JPH03274234A - Manufacture of aluminum series metal matrix composite and its manufacture - Google Patents

Abstract

PURPOSE:To satisfactorily show a reinforcing effect by whiskers ion a composite by forcing a molten metal into a preform obtd. by coating aluminum borate whiskers with spinel. CONSTITUTION:Al borate whiskers shown by 9Al2O3.2B2O3 or 2Al2O3.B2O3 are coated with spinel. The molten metal of Al (alloy) is poured on the preform of these whiskers and are infiltrated into the voids of this preform. Thus, the composite in which a reinforcing effect by the whiskers are satisfactorily shown can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for strengthening aluminum borate whiskers.

[Conventional technology]

Among metal materials, argonium and argonium alloys are
Due to its small specific gravity, easy processing, and low price, it is used in aircraft, automobiles,
It is used for various purposes as a building material.

Recently, in order to improve the mechanical properties of these aluminum metals, whiskers or short fibers of silicon carbide, silicon nitride, carbon, alumina, potassium hexatitanate, etc., which have high strength and high elasticity, have been used as reinforcing materials. Development efforts are actively underway to combine these materials with metals.

Among these, potassium hexatitanate whiskers are unsuitable as reinforcing materials because they react with molten aluminum. 9^1.0.・Aluminum borate whiskers represented by 2B2O3 can be synthesized by a liquid phase method using a melting agent, so the manufacturing cost is lower than that of silicon carbide and silicon nitride, which can only be synthesized by a gas phase method.Aluminum borate whiskers, represented by 2B2O3, can be synthesized by a liquid phase method using a melting agent. Since it is stable against Al≧Nium metals, it is suitable as a reinforcing material for aluminum-based metals.

[Problem to be solved by the invention]

However, aluminum borate whiskers have an alumina component of 9^120.・87% for 2B2O3, 2
In the case of A1gOs・Bias, it has 75%, but the remaining 820. Because the components are likely to react during compounding,
In particular, problems arise when an aluminum alloy containing magnesium is used as a matrix.

That is, BtOs and magnesium react to form boron and magnesium oxide, and the latter reacts with the alumina component in the whisker or alumina produced when aluminum metal is oxidized during compounding to form spinel (MgAl□
04) is formed.

Since this spinel formation is in a small amount, it does not interfere with basic strength development, but the magnesium metal that is originally added to aluminum metal to improve hardness disappears, and the expected hardness is not achieved. The problem is that it cannot be done.

The compounding method most suitable for industrialization is the molten metal forging method. This is a method in which a preformed body is formed using whiskers, and molten aluminum is press-fitted into this preformed body. The preform is usually formed by first dispersing the whiskers in water or the like in which several percent of an organic binder such as polyvinyl alcohol and an inorganic binder such as silica sol are dissolved or dispersed, filtering or concentrating the dispersion, and then applying pressure. The organic binder is added to improve the moldability, and the inorganic binder is added to the obtained preformed body to give it sufficient strength for press-fitting aluminum by heating and baking it. Organic binders disappear when the preform is fired, so there is no problem at all, but inorganic binders are mainly silica-based, so as mentioned above, in the case of aluminum alloys containing magnesium, The reality is that during compositing, an oxidation-reduction reaction occurs to produce spinel, causing the problem that magnesium disappears from the matrix alloy phase.

The method of the present invention solves these problems by using aluminum borate ξ
The present invention provides a method for manufacturing a metal matrix composite material reinforced with aluminum whiskers.

[Means to solve the problem]

In view of these circumstances, the inventors of the present invention have carried out extensive research and testing, and have found that by coating the surface of aluminum borate whiskers with spinel, which is stable against molten aluminum and magnesium, and using this as a reinforcing material, these The present invention has been completed by discovering a solution to the above problem.

According to the present invention, the aluminum borate whisker used as a raw material may be obtained by an already known manufacturing method, and its particle size is not restricted, but usually the fiber diameter is 0.1 to 10 μm, A fiber length in the range of 5 to 500 μm is suitable.

As a method for coating the surface of aluminum borate whiskers with spinel, for example, (1) a method in which a precipitate of aluminum and magnesium hydroxides is deposited on the surface, and this is fired to form an oxide. ■A method in which aluminum and magnesium oxide precursors are coated and fired using the sol-gel method.

(2) There are methods such as the so-called PVD method and CVD method, in which metal aluminum and magnesium are vapor-deposited and oxidized, or metal aluminum and magnesium compounds are decomposed in an oxidizing atmosphere.

