JPS6021213B2 - Aluminum composite and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates generally to reinforcing metals with fibers, and more particularly to the production of composites of alumina fibers and aluminum.

A problem that limits the use of Yama 203-AI composites (made from Q-AI 203 fibers, e.g., as committed by Semen in U.S. Pat. No. 3,808,015) is that the molten aluminum adequately wets the alumina This meant that there was no practical way to make the composite. This time, polycrystalline alumina fibers were infiltrated with a molten aluminum alloy containing about 1 to 8% IJ thium by weight.
ate) to form a reinforced composite having a reactive sheath thickness of less than 15% of the total fiber diameter on the fibers, and then cooling the composite. It was discovered that it is possible.

In this way, composites can be produced that are substantially free of brittle interfaces and have good mechanical properties. Such composites contain 15 to 7 percent by volume polycrystalline alumina fibers, 0.5 to 5 percent by weight of the matrix.
．． It contains a matrix of 5% by weight lithium with the remainder aluminum and aluminum alloy impurities and a reactive sheath on the fibers having a thickness less than 15% of the total fiber diameter. The composite of the invention has a fiber volume fraction of 15-7% cough volume.

Below one chord volume percent, there is little practical benefit in terms of strength or modulus in some applications.

Above about 7 volume percent, the fibers tend to contact each other and each point of contact becomes a stressed area;
There is a risk that it will start to crack. The composite may contain either continuous filaments or discontinuous fibers of polycrystalline alumina. The total aluminum of the matrix of the composite of the present invention contains 0.5-5.5% by weight of lithium, with 0.5% by weight of lithium.
If it is less than 5% by weight, it is not preferable because the fiber does not have a surface that can be wetted by molten aluminum.
．． If the amount exceeds 5% by weight, it is not preferable because it reduces the strength of the fiber. In either case, the strength of the composite is reduced as a result. On the other hand, the lithium content of the aluminum alloy used for manufacturing the composite of the present invention is 1 to 8% by weight,
The lithium content in the matrix alloy of the composite is higher than the lithium content because some lithium is consumed in forming a reactive sheath around the fibers and additional losses are lost during composite manufacturing, as discussed below. This is because it is produced by reaction with citrate, promotion and/or oxidation.

As used herein, "continuous filament" refers to fibers having a length equal to the length of the composite when measured in the direction in which the fibers are aligned.

The discontinuous fibers are about 0.10 side, preferably at least 3
It has a minimum book length. When the composite contains substantially continuous filaments, a fiber fraction of about 30 to 6 volume percent is preferred for best fiber distribution and packing in the composite. If the composite contains discontinuous fibers arranged substantially randomly, about 15
~3 tsubo volume percent is a suitable fiber fraction. The fibers in the composite can be oriented in a particular direction or in several directions as desired to provide maximum strength or modulus.

Such alignment can be parallel, perpendicular, or at some other angle to any axis in the composite. Fibers can also be randomly arranged within the composite structure. Examples 1-4 demonstrate unidirectional fiber reinforced composites; such composites have the highest strength and modulus in the direction of fiber alignment.

In some applications, a more isomerial property is desired, which involves using parallel layers (plies) of fibers oriented in a unidirectional manner, with the plies oriented in different directions relative to adjacent plies. (for example, 4?). More isotropic properties can also be obtained by using a random arrangement of discontinuous fibers throughout the composite, but such a fiber distribution can increase the fiber loading up to Limited to about 3 percent by volume. The fibers used in this invention are high modulus, high strength polycrystalline alumina fibers.

