Influence of Ca and Zn synergistic alloying on the microstructure, tensile properties and strain hardening of Mg-1Gd alloy

Abstract

Influences of Zn, Ca, and their synergistic additions on the microstructures, tensile properties, and strain hardening behaviors of extruded Mg-1Gd alloy sheets were investigated. The grain size of Mg-1Gd sheet was slightly refined with the sole addition of Zn or Ca, while a striking grain refinement was observed with the synergistic addition of Zn and Ca. Sole Zn addition resulted in an increase of both yield strength and ductility of Mg-1Gd sheet. Sole addition of Ca enhanced yield strength but decreased ductility of Mg-1Gd sheet, in which an inhomogeneous distribution of coarse Mg2Ca particles was observed. With the Zn and Ca synergistic addition, the alloy sheet showed much higher strengths. The ultimate tensile and yield strengths of Mg-1Gd-0.7Zn-0.7Ca sheet were ~339 MPa and ~135 MPa along extrusion direction, and ~329 MPa and ~172 MPa along transverse direction, respectively. Meanwhile, the ductility of Mg-1Gd-0.7Zn-0.7Ca sheet along extrusion and transverse direction were also increased up to ~28.5% and ~18.6%, respectively. The improved mechanical performance of Mg-1Gd-0.7Zn-0.7Ca sheet was ascribed to a combined effect of many factors such as fine grain size, homogenous distribution of fine Mg2Ca particles, high prismatic slip activity, suppression of grain boundary cracking, and enhancement of strain coordination capability.