Mechanism of plasticity enhancement of AZ31B magnesium alloy sheet by accumulative alternating back extrusion

Accumulative alternating back extrusion was a potential fine-grain modification method. In this paper, it was an innovative attempt to develop high-performance magnesium alloy sheet by this process. Under the condition of 350 K, commercial AZ31 magnesium alloy was made into billet by accumulative alternating back extrusion, and then extruded into fine-grain magnesium alloy sheet. Through a systematic study of its microstructure and mechanical properties, the results showed that the initial state had an important influence on the evolution of the structure during extrusion. After accumulative alternating back extrusion to produce the billet, the grain size of the sheet obtained by extrusion was significantly refined, which was related to the accumulation of deformation and grain refinement during the alternating loading process. Grain refinement caused the proportion of dynamic recrystallization inside the sheet with 2 cycles of accumulative alternating back extrusion to drop to 27%. With the increase of extrusion cycles from 2 to 4, the high density of dislocations led to an increase in the proportion of dynamic recrystallization and finer grains. The texture changed from strong basal texture to weak bimodal texture. The results of uniaxial tensile test show that due to grain refinement and texture change, the yield strength was significantly reduced, and the plasticity was significantly improved. It was verified that accumulative alternating back extrusion was meaningful for subsequent processing, and it also provided scientific guidance for the development of fine-grained magnesium alloy sheet.