Effect of alloying elements on the microstructure and mechanical properties of squeeze cast Mg-Al-Zn-X alloys

The present study is aimed at improving the mechanical properties of Mg-Al-Zn alloys by squeeze casting and alloy modification. Alloying elements used were Si, P and Ca. It shows that the addition of Si to Mg-Al-Zn alloys results in the formation of Mg₂Si particles in two morphologies; coarse polygon and chinese script. The formation of chinese script type Mg₂Si particles becomes pronounced as the Al content decreases. The chinese script type Mg₂Si particles act as crack nucleation site. Hence the mechanical properties of Si containing alloys are, less than desirable due to the unfavorable morphology of Mg₂Si particles. Additional alloying elements have been used to modify the morphology of Mg₂Si particles. It has been shown that the addition of Ca or P promotes the formation of fine polygonal type Mg₂Si particles by providing the nucleation site for Mg₂Si particles. P or Ca modified Mg-Al-Zn-Si alloys have no chinese script type Mg₂Si particles which deteriorate the mechanical properties. Such improved microstructure is accompanied by the improvement of mechanical properties.