Effect of Sn to Ca Ratio on the Processing Maps and Hot Deformation Mechanisms in Mg-Sn-Ca Alloys


The effect of Sn/Ca ratio on the hot deformation mechanisms in Mg-Sn-Ca alloy has been studied by analyzing the processing maps for a series of alloys classified into two sets. In set 1, the Sn content is increased from 2 to 6 wt.% keeping the Ca content constant at 2 wt.%, and in set 2, the Sn/Ca ratio is maintained at 3 by using different amounts of Sn and Ca. For set 1 alloys with Sn/Ca ratio less than 2.5, the microstructure consists of CaMgSn phase in the matrix and Mg2Ca phase at the grain boundaries, while it is entirely CaMgSn phase for Sn/Ca of 3 for set 2. The processing maps exhibited two domains of dynamic recrystallization (DRX). In Domain 1, where basal slip+climb occurs to cause DRX, the increasing volume content of CaMgSn phase with increasing Sn content (set 1) generates higher back stress which requires higher temperatures for continuing slip. At higher temperature where Domain 2 occurs, second order pyramidal slip + cross-slip causes DRX. In set 2, the maps are essentially the same, although the domain sizes got smaller with higher alloying content due to an increase in the volume content of CaMgSn particles.
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