Preferred fibers contain at least 60% aluminum oxide (mountain 203) by weight. All else being equal, the mechanical properties of the composite, such as maximum modulus and heat resistance, generally improve as the amount of peaks 203 in the fiber increases. Therefore, at least 80%
of AI203, preferably of at least 95% AI2Q
Most preferred are fibers containing . Generally, the most preferred fibers contain mountains 203 in the form of alpha alumina. The fiber is US Patent No. 3,808,015
Schuchert in the issue, also U.S. Patent No. 385.
Am-brosio in issue 3688
can be manufactured as described. The strength of some such alumina fibers is increased by a silica coating having a thickness of about 0.01 to 1 micron. A method for providing fibers with such a silica coating is described by Tietz.
and Green in U.S. Pat. No. 3,837,861 and Shigeru No. 49,181, respectively. This kind of silica coating is
A high quality composite using an alloy that also promotes wetting by the aluminum-lithium alloy and has a lower lithium content than that required in the non-silica coated fibers using the same infiltration time and temperature. enables the production of In addition to being as strong as possible, it is also desirable for the fibers to be as dense as possible because as the fiber density increases, a higher degree of fiber strength is retained in the composite. be. When fibers are manufactured by the general method described by Schuhert, the density of the fibers is determined by the final binding (firing) of the uncoated fibers until the coated fibers reach their maximum tensile strength. This can be increased by operating at only slightly higher temperatures. Since there is a correlation between the speed of the fibers in the flame, the type of equipment used, the denier and number of fibers, etc., the exact temperature to use in each case depends on the factors involved in the correlation. It is necessary to decide according to the overall balance. For example, the temperature at which the fibers achieve their maximum tensile strength with
Dawn silk by passage of a 1700-1800 denier yarn consisting of about 200 fibers through a flame at a rate of 18.3 h per minute in a chimney at a temperature of 100° C. is used in the composite of the invention. provide suitable fibers for
Although the fiber composition is the same, materials fired at higher temperatures are finer, denser, and have different microstructures as determined by scanning electron microscopy.
As a result, fibers fired at relatively high temperatures can withstand longer exposures to aluminum-lithium alloys while substantially retaining their initial fiber strength than identical fibers fired at lower temperatures. can. Therefore, although the strength of the fibers added to the composite may be lower than the maximum strength of the fibers as a result of the relatively high firing temperature, the strength of the fibers in the composite is The strength will be much higher than that for full tensile strength fibers because they will not be attacked by the alloy to the same extent as less dense fibers. Suitable fibers also have a silica coating. In confirming the increase in density brought about by the relatively high temperature firing process described above, commonly used density measurements are not sufficient to distinguish between relatively hot and relatively low temperature fired structures. Sensitivity is not high.

More sensitive measurements are needed. It has been found that as the density of the fibers increases as a result of higher firings, the microstructure changes such that the fibers exhibit an orientation that is more transparent to light. This phenomenon can be used to distinguish dense fibers imparted by relatively high temperature calcinations from less dense fibers of similar composition and diameter by their translucency values. The translucency value is the average of measurements on 30 random samples obtained by observing the fiber length in air at 600-120 pigs, preferably 120 ships, using transmitted light.
The amount of light transmitted by a fiber is rated as a translucency value on a scale of zero to six. A translucency value of 6 is given for the most translucent fiber of a particular composition and diameter.

Such fibers exhibit a bright band in the center of the fiber and along the entire length. This bright band has two opaque (black) strips about 1/3 the width of the fiber diameter and each extending from the edge of the fiber to the green outside of the bright central band.
It is sandwiched between the obi. When the intensity of the light transmitted by the central band decreases, the translucency value decreases. At a translucency value of zero, the fibers appear opaque and the central band cannot be discerned. The relationship between a fiber's opacity and its translucency value is approximately linear. Fibers with a translucency value of 4 to 5.5 are suitable for the present invention.

Translucency values can be measured in a similar manner for fibers with a coating of silica. Preferred fibers further have a diameter of about 15 to 30 fibers and a weight of at least 70 kg'.
and a Young's modulus of at least 14,000 k9/h.

In addition to N1203, the fibers may include, for example, SiQ, Mg0
, Tho2, Zr02, Z's 2-Ca○, Z[]2-M
g○, Zh02 - Si02, Ce203, Fe20
3, Ni○, Coo, C can also have other refractory oxides and/or refractory oxide systems, such as 03, Hf02, Ti02, etc. These fibers must have a melting point of at least 100,000.
Preferably, the fibers are used in the form of continuous alumina filament tows. The aluminum alloy of the composite matrix contains 0.5-5.5% by weight lithium, the remainder being aluminum and impurities. The concentration of lithium in the matrix is generally lower than the concentration in the starting alloy because some lithium is consumed in forming the reactive sheath around the fibers. Additional losses may occur due to crucible reaction, sublimation and/or oxidation during manufacturing. The aluminum alloy of the matrix of the composite of the present invention contains impurities that are unavoidably mixed in from the raw materials, such as beryllium, bismuth, boron, cadmium, calcium, chromium, cobalt, gallium, lead, sodium, strontium, vanadium, zirconium, etc. Contain trace impurities of 1% or less by weight of the matrix, such as mixtures thereof.

It will be clear that for most applications the matrix in the composite must be ductile.

