Investigation On Preparation And Properties Of SiC/Mg Composites With Bimodal Particles By Vacuum Pressure Infiltration Precess

SiCp/Mg composites are received widespreadly attention, owing to its low density, high thermal expansion behaviour and wear resistant. Particular, magnesium matrix composites of having high volum fractions of SiC particles are investigated in recent years. The matrix used in AZ91D magnesium alloy, and silicon carbide particles were used as the reinforcement phase, SiC/Mg composites with bimodal particles were infiltrated by vacuum pressure in the paper. The micostructural examinations of composites were analyzed by means of optical microscope (OM) and scanning electron microscopic (SEM) and X-ray diffraction (XRD). Tests of thermal expansion behaviour and wear resistant were carried out, and the law and the factors influenced on thermal expansion behaviour and wear resistant were discussed. In addition, tensile property of composites was analyzed. The main results are as follows:SiC particles make to cover magnesium alloy melt protection, which is simple and effective method that SiC/Mg composites with bimodal particles are infiltrated by vacuum pressure. In this way, the largest volume fraction of composites is 71%, and its density is 99.1%, when the coarse-fine particle diameters is 100 and 11μm, and the weight ratio is 3:1.The micostructural examinations of composites show that coarse-fine particle has good match, but few pores existe in the vertex angle and thin narrow channel of near contact face of particles; XRD analysis show: The few Mg2Si phase is found in the infiltration, and the content of Mg2Si phase increases with increasing infiltration temperature and prolong solidification.The test results of thermal expansion properties indicate that the addition of SiC particles considerably reduces the coefficient of thermal expansion (CET) of matrix alloy. The CET of 47/5μm, 3:1weight ratio, 56.2vol.% composites is 7.716×10-6/K in the temperature between 30 and 100℃. The results also indicate that the CET of composites reduces with increasing of the particle volume fraction, When the particle diameters is unvaried; The particle diameters is smaller, the CET of composites is lower, When the particle volume fraction is approximate; The influence on thermal expansion behaviour is more prominent for particle diameters than volume fraction. Moreover, With reducing the density, increasing the Mg2Si content and the matrix grain size, the CET of composites reduces.The test results of wear resistant indicate that the addition of SiC particles obviously improves wear resistance of matrix alloy, also reduced the oxidation,adhesion and abrasion of worn surface. The abrasion of 245/21μm, 3:1weight ratio, 62.7vol.% composites is 1/50 times as matrix alloy. The results also indicate that the wear resistance of composites increases with increasing of the particle volume fraction, When the particle diameters is unvaried; When the particle volume fraction is approximate, with decreasing the particle diameters, the wear resistance of composites reduces, and grooves and adhesion increased. The influence on wear resistance is more prominent for particle diameters than volume fraction. But the micro-crack of matrix alloy reduces with increasing particle diameters; In addition, preliminary analysis of tensile property discovere that the elastic modulus of composites is higher than matrix alloy, but the poisson's ratio is lower.