Among these methods, method (2) is the easiest. Specifically, first, water-soluble aluminum and magnesium salts are added to the stoichiometric amount of spinel, that is, aluminum/magnesium = 2.
/1 (mole ratio) Prepare a slurry in which aluminum borate whiskers are uniformly dispersed in dissolved water. Corresponding salts include aluminum chloride, aluminum sulfate, aluminum nitrate, magnesium chloride, magnesium sulfate, magnesium nitrate, and the like. Furthermore, even water-insoluble materials such as aluminum hydroxide and magnesium hydroxide can be used because they can be dissolved by lowering the p i+ with hydrochloric acid or the like. The ratio of these raw materials to the argonium borate whiskers is related to the thickness of the coating film, but the weight of the spinel produced is 1 to 30%, preferably 3 to 1
It is appropriate to set it to 0%.

While thoroughly stirring the prepared slurry, an ammonia aqueous solution was added dropwise to gradually raise the pH.
Aluminum hydroxide precipitates in the vicinity, followed by magnesium hydroxide precipitates around pH=9. If the ammonia aqueous solution is subsequently added dropwise, the aluminum hydroxide will be redissolved, so the dropping should be stopped at a pH of 11 or less, preferably 1O or less.In order to improve the bottom formability of the subsequently preformed product, polyvinyl alcohol, etc. An aqueous organic binder solution is added at this point, but this is not an essential requirement in the present invention.

The slurry prepared as described above is filtered or press-molded as it is or after being concentrated to form a preform.

Next, in order to remove the water contained in the preform,
After drying at 200'C, it is heated in the air to 700-1200C, preferably 800-1100C. As a result, the aluminum and magnesium hydroxides deposited on the whiskers turn into oxides, and then into a composite oxide to form the desired spinel coating film. At this time, the spinel of the coating film also plays the role of a binder that aggregates the whiskers together, and the obtained preform has mechanical strength that can withstand press-fitting of molten metal. This point is also a major feature of the method of the present invention.

When the pre-molded body was observed with a scanning electron microscope, it was confirmed that the whisker surface was covered with particles,
In addition, a uniform distribution of magnesium on the whisker surface was observed by micro X-ray analysis, and formation of a spinel phase was confirmed by X49 diffraction analysis.

In addition to this method, the solid content is once recovered from the neutralized slurry using a filter or centrifugal separator, and spinel-coated whiskers are obtained by drying and heat treatment. It is also possible to form a pre-molded body by adding an inorganic binder. In this case, heat treatment at 800 to 1100°C is required to degrease the organic binder and remove the amorphous binder from the bottom.

In addition, among the above operations, an ammonia aqueous solution is most suitable as the alkaline aqueous solution used for neutralization. Since the salts produced by this neutralization are ammonium chloride, ammonium nitrate, and ammonium sulfate, they are easily decomposed or sublimed by the heat treatment performed later and removed from the coating film.

If sodium hydroxide or potassium hydroxide aqueous solution is used as the neutralizing liquid, sufficient washing is required when separating solids.
It is necessary to first use a buffer solution and then wash with water so that the pH does not change significantly during washing.

The whisker preform thus completed is assembled into a mold designed to have a predetermined shape, a predetermined amount of molten aluminum or aluminum alloy is poured into the mold, and the molten metal is poured into the voids of the whisker preform by applying pressure with the upper punch. Let it penetrate. The pressure for penetrating the molten metal is 300~2.
000 kg/cd, and the mold temperature is 20
0~500℃, molten metal temperature is 700~900''C1, and the temperature of the preform should be about the same as the molten metal temperature.If the mold temperature is raised too much, the solidification rate of the molten metal will be slow and the performance will not be good. It can be done, but the productivity will decrease.On the other hand, if the mold temperature is low, the preform and molten metal will solidify quickly and penetration will be insufficient.For the same reason, the preform should also be preheated sufficiently. It is necessary.

As aluminum and its alloys used in carrying out the present invention, advanced materials and cast materials specified by JIS are suitable.

These composite materials can be used as final parts by undergoing heat treatment specified by JIS, hot extrusion using a die, or machining.

As a result of X-ray diffraction and scanning electron microscopy observations of the aluminum straw composite material produced as described above, aluminum borate whiskers did not react at all with the matrix aluminum and aluminum alloys, especially aluminum alloys containing magnesium. I found out that I didn't.

