A Study On Mg₂Si/Mg In-Situ Composites

Magnesium matrix composites have been widely used in spaceflight, mechanical electron, automobile manufacture etc because of their low density, high specific strength and rigidity and good damping capacity. So, magnesium matrix composites are one of the focuses at present. Intermetallic compound Mg₂Si is an ideal reinforcing phase in metal matrix composites. Making using of the characteristics of Mg-Si alloy, Mg₂Si phase can be formed in the process of solidification. However, Mg₂Si often exists in the shape of coarse Chinese script in the matrix, which greatly damages the strengthening effect of Mg₂Si. On the base of the analysis of the formation process of Mg₂Si phase, the effects of Si and Al content on the microstructure of Mg₂Si/Mg composites were systemically studied, and the modifying effect of Sb, Al-Ca and mischmetal on Mg₂Si phase in the composites was also studied. Finally, the wear resistance of the prepared Mg₂Si/Mg composites was investigated. The results show that, with the increase of Si content in Mg-Si alloy, the amount of Mg₂Si in the solidified samples increases, and its shape becomes more full Chinese script. The addition of Al in the alloys can increase the hardness of the matrix of the prepared composites. As a result, the wear resistance of the composites can be further improved. Among the used modifiers, the modifying effect of metal Sb is the best. When 1.2 wt. % Sb was added into the alloys, the shape of Mg₂Si could be transformed from the Chinese script into uniformly dispersed particles. Therefore, Mg₂Si/Mg composites with more desirable microstructure can be obtained under common gravity casting, whose wear resistance is 7.6 times than AZ91 alloy.