Preparation method for magnesium matrix composite

Abstract

The invention relates to a preparation method for a magnesium matrix composite. The preparation method comprises the following steps: (1) preparing magnesium ingots as raw materials and salt flux and reinforcements; (2) placing the salt flux in a crucible, performing heating to prepare salt flux melts, adding the reinforcements; (3) performing pouring into a normal-temperature crucible, and performing cooling to obtain precursors; (4) adding the raw materials in an iron crucible, and performing melting at 953K-1043K; (5) placing the precursors in raw material melt, after stirring, under a condition of 953K-993K, performing standing so that scum and melt are obtained; and (6) removing the scum, lowering temperature to 973K-982K, and performing casting. The method provided by the present invention is simple in process and low in cost. The method can be used for preparing bulk structural members of the magnesium matrix composite, and can be used for automatic production.

Description

BACKGROUND OF THE INVENTION1. Field of the Invention[0001]The present invention relates to a preparation method for composites, in particular to a preparation method for a magnesium matrix composite.2. The Prior Arts[0002]Magnesium alloys have the advantages of being low in density, high in specific strength, excellent in vibration-damping performance, electromagnetic shielding performance and machinability, and the like; the magnesium alloys are an ideal material adopting a lightweight structure; and research and application of the magnesium alloys are highly valued in recent years. However, the magnesium alloys also have the shortcomings of being high in melt casting difficulty, difficult in plastic deformation, poor in high-temperature creep resistance, poor in corrosion resistance and the like, wherein the low strength and easy occurrence of yield deformation restrict the application of the magnesium alloys; the magnesium alloys are generally applied to secondary load-bearing co...

AI Technical Summary

Benefits of technology

The present invention provides a method for preparing a magnesium matrix composite by improving the wettability of reinforcements and solving the problem of wettability between the reinforcements and a matrix. This is achieved by dispersing the reinforcements in a molten salt flux and adding them to a magnesium melt. The strength of magnesium matrix composite is improved while the process is simplified. The use of barium chloride and other salts improves the wettability of the reinforcements, allowing them to be easily dispersed in the matrix. This method is simple, low-cost, and can be used for preparing bulk structural members of the magnesium matrix composite, automatic production, and significant in the development of magnesium industry.

Problems solved by technology

However, the magnesium alloys also have the shortcomings of being high in melt casting difficulty, difficult in plastic deformation, poor in high-temperature creep resistance, poor in corrosion resistance and the like, wherein the low strength and easy occurrence of yield deformation restrict the application of the magnesium alloys; the magnesium alloys are generally applied to secondary load-bearing components only, which restricts the application field of the magnesium alloys severely; and therefore, it is urgent to produce the lightweight magnesium matrix composite having the advantages of being low in cost and high in performance.

The key problem for preparing the magnesium matrix composite is how to distribute the reinforcements in the metal melt uniformly; however, most of the reinforcements are often aggregated or precipitated when entering into the molten metal melt, and accordingly are hard to disperse in the metal melt uniformly; in the stirring process, gas impurities can be mixed along with stirring, and the melt viscosity can be increased by reinforcement particles, so that gas is hard to escape; and therefore, there are very high requirements for mechanical stirring.

The reinforcements generate such phenomenon in the melt that mainly because of density difference between the reinforcements and metal, gravity segregation certainly occurs; and because of the poor wettability of the reinforcements for liquid metal, the reinforcements cannot be dispersed in the matrices properly.

However, the problem of influence of pressure on the casting quality exists; under high pressure, molten magnesium can generate turbulent flow, resulting in such phenomena of magnesium oxidization and gas hold-up; and under low pressure, a part of gas cannot be removed, resulting in the phenomenon that the castings are not compact.

In addition, the squeeze casting method cannot be used for production of bulk castings or automatic batch production.

Metal atomization and hybrid deposition are two major influence factors of the injection molding method; in the metal atomization process, the parts often have higher porosity and shrinkage phenomenon along with gas transfer; if solidification rate is too fast after deposition, the reinforcements and the matrix are poor in compound effect, or even are not compounded; if the solidification rate is slow, the reinforcements can be distributed unevenly, or even segregated; and the injection molding method, as a novel composite preparation method, is high in cost, and therefore, is not applicable for automatic batch production.

The method is low in cost and simple in technological process, and the obtained part is high in quality; and however, the method for generating the reinforcements by chemical reaction has limitations of less reinforcements, so the requirements of batch production cannot be obtained.

However, due to significant difference in size, shape and performance between the reinforcements and the matrix alloys, compared with the interface bonding strength of the composite produced by the casting method, the interface bonding strength of the composite can be reduced after combination.

In addition, the powder metallurgy method is not applicable for larger structural materials, but applicable for functional materials of small parts; the technological process of the powder metallurgy method is relatively complicated, and high in cost; and problems exist in a transportation process.

Therefore, the powder metallurgy method greatly restricts preparation and production of the magnesium matrix composite as a structural material.

The rare earth oxide particle reinforcements are high in melting point, cannot be molten after being added to magnesium or magnesium alloy solutions, and besides, cannot produce chemical reaction with the matrix; if the reinforcements can exist in the matrix uniformly, segregation of interstitial impurities at the grain boundary is reduced, and the grain boundary strength can be improved; in addition, rare earth oxides achieve the effect of pinning for dislocation, and prevent dislocation from moving, so that the strength of magnesium alloy is improved, and the plasticity cannot be reduced greatly; and however, if the rare earth oxides are directly added to the matrix melt, the particles can be agglomerated due to poor wettability, and cannot be dispersed in the matrix properly, so that the effect of dispersion strengthening is not achieved.

Images