Strength and ductility improvement in a heterostructured Mg-Gd-Y alloy with inversely-gradient hardness distribution

Abstract

The Mg-8.75Gd-2.85Y (wt%) alloy processed by surface mechanical attrition treatment (SMAT) was annealed at 350 °C followed by peak-ageing. Recrystallization occurred in the surface layer of the specimen induced by the annealing treatment. The obtained heterostructure contained a fine-grained (FG) layer with thickness of about 350 μm on the top and a coarse-grained (CG) layer at the bottom. The sample exhibited a reversely-gradient distribution in hardness, in which the FG layer showed lower values than the CG layer. It was related to the different behaviors of recrystallization and precipitation. Compared with the homogeneous CG alloy, the heterostructured sample exhibited enhancement in both strength and ductility. The increase of yield strength was mainly ascribed to grain boundary strengthening and dislocation strengthening. The random texture of the FG layer and the synergetic effect of the heterostructure were beneficial to the improvement of ductility. This work provides valuable insights for developing gradient-structured Mg-RE alloys for high performance in engineering applications such as automotive, aerospace and defense industries.

Keywords

• Magnesium alloy
• Gradient structure
• Recrystallization
• Strengthening mechanism
• Strength-ductility synergy