber ob-
tained by contacting with moisture is not molten by heat, and
therefore may be calcined in an atmosphere containing mole-
cular oxygen gas, for instance in air, to gi~e readily the de~
sired alumina fiber or alumina-silica fiber without loosing
the fiber form. The precu~sor fiber may be substantially changed
to alumina fiber or alumina-silica fiber by calcining at about
700C in an atmosphere containing oxygen, e.g. in air, and may
gi~e the desired alumina fiber or alumina-silica fiber being
transparent and having excellent strength by calcinlng at about
1 ,(~00C,
- 8 -
~l~S~3~5
That is, when the precursor fiber i~ calcined in an
atmosphere containing oxygen e.g. in air, it looses water and
the organic components by about 600C, and the fiber strength
increases with rai~ing the calcining temperature. However,
when a pure alumina fiber containing no silica is calcined, the
fiber-forming y-alumina phase is transformed into a-alumina
phase at about 1,000 to 1,100C, by which the fiber strength
may be significantly decreased. On the other hand, when an
alumina fiber containing silica i9 calcined, the transforma-
tion temperature may be moved to higher temperature with in-
crease of the silica content thereof, and in case of the silicacontent being 25 to 28 % by weight, the transformation tempera-
~ure is about 1,550C.
In order to obtain an alumina-silica fiber having
excellent strength, the calcination temperature may be lower
than the transformation temperature indicated abo~e.
The phases forming the fiber at a temperature of from
ltO00C to the transformation temperature may be y-alumina
phase, amorphous silica and mullite phase in case of the silica
content being not more than 28 % by weight. These phases may
2~ be transformed at the transformation temperature or higher tem-
perature into -alumina phase and mullite phase.
Accordingly, the alumina fiber or alumina-silica flber
having large fiber strength which contains 100 to 72 ~o ~y weight
of alumina (A1203) and 28 to O % by wei~ht of silica (SiO2),
must exhibit substantially no ~-alumina reflection by
X-ray diffractionO
When the alumina fiber or alumina-silica fiber satis-
~ies these conditions, the mechanical properties of the pure
alumina fiber having no silica are tensile strength: about 10
3~ to 15 t/cm2 and tensile modulus: about 1,000 to 1,500 t/cm~ in
'~
~15~3~
case of the fiber diameter being 10 ~. These numerical values
lncrease with increase o- the silica content, and when the
sillca content .,i9 about 10 to 25 ~ by weight, the tensile strength
and the tensile modulus become about 25 to 30 t/cm2 and about
2,500 to 3~500 t/cm2, respectively.
According to the above proce~s, it i8 possible to pro-
duce an alumina-silica fiber having a high silica con-tent,
for instance a silica content of 50 % by weight. ~owever,
the preferred alumina fiber or alumina-silica fiber used in
the present invention has an alumina content of 72 to 100 %
by weight9 preferably 76 to 98 ~o by weight and a silica con-
tent of 0 to 28 ~ by weight, preferabl~ 2 to 24 ~o by weight.
When the silica content is less than 2 ~ by weight, the fiber
is a little inferior in the mechanical strength, and on the
other hand, when the silica content is more than 24 ~o by
weight, the fiber is inferior in the wettability with aluminum
or aluminum-base alloy.
The alumina fiber and the alumina-silica fiber ob-
tained by the ab:ove process have usually a diameter of from
0.6 to 400 ~1 on an average. When aluminum or an aluminum-base
2`0 alloy is reinfor;ced with these fibers, the diameter t~.ereof is
not restricted. However, when the fiber having a diameter of
more than 200 ~L iS used as the reinforcernent, it is not easy
to prepare a thin) flexible composite sheet product because of
the poor flexibility thereo~, and on the o*he~ hand, when the
fiber having an extremely thin diameter is used as the reinforce-
ment, the fiber is consumed by the formation of a reaction pro-
duct of the fiber with the matrix metal as mentioned below and
the effect of reinforcement is lowered~ There~ore, the diameter
of the fiber used in the present invention is preferably not
less than 6 ~.
