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 Sn-x(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 Sn-x(Nd,Pr)(y) phase changes to a stick-shaped Sn-x,(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. (c) 2006 Elsevier B.V. All rights reserved.