JPH0587575B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an aluminum-based metal matrix composite material using alumina-based short fibers as a reinforcing material. [Prior Art] Among metal materials, aluminum and aluminum alloys have a low specific gravity, are easy to process, and are inexpensive, so they are used in various applications including aircraft, automobiles, and building materials. Recently, in order to improve the mechanical properties of these aluminum-based metals, silicon carbide, silicon nitride, carbon, alumina-based metals, which have high strength and high elasticity,
BACKGROUND ART Developments are actively underway to combine short fibers such as potassium hexatitanate with metals as reinforcing materials. Among these, potassium hexatitanate short fibers are not suitable as a reinforcing material because they react with molten aluminum. Aluminum borate short fibers represented by 9Al ₂ O ₃・2B ₂ O ₃ 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. Since it contains a large amount of alumina and is stable against molten aluminum metal, it is suitable as a reinforcing material for aluminum-based metals. [Problem to be solved by the invention] However, although aluminum borate short fibers have an alumina component of 87%, the remaining
Since the B ₂ O ₃ component reacts during compositing, problems arise especially when an aluminum alloy containing magnesium is used as a matrix. That is, the B ₂ O ₃ component and magnesium react to form boron and magnesium oxide, and the latter reacts with the alumina component in short fibers or alumina produced by oxidation of aluminum metal when composited, producing spinel. do. 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 reduced. The problem is that it cannot be obtained. The compounding method most suitable for industrialization is the molten metal forging method. This is a method in which a preformed body of short fibers is prepared and molten aluminum is press-fitted into it. The preform is usually produced by dispersing short fibers 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 mixture, and then applying pressure. The organic binder is added in order to improve moldability, and the inorganic binder is added in order to heat and sinter the obtained preform to give it sufficient strength to withstand press-fitting of aluminum. However, 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, When compounded, an oxidation-reduction reaction occurs to produce spinel, causing a problem in which magnesium disappears from the matrix alloy phase. The method of the present invention provides an alumina-based short fiber-reinforced metal matrix composite material that solves these problems and a method for producing the same. [Means for Solving the Problems] In view of the above circumstances, the inventors of the present invention have conducted intensive research and testing, and have found that aluminum borate short fibers having a composition of 9Al ₂ O ₃ and 2B ₂ O ₃ are The alumina-based short fibers with a high alumina component, which are heated to 1600℃ and the B ₂ O ₃ component is volatilized, retain the same shape as the raw material aluminum borate short fibers and have the formula 9Al ₂ O ₃ .
It can be converted _into alumina-based short fibers having the _composition represented by The present invention has been completed by discovering that the intended purpose can be achieved in some cases. According to the invention, used as raw material
Short fibers with a composition of 9Al ₂ O ₃・2B ₂ O ₃ can be obtained by already known manufacturing methods, and short fibers such as 2Al ₂ O ₃・B ₂ O ₃ can also be obtained during heating. B ₂ O ₃ evaporates and 9Al ₂ O ₃ .2B ₂ O ₃ is produced, which can be used as a raw material. The alumina-based short fibers used in the present invention produced by heating are the same as the raw material aluminum borate short fibers, and preferably have a fiber diameter of 0.1 to 10 μm and a fiber length of 1 to 500 μm. To specifically explain the embodiment of the present invention, after adding and dispersing raw short fibers in water or an organic solvent containing several percent of an organic binder to form a slurry,
After suction filtration or concentration, pressure is applied to form a preform, which is then heated in the atmosphere at approximately 800°C to degrease the organic binder that becomes an obstacle during compounding.
1200~1200 to volatilize _{the B2O3}
Heat at a temperature of 1800℃ for 30 minutes to 8 hours. By changing these heat treatment conditions, it is possible to change the Al ₂ O ₃ /B ₂ O ₃ ratio in the short fibers. That is, the higher the temperature and the longer the heating time, the higher the alumina content. In this heat treatment, heating under reduced pressure or vacuum allows the heating temperature to be lower than that in the air. The short fibers in the preform thus obtained have almost no difference in shape from the raw material aluminum borate short fibers. The decrease in weight caused by heating was determined by the atomic absorption spectrophotometry of the obtained alumina short fibers.
