Microstructure and Mechanical Behavior of Mg-0.5Si-xSn Alloys

Mg-0.5Si-xSn (x=0.95, 2.9, 5.02wt.%) alloys were cast and extruded at 593K (320 C) with an extrusion ratio of 25. The microstructure and mechanical properties of as-cast and extruded test alloys were investigated by OM, SEM, XRD and tensile tests. The experimental results indicate that the microstructure of the Mg-0.5Si-xSn alloys consists of primary α-Mg dendrites and an interdendritic eutectic containing α-Mg, Mg Si and Mg Sn. There is no coarse primary Mg Si phase in the test alloys due to low Si content. With the increase in the Sn content, the Mg Si phase was refined. The shape of Mg Si phase was changed from branch to short bar, and the size of them were reduced. The ultimate tensile strength and yield strength of Mg-0.52Si-2.9Sn alloy at the temperature of 473K (200 C) reach 133MPa and 112MPa respectively. Refined eutectic Mg Si phase and dispersed Mg Sn phase with good elevated temperature stability are beneficial to improve the elevated temperature performance of the alloys. However, with the excess addition of Sn, large block-like Mg Sn appears around the grain boundary leading to lower mechanical properties.