JPH0685996B2 - Manufacturing method of metal matrix composite material - Google Patents

Description

The present invention relates to a method for producing a fiber-reinforced metal matrix composite material, and in particular to a Mg material containing a SiC fiber or the like as a reinforcing material by a pressure casting method. The present invention relates to a method for producing a metal-based composite material, which can effectively prevent the occurrence of Mg segregation anomaly in the method for producing a composite material containing Al alloy.

(Prior Art) Generally, SiC-based, Al ₂ O ₃ -based, C-based, B-based, etc. are known as fiber raw materials used for fiber-reinforced metal matrix composite materials. In particular, short fibers, particles or whiskers of SiC whiskers, which have excellent wettability with Al, are often used for strengthening Al alloy materials.

Further, as a method for producing a fiber-reinforced metal matrix composite material, conventionally, a high pressure casting method (infiltration method), a powder metallurgy method, a diffusion bonding method and the like are known, but the high pressure casting method is particularly suitable for mass production and is lightweight. It is widely applied in the field of manufacturing reinforcing materials.

By the way, by a high pressure casting method, when a Mg-containing Al alloy is used as a matrix, for example, when a composite material reinforced with SiC whiskers is produced, significant Mg segregation occurs in the composite portion of the matrix and SiC whiskers, and a composite with a uniform composition is formed. A phenomenon peculiar to the Mg-containing Al alloy-based composite material is recognized in that the structure is not formed, and therefore, sufficient strength characteristics as the composite material cannot be obtained. This is because the SiO ₂ component present in the surface layer of the SiC whisker selectively reacts with the Mg component to form Mg ₂ Si. Therefore, as a countermeasure against this Mg segregation, it has been proposed to use a SiC whisker with SiO ₂ removed from the surface layer.

From this, the inventors have found that the amount of SiO ₂ is 0.2 to 0.35% w
A SiC whisker reinforced 6061Al alloy composite material was prototyped by a high pressure casting method using an extremely small amount of SiC whiskers.
The manufacturing method in this case is shown in FIGS.

First, a preform 1 obtained by solidifying a SiC whisker into a cylindrical shape by a pressing method is prepared and inserted into a heating furnace 2.
The preform 1 is preheated in the atmosphere for 20 to 60 minutes by heating the heater 3 so that the temperature of the entire preform 1 becomes 500 to 700 ° C (Fig. 5 (A)). Next, use the heater 4 in advance at 350 ℃ -650 ℃
The preform 1 is set in the mold 5 that has been preheated (FIG. 2B). Then, the molten matrix metal 6 is poured into the mold 5 (FIG. 2C), and is pressurized by the piston 7 to fill the preform 2 with the molten matrix metal 6.
A SiC whisker reinforced 6061 Al alloy material 8 is created (Fig. (D)).

FIG. 6 shows a cross section after the SiC whisker reinforced 6061 Al alloy material 8 thus created is halved and heat treated. The 6061 Al alloy matrix portion 9 had a metallic color, the shaded portion 8a of the composite portion 8'had a dark green color, and the frost pattern portion 8b below the composite portion 8'had a metallic color.

To investigate the unique cause of such a composite unit 8 ', it was performed chemical analysis and mechanical tensile test for each of the representative unit u ₁ ~x ₁ shown in Figure 6. As a result, regarding the chemical analysis, the elements other than Mg were almost the same in each representative part, but the concentration of Mg was x ₁ compared to u _{1 to} w ₁ as shown in Table 1 below. It was confirmed that the value was remarkably decreased in. The tensile strength of the low Mg concentration region x ₁ was almost the same as that of the 6061 Al alloy as the matrix material.

