Effect of twin and grain size strengthening on tensile properties of a multi-directionally impact forged Mg–Gd–Y alloy

Abstract

The microstructure and tensile properties of twin and grain size strengthening Mg–6.85Gd–5.79Y–0.44Zr alloy have been investigated and characterized by optical microscopy (OM), scanning electron microscopy (SEM), and electron back-scattering diffraction (EBSD). Their room temperature tensile results exhibit that twin strengthening can enhance the strength of Mg–Gd–Y–Zr alloy but sacrifice its ductility or toughness. This should be attributed that lenticular {10−12} twins with high-stress localization directly lead to a brittle failure. In contrast, the strength, ductility, and toughness were synchronously improved for the grain size strengthening Mg–Gd–Y–Zr alloy, i.e., the ultimate tensile strength, uniform elongation, and static toughness increased to 254 (259–245) MPa, 1.02 (1.40–0.55)%, and 5.7 (6.7–4.2) MJ/m3, respectively. This ductility increment should have resulted from fine recrystallization that was free from stress concentration and accommodated the tensile strain by more non-basal slip and grain boundary sliding or grain rotation.