- 10 ~
~OS~3~5
Besides, the alumina fiber and the alumlna-silica
fiber uc~ed in the present invention should exhibit substantially
no ~-alumina reflection by X-raY diffraction. G~ne-
rally, when an inorganic fiber is heated nnd calcined up to
an unfavQrably hi~h temperature, the fiber-formin~ inorganic
materials crystallize into small ~rains which grow as the
caicining temperature is raised, and since thesc ~rains are
only weakly bonded with one another, the fiber becomes brittle
breaking easily at the grain boundaries under stress to in-
duce the significant lowerin~ of the fiber strength, More-
over, with the growth of the crystalline grain3, the sur-
~ace activity of the fibers decreases. When such fiber is
used for reinforcing the aluminum, it shows inferior reinforc~
ing effect because of its inferior wettabïlity and inferior
adhesiveness. It has been o~served by the present inventors that
the growth of the crystalline grains is characterized by
the appearance of a-alumina reflection in the X-ray diffrac-
tion o~ the alumina or alumina-siiica fiber. Accordingly9
the alumina fiber and the alumina-silica fiber used in the
present invention should be prepared so that no a-alumina re-
- flection appears.
Thus, the alumina fiber and the alumina-silica fiber
useful in the present invention have a very low degree of crystal-
linity and comprise substantially y-alumina, amorphous silica
and a slight amount of microcrystalline mullite. The surface
of the fibers is comparatively active, and when a composite
material is produced therefrom, an extremely thin layer of the
reaction product of the fiber with the matrix (aluminum3 is
~ormed at the interface thereof, which may cause the excellent
wettability of the fiber with the aluminum or aluminum-base
alloy.
~5~3~S
The metals to be reinforced by t~e present invention
include commercially available alumimum or aluminum~base alloy
containing one or more kinds of metals selected from the group
eonsisting of beryllium, cobalt, chromium, copper, iron,
magnesium, manganese, nickel, silicon, tin, titanium, æinc
and zirconiumO
As explained above, the excellent wettablity of the
present aluminn fiber or alumina-silica fiber ~rith aluminum
or aluminum-base alloy o~les to the low crystallinity, and
therefore, any alumina fiber or al~ina-silica fiber produced
by any other process may be used unless it shows an a-alumina
~e~lection by X-ray diffraction. For instance, the useful
fibers may be produced by calcining the following filaments
or fibers at a temperature lower than the temperature at which
u-alumina is formed, for instance, filaments being prepared
by mixing an aluminum-containing compound ~e.g~ alumina sol
or aluminum salt) and a silicon-containing compound (e.g. silica
sol or ethyl silicate) with a solution of an organic high mole-
cular compound (e.g. polyethylene oxide or polyvinyl alcohol)
... . .
and spinning the resulting viscous solution; fllaments being
prepared by mixing a silieon-containing compound with an aque-
ous solution of an aluminum salt of a carboxylic acid, concent-
rating the solution and spinning the resulting viscous solution;
or organic fibers being prepared by dipping organic fibers in
a solution of an aluminum salt and a solution containing silieon
and thereby impregnating aluminum ~nd silicon thereto.
The volume amount of the alumina fiber or alumina
silica fiber in the composite material according to the pre-
sent invention is 5 to 80 ,~, prefcrably 30 to 60 $ by volume.
- 12 -
~35~30~
The composite material comprising a matrix of aluminum
or an aluminum-base alloy and a rei.nforcement selected from
the alumina fiber and the alumina-silica fiber may be produced
by any conve~tional method which has been used for the produc-
tion of a composite material by using a boron fiber or a carbon
~iber as the reinforcement, lor instance, an impregnation with
fused matrix, a hot press of the ~iber,coated with the matrix,
~oil metallurgy, powder metallurgy, hot rolling, or the
like. Particularly, since the present alumina -~iber and alumina-
silica ~iber are chemically and thermally very stable, the im
pregnation with fused matrix is effectively applicable, and
therefore, the desired compos,ite material having excellent
mechanical strength with least defects can be easily produced.
Owing to the excellent stabilities of the alumina fiber
and the alumina-silica fiber, the desired composite ~aterial
can be produced even at a temperature higher than the melting
point of the matrix, and therefore, the composite material
of the present inven,t,ion has larger volume fraction o~ the -
reinforcement but less.defects in compariso.n with that pro-
duced by using the conventional boron fiber or carbon fiber~
which is one o~,the characteristics o~ the present invsntion.
., . . . . . _ ...
The alumina fiber and the alumina-silica fiber may optionally
be used together with the other conventional fibers such as
boron fiber and carbon fiber.
