Effects of long period stacking ordered phase morphology and dislocation configuration on mechanical anisotropy of Mg-Gd-Y-Zn-Zr alloy during rotary forward extrusion

Abstract

The effects of long period stacking ordered (LPSO) phase morphology and dislocation configuration on mechanical anisotropy of Mg-Gd-Y-Zn-Zr alloy during rotary forward extrusion (RFE) are systematically analyzed. The microstructure is observed by using electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The results show, the RFE-extrusion direction (ED) sample has an optimal strength (tensile yield strength of 228.2 MPa and ultimate tensile strength of 350.8 MPa) and ductility (elongation of 20.2 %), and a large number of mesh tearing ridges and a few dimples are found on the fracture feature of the RFE sample. Compared with the repetitive upsetting-extrusion (RUE) samples, the strength and ductility of RFE samples can be synergistically improved, and the mechanical anisotropic behavior can be greatly weakened. Severe bending and breaking appears in lamellar LPSO phases, and partial re-dissolution occurs in bulk LPSO phases during RFE treatment, which indicates that the influence of morphological differences of LPSO phases in different directions on mechanical anisotropy can be greatly weakened. At the same time, a large number of basal plane stacking faults (SFs) originate from the partial dislocation emission at grain boundary interfaces, which is intricately linked to the elevated hydrostatic pressure conditions generated by the RFE treatment. The density difference of SFs in different directions has been the principal cause of the mechanical anisotropy of RFE samples.