KR830000066B1 - Production method of composite material - Google Patents

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Description

Production method of composite material

The present invention relates to a process for producing a composite material of aluminum or aluminum alloy containing alumina fibrous or Whisker mat material.

Various attempts have been made to increase the strength of aluminum or aluminum alloy materials, and many attempts have been made to use different forms of alumina as reinforcing materials. The main difficulty encountered in this approach is that molten aluminum and its alloys do not mix with alumina in the form of single crystals or polycrystals. See Wolf et al., Chemical Engineering Progress Volume 62 (3), page 74-78 (1966) (wolf et al, chem. Eng. Volume 62 (3) page 74-78 (1966)).

One way to approach this problem is to first use nickel or tungsten (all of which form volatile carbonyls, chromium (which forms volatile dicumene derivatives) or gastric derivatives such as titanium or copper). Alumina is applied together with the metal to be formed, and the sequential plating of these two metals has already been carried out: A homogeneous metal mixture of alumina plated in fibrous or whisker form is hot pressed in the form of a solid. The temperature and pressure should be chosen so that the partial liquefaction of the metal occurs during the pressing operation.The materials produced are of varying properties depending on the part of the sample and are used as reinforcing materials. As the amount of alumina used increases, it has a marked porosity. causes a decrease in the strength of rix) A high temperature pressurization method up to 450 ° C. has been used in this work.

Another way to approach this problem was to use molten aluminum alloys containing 1-8% by weight of lithium with continuous filaments or discontinuous fibers of polycrystalline alumina. These filaments and fibers can be provided as thin platelets of silica to enable the use of less lithium content. It should be noted that in this process, a reaction occurs between the surface of the filament and the fiber and the lithium of the aluminum alloy, wherein the surface is gray to black and no fiber of 20% or more in diameter should be included. The intermediate sheath allows the alumina filament or alumina fibers to bind with aluminum or its alloys. At this time, a pressure of about 0.14-0.9㎏ / ㎠ is applied to overcome the resistance of molten metal to penetrate the aluminum structure. The material produced by this method inevitably contains lithium.

It is an object of the present invention to provide a method for producing a composite material based on the use of unmodified alumina fibers or whiskers.

According to the invention there is provided a process for the production of composites containing aluminum and / or aluminum alloys and fibers of alumina as a reinforcing material or whisker mats. The reinforcing material then enters the mold, including the mat of fibers or whisker alumina, unchanged. Here, the mold and its contents are preheated to temperatures between 700 ° C and 1050 ° C, and molten aluminum or molten aluminum alloys with one or more alloying elements that do not react with alumina at temperatures between 700 ° C and 1050 ° C are below 1050 ° C. It is covered by the molten metal at a temperature not exceeding, which overcomes the surface tension between the alumina and the molten metal by varying the pressure on the contents in the mold, so that the molten metal penetrates into the space between the gaps of the mat. This allows the molten metal to solidify in contact with the mat.

-Alumina)이다. 이러한 형태의 알루미나 위스커의 생산 방법은 영국특허 1489346과 3947562에 상술되어 있다. 알루미나의 섬유형태가 사용될 때 그것은 고강도이며 본질적으로는 알파 알루미나인 고계수 다결정(high modulus polycrystalline)인 섬유재료이다. 이것의 전형적인 생산방식은 미국특허 3808015와 3853688에 상술되어 있다. 어러한 모든 알루미나는 인공적으로 생산되는 알루미나의 형태로 간주되어 질 수 있다.The alumina used in this method may be in the single crystal form or the polycrystalline form of alumina. Single crystal forms of alumina are actually pure alpha alumina (

-Alumina). Methods of producing alumina whiskers of this type are detailed in British Patents 1489346 and 3947562. When fiber forms of alumina are used it is a high modulus polycrystalline fibrous material that is high strength and essentially alpha alumina. Typical production methods for this are detailed in US Patents 3808015 and 3853688. All such aluminas can be regarded as a form of artificially produced alumina.