The ductility of the matrix can be confirmed by a failure strain of greater than 0.2% for the composite. When using continuous alumina filaments, the upper limit of strain measured in the direction of filament alignment is:
The fracture strain can be made comparable to the fracture strain of alumina filament. When using discontinuous alumina fibers (staple fibers), the failure strain of the composite is limited by the ductility of the matrix, the amount of fill, fiber placement, and other such factors. All matrices in the embodiments of the invention are ductile by this definition. The lithium-aluminum alloy used in the present invention chemically greens the fibers, thus providing a composite with excellent fiber-matrix bonding and good high temperature performance. Preferred complexes of the invention have at least 4.9
It has a longitudinal short beam shear strength of k9/260°C (measured at lukewarm room temperature 260°C). The short beam shear value is a measure of the overall composite quality, including the degree of bonding between the fibers and the matrix, the strength of the matrix, and the strength of the original fibers.
The composites of the present invention have a porosity of 10% or less, preferably 5% or less, most preferably 2% or less. At porosity of 10% or more, the composite has relatively low overall properties.

At porosity of 10% or more, stress concentration phenomena can lead to poor fatigue properties.

A porosity of 25% or greater would indicate that the alloy does not wet the fibers.

Preferred complexes of the invention have at least 105
A modulus of about 17,600 k9' to about 31,600 k9' is most preferred.

Further preferred composites have a flexural strength between 30 and 6 volume percent equal to or greater than the product of the fiber volume in % and 1.34 k9/secretion. . Thus, a composite containing 5 tsubo volume percent fibers will have a flexural strength of at least 67k9/Iso. Method of Manufacturing The composite matrix is manufactured from an aluminum alloy containing about 1-8%, preferably 2-5% IJ thium by weight of the alloy.

Composites with the best mechanical properties can be produced at suitable concentrations of IJ thiium and aluminum in the alloy melt and matrix. The composite structure is made of AI2, which is made by putting molten aluminum alloy into the metal.
Manufactured by infiltrating Q fibers.

A common method for infiltration is Dhing
a) in US Pat. No. 28,839. In this case, superior composites can be produced by impregnating alumina fibers with an aluminum alloy melt containing a small amount of lithium under appropriate conditions of heating temperature and time.

The fibers undergo a reaction with the glue in the alloy melt, which is believed to be responsible for wetting the fibers by the molten metal and good fiber-matrix bonding. This reaction forms a sheath around the fibers. At the minimum useful response, the sheath will not be visible to the naked eye in cross section. However, if any reaction occurs, no matter how small, the fiber surface becomes black or gray compared to the initial white color. Li
The presence of AI02 can be detected by X-ray analysis of fibers recovered from the composite. Therefore, although the sheath is not visible in cross-section, the fibers can be removed from the composite, for example by dissolving the matrix in a 20% aqueous hydrochloric acid solution, and the fact of reaction can be confirmed from the color change. . As the amount of reaction that occurs increases, the sheath on the fiber becomes progressively larger and more visible, while the unreacted core (obviously at the same time) becomes progressively smaller. When the sheath grows to about 20% of the fiber diameter, cracks or splits often occur. In extreme cases of reaction, the fiber core may crack into several parts. To preserve the useful strength of the fibers, the reactive sheath in the composite should be about 15% of the total diameter of the reacted fibers (including the sheath).
It must have a thickness less than %.

If the total diameter of the fiber including the reactive sheath is (d,), then
The thickness of the reactive sheath (t) is half the difference between d, and the diameter of the unreacted fiber core (d2), and the reactive sheath percentage is t/
d, (100). Therefore, reaction conditions must be adjusted so that no reaction bulk of 15% or more occurs. Since the amount of reaction that occurs increases with increasing temperature, increasing reaction time, and increasing concentration of lithium in the melt, the interaction between these factors must be carefully controlled. For example, lithium is a highly reactive metal, so as the concentration of IJ lithium in the alloy increases, the alloy melt becomes more reactive with the AI3Q fibers. Thus, impregnation of fibers with alloy melts having relatively high lithium concentrations needs to be carried out at lower temperatures or for shorter times than used in melts containing relatively low concentrations of lithium. becomes. Generally, composites with a reactive sheath thickness less than 15% of the total diameter of the fibers are approximately 1 to 1% by weight.
using a reaction time of less than about 18 minutes at a temperature in the range of 25 to 100 °C above the melting point of an aluminum alloy containing 8%, preferably 2 to 5% lithium,
can be manufactured.

