Influence of Bismuth Addition on the Microstructure and Mechanical Properties of Insitu Formed Mg/Mg2Si Composite

The present study is aimed at improving the mechanical properties of Mg/Mg2Si in-situ composite through the modification of Mg2Si morphology by bismuth (Bi) addition. The morphological modification of primary and eutectic Mg2Si phases by Bi addition in Mg-5wt.% Si alloy and its influence on mechanical properties was investigated. It was found that with addition of 0.5wt.% Bi, the morphology of primary Mg2Si precipitates was altered from coarse dendritic to polygonal shape, and their mean size was obviously decreased from more than 70 μm to about 30 μm. Moreover, the rod-like eutectic Mg2Si in modified composite solidified much finer than that of the base alloy. Such improved microstructure of the modified composite resulted in an average about 10% tensile strength and 15% elongation improvement in both room and elevated temperatures. Also, both particle fracture and particle decohesion were observed in the fracture surfaces. But, Bi addition reduced the amount of particle fracture. The isotropic growth manner of primary Mg2Si particles in modified alloy was attributed to poisoning of growth in preferred directions by dissolving Bi atoms in Mg2Si lattice.

Keywords:

Mg/Mg2Si in-situ composite , Modification , Microstructure , Bismuth , Mechanicalproperties