Enhanced microstructure homogeneity of extruded Mg-6Zn-0.5Zr alloy by Ca addition

Abstract

Commercial Mg-6Zn-0.5Zr (ZK60) alloys with different contents of alloyed Ca were subjected to indirect extrusion processing at an initial temperature of 250 ℃ and subsequently the effect of Ca alloying on the microstructure of the extruded alloys was investigated with particular emphasis on recrystallization and grain growth during the hot extrusion. It was found that alloying with Ca results in the refinement of recrystallized α-Mg grains and also it contributes to enhancing the homogeneity of grain size in the extruded condition. Besides, two different types of second-phase precipitates, MgZn2 and Ca2Mg6Zn3, were found to exist in the Ca-containing ZKX600 alloy, although only MgZn2 precipitates appeared in the ZK60 alloy without alloyed Ca. Such microstructural changes in grain size and its homogeneity attained by Ca addition are mainly attributed to the presence of Ca2Mg6Zn3 precipitates, which appear to have better thermal stability than MgZn2 precipitates.