Satisfactory composites can be produced at even shorter reaction times and lower temperatures if the alloy contains more than about 5% lithium. on the other hand,
Similar composites can be obtained using short reaction times at temperatures as much as 20 pio above the melting point of alloys containing 2-3% lithium by weight. Thus, the reaction time and concentration of lithium in the aluminum alloy melt can be reduced to 15% of the total cross-sectional diameter of the fibers on the fibers in the composite.
can be adjusted relative to each other as necessary to achieve a reactive sheath with a thinner thickness. The mechanism of composite production that must comply with the above conditions varies depending on the size of the composite to be produced.

A small composite (Example 1 herein) can be produced by manually inserting the fibers into a small single mold, while a larger composite (Example 3 herein) ) can be produced by inserting a preform of fibers in an organic polymer matrix into a mold, then heating it to remove the organic polymer, cooling and shaking it. For infiltration, a mold containing the fibers or a tube leading to the mold is inserted into a crucible containing the molten alloy.
Stainless steel molds and silicon carbide crucibles have been found to be convenient. Molten metal has a temperature of about 2 below its melting point.
The temperature can be as high as 5 to 200. As described in Example 1 herein, small molds can be inserted directly into the melt and brought to equilibrium, but the preferred method for larger molds is to This method involves preheating the mold before soaking the beans.

The longitudinal axis of the mold can vary from near horizontal to vertical during infiltration, depending on the length of the mold.

The use of a horizontal or near-horizontal position provides better mold temperature control and a lower pressure head of molten metal while reducing the likelihood of warping or bowing.
Penetration of the molten metal into the mold containing the fibers is accomplished by creating a pressure differential, either by applying a vacuum to the mold or applying pressure to the metal, or a combination of both. can do.

The pressure differential must be sufficient to overcome the resistance to flow created by the mold and fibers, as well as the pressure due to the head of molten metal. Excessive pressure can cause channeling in the mold. For producing alumina-aluminum composites, a pressure difference of about 140 to 980 degrees Fahrenheit is convenient. After the mold containing the fibers has been sufficiently infiltrated, it is removed from the molten metal and allowed to cool to room temperature.

The mold may remain as a coating or may be removed. The coated composite is suitable for subsequent rolling, forging, drawing, hydraulic extrusion or thermostatic pressing operations. The products of the present invention are useful in applications requiring light weight and high stiffness and strength, particularly as components in aircraft and missiles. These products are also useful in high temperature structural applications, such as in airplane engines and turbines. Concession and ring quasi-metallographic examination Cross-sections of the composite specimens were metallographically examined to estimate the completeness of penetration of the metal matrix between the alumina fibers and the degree of reaction between the fibers and the alloy matrix. inspect.

The specimen is mounted in a suitable resin such as phenol formaldehyde, epoxy or polyester and polished using a series of abrasive powders starting at about 100 grit and ending with 0.3 micron (r) diamond paste. In each example, metallographic examination of the polished cross-section at a magnification of 600× fiber-matrix anti-corrosion can be used to determine the reactive sheath, which has a distinct appearance from the unreacted core. , record the thickness of this reaction sheath in microns (French).

Samples that appear to have unreacted fibers are considered to have undergone a minimal amount of reaction with the matrix, and their fiber reaction sheath is recorded as "<0.5 French" in each example. . That a reaction is occurring can be confirmed by extracting the fibers from the composite and noting their black or gray color. Composite Product Date The porosity of the cross section is determined by examining the polished cross section described above at a magnification of approximately 6 degrees and estimating the area of the voids compared to the total area of the cross section.

Porosity is caused by imperfect composite manufacturing techniques and/or insufficient wetting of the fibers by the metal. Thus,
Porosity (%) is a useful quality control measure. The porosity was determined by vacuum-depositing aluminum on the polished cross-section, and then using a reflected light microscope and contimet (Q) to measure each cross-section.
uantimet) 720 instrument [M.Cole
), American Laboratory, June 1971. .

The cross section is analyzed by observing a number of separate and distinct fields of view that approximate the entire cross section. This measurement system has a diameter of 2
Operate under conditions to detect small voids the size of mountains. The voids are seen as black due to the relatively high reflectivity of the aluminum coated fibers and solid matrix. A single fiber was tested using an Instron tensile tester TM model.
．． Cut at a crosshead speed of 0.51 ribs per minute using gauge lengths of 64 and 25.4.

