Tensile behavior at various temperatures of the Mg-Gd-Y-Zn-Zr alloys with different initial morphologies of LPSO phases prior to extrusion

Abstract

The tensile behavior at (−100)-300 °C of the extruded and peak-aged Mg-5Gd-3Y-xZn-0.5Zr (x = 1 and 2 wt%, designated as VWZ531K and VWZ532K) alloys was investigated in the aspects of microstructural evolution, deformation modes, mechanical properties, etc. The higher Zn content endows the VWZ532K alloy with more intragranular lamellar LPSO phases and larger interdendritic ones at the initial homogenized status, which induces the lower DRX ratio, finer DRXed grain size, and negligible aging hardening response subsequently. During extrusion, precipitation of intragranular LPSO phases occurred in the VWZ531K alloy and partial DRXed grains formed a special texture component with the c-axis aligning parallel to the extrusion direction. However, the VWZ532K alloy experienced the dissolution of intragranular LPSO and dynamic precipitation of β phases. During tensile tests, deformation modes (including twinning, basal slip and non-basal slip) were modified by the testing temperature, grain orientation, LPSO morphology, etc. Compared with the β′ precipitates, LPSO phases are more thermostable to maintain the high-temperature strength, which induce the higher tensile yield strength of the peak-aged VWZ532K alloy (182 MPa) at 300 °C. The larger volume fraction of tension twins and lamellar LPSO phases result in the abnormal high elongation (17.9%) at −100 °C for the VWZ531K alloy.