Deformation behavior upon two-step loading in a magnesium alloy sheet

Abstract

Two-step loading tests were performed on an AZ31 rolled magnesium alloy sheet with strong basal texture in the normal direction, and the deformation behavior such as a stress-strain curve, Lankford value, and texture evolution was investigated both experimentally and numerically. When the sheet was subjected to compression in the rolling direction followed by tension in different directions, the following characteristic deformation was observed during the second loading: The sigmoidal shape of the stress-strain curve was more pronounced when the sheet was stretched in the rolling direction but less pronounced as the loading direction approached the transverse direction. The Lankford value during the second loading was much smaller than that of the virgin sheet. Observation of the microstructure showed that the detwinning activity during the second loading decreased as the loading direction approached the transverse direction. The aforementioned deformation behavior was qualitatively well predicted using a crystal-plasticity finite-element method. The crystal-plasticity analysis was then used to investigate the underlying deformation mechanism upon two-step loading, focusing especially on the effect of twinning and detwinning activities.