Tests and Finite Element Simulation of Yield Anisotropy and Tension-Compression Strength Difference of an Extruded ZK60 Mg Alloy

Abstract

Multiroute yield experiments were carried out on extruded ZK60 magnesium alloy samples under 200 °C and strain rate of 10−2 s−1 by a thermomechanical simulator. A hypoelastoplastic large deformation constitutive relationship was employed to simulate large deformation yield subjected to uniaxial loading, biaxial loading, loading-reverse loading, and orthogonal loading in the finite element (FE) software with user subroutine. The results showed the following: (1) As the accumulative plastic strain increased, the convex yield surface in the 2D stress space gradually expanded or shrank, rotated, and distorted from the approximate ellipse at low accumulative plastic strain. At the same accumulative plastic strain, uniaxial tensile or compressive yield values along different directions were not the same. In addition, the tensile yield value differed considerably from the compressive one. The large deformation yield of ZK60 magnesium alloy showed significant anisotropy, tension-compression strength difference, and evolution effect. (2) FE simulations based on the hypoelastoplastic constitutive relationship could accurately capture the strongly evolving asymmetric yield behavior under complex loading routes. The stress-strain relationships and hardening rates were in better accordance with the experimental results and reflected the yield behavior more realistically compared to simulations without the evolution effect or with traditional linear interpolation. Deformation at low temperature and high strain rate is important to save process costs and improve processing efficiency, but it may cause evolving asymmetric yield during large deformation. It is believed that the simulation approach used herein is reliable for the prediction and optimization of severe plastic deformation processes of hexagonal close-packed (HCP) alloys.