Unexpected influence of Mn addition on the creep properties of a cast Mg-2Al-2Ca (mass%) alloy

The addition of 0.3% Mn to a Mg-2Al-2Ca (mass%) alloy improves the minimum creep rate by one order of magnitude compared with the Mn-free alloy. Network-shaped Mg2Ca (C14 structure) and (Mg,Al)2Ca (C36 structure) compounds coexist in the interdendritic regions, while plate-shaped Al2Ca (C15 structure) phases are dispersed in the matrix. Ordered Guinier-Preston (GP) zones form dynamically on the basal plane of the α-Mg matrix during creep deformation. The number density of the fine GP zones in the Mn-containing alloy was found to be higher than that in the Mn-free alloy.