Microstructures and mechanical properties of Mg-6Gd-1Er-0.5Zr alloy sheets produced with different rolling temperatures

Abstract

In this study, we investigated the microstructures and mechanical properties of Mg-6Gd-1Er-0.5Zr (GE61K) sheets. The results show that the rolling temperature has a remarkable influence on microstructures, age-hardening responses and mechanical properties of GE61K sheets. The microstructures varies with the increase in rolling temperatures, i.e. microstructures were dominated by the mixture of dynamic recrystallized (DRXed) grains and un-DRXed grains at 300 °C, by DRXed grains at 350 °C, and by un-DRXed grains at 400 °C and 450 °C. Rolling at 300 °C leads to a formation of the bimodal microstructure which contains equilibrium Mg5(Gd, Er) precipitates and a large number of dislocations. These dislocations leads to a formation of novel chain-like precipitates which comprise dominant β', β′F (or β′T), tail-like “hexagonal ring” layers, individual “zig-zag” chain and individual “hexagonal ring”, eventually improving age-hardening responses. The chain-like precipitates are beneficial for achieving a good strength-ductility balance by dividing the matrix into nano-scale units and forming subsequent honeycomb structures. As a result, the R-300 °C sheet shows good mechanical properties, i.e. ultimate tensile strength (UTS) of 367 ± 3 MPa, yield strength (YS) of 349 ± 4 MPa and elongation (EL) of 9.1 ± 1.5%, respectively. However, such strength-ductility balance is destroyed sharply as soon as the rolling temperature increases to 400 °C because of the microstructure variations.