In the present invention, no modification of the fibers or whiskers, such as plating the surface with one or another metal, is necessary. Fibrous or whiskers are produced in this method without any deformation prior to use.

The matrix is an aluminum or aluminum alloy containing one or more elements that do not react with alpha alumina at the previously mentioned temperature conditions. The main alloying elements are silicon, metals such as magnesium, copper, zinc, tin, manganese, nickel and iron. The alloys used may be in different forms, such as cast alloys, general purpose alloys, heavy duty alloys or special alloys. A list of these alloys is listed in British Standard 1490 (1790), pages 12-13. Most of these alloys contain, as essential elements, one or more of silicon, copper, magnesium, manganese and nickel but are inevitably present. It may contain a small amount of some metals as impurities to be made or as additives for special purposes such as titanium.

In the composite material prepared by the process of the present invention, aluminum or aluminum alloy accounts for most of the weight ratio of the product, and is composed of at least 85% by weight of aluminum or aluminum alloy and the remaining 15% of alpha alumina fiber or whisker composite material. do. In most cases, composites contain more than 90% by weight of aluminum or aluminum alloy and less than 10% of alumina in the form of fibers or whiskers.

Compared to composites without reinforcements, the use of sufficient fibers and / or whiskers is necessary to increase the strength of the composites produced. In other words, the volume ratio of alumina to metal can be up to 20%.

The process of the present invention can be easily carried out in an electric furnace equipped with a method of applying a vacuum or a method of applying a pressure such as a hydraulic ram. Molds containing unmodified alumina fibers and / or whiskers are placed in a furnace and preheated to around 700 ° C.-1050 ° C. In the meantime, many aluminum metals or aluminum alloys are heated until they melt, usually at least 50 ° C above their melting point. The molten metal is thus poured over the preheated mold and the charge in the furnace. At this time, the temperature of the aluminum or alloy should not be high enough to smooth the unchanged alumina fibers or whiskers. Alumina fibers contain small amounts of other oxides, such as magnesia, and should be considered in determining the proper temperature of the molten metal. Several experiments from a given material suggest a convenient temperature range for the molten metal. The entire charge must enter the preheated mold as molten before other processes can begin. Typical temperature conditions when pure aluminum is used are pure aluminum poured at 900-950 ° C and unmodified alumina mat at 800-850 ° C. When aluminum-silicon base alloys are used, the temperature can be slightly lowered, for example, unaltered alumina mat is 800-850 ° C. and molten alloy is 850-900 ° C.

It will be explained next that a molten metal having a higher temperature than unaltered alumina is preferred. The pressure acts on the contents in the mold by applying a force in the next step by attaching the piston of the hydraulic ram to the molten metal in the mold. Therefore, the actual pressure acts on the surface of the molten metal, which pushes the molten metal into the gaps of the unaltered alumina mat and overcomes the surface tension between the metal and the alumina mat. Thus, the metal and the unmodified alumina are bonded directly. It is desirable to vacuum the interior of the mold before pressure is applied. This ensures that no air is present in the molten metal in the mold during hydraulic ram operation. Doing so causes the molten metal to solidify near the alumina mat, resulting in an enhanced cast body. The solidified casting can then be separated from the mold.

The pressure used in this process is practical. A pressure of 75-375 kg / cm 2 was used to obtain satisfactory results in the experiment. Higher pressures are possible but not necessary when suitable equipment is available. The use of lower pressures mainly depends on the degree of reinforcement desired and the degree of separation of each alumina fiber and / or whisker. In our experience, it is desirable to use a minimum pressure of 75 kg / cm 2. There is a correlation between the temperature of the material in the mold and the pressure to be applied. A pressure of about 375 kg / cm 2 is required to obtain satisfactory results when the temperature of the material is around 700 ° C., but the pressure does not have to exceed 75 kg / cm 2 when it is about 850 ° C.