Based on the measurement results of the molar ratio of B ₂ O, it was recognized that this was due to the volatilization of ₃ minutes of B 2 O. Furthermore, according to the results of X-ray diffraction, the obtained alumina-based short fibers have a diffraction pattern of 9Al ₂ O ₃ 2B ₂ O ₃ and α-alumina, but electron diffraction shows that only one short fiber Since the existence of both can be confirmed from
The center of the fiber from the volatile point of B ₂ O ₃ min is
It can be assumed that the surface layer of 9Al ₂ O ₃ .2B ₂ O ₃ is α-aluminated, and it is possible to control the ratio of both by changing the heating conditions. The preformed body obtained in this way is heated to approximately 800°C.
The mold is preheated to 200 to 500℃ and immediately infiltrated with molten aluminum or aluminum alloy at a pressure of 300 to 2000 kgf/cm ² to form the desired aluminum-based metal matrix composite. material can be obtained. The above method involves making a preform of aluminum borate short fibers with a composition of 9Al ₂ O ₃ 2B ₂ O ₃ and then converting them into short fibers with a high alumina content. When used, the problem of magnesium disappearing during compounding does not occur, so inorganic and organic binders are added to alumina-based short fibers with a high alumina content obtained by heat treatment under the above-mentioned conditions, and the above-mentioned method is used. It is also possible to form a preform according to. The present invention will be specifically explained below using Examples and Comparative Examples. Example 1 The composition formula with a fiber diameter of approximately 1 μm and a fiber length of 10 to 30 μm is
Aluminum borate short fibers represented by 9Al ₂ O ₃ and 2B ₂ O ₃ (product name: “Alborex G”, Shikoku Kasei Kogyo Co., Ltd.)
Co., Ltd., is dispersed in water in which 20 g of polyvinyl alcohol has been dissolved in advance, and stirred for 20 minutes while irradiating ultrasonic waves to prepare a uniformly dispersed slurry. Next, this is concentrated to about 10% water content, the contents are taken out, placed in a cylinder-shaped vinyl chloride mold with an inner diameter of 10 cm, and compressed with a vinyl chloride piston until the height of the contents reaches 8 cm. Make a fiber preform. The demolded preform is dried at 150°C for 2 hours, and further heated at 800°C for 1 hour to burn off the polyvinyl alcohol. The short fiber volume fraction (Vf) at this point is
It is about 20%. The above preformed body is heat-treated under the conditions shown in the following table to volatilize and remove the B ₂ O ₃ component and sinter, converting it into a preformed body with high mechanical strength and high alumina content. The short fibers in the preform thus obtained had almost no difference in shape from the raw aluminum borate short fibers. Next, the preformed body preheated at 800°C was placed in the center of the bottom of a cylindrical mold with an inner diameter of 12cm kept at 300°C, and the aluminum extensible material (JIS A6061 alloy) melted at 800°C was poured into the mold. Then, quickly apply pressure with the piston at the top of the mold to infiltrate the molten aluminum alloy into the preform. The pressure at this time is 800
Kg/cm ² , and the molten metal finished penetrating and solidified within about 1 minute, so it was removed from the mold to obtain a composite material. The composite thus obtained was cut into semi-cylindrical shapes, and the size of the magnesium deficient area was measured. In normal compounding, an abnormal segregation area due to magnesium deficiency exists at the final injection site of the molten metal, but in this example, the abnormal segregation area due to magnesium deficiency was significantly reduced or completely disappeared.

