The microstructure and mechanical properties of permanent-mould cast Mg–5 wt%Sn–(0–2.6) wt%Di alloys

The didymium (neodymium–praseodymium mixed metal, neodymium:praseodymium = 3:1) addition to the Mg–5 wt%Sn alloy results in the formation of a feather-shaped Snx(Nd,Pr)y phase mainly on the grain boundaries, and gives rise to grain refinement when the addition is below 2 wt%. The tensile strength and elongation of the alloys are improved with the addition of didymium, and optimum mechanical results are attained at an addition of 2.0 wt% didymium, where the UTS increased by 26.9% and the elongation by 7.7%. The feather-shaped Snx(Nd,Pr)y phase changes to a stick-shaped Snx(Nd,Pr)y phase when the didymium addition is over 2 wt%. As a consequence, the tensile strength and especially the elongation show an obvious decline.