This process requires the fibers and / or whisker mats of the molten metal and alumina and the mold containing the mat to be at or above the temperature at which the molten metal begins to solidify, between the molten metal and the alumina mat even under the applied pressure. Direct contact is possible without cooling to the solidification temperature of the molten metal. In fact, the mold and alumina mat can be brought to a higher temperature than the molten metal at the time of contact. If the temperature of the material is too high, a reaction may occur at the interface between the alumina and the molten metal. This reaction is unlikely to occur in a significant range up to 1050 ° C. Therefore, 1050 ° C is the upper limit of the temperature, but it is recommended to work at a temperature not exceeding 950 ° C. On the other hand, the nature of the molten metal affects the choice of temperature, but it is usually better to work at 700-900 ° C. The nature of the bonds formed at the interface is not known at this stage.

The following examples illustrate the nature of the invention.

Example 1

Commercially available pure aluminum was used in this example. This was not a separate analysis, but analysis of the product suggested a purity of more than 99.7% by weight. For the preparation of crystalline alumina whisker materials, the method of British patent 1489346 was used, which was contained in a graphite lined mold. The mold containing the alumina whisker was heated to a temperature of 800-850 ° C. in an electric vacuum furnace with a plunger. At the same time, ordinary pure aluminum, which will cover a sufficient amount of whisker mat, is heated to around 950 ° C and molten metal is poured into the whisker at a temperature between 900 and 950 ° C. The plunger centered on the mold is partially lowered below. All gases are then removed by operating the vacuum pump and the plunger is lowered completely to apply a pressure of 75 kg / cm 2 to the surface of the molten aluminum. The piston end of the plunger to be used is a fireproof surface of graphite.

On continuous reading of the recorded pressure over several minutes, the plunger is withdrawn and the contents of the mold begin to cool before being removed from the furnace. Examination of the product reveals that molten aluminum has penetrated between the void gap of the alumina mat and the graphite refractory of the mold.

Example 2

The procedure of Example 1 was repeated using aluminum alloy gold heated at 900 ° C. containing 1.0% magnesium by weight, 1.1% silicon and 0.7% manganese, instead of commercially pure aluminum. The working pressure was about 110㎏ / ㎠ and similar results were obtained.

Example 3

The procedure of Example 1 is repeated for aluminum special alloys containing 1.2% copper by weight, 1.3% manganese, and 11.5% silicon instead of commercially pure aluminum and heated to about 850 ° C., with the mold and whisker mat being 775 ° C. It heated up to and the working pressure was about 225 kg / cm <2>. Similar results were obtained.

Example 4

The procedure of Example 1 was repeated for aluminum base alloys heated to about 850 ° C. containing 1.20% magnesium and 2.2% nickel instead of commercially pure aluminum. At this time, the mold and the whisker material are heated to about 775 ℃ and the working pressure is about 200㎏ / ㎠. At this time, the same result was obtained.

Example 5

The procedure of Example 3 was repeated using continuous alumina filaments aligned on a commercially available graphite refractory mold instead of an alumina whisker mat. The alloy used, the heating temperature and the applied pressure were the same as in Example 3. Experiments show that there is a significant amount of reinforcement.

The products of this method have exceptionally low 1-2% porosity. In addition, the product shows very good tensile strength at high temperature and its properties are very uniform.

Claims (1)

Molten aluminum containing one or more elements that do not react with alumina until the mat is covered by molten metal within 1050 ° C entering a mold containing unmodified alumina fibers or whiskers preheated to 700 ° C-1050 ° C. Or aluminum alloy, which allows the molten metal to penetrate into the space between the gaps of the alumina mat and to overcome the surface tension between the alumina and the molten metal by changing the pressure on the contents of the mold. A method of producing a composite material comprising aluminum and / or aluminum alloy and alumina fibers or whisker mats as reinforcing materials to enable solidification in contact with the resin.