The Study On The Preparation And Properties Of Mg-Al Based Composition Materials Enforced By Mg₂Si Particles

In order to improve the mechanical performances of Mg alloys especially at high temperature, this paper mainly deeled with the effect of mixed RE, Sr and Mg₂Si in-situ particles on the microstructure, mechanical performances at room/high temperature and the high-temperatur properties stability of Mg-Al alloys, respectively. On the base of the analysis of thermodynamics and kinetics, the reaction feasibility of Si with My-Al alloy melt was discussed; The reaction mechanism of SiO₂ and Mg-Al alloy melt was inferred and reaction kinetics models were established.It was found that the addition of Sr is of excellent refinement effect on the microstructure of Mg-Al alloy. The grain size after solution treatment decreased from 120-160-μm to 50-80μm under the addition of 0.1% Sr. The tensile strength at room-temperature increased from 147.77MPa to 183.25MPa and Vickers hardness increased from 85 to 102 at T6 state. The addition of RE showed an excellent effect on improving the mechanical performances especially the heat-resistant ability of Mg alloy containing Al. The high melt-point phase of Al₁₁RE₃ with the morphology of needle or plate was formed at the condition of 2wt% RE addition, which crossed the grain boundaries and penetrated into grain particles. The tensile strength and Vickers hardness of the Mg-Al alloy with 2wt%RE were 173.25MPa and 103 under T6 state respectively. The morphologies of fracture changed to the hackly combined fracture of low ductile sockets and narrow sidesteps.The in-situ reaction between SiO₂ powder and Mg-Al-Zn alloys resulted in the formation of the enhanced phase of Mg₂Si. With the increase of SiO₂ addition, the morphology of Mg₂Si particle change from needle or strip of eutectic morphology toarrowhead or Chinese characters of nascent morphology. The tensile strength and Vickers hardness of the composite were increased by 20.7% and 36.8% respectively at T6 state, the high temperature tensile strength of 200 °C and 250 °C was 111.2MPa and 79.6MPa respectively.In addition, it was found that the addition of Sr could minish the dimension of Mg2Si partical because of its metamorphism for Mg2Si. Likelihood attribute to the adsorption each other of AI11RE3 and Mg2Si or the new phase morphology of RE-Si, the mass of RE% Si appeared from the needle or sheet area in the structure. The tensile strength of composition were increased by 7.2% and 5.1% respectively at T6 state after Sr and RE alloying, the high temperature tensile strength of 200°C increased to 123.4MPa andl43.3MPa, 250°C to 87.6MPa and 95.5MPa respectively.The research of performance thermal stability of composition showed that, under the condition of 300°C treatment, the performance peak of the material appeared after 12-16 hours treatment, subsequently the performance declined rapidly; relatively, the curve of composition was verified smoothly after Sr metamorphose and RE alloying, therefore the excellent thermal stability was showed in the research.