Tensile strength is determined from the gauge length of 0.64 arc. Modulus (Young) is obtained by plotting the reciprocal of the modulus (1/M) obtained at two gauge lengths against the reciprocal of the gauge length (1/G), and using the value of 1/M when 1/G is zero. It can be determined by calculating (extrapolating) the modulus reported by This method is performed to compensate for fiber slippage during testing. Similar results can be obtained with relatively shorter fibers, for example, by using gauge lengths of 0.64 and 2.5 arcs. Mechanical Properties of the Composite In addition to the metallographic examination of the composite as described above, the mechanical properties are another measure of the quality of the composite.

Mechanical properties such as flexural strength and modulus are indicators of the mechanical performance of composites, especially as structural materials. The strength, Okayama thickness, and fracture strain of the composite can be determined by a bending test. Bending strength, modulus and failure strain are in accordance with ASTM D-790-71 except that circular twills are used instead of rectangular twills.
Measure using the method.

Short beam break strength value is ASTM D-2344
-67 method can be used for composites containing randomly arranged fibers as well as aligned fibers.

Typically, the portion of the specimen that remains after measuring the bending strength is used for this test. Unless there are other concerns,
All values in each example are measured in the machine direction, ie on a bar or rod with longitudinally aligned fibers, at room temperature.

Analysis of MetalsThe alloys and the composites themselves were analyzed for metals by dissolving the matrix in a mixture of equal volumes of concentrated hydrochloric acid (35%) and water from approximately 0.2 $ samples of the composites. do.

The resulting solution is diluted to 100% with water and then analyzed using an atomic absorption spectrophotometer (Perkin-Elmer Model 503). The fibers in the composite do not appear to be attacked by acid. The properties obtained by the above tests and other detailed information about the composites are shown in the examples below, in which all parts and percentages are by weight, unless otherwise indicated. be.

All fibers in each example are made by the method generally outlined in US Patent No. 38,015. Example 1 A lithium-aluminum alloy was prepared as tl1
A silicon carbide crucible is heated to 700 qo in a furnace and sufficient flux (L
Add iCI:LiF (3:1 by weight), add 500 g of commercially available pure aluminum grains (99.5 Alcoa), melt, then add additional brooding agent to completely cover the aluminum, and A small piece of commercially available AL-Li alloy with a nominal 10% Li content (1.3 x 1.3 x 2.5 pieces)
was added, and the alloy piece was submerged and rubbed with a '5' stainless steel plate.

Fluxing agent was added to minimize lithium loss.
Addition of AI-Li alloy was repeated until 500 g of alloy had been added.

Analysis of the melt showed 3.9% lithium; the resulting alloy had a melting point of about 6370. Ninety-five continuous filaments of polycrystalline alumina (average diameter 23.3 ± 4.3 mm; nominal tensile strength SI 40-168 k9/ground, tensile modulus 35×
A 10-arc length thread containing IQk9/Palisade was used.

This filament contains approximately 0.2% Mg○, with the remainder being predominantly (>90%) N in the alpha form.
It is 203. These filaments are about 0.02~0
．． Coated with a layer of silica 2 Buddhas thick. These filaments were connected to a stainless steel tube with a length of 30.5 mm (diameter 0.6 mm).
It was packed tightly into one end of a 4-barrel, wall thickness 0.8 gw, to obtain a filling rate of about 6 vol. percent. These filaments were used to move the tube into a vertical comb-shaped vibrator [AG.
The tubes were kept in a perpendicular position to the EI type manufactured by C.M. Appa, Z.R.Mk) to separate and evenly distribute them over the inner diameter of the tube. The rise of the tube was connected by a Y-fitting and a flexible vacuum hose to a needle valve (closed) in series with a U-tube mercury vacuum gauge and a vacuum source. The lower portion of the tube containing the aligned filaments is placed below the surface of the flux and alloy melt at a temperature of 0 to 70 mm, and the tube and fibers are brought to the melting temperature by approximately 1. It lasted for a minute. The pressure in the mold was then changed from atmospheric to 60-70 degrees of mercury over a period of 2-4 minutes by slowly opening the valve. During this process, the melt entered the mold, formed into fibers, and immediately solidified in the mold above the level of the melt. The tube was immediately removed from the melt and allowed to cool. After removing the flux and alloy from the outer surface, the steel tube was mechanically removed and the remaining composite was ground into a 10 mm long bar with a diameter of 3.53 ± 0.3, avoiding the center. . The mechanical properties of the ground rods at room temperature are shown in Table 1 under item a.

