Influence of plastic zone ratios on microstructural changes in AZ31B magnesium alloy plates after straightening

This study focuses on the development of straightening schemes for AZ31B magnesium alloy plates produced through rolling processes. These plates are prone to defects such as warping, waving, and edge cracking due to the strong basal texture and limited plastic deformation ability of the alloy. By utilizing the asymmetric tensioncompression model, the neutral layer offset model, and the traditional plastic deformation ratio calculation model, straightening schemes with a plastic zone ratio ranging from 50% to 70% were developed to improve the flatness of the plates. Microstructural analysis using EBSD revealed a change in grain orientation during the straightening process, resulting in the weakening of the basal texture. Some grains still exhibit a preferred orientation for prism slip. However, the high CRSS (critical resolved shear stress) makes it difficult to initiate prism slip, and twinning is required to coordinated plastic deformation. The occurrence of decrease in the volume fraction of twinning was observed at a plastic deformation ratio of 60%. However, at a plastic deformation ratio of 65%, there was an increase in the volume fraction of twinning along with a significant growth in the proportion of dual tensile twin boundary. Excessive plastic deformation at room temperature can lead to dislocation accumulation, uncoordinated plastic deformation, and the formation of micro-cracks and macroscopic defects. By implementing a plastic zone ratio of 60% during the straightening process, the occurrence of defects can be effectively controlled, thus improving the overall quality of the product.