Enhancing strength and ductility of low RE content Mg-Gd-Y-Zr alloy via a novel thermomechanical treatment based on multi-directional forging

Abstract

The high strength of most Mg-RE alloys is frequently accomplished by high RE addition, but their high density and poor plasticity restrict their applications in the field of aerospace. Focused on this problem, a novel process of the thermomechanical treatment based on multi-directional forging is developed to improve the strength and ductility of low RE content Mg-6.5Gd-1.2Y-0.49Zr (wt%) alloy simultaneously. The mechanisms of high strength and good ductility are revealed by analyzing the deformation behavior, the dynamic recrystallization (DRX) behavior, the work hardening behavior and the strengthening mechanism. The bimodal grain structure, along with the fine grain size of ∼0.8 µm and the coarse grain size of ∼11.6 µm, is prepared after a 4-pass-MDF process, which is ascribed to DRX during MDF and recovery during the interpass annealing. After a peak aging treatment, the ultimate tensile strength reaches 378.4 MPa, the yield strength 324.3 MPa and the elongation to failure 19.0%, respectively. The enhanced strength is more related to the combined effect of aging precipitation of β′ phase and grain refinement, while the good ductility benefits from the ability of bimodal structure to coordinate deformation, the excellent work-hardening effect and the full activation of<c + a> slip.