Understanding the Twinning Behavior and Deformation Mechanisms of Mg Single Crystals during Erichsen Test Using Crystal Plasticity FEM

Abstract

Magnesium (Mg) alloys with a density of 1.74 g/cm3 are the lightweight structural materials and their superior mechanical properties make Mg alloys more attractive for various applications. Mg alloys have become the key materials especially in the automotive industry for improvement in the fuel efficiency due to their low density, excellent specific strength and stiffness, exceptional dimensional stability and high damping capacity. In recent years, the cast Mg alloys have widely been used to produce the majority of Mg alloy products. However, the cast Mg alloys fail to meet most of the current requirements and the wrought Mg alloys showing both better strength and toughness are newly expected to be utilized. However, there are still several technical issues to achieve high performance of wrought Mg alloys. Mg usually develops strong basal texture during plastic deformation, resulting in anisotropic mechanical properties and poor formability. Additionally, fundamental observations such as orientation dependency on the slip and twinning modes as well as interactions between deformation modes are still rarely reported. Thus, in the present study, the twinning behavior and deformation mechanisms of pure Mg single crystals were investigated via Erichsen test at room temperature (RT). In order to establish the unique twinning behaviors according to the position of a deformed specimen, microtexture analyses were performed on two cross-sections of a deformed specimen via the electron backscatter diffraction (EBSD) technique. The EBSD results revealed that thin twin bands with different types of twin variants were developed throughout the deformed specimen. The crystal plasticity finite element method (CPFEM), in relation to both the crystallographic slip and deformation twinning, was used to explain the heterogeneous evolution of the twin bands throughout the deformed specimen during Erichsen test at RT. CPFEM results such as strain components, relative activity of deformation modes, and accumulated volume fraction of twin variants can effectively explain the experimentally observed heterogeneity of the twin bands.