[Table] Example 2 The composition formula for fiber diameter of approximately 2 μm and fiber length of 20 to 60 μm is
Using aluminum borate short fibers represented by 9Al ₂ O ₃ and _{2B 2} O ₃ , slurry preparation, molding, and degreasing of the binder were performed in the same manner as in Example ₁ . A preformed body in which short alumina fibers having a composition of Al ₂ O ₃ /B ₂ O ₃ =9:0.5 was self-sintered was formed by heat treatment at a temperature of 4 hours. The weight reduction rate at this time was 9.2%, and the original short fiber shape was maintained. When this heat-treated preform was composited using JIS A6061 alloy in the same manner as in Example 1, there was no magnesium-deficient phase. Example 3 The composition formula with a fiber diameter of approximately 0.5 μm and a fiber length of 10 to 20 μm is
Using aluminum borate short fibers represented by 2Al ₂ O ₃・B ₂ O ₃ , slurry preparation, molding, and binder degreasing were carried out in the same manner as in Example 1, and then the temperature was heated to 1600 °C to volatilize B ₂ O ₃ . A preformed body in which short alumina fibers having a composition of Al ₂ O ₃ /B ₂ O ₃ =9:0.5 was self-sintered was produced.
The weight reduction rate at this time was 22.6%, and the original short fiber shape was maintained. When this heat-treated preform was composited using JIS A6061 alloy in the same manner as in Example 1, there was no magnesium-deficient phase. Example 4 Using the same aluminum borate short fibers as in Example 1, 100g of it was placed in a crucible and heated at a temperature of 1500°C.
By heating for a period of time, short alumina fibers having a composition of Al ₂ O ₃ /B ₂ O ₃ =9:0.2 are obtained. These short fibers are dispersed in 1 water in which 5 g of polyvinyl alcohol and 4 c.c. of a 30% aqueous solution of 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 about 10% water content, the contents were taken out, placed in a cylindrical vinyl chloride mold with an inner diameter of 10 cm, and compressed with a vinyl chloride piston until the contents reached a height of 2 cm. A preform was formed. The demolded preform is dried at a temperature of 150°C for 2 hours, then heated at 800°C for 1 hour to burn out the polyvinyl alcohol, and the silica sol is gelled and sintered to create a preform with high mechanical strength. And so. The short fiber volume fraction (Vf) at this time was about 20%. Subsequently, in the same manner as in Example 1, aluminum expanded material JIS A2014 was used as a matrix alloy to form a composite, and after T4 heat treatment, hot extrusion was performed at 500°C to produce a wire rod with a diameter of 12 mm. This composite had a tensile strength of 44 Kg/mm ² and a Young's modulus of 8.7 ton/mm ² . The values of tensile strength and Young's modulus when only the expanded aluminum material A2014 is treated in the same way are as follows.
37Kg/mm ² and 7.5ton/mm ² , and it was confirmed that the short fiber composite had a considerable reinforcing effect. Effects of the Invention According to the present invention, it is possible to produce an aluminum-based metal matrix composite material that takes advantage of the characteristics of matrix metal, and it can be used as a material for various metal parts.

Claims (1)

[Claims] 1 Containing alumina-based short fibers _{having a} composition represented by the formula 9Al ₂ O ₃ . An aluminum-based metal matrix composite material characterized by: 2 A preformed body _of alumina short fibers having _a composition represented by the formula 9Al ₂ O ₃ · 1. A method for producing an aluminum-based metal matrix composite material, which comprises infiltrating aluminum or aluminum alloy under pressure. 3 Alumina-based short fibers having the composition shown by the formula 9Al ₂ O ₃・2B ₂ O ₃ are molded and heated to form B ₂ O ₃
The components are volatilized and the formula 9Al ₂ O ₃・XB ₂ O ₃ (However, in the formula
represents a value greater than or equal to 0.01 and less than 2.0)
A method for producing an aluminum-based metal matrix composite material, which comprises converting the alumina-based short fiber preform into an alumina-based short fiber preform having the composition shown in the following, and infiltrating the preform with molten aluminum or an aluminum alloy under pressure.