Then, a test piece was cut out and its mechanical strength was measured. As a result, it was confirmed that the reinforcing effect of the whiskers was sufficiently exerted.

〔Example〕

Hereinafter, the present invention will be specifically explained using Examples and Comparative Examples.

Example 1 67.9 g of aluminum chloride hexahydrate and 28.6 g of magnesium chloride hexahydrate are dissolved in 51 g of water. Among these, 9AI
, 400 g of 2B2O3 whiskers ("Arborex G" manufactured by Shikoku Kasei Kogyo ■) are added and sufficiently dispersed with a stirrer to prepare a uniform slurry. A pH meter is set in this slurry, and an ammonia aqueous solution having a concentration of 25 to 28% is added dropwise to the slurry while stirring. Through this operation, dissolved aluminum ions and magnesium ions precipitate and deposit on the whiskers as fine hydroxides. When the pH reaches 9, the dropwise addition is terminated and only stirring is continued for 10 minutes. Next, add 1 portion of polyvinyl alcohol adjusted to a concentration of 5% in advance.
00 cc was added and stirring was continued for an additional 10 minutes.

Next, set the filter paper in a Nutsche with an inner diameter of 10 cm and a height of 2.
An Oc- vinyl chloride cylinder is placed, and the slurry prepared above is appropriately poured into the cylinder, followed by suction filtration. After the entire slurry has been filtered, the cylinder containing the solid content is removed from the Nutsche and compressed with a vinyl chloride piston until the content reaches a height of 8C111 to form a whisker molded body. The demolded preform is dried at 150° C. for 2 hours and further heated at 900° C. for 2 hours to degrease the polyvinyl alcohol and convert the hydroxide on the whisker surface into spinel. At this time, the whisker volume fraction (V
) is approximately 20%, and since the spinel acts as a binder, a preformed body with high mechanical strength can be obtained. When a part of this molded body was observed with a scanning electron microscope, it was found that aluminum borate It was confirmed that fine particles adhered to the whisker surface to form a uniform coating film. Also, micro X-ray analysis confirmed a uniform distribution of magnesium on the whisker surface, and X-ray diffraction revealed that the spinel Formation of a phase was confirmed.

Next, the preform preheated at 800°C was placed in the center of the bottom of a cylindrical mold with an inner diameter of 12C11 kept at 300'C, and an aluminum extensible JIS A6061 alloy melted at 800'C was poured into the mold. After boiling, the molten aluminum alloy was quickly pressurized with the upper piston of the mold to penetrate into the preform.The pressure at this time was 800 kg/cm2, and within about 1 minute, the molten metal finished penetrating and solidified. ,
The mold was demolded to obtain a composite material.

The composite material thus obtained was cut into semi-cylindrical shapes, and the size of the magnesium-deficient portion was measured.

Normally, there is an abnormal segregation area due to magnesilium deficiency at the final injection site of the molten metal, but in this example, no such area was observed. In addition, the Brinell hardness of the T6-treated composite material under a 1000 kg load is 200 kg/
am'', and a sufficient improvement in hardness was confirmed.

Comparative Example 1 Aluminum borate whisker 40 used in Example 1
0g was added to 5N water in which 5g of polyvinyl alcohol had been dissolved in advance, and sufficiently dispersed with a stirrer to prepare a uniform slurry. This was filtered, molded and degreased in the same manner as in Example 1 to produce a whisker preform, and then treated in the same manner using an expanded argonium JIS^6061 alloy to obtain a composite material.

At the center of this composite material cut into a semi-cylindrical shape, a magnesium deficient area as shown in Figure A was observed. As a result of measuring the Brinell hardness under a load of 1000 kg after T6 treatment, the non-magnesium-deficient part was 190 kg/m-, while the magnesium-deficient part was 170 kg/m1, showing a large difference. Moreover, this value was lower than the value of Example 1 even in the non-deficient area.

Example 2 After dispersing 44 g of aluminum hydroxide and 16 g of magnesium hydroxide in water 51, hydrochloric acid was added to dissolve them all. In this, the fiber diameter is about 2 μrn, the fiber length is 20 to 5
0μm 9AhO+' 28203 Whisker 40
Add 0g and thoroughly disperse with a stirrer to prepare a uniform slurry. A p I-1 meter was placed in the slurry, and a 10% aqueous sodium hydroxide solution was added dropwise while stirring. p) When 1 becomes 10, dropwise addition is completed and only stirring is performed for 10 minutes. Next, a vinyl chloride cylinder with an inner diameter of 10 cm and a height of 20 cm was placed in the Shitanuche, where the filter paper was set, and the slurry adjusted above was appropriately poured into the cylinder to perform suction filtration. After completing the filtration of all slurry,
Chlorine ions and sodium ions are removed by washing with an NH40H-NH4C1 buffer solution having a pH of 1O.