The aluminum or aluminum-base alloy reinforced by
the alumina fiber or alumina-silica fiber o~ the present in-
vention has usually a density of 2.6 to 2.8 g/cm3, a tensile
strength of 2 to 1~ t/cm2 and a tensile modulus of 800 to 2,000
~cm g which values do almost not vary at a temperature of 20
~o 500C.
The present invention is illustrated by the following
~xamples but not llmited thereto.
30~
Example 1
(a) In order to prepare alumina-~illca flber9 ethyl
silicate was dissolved in a solution of polyethylaluminoxane
in dioxane. The mixture was concentrated to give a solution
containing the polyaluminoxane in concentration of about 60%
by weight. The viscosity of the solution thus obtained was
about 200 poises at room temperature.
The solution thus obtained was used as a spinning
solution. This solution was extracted from a 100~ diameter
spinning nozzle at room temperature and the extruded fiber
was wound at a rate of 50m/minute in air. The fiber thus
obtained ~as contacted with saturated stream and calcined
while raising the temperature from room temperature to 1200C
at a rate of 300C/hour in air to give transparent alumina-
silica fiber containing 10% by weight of silica. The alumina-
silica fiber thus obtained has a fiber diameter of 12~, a
tensile strength of 30.1 t/cm2, a tensile modulus of 3,050 t/cm2
and a density of 3.1 g/cm3.
. (b) The fibers are bundled in a length of 120 m~ and
the bundles thus obtained are put in an alumina tube having an
inside diameter of 8 mm. One end of the alumina tube i~ dipped
lneo fused aluminum being 99.~% in purity, which is kept at
800~C in an atmosphere of argon gas, and the pressure in the
alumina tube is gradually reduced by sucking from the other
end thereof, by which the fused aluminum is sucked up through
the alumina tube to impregnate the fibers therewith. The whole
system is gradually cooled to solidify the aluminum to give a
unidirectionally reinforced aluminum pole.
According ts the above process, varlous composite
materials having a volume fraction of fiber of 51 10, 20, 30,
40 or 50% are produced, on whlch the tensile s~rength and
- 14 -
u
~L0S~3~5
the tensile modulus are measured ~t room temper~ture. The
results are shown in Fi{~ure 1.
As made clear from the Figure 1, the tensile strength
and the tensile modulus of the composite materials increase
approximately linearly with the increase o-f the volume frac-
tion of fiber, and when the volume fr~ction of fiber is 50 %,
the reinforced aluminum thus obtained ha~ excellent mechanical
properties, such as a tensile strength o~ 11.9 t/cm2, a tensile
modulus of 1,800 t/cm2 and a density of 2.8 g/cm3. According
to the scanning electron microscopic photo~raph of the break
~ection of the composite material, no fiber pull-out is ob-
~erved, which means -that the ~ibers are closely bonded with the
aluminum.
Example 2
The alumin~-silic~ fibers as used in ~xam~le 1 are
laid in parallel with each other in sheet-like fashion and
piled mutually and repeatedly with an aluminum foil having a
purity of 99.5% and a thickness of 0O05 mm in a carbon mold, so
that the volume fraction of fiber in the formed composite material
is 45~. The resultant is pressed for 5 minutes at 620C under
20 - a pressure of 120 kg/cm in a vacuum of 10 Torr. The composite
material thus obtained is cut to give a dumbbell specimen having
a total length (in fiber direction) of 60 mm, a length of the
parallel part of 7 mm, a width of 5 mm and a thickness of 3mm, on
which the tensile strength is measured in a vacuum. The
composite material obtained shows a tensile strength of 9.8, 908,
9.1 and 8.4 t/cm2 at room temperature, 300C, 400C and 550C,
- respectively.
- 15 -
~0~03~5
Example ~
In the slmilar manner as described in ~xample 19 a
composite material having a volume fraction of fiber of 50 /~
iB produced by using a matrix of aluminum-base alloy consist-
ing of 3.7 ~ by weight of copper, 1.5 % by weight of magnesium,
2.0 % by weight of nickel and 92 % by weight of aluminum. The
composite material thus obtained shows a tensile strength of
12.5 t/cm2 and a tensile modulus of 1~740 t/cm2 at 360Q~ in air.
... .
- ' ' ` .
- 16 -
