Improving mechanical properties of AZ31 alloy sheets via novel turned-bearing extrusion by introducing shear strain

Abstract

In this work, novel turned-bearing extrusions (TBE) conducted by using the dies with the single corner and double corner, named SC-TBE and DC-TBE respectively, are developed to introduce additional shear strain during the preparation of AZ31 alloy sheets, which is expected to improve the strengths of sheets. Numerical simulations are conducted to uncover the effect of additional shear deformation on the microstructure during the TBE. The results show that the high strain during the TBE leads to a high nucleation rate for dynamic recrystallization (DRX), resulting in grain refinement of the extruded Mg alloy sheet. However, the high strain also increases the temperature of the material due to the heat generated by plastic deformation, which provides a great driving force for grain growth and consumes dislocations. As these two effects compete with each other when increasing the strain near the die orifice, the SC-TBE sheet has finer grains and a higher residual dislocation density compared to the DC-TBE sheet or the sheet prepared by the conventional extrusion (CE). Fine-grain strengthening and substructure strengthening work together and enhance the tensile yield strength (TYS) of the SC-TBE sheet. The TYSs along extrusion direction (ED), transverse direction (TD) and 45° direction (the half angle between ED and TD) of the SC-TBE sheet are improved by 32 MPa, 65 MPa and 35 MPa respectively compared with the CE sheet. The findings of this research provide some new insights into the development of new preparation methods for Mg alloy sheets with higher strength.