Simultaneous improvement of strength and ductility in ZK60 magnesium alloy by constructing the bimodal grain structure

Abstract

In this study, the microstructure and mechanical properties of the commercial magnesium (Mg) ZK60 alloy were conducted to promote the application of Mg alloys. Scanning electron microscopy, tensile and compression tests, electron back scattering diffraction, transmission electron microscope and visco-plasticity self-consistent methods were employed to analyze the microstructure evolution and the strengthening and toughening mechanisms. By direct extrusion in the as-cast state, a bimodal microstructure was obtained, and the mechanical properties were enhanced. The ZK60 alloy, with a bimodal grain structure, exhibited a good combination of strength and ductility. The tensile yield strength (TYS), ultimate tensile strength (UTS), compressive yield strength (CYS) and fracture elongation (FE) reached 272 MPa, 347 MPa, 289 MPa, and 36.2%, respectively. Compared with the traditional extrusion ZK60 alloy, the increment in TYS, UTS, CYS, and FE was 15 MPa, 31 MPa, 25 MPa and 8.6%, respectively. The formation of the bimodal structure in the ZK60-CE sample is attributed to the combination of the PSN and Zener pinning effects. The improvement in strength is mainly attributed to the residual dislocations in the un-DRXed grains and the good ductility is ascribed to the activation of the non-basal slip. This study provides a low-cost and efficient strategy for the preparation of the bimodal structure by regulating the pre-extrusion microstructure to improve mechanical properties.