JPH0132297B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for uniformly mixing molten metal and ceramic, which are difficult to mix with each other, to produce a homogeneous composite.

Recently, in order to obtain materials with properties suitable for various purposes, metals have been mixed with various ceramic particles to form composites.
For example, fine graphite particles are added to aluminum or copper alloys to make anti-friction materials, ultra-light vitreous microscopic hollow spheres such as glass balloons are mixed into aluminum at a high blending rate to make lightweight composite materials, and aluminum and other Adding fillers such as short carbon fibers, oxides, and carbides to metal to increase its strength, and adding particles containing foaming sources such as shirasu, mica, and calcium carbonate to molten aluminum to make it foam and make it ultra-lightweight. It is known to use foamed aluminum.

However, the ceramics that are generally mixed into these metal composites have poor wettability with molten metal.
Furthermore, since there is a difference in specific gravity between the two, it is difficult to completely disperse the two even if ceramic particles are added to the molten metal and thoroughly stirred, and the two inevitably separate during cooling and solidification. Up until now, methods to solve these difficulties have included coating the surfaces of ceramic particles with metal in advance, adding this to molten metal, and strictly controlling the temperature of the molten metal, alloy components, and mixing conditions of the ceramic particles. However, this method is not yet fully satisfactory as an industrial method because the processing is complicated and the expected effects are not obtained. Another known method is to first add an alkali metal or alkaline earth metal to the aluminum to improve wetting with the ceramic when dispersing ceramic hollow fine spheres in the aluminum. In addition to the material being limited to aluminum and the filling material being limited to glass hollow spheres,
In order to obtain uniform dispersion, a considerably large amount of alkali metal or alkaline earth metal is required, which is not necessarily satisfactory in practical use. In addition, as a method to increase the viscosity of molten metal and make it possible to disperse ceramics, we use alloy components that have a wide temperature range between the solidus and liquidus lines. A method in which strong stirring is performed to form a highly viscous solid-liquid coexistence melt in which solid phase particles are uniformly dispersed, and ceramic particles such as silicon carbide, aluminum oxide, and silicon oxide are added to this, or in molten metal. A method of obtaining a metal foam liquid by blowing and stirring a gas such as air, oxygen, or carbon dioxide, and thickening the molten material with fine oxide particles that are uniformly generated in the melt, and then adding and mixing foamable ceramic to this. etc. are known. However, these thickening methods have limitations on the molten metals and ceramics to which they can be applied, and require strict control of conditions, and cannot be said to be universally applicable.

The present inventors can apply the same to many metals. As a result of intensive research to develop a method for uniformly mixing molten metal and ceramic, we have successfully mixed molten materials such as aluminum, magnesium, tin, lead, and zinc containing small amounts of metallic calcium in the presence of oxygen. It has been found that continued vigorous stirring significantly increases the viscosity, and that a sufficiently dispersed state can be obtained when ceramic particles are added, and based on this finding, the present invention was accomplished.

That is, in the present invention, after melting a metal-calcium mixture of one metal selected from aluminum, magnesium, tin, lead, and zinc and 0.05 to 5% calcium based on its weight, A ceramic-metal composite characterized in that the molten mixture is continuously stirred vigorously in the presence of oxygen to promote oxidation until a viscosity suitable for addition and mixing of ceramic particles is reached, and then ceramic is added and dispersed. The present invention provides a method for manufacturing.

It is generally observed that the addition of metallic calcium to a melt of the metal slightly increases the viscosity. This phenomenon of thickening due to alloying is well known and is an important phenomenon in casting, as can be seen, for example, when titanium, iron, copper, etc. are melted into molten aluminum. However, by increasing the viscosity due to the dissolution of calcium alone, it is not possible to obtain sufficient viscosity to allow the arbitrary addition and mixing of various ceramic particles, and only a small possibility has been recognized in the aluminum-glass hollow sphere system. It's just a matter of getting caught.

On the other hand, the mechanism of thickening of molten metal containing calcium by stirring in the presence of oxygen can be considered as follows. In other words, since calcium is the element with the greatest affinity for oxygen, after being added to the molten metal and dissolved, the calcium component that comes into contact with the air is immediately oxidized to become fine calcium oxide, which is then dispersed in the molten metal by stirring. do. With continued stirring, the amount of calcium oxide in the molten metal gradually increases, and at the same time the apparent viscosity increases significantly. A feature of the present invention is to utilize such preferential oxidation of calcium in molten metal.