From Table 1, the Mg concentration of the matrix part 9 is 1.01% and JIS
Although the standard value (0.8 to 1.2%) is satisfied, the Mg concentration of the dark green composite part 8a is 1.4 to 1.62%, which exceeds the JIS standard value, while the composite color of the composite part 8b exhibiting a metallic color is Mg concentration is 0.01%
It is recognized that the value is extremely small and is close to that of pure Al. Regarding the tensile strength, the dark green composite part
8b is as large as 44-46Kgf / mm ² , whereas the metal-colored composite part 8b is as small as 31Kgf / mm ² and SiC whisker reinforced pure Al
It can be seen that only the strength of the material can be obtained.

This phenomenon is because in the process of impregnation of the molten aluminum alloy into the preform after preheating, Mg having a strong activating action reacts with SiO _{2 in the} surface layer of the SiC whiskers, and Mg is trapped. It is considered that the Mg concentration of the is decreased.

That is, even if a SiC whisker containing a small amount of SiO ₂ was used, Mg segregation occurred at a rate that was unpredictable from the SiO ₂ amount, and therefore, the SiC whisker from which SiO ₂ in the surface layer portion was removed was generated. Just using, Al containing Mg
It became clear that it was impossible to prevent Mg segregation of the alloy.

When such Mg segregation occurs, the portion that can be used as a composite material having a predetermined strength is limited, and the yield of the material deteriorates. Further, when the billet of the composite material is subjected to plastic working by rolling or extrusion, depending on the position of Mg segregation and the situation, a portion with a low Mg concentration is formed on the entire surface of the worked material, and the characteristics of the worked material are significantly impaired.

(Problems to be solved by the invention) When a metal matrix composite material in which an Al alloy matrix containing Mg is reinforced with SiC short fibers, particles or whiskers is prepared by a high pressure casting method, SiC whiskers and Al which are reinforcement materials are used.
There is a problem that significant segregation of Mg element occurs in the composite portion with the alloy, sufficient characteristics as a composite material cannot be obtained, and the yield of the material deteriorates.

The present invention has been made in view of such circumstances, as an Al alloy containing Mg as a matrix, SiC short fibers,
An object of the present invention is to provide a method for producing a metal-based composite material, which is free from anomalous Mg segregation when forming a composite portion with particles or whiskers, and which is capable of achieving uniform properties and improved quality and yield.

(Structure of Invention) (Means and Actions for Solving Problems) It is effective to reduce the amount of Mg segregation by removing SiO ₂ from the SiC short fibers, particles or the surface layer of whiskers and using it as a reinforcing material. Is as described above.

By the way, in the manufacturing method by the high pressure casting method, in order to allow the molten Al alloy to be easily impregnated into the preform,
It is necessary to preheat the preform to a high temperature state in advance. The inventors have conducted a number of basic experiments and research analyzes on this preheating temperature and its atmosphere. As a result, even if a SiC reinforcement containing only a trace amount of SiO ₂ is used,
By preheating the preform for a long time in a high-temperature atmosphere, free Si existing in the surface layer of the SiC reinforcement reacts with oxygen in the atmosphere to form SiO _2, which results in Mg segregation of the composite part. It was found that the amount increases.

Further, when the molten Al alloy is filled into the preform at high pressure, if active gas exists in the pores of the preform, Si
It was experimentally clarified that even if a preform having a small amount of O ₂ is used, the amount of Mg segregation increases as a result.
It is speculated that the reason for this is that free Si in the surface layer of the SiC reinforcement reacts with an active gas such as oxygen at a high temperature within an extremely short time, and this reaction is further accelerated under high pressure.

The present invention is based on such findings, in the preform in which SiC short fibers, particles or whiskers are accumulated, Mg-containing
A method for producing a metal-based composite material by pressure-impregnating a molten Al alloy as a matrix, wherein the preform is a metal base formed by using SiC short fibers, particles or whiskers of which SiO ₂ in the surface layer portion is removed. In the method of manufacturing a composite material, first, the preform is put into a mold, the mold is hermetically sealed, and a vacuum pump is used to heat it to a temperature of 500 ° C to 700 ° C in a vacuum state so that the moisture in the preform is completely removed. After disappearing, the Mg-containing Al alloy matrix molten metal was filled from the inert gas tank with Ar and other high-purity inert gas to prevent the active gas from entering the pores in the preform by filling the mold. It is characterized by pouring molten metal and impregnating it under pressure.

