Mechanical responses and microstructure evolution of DP780 in complete σxx-σyy space: Experiments and crystal plasticity characterization

Abstract

During practical forming processing, strong anisotropic mechanical behavior of dual phase (DP) steels is usually detected due to texture, which further determines subsequent processing optimization with loading paths changing. In order to clarify the underlying deformation mechanisms of DP steels under multi-axial loading, the mechanical response of DP780 under different biaxial loading paths was examined in detail. More precisely, anisotropic behavior of DP780 in complete “σ_xx-σ_yy” space was investigated through mechanical testing, microstructure characterization, and crystal plasticity computation based on dislocation density. In particular, biaxial compression test of thin plate is realized by using specifically designed fixture, and consequently yield loci in complete “σ_xx-σ_yy” space is detected experimentally. It is found that stronger anisotropy is observed under biaxial loading compared with that under uniaxial loading at macro scale, and biaxial Bauschinger effect is detected with biaxial preloading. At the micro scale, the texture evolution is affected directly by loading paths, and the compression load contributes more to the texture evolution. The distribution of the Taylor Factor under different biaxial loading paths reveals the impact of tension and compression on the main activated slip systems (MASS). Under biaxial tension and biaxial compression loading, the MASS of DP780 is the {112} slip system. Under combined biaxial tension and compression loading, the MASS is the {110} slip system. Using crystal plasticity, the evolution of dislocation density under different biaxial loading is captured. The relationship between the biaxial Bauschinger effect and MASS is clarified. It is found that the dislocation multiplication of the {112} slip system is more affected by changes in loading path than the {110} slip system. And during the subsequent loading process, the {110} slip system transform to {112} by preloading. Additionally, the relationship between the alteration of the MASS and the evolution of texture, as well as the resulting macroscopic anisotropic behavior has been elucidated.