Below, the bottom molding, drying, and firing were carried out in the same manner as in Example 1, and as a result of compounding using aluminum casting alloy AC7^, no magnesium-deficient portion was generated.

Example 3 After dissolving 53 g of aluminum nitrate≧nium nonahydrate and 18 g of magnesium nitrate hexahydrate in 51 water, the fiber diameter was approximately 0.
．． 5#m, fiber length 10-20μm 2A110m・B
Add 400 g of zO and whiskers and thoroughly disperse with a stirrer to prepare a uniform slurry. A pH meter is set on this slurry, and while stirring, an ammonia aqueous solution is added dropwise in accordance with Example 1 to deposit hydroxide on the whisker surface.

After that, as in Example 1, addition of a polyvinyl alcohol aqueous solution, filtration, bottom molding, drying, and firing were performed, and as a result of composite formation using aluminum casting alloy ACD5, no magnesium-deficient portion was generated.

Example 4 17.0 g of aluminum chloride hexahydrate and 7.2 g of magnesium chloride hexahydrate are dissolved in water 11. 200 g of the same whiskers used in Example 1 were added into this mixture and thoroughly dispersed with a stirrer to prepare a uniform slurry. Set a pH meter on this slurry, and while stirring,
An ammonia aqueous solution having a concentration of ~28% is dropped to precipitate and deposit aluminum ions and magnesium ions as fine hydroxides on the whiskers. When the pH reaches 9.75, the dropwise addition is completed and only stirring is continued for 10 minutes. The solid content is collected from this slurry using a centrifuge, dried, and then heated at 1000°C for 4 hours to form spinel on the whisker surface.

The treated whiskers are dispersed in 11 water in which 5 g of polyvinyl alcohol and 4 cc of 30% aqueous silica sol are dissolved in advance, and stirred for 20 minutes while irradiating with ultrasonic waves to prepare a uniformly dispersed slurry. Next, this was concentrated to a moisture content of about 10%, the contents were taken out, and placed in a cylindrical vinyl chloride mold with an inner diameter of IQ cm.
The contents were compressed with a vinyl chloride piston until the height of the contents reached 2 cm to produce short fiber OI shapes. The demolded preform was dried at 150°C for 2 hours and further dried at 800°C.
Heat at C for 1 hour to burn off the polyvinyl alcohol,
Furthermore, the silica sol is gelled and sintered to obtain a preformed body with high mechanical strength. At this time, the whisker volume fraction (Vf
) is approximately 20%.

Subsequently, in the same manner as in Example 1, the matrix alloy was composited with aluminum expanded material JIS A2014, subjected to T4 heat treatment, and then hot extruded at 500'C to form a wire rod with a diameter of 12. The tensile strength of this composite material is 44
kg/am", the Young's modulus is 8.7 ton/s-, and the tensile strength of the aluminum extensible material without whiskers is 37 kg10hm2, and the Young's modulus is 7.
．． 5 ton/am'', and it was confirmed that the reinforcing effect was sufficiently exhibited.

〔Effect of the invention〕

According to the method of the present invention, it is possible to obtain a metal matrix composite material using relatively inexpensive aluminum borate whiskers that have excellent affinity with aluminum metal and do not react with aluminum.

[Brief explanation of drawings]

The drawing shows a cross-sectional state of a composite material shown in a comparative example of the method of the present invention, and A in the drawing shows an abnormal segregation area due to magnesium deficiency.

Claims (4)

[Claims] (1) As a reinforcing material, the surface has the chemical formula MgAl_2O_4
1. A method for producing an aluminum-based metal matrix composite material, the method comprising using aluminum borate whiskers coated with spinel. (2) The method for producing an aluminum-based metal matrix composite material according to claim (1), using aluminum borate whiskers represented by the formula 9Al_2O_3.2B_2O_3. (3) The method for producing an aluminum-based metal matrix composite material according to claim (1), using aluminum borate whiskers represented by the formula 2Al_2O_3·B_2O_3. (4) The method for producing an aluminum-based metal matrix composite material according to claim (1), characterized in that molten metal is press-fitted into the whisker preform.