Punching shear failure behavior of fine-grained ZK60 Mg alloy processed by a novel forward shear normal extrusion process at room and elevated temperatures

Abstract

The shear punch test (SPT) of ZK60 Mg alloy hot deformed by a novel sever plastic deformation technique called the forward shear normal extrusion (FSNE) was carried out at room and elevated temperatures, and the influence of FSNE process temperature on shear deformation behavior was clarified. FSNE of Mg alloy was carried out at temperatures of 200 °C, 250 °C, 300 °C and 350 °C and then SPT behavior of deformed samples was studied at temperature range of 25–250 °C. The results demonstrated that the deformation behavior and mechanical properties during SPT were significantly affected by the initial microstructure owning to different temperatures of the FSNE process. The microstructures in 200 °C, 250 °C and 300 °C FSNE processed specimens were composed of coarse deformed grains and ultra-fine DRXed grains with a near fully DRXed structure in the highest temperature (350 °C). Basal plane intensity was the maximum value in the 200 °C FSNE processed specimen, whiles with increasing FSNE process temperature, the random crystallography orientation was gradually dominated. Mechanical properties results showed that the 350 °C processed specimen presented the superior RT shear properties with the ultimate shear strength (USS) of ∼ 159 MPa and peak shear strain (PSS) of 81% as well as the highest thermal stability. Shear failure surface was mainly composed of rollover, burnished, fractured and burr areas. The percentage of burnished area in punching-out specimens was affected by initial microstructure and strength and for the specimens having high strength, the percentage of this area was low. In each SPT process temperature, higher peak strain postponed rapture and resulted in higher burr area.