The values in k9/rail obtained at 315°C and 4820 are as follows: bending strength and 73.8; modulus (Mi) 26700 and 232.
00: Short beam shear 9.8 and 4. Metallographic examination of polished cross-sections of the tow composites revealed little or no secondary phases in the matrix.

It appears that a "supersaturated" solid solution of lithium in the aluminum matrix did not occur. A sample of this composite was treated with an aqueous hydrochloric acid solution, the fibers were recovered from the acidic matrix solution, and the solution was analyzed for lithium. The analysis showed 1.9% IJ thium in the matrix compared to 3.9% in the melt used. It is believed that a significant amount of the initial lithium in the melt is in acid-proof form in the reaction envelope.
The recovered fibers were black rather than white, indicating that they had reacted with the lithium, and retained 83% or more of their original tensile strength. Example 2 This example item shows the effect of lithium content and infiltration temperature and time on an AI-Li/polycrystalline alumina fiber composite.

Various AI- Composites were prepared using Li synthesis.

The yarns of items a, b, f, g, k and q in Table 1 each have a diameter of about 23±4 French and contain about 99.8% AI203, primarily in the alpha form. It contained 95 continuous filaments of polycrystalline alumina and the remainder contained 210 continuous filaments. The fiber code in Table 1 indicates the nominal tensile strength of the starting filament as follows: AI26-141k
9/Match B 141-168k9'Iso B-2 1 spot. At fiber loadings ranging from 7 to 183k9', the highest possible bending strength for the composite is directly proportional to the strength and density of the starting fibers.

All fibers had a modulus of approximately 35,000 k9/h. All composites contained about 5 volume percent fiber, excluding items a (Example 1) and b containing about 6 volume percent fiber and item f containing about 55 volume percent. Item c kept in Yukina for 18 minutes after infiltration
, and the entire complex except for item h, which was kept in Yunaka for 5 minutes.
It was removed from the metal rack within 3 minutes. Items a, b, d, e,
f, h, k and q represent preferred products of the invention.

The extent of fiber reaction was minimal and the thickness of the fiber reaction sheath was less than about 2% of the total fiber diameter. A useful but less preferred class of composites includes items i, i, and item 1, which has a maximum fiber reactive sheath thickness of 3 peaks (about 13% of the total fiber diameter).

Items c and m contain 4 to 8 French (approximately 20% of the reacted fibers)
Comparative Example for a composite outside the scope of the present invention having a fiber reactive sheath of 17-33% of the diameter of 4 mm.

A comparison of the flexural properties of items c and d shows the window effect of the thick reactive sheath caused by too long exposure at 700°C. Item m has a porosity greater than 10% on average and exhibits the adverse effects of a higher than normal infiltration temperature (900 qo). The other two composites q and r were made from N-Li alloys containing about 4.8-5.5% IJ lithium in alumina fibers C and D (about 5% by volume), respectively. Produced in the same manner as item k.

Fiber C is a paper yarn mixture (which contains 60% final A in the fiber)
77% of the alpha-alumina particles (50% have an equivalent diameter of 0.2 to 5r) and 23% of the particles have a diameter of 0.005r to 0.07. U.S. Pat. No. 3,808,015 except that it consists of gamma alumina particles having
The fiber was polycrystalline alumina fiber (diameter approximately 23 mm) manufactured using the same machine as Example 8 of the No. 1 issue. Fiber D (approximately 23 threads in diameter)
Fiber C was prepared in the same manner as Fiber C, except that gamma alumina particles accounted for approximately 40% of the solid particles in the binding mixture. Fibers C and D were used in the form of threads containing 9 $ continuous filaments. The silica-coated filament of this example contains about 0.19 to 1.9% S, corresponding to a silica coating thickness of about 0.02 to 0.2 um for a 23A diameter starting filament.
Contains j02.

Table 1 Example 3 Using the preforming method of Example 1 of the United States Patent No. 2-8Y for Dhjnra, approximately 2.
9 continuous filaments of polycrystalline alumina containing about 99.8% AI 3 in the alpha form (more than 90%) with a diameter of 3r (nominal tensile strength 105-126k9/pine; Tensile modulus 35×1 pik
9/fence), wind the thread on the mandrel,
5 of polyethyl allylate in methyl ethyl ketone
% solution was applied to the yarn layer, dried in air for about 5 minutes, and taped by drying the winding and application.

