Effect of gradient microstructure on the bendability of AZ31 alloy sheet

Abstract

Extensive researches have elucidated the pronounced benefits of gradient microstructures for the mechanical properties of metallic materials. However, the ramifications of gradient microstructures on formability, particularly regarding their effects on bendability, remain inadequately understood. In this work, the effects of gradient microstructure on the bendability of AZ31 Mg alloy sheet are systematically investigated by comparing the microstructure evolution and strain distribution in the sheets with uniform microstructure (grain size = 12.8 µm and 91.3 µm) and gradient microstructure (grain size = 11.5–75.4 µm). The results show that the bendability of the sheet with gradient microstructure is significantly improved when the fine grains (FGs) are placed at the outer side (TBE-FG sample) and the bendability is increased by 93.1% compared to the sample with fine and uniform microstructure (CE-FG sample). With coarse grains (CGs) placed at the inner side, the strain at the compressive region of the TBE-FG sample is higher than its counterparts, while the tensile strain at the extended region is lowest among the four samples. Quasi-in-situ bending experiments reveal that the CGs at the inner side of the TBE-FG sample undergo more twinning. Moreover, the increment of residual dislocation density at the outer side of the TBE-FG sample is lower than those of other samples, which extends the bending potential. This work provides a novel perspective to improve the bendability of the Mg alloy sheet.