As previously described, a method of increasing the apparent viscosity by forcefully oxidizing molten aluminum by blowing air or the like into it, but according to experiments conducted by the present inventors, this method requires a considerable amount of viscosity to achieve a thickening effect. It requires long air blowing and is dangerous for magnesium, and air blowing has little thickening effect on tin, lead, and zinc. Further, the thickening method using the solid-liquid coexistence region of an alloy cannot be applied to any metal such as a pure metal or a eutectic alloy. Furthermore, a method in which ceramic fine particles are coated with a metal film in advance is economically disadvantageous. In contrast, the method of the present invention preferentially oxidizes the added calcium rather than oxidizing the molten metal itself, so the oxidation rate is high, the thickening time is short, and it can be applied to any pure metal. Furthermore, it has excellent features such as being able to use any material or shape of the ceramic particles to be composited.

In the past, there have been very few examples of adding calcium to metals, and only a very small amount (0.01 to 0.02% or less) is known as an antioxidant or deoxidizing agent. However, since calcium generally has the effect of embrittling metals, it should be avoided to add a large amount. As a result of careful consideration of this point, the present invention found that the thickening effect becomes noticeable when the amount added is 0.05% by weight, and when it exceeds 5%, the thickening effect becomes even greater, but the metal itself becomes significantly brittle. Since properties may be lost, the amount added is selected within the range of 0.05 to 5%. It is preferably in the range of 0.5% to 1%, but it varies depending on the type of molten metal, the amount of ceramic particles added, etc.

As already mentioned, the field of application of the present invention lies in the production of various ceramic metal composites that require the dispersion of ceramic particles in metal, and specifically, for example, graphite for the purpose of anti-friction material, metal system complex,
Lightweight vitreous micro hollow sphere metal composites for the purpose of lightweight metals, oxides and carbides for the purpose of strengthening,
It is also extremely effective for foamed metals using ceramics containing foaming sources such as nitrides, carbon, short fibers, and metal composites that contain foaming sources such as shirasu, mica, carbonates, and hydrides for the purpose of ultra-lightweight metal composites. .

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 10g of calcium was added and mixed to 1kg of pure aluminum with a purity of 99.95% kept in a molten state at 720℃ in a #10 graphite crucible using an electric furnace, and mechanically heated with a rotary blade for about 5 minutes to thicken the mixture. After stirring, water displacement specific gravity that has been sufficiently dehydrated
After gradually adding and mixing 500 ml of shirasu balloons (vitreous micro hollow spheres made from shirasu deposited in southern Kyushu) having an average particle size of 150 μm, the mixture was cooled and solidified to obtain a composite. This composite has shirasu balloons homogeneously dispersed in the matrix aluminum, and has a specific gravity of
It was a lightweight material of 1.55. In addition, when calcium was not added, a separation phenomenon was observed during the mixing of the shirasu balloon, and it was impossible to produce a composite.

Example 2 Using the method of Example 1, 1% calcium was added to 400 g of molten pure aluminum to thicken it, and then flaky natural graphite with an average particle size of 3 mm was mixed in with stirring, and the mixture was cooled and solidified. did. Although some foaming was observed in the obtained composite due to volatile matter from the graphite particles, the graphite particles were uniformly dispersed.
No pretreatment of graphite particles was necessary. Note that when calcium was not added, it was almost impossible to mix graphite particles.

Example 3 Shirasu balloons, shirasu powder, titanium boride, silicon nitride, aluminum nitride, aluminum oxide, magnesium oxide, etc. were added to approximately 200 ml of each molten metal of tin, lead, and zinc kept at a temperature approximately 50°C higher than their respective melting points. In an experiment of adding ceramic fine particles, 0.5% calcium was added to each molten metal beforehand.
It was confirmed that when viscosity-enhancing treatment was performed by adding . However, in the case where calcium was not added, some of the ceramic particles were mixed in at first, but as the amount added was increased, a separation phenomenon was always observed, and complete mixing was impossible.

Example 4 In the method of Example 5, 200 ml of magnesium was used as the molten metal, and 5 ml of calcium was added to it per weight.
Shirasu balloon, Shirasu powder, magnesium oxide,
When experiments were conducted to mix ceramic particles such as graphite particles, a sufficiently uniform mixture was obtained in all cases. Note that when the amount of calcium added was 1% or less, a separation phenomenon occurred during the mixing of the whitebait balloon and whitebait powder, making it impossible to produce a composite.

Claims (1)

[Claims] 1. After melting a metal-calcium mixture of one metal selected from aluminum, magnesium, tin, lead, and zinc and 0.05 to 5% calcium based on its weight, ceramic particles are added and mixed. A method for producing a ceramic-metal composite, which comprises continuing to vigorously stir the molten mixture in the presence of oxygen to promote oxidation until it reaches a viscosity suitable for viscosity, and then adding ceramic and dispersing it.