The tape was removed from the mandrel, cut and compressed to fit a prefabricated rectangular mold. The stainless steel mold has a 12.7 x 8.9 x 1.27 inner diameter and has a tube attached to one edge of the 8.9 arc and the other 8.9 arc. The rim was open. The polyethyl acrylate was removed by heating the filled mold to 600 qC while sucking the air therein. The fibers in the mold were washed with acetone, dried, and then vibrated. The fibers in the mold were impregnated with an AI-Li alloy containing 4.9% Li and having a melting point of about 630°C for about 5 minutes at 710:00.

The mold was removed by machining and the composite containing 4 percent fiber by volume was divided into two pieces 0.48 mm thick;
It was polished to a thickness of 0.318mm. The composite contains 2.2% lithium in the matrix, and the fiber reaction sheath has a thickness of 2.5 µm (approximately 11% of the total fiber diameter) and a porosity of 2%. Was. The lateral strength and modulus of specimens cut from the above specimens are as follows: For example, AI/B, Mg/AI2
Given that other metal/fiber composite systems, such as Q and AI/C, show a significant decrease in properties at 315q C, it is reasonable to assume that this composite retains these lateral properties at 315qo. was unexpected.

Other specimens taken from the same composite showed k9 at room temperature.
The ground unit had the following average longitudinal bending properties: strength 50, modulus 18200 and short beam shear 7.7.

The lower strength compared to Example 1 is due to the fiber filling ratio (approximately 4
%), due to the use of relatively weak starting fibers and a relatively large degree of fiber reaction. Example 4 30% alpha-alumina particles, 41.3% solid aluminum chlorohydroxide [AI2(OH)5CI.2
．． A mixture of 0.6% M, 2.2% concentrated hydrochloric acid, and 258% water was prepared and concentrated by removal of water to about 800 poise at 3 and 0. The paper yarn dope had a viscosity of .

The spinning dope is extruded from a paper spinneret into a heated spinning tube, and the precursor fibers are transported by two feed rolls to
It can move forward at a speed of 74 m/min and crush it.
Wound onto a fireproof bobbin. The bobbin was stored in a room at 10% relative humidity until firing. Place the bobbin in a cold oven and then heat it to 550 qo for 2 hours.
The mixture was heated to a temperature of 45 minutes, and then allowed to cool. The thread was then passed vertically downward through a chimney equipped with a ring burner with a propane-oxygen flame at a rate of 18.3 h/min to a temperature of approximately 1555° C., measured by an optical pyrometer without correction for emissivity. Firing was performed at the apparent yarn temperature. This temperature was above the temperature at which the fibers exhibited maximum strength. This thread will be referred to as (F) below. A second yarn (E below) is spun from the same paper yarn mixture on a different day in a slightly different chimney with a propane-oxygen ratio adjusted to give near maximum tensile strength of the fibers. was produced in the same manner.

It is estimated that such firing conditions in the firing apparatus used for yarn E' produced an apparent yarn temperature of about 1500 to 1530 hours. A comparison of the two yarns is as follows: Both yarns were then treated to provide a 0.02 to 0.05 mm thick coating of silica on their fibers.

Using the method of Example 1, a lithium-aluminum alloy was produced using pure lithium (99.% pseudo).

Using the method described in Example 1, from yarns E and F,
Composites (s and t) were prepared, respectively. Details of product characteristics and test pay are shown in Table 2. Both composites contained 6 volume percent fiber. Approximately 18%
The fibers recovered from the composite (black) after dissolving the matrix in acid of 100% had a tensile strength of 70 and 1000% of the starting fibers for items s and t, respectively.

Thus, the starting fibers of item t, which were more delicate, gave stronger composites than item s, despite having a lower initial tensile strength. For comparison in Table 2, the translucency values for the fibers used to manufacture items a, b, c, d, g and i in Table 1 are 5.1 and 5.1, respectively. ,2.2,2.2,5
．． They were 0 and 2.7.

Example 5 Polycrystalline alumina (tensile strength 154±13k9/
A thread containing 210 continuous filaments (average diameter 23〃) of 99% AI203 was cut to approximately 3.1 skin length and placed in a stainless steel mold (14.6 x 7.0 x 1 ．．
27) It fell inside.

