Controlled radial deformation of AZ31B magnesium alloy bar during cyclic rotating-bending process

Extruded magnesium alloy bars are susceptible to uneven microstructure after the heat treatment process, which is characterised by coarse grain size in the surface, thus affecting the further processing properties of the overall bars. In this paper a new cyclic rotating-bending (CRB) process is proposed to improve the microstructure by achieving a gradient plastic deformation of the bars from the surface to the core. The paper is based on finite element simulations to qualitatively and quantitatively investigate the plastic strain distribution and evolution in the middle radial section of the bar under different CRB processes. In addition, the influence on the microstructure distribution under the processes is also further clarified. The results show that during CRB deformation, the plastic strain in the middle radial section of AZ31B magnesium alloy bars gradually decreases from the surface to the core radially, and the plastic strain in the surface is significantly positively correlated with the bending angle and the period of rotation. When the bending angle reaches 150°–170° and the period of rotation reaches 30 r, the section of the bars is fully plastic deformed. Simultaneously, compared to the initial microstructure, significant twinning deformation occurs in the surface of the bars after different CRB processes, which further promotes grain refinement.