According to the present invention, S is added to the surface layer of the SiC reinforcement in the preform.
Since no iO ₂ component is formed and active gas is prevented from entering the preform during the infiltration process, Mg ₂ S
The precipitation of i can be completely prevented. As a result, in the production of a composite material using a Mg-containing Al alloy as a matrix,
It becomes possible to solve the problem that the composition abnormality such as segregation of Mg occurs in the composite part.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 4. In this example, 6061 Al containing 1.01% of Mg element was used as the Al alloy as the matrix, and SiC whiskers were used as the reinforcing fibers. The SiC whiskers, hydrofluoric acid and SiO ₂ and the free Si surface layer portion, is removed by acid solution such as nitric acid, and the amount of SiO ₂ and 0.025%.

The manufacturing process is shown in FIGS. 1 (A) to (C).

First, a small amount of water is uniformly mixed with SiC whiskers, which are inserted into a preform mold and compression molded. The preform 12 thus created is installed in the mold 13, and the Al alloy sprue 14 and the upper part 15 of the mold are hermetically sealed, and then the vacuum pump
Vacuum the inside of the mold with 16. After that, the heater 17 on the outer periphery of the mold 13 is heated to a predetermined temperature (500 ° C to 700 ° C) to completely remove the moisture in the preform, and then Ar
The mold 13 is filled with high-purity Ar gas from the tank 18, and the preform 12 is preheated for 20 to 60 minutes (FIG. 1 (A)). Next, the molten Al alloy 19 is injected into the die 13 from the sprue 14 in a state where Ar gas in the preform 12 is not lost (FIG. 2B). After that, the upper part 15 of the mold is removed and the pressure piston 20 is inserted from the upper part.
Is impregnated into the preform 12 (FIG. 2C). After the solidification, the composite billet is taken out of the mold.

Figure 2 shows SiC whisker reinforced 6061A manufactured in this way.
1 shows a vertical cross-sectional shape obtained by heat-treating a composite billet 21 in half.

The 6061 Al alloy matrix part 22 has a metallic color, the majority part 21a of the composite part 21 'has a dark green color, and a slight metallic color part 2 at the bottom.
1b is recognized. Table 2 below shows the results of the Mg concentration analysis and the tensile test for the representative parts u _{2 to} y ₂ of each part.

In the composite portion 21a corresponding to v _{2 to} x ₂ , the Mg element is contained almost uniformly, and the tensile strength thereof is 45 to 46 Kgf / mm ^2, which is a sufficient composite result.

However, the Mg concentration of the metallic color composite part 21b is 0.02%.
And the segregation of Mg occurs. This is probably due to the trace amount of SiO ₂ (0.25% wt%) contained in the received SiC whiskers. Therefore, by using SiC whiskers with a smaller amount of SiO _2,
It is speculated that g segregation can be completely prevented.

Next, the reduction degree of the amount of SiO ₂ existing in the surface layer portion of the SiC whisker for forming a preform by the infiltration process of the above-mentioned example was investigated by comparing with the conventional method, and the results are shown in FIGS. 3 and 4.
Consider the figure.

FIG. 3 shows that the initial amount of SiO ₂ is 0.2 to
Preform consisting of 0.35% SiC whiskers
Shown are the results of measuring the amount of SiO ₂ after heating for 60 minutes each in the atmosphere of ℃ to 900 ℃ and in the high-purity Ar gas atmosphere.

It can be seen that with heating in the atmosphere, the amount of SiO ₂ increases remarkably as the heating temperature rises, reaching more than 10 times the initial amount of SiO ₂ .

