Effects of hot compression on the fracture toughness and tensile creep behaviors of a Mg-Gd-Y-Zn-Zr alloy

Abstract

The effects of hot compression on the fracture toughness and tensile creep behaviors of a Mg-Gd-Y-Zn-Zr alloy were researched in detail. The hot compression was performed to a true strain of 0.5 along the extrusion direction at 703 K with a strain rate of 3 × 10-1 s-1. Two types of samples were used in this work: one was the annealed sample without hot compression (NHC sample), the other was the annealed sample with hot compression (HC sample). Uniaxial tensile tests were performed with a strain rate of 3 × 10-3 s-1 at room temperature and 523 K. Fracture toughness tests were performed with a strain rate of 3 × 10-3 s-1 at room temperature. Tensile creep tests were carried out at 523 K under various applied stresses ranging from 90 to 130 MPa. All tests were conducted along the extrusion direction. The results showed the improved mechanical properties were obtained in the HC sample at room temperature. At elevated temperature, the yield strength of the HC sample was improved, while the ultimate tensile strength and elongation were decreased. Compared with the NHC sample, the room temperature fracture toughness of the HC sample was apparently improved due to 14H LPSO phases and kink bands had excellent blocking effects to cracks growth and turned the crack propagation direction, which helped to release stress and absorb energy. However, the creep resistance of the HC sample was poorer than that of the NHC sample at 523 K. The creep mechanism of the NHC sample was basal slip, while the HC sample were dominated by pyramidal <c+a> slip and grain boundary migration. Besides, the dynamic precipitation of β′ phases occurs during hot compression. Although pyramidal <c+a> slip and β′ phases had positive effects on the creep resistance, they could not offset the detrimental impacts derived from grain boundary migration and cracks nucleation at kink bands. As a result, a decreased creep resistance was obtained in the HC sample.