The mold is closed except in the center where it is welded to a tube with an outside diameter of 6.3 ribs - the two narrow sides (1.2
7×7. The opposite narrow side was open. After adding a layer of fibers on each side 6.3 and 1.1
Gently pack this fiber using a full stick. This quiet filling is performed on virtually one side (1.27 x 7.0
This resulted in a filling of fibers arranged randomly in the plane (parallel to the side of the cathedral). The final loading of fibers was 2 volume percent and sufficiently packed so that the fibers did not fall out when the mold was inverted for infiltration. The fibers in the mold were impregnated with an aluminum alloy containing about 4.0% lithium (melting point about 0°C) at a total temperature of 0-700°C. After the mold was removed by machining, specimens were cut from the composite plate with a parallel plane on the 1.27×7.0 arc side. The dimensions of the final composite specimen after final polishing are 0.318 x 1.14 x 6.8 x 1
．． It had a surface containing randomly arranged fibers parallel to the sides of a 14 x 6.86 arc. The composite contained 3.7% lithium in the matrix, the fiber reaction sheath had an average thickness of lr, and had a porosity of about 5%. The average tensile strength and modulus flexural properties of the specimens at room temperature are 12.2 and 8.8×, respectively.
IQk was 9/. Due to the random fiber arrangement on one side, the strength of the composite is given by: OC=.

M(1-VF-VP)+1/3FVF where:. C=
Strength strain of the composite M = flow stress of the aluminum matrix at fiber cutting strain Vp = fiber volume fraction VP = volume fraction of porosity.

F = As-cast AI-4% by weight comparable to fiber strength
The flow stress (〇M) of Li was 4.36k9/m.

The calculated composite strength was: 13.524
．． 36 (1-0.20-0.05) 11/3 (154)
0.20 A mixture of over 90% of theory was thus obtained.

The measured modulus build-up is the same for the unreinforced alloy (720
This shows an improvement in stiffness of about 23% compared to 0k9/masu). Other specimens taken from the same composite had the following room temperature flat flexural strength properties: strength 29k9/
Pine and short beam shear 3.3k9/fence.

The lower strength compared to Example 1 is due to the relatively low volume filling factor (2 eave volume percent) and random arrangement of the fibers. Another specimen taken from the same composite had the following average bending properties in k9/Iso units, measured at 316°C: strength 32, modulus 5900 and short pea shear 4. & high quality A
It should be noted that I-Li alloys cannot be manufactured in substantially the same manner as most conventional aluminum alloys, because lithium is much more sensitive than aluminum. It has a lower density, a much lower melting point, a high vapor pressure, and oxidizes even at room temperature.

It is therefore desirable to first melt the aluminum and to soak the lithium into the pool of molten aluminum. Such a method reduces loss of lithium due to sublimation. High-quality alloys (i.e., those containing no oxides) can be prepared under an inert atmosphere, such as argon (a nitrogen atmosphere is not preferred as lithium nitride is formed at room temperature), or by suitable melting on a molten metal surface. can be manufactured by using a protective layer of agent. The use of a flux such as LiCI:LiF in a ratio of 3:1 by weight is preferred as it is an economical way to prevent oxidation and sublimation of the lithium. Another substantial advantage of the method of using a flux compared to the use of an inert atmosphere is that the flux forming on the surface of the melt can be skimmed off and the flux layer replenished as needed. This means that the alloy can be manufactured using more practical casting techniques.
After producing high quality AI-Li gold and cooling it to room temperature, a high quality melt can be obtained by reheating the alloy with a protective layer of enemy agent. Although the foregoing description is for illustrative purposes only, and the invention has been described in considerable detail herein, those skilled in the art will appreciate that changes may be made thereto without departing from the spirit and scope of the invention. You should understand that you may be able to do so.

Claims (1)

[Claims] 1. An aluminum alloy matrix reinforced with 15 to 70% by volume of polycrystalline alumina fibers and containing 0.5 to 5.5% by weight of lithium, with the remainder being aluminum and impurities. An aluminum composite of good bending strength, in which the fibers have a reactive sheath thickness of less than 15% of the total fiber diameter and the composite has a porosity of less than 10%. 2 Polycrystalline alumina fibers are placed in a mold and molded with a molten aluminum alloy containing 1 to 8% by weight lithium for a time sufficient to cause the fibers to form a reactive sheath with a thickness of less than 15% of the total fiber diameter. 15 by infiltrating the fibers of
reinforced with ~70% by volume of said fibers, containing 0.5-5.5% by weight of lithium, the remainder being aluminum and impurities, and having an aluminum alloy matrix of 10% by volume.
A method for making an aluminum composite reinforced with alumina fibers and having good bending strength, comprising the steps of forming a composite having a porosity of less than % and cooling the composite.