Investigation of Strengthen Phase Mg_2Si Growth Mechanism on Al-20Si Alloy In-situ Synthesis Composites

摘要

Al-20Si alloy in-situ synthesis composites were prepared by using in-situ synthesis technique. By means of the German ZEISS Axioskop2 optical micrograph, the microstructures of Al-20Si alloy in-situ synthesis composites were investigated. The evolvement rule of Mg_2Si microstructure was analyzed. The growth mechanism of Mg_2Si was studied. The results indicate that Al-20Si alloy in-situ synthesis composites are prepared successfully when the certain contents of magnesium are added in Al-20Si alloy melt. The morphology of primary Mg_2Si is the coarse block and eutectic Mg_2Si begin to appear which the morphology is the Chinese characters-like shape or stripe ones when the content of magnesium is 8%. While the coarse block of Mg_2Si decrease, and the morphology of Mg_2Si is Chinese characters-like shape, dendritic shape and fishbone shape with 6% magnesium. In the process of Mg_2Si growth, Mg_2Si push out more aluminum to solid-liquid interface, so the redistribution of solute elements happens in solid-liquid interface. The equilibrium structure of interface is that of the minimum free energy. Mg_2Si growth mechanism is in conformity with the interfacial energy minimum principle.