On the other hand, in the case of heating in the Ar atmosphere, the amount of increase is very small, and it is recognized that even after heating for 60 minutes, it is almost equal to the initial amount of SiO ₂ .

Further, FIG. 4 shows the results of examining the behavior of generation of the amount of SiO ₂ when the heating temperature in air is changed while the heating temperature is kept constant. The preheating time of the preform depends on its size, but even a small preform requires 10 to 20 minutes or more. It can be seen that the amount of SiO ₂ rapidly increases even by heating in the atmosphere for such a short time.

Thus, even if the amount of SiO _{2 on the} surface of the SiC whisker is very small at the initial stage, Si released to the surface of the whisker reacts with oxygen in the atmosphere in a high-temperature atmosphere, thus forming a preform. SiO ₂ increases on the surface of the SiC whiskers.

Incidentally, as the Mg-containing Al alloy to which the present invention is applied, AC8
2024,5052,6061,7075 and the like, which are represented by Al alloys for casting of A, AC4C, AC4D, etc., or for wrought materials, are suitable.
That is, the Mg content of these Al alloys is in the range of 0.2 to 3.0%, which is the Mg-containing region to which the present invention can be most effectively applied. However, even in a Mg-containing Al alloy having a Mg content of 3.0% or more, the segregation phenomenon occurs due to the lightness and darkness of the Mg content, and thus the present invention can be effectively applied.

In addition, in the above-mentioned embodiment, the case where the preform is formed by the SiC whiskers is described, but the present invention can obtain the same effect as the above-mentioned embodiment also in the case where the preform is formed by using the SiC short fibers or particles. it can.

(Effects of the Invention) As described above, according to the present invention, a preform prepared by using SiC short fibers, particles or whiskers of which SiO ₂ in the surface layer portion is removed is vacuum-molded in a mold under a vacuum condition of 500 By heating at a temperature of ℃ ~ 700 ℃ to completely eliminate the moisture in the preform, then fill the mold with high-purity inert gas, the invasion of the active gas into the pores in the preform By adopting the process of pouring the Mg-containing Al alloy matrix melt while blocking the above, it is possible to easily perform the work using the same mold, and at the same time perform vacuum heating first and then in an inert gas atmosphere. By a series of steps of pouring the molten metal in the above, it is possible to surely obtain a stable product with a good material yield and no Mg segregation.

[Brief description of drawings]

1 (A), (B), and (C) are process drawings for explaining one embodiment of the present invention, and FIG. 2 shows a cross-sectional state of a SiC whisker reinforced 6061Al composite material obtained by the above embodiment. Schematic diagrams, Fig. 3 and Fig. 4 show SiO ₂ preforms made of SiC whiskers in the atmosphere and Ar gas atmosphere
A graph showing the results of examining the change in the amount, FIG. 5 (A),
(B), (C) and (D) are process drawings for explaining a conventional manufacturing method, and FIG. 6 is a SiC obtained by the conventional method.
FIG. 3 is a schematic view showing a cross-sectional shape of a whisker-reinforced 6061Al composite material. 12 …… Preform, 13 …… Mold, 19 …… Molten metal.

Claims (1)

[Claims] 1. A method for producing a metal matrix composite material by impregnating a preform in which SiC short fibers, particles or whiskers are accumulated with a molten Mg-containing Al alloy as a matrix to produce a metal-based composite material. Removed SiO ₂ from the surface layer
In a method for producing a metal-based composite material using short fibers of SiC, particles or whiskers, first, the preform is placed in a mold, the mold is hermetically sealed, and a vacuum pump is used to produce a vacuum state at 500 ° C. After heating to a temperature of 700 ° C to completely eliminate the water content in the preform, fill the mold with Ar or other high-purity inert gas from the inert gas tank to activate the pores in the preform. A method for producing a metal-based composite material, which comprises pouring a molten Mg-containing Al alloy matrix and impregnating it under pressure while preventing gas from entering.