Research on Microstructure of Az31 Alloy Sheets Processed by a New Severe Plastic Deformation

An innovative severe plasticity deformation technique was introduced to investigate microstructure, texture and hardness by finite element method, optical microscopy, electron back-scattered diffraction, transmission electron microscope and hardness tester. The results show that Grain refining gets better as the temperature drops, Because of the largest local relative deformation, leads to the maximum effective-strain at lower temperatures, greater deformation temperatures tend to create a bigger Zener-Hollomon value, resulting in coarse recrystallized grains, faster grain boundary movement, and considerable grain expansion. Meanwhile, the dominant slip mode is to convert basal slip or pyramidal slip into pyramidal slip from a lower temperature to a higher temperature, which allows for a significant weakening of the basal texture. Furthermore, at higher temperatures, plenty of {10-11} contraction twins arise, which are devoted to triggering pyramidal slip, which effectively weakens basal texture. Besides, DRX has occurred, but the extent of it is very limited, and only the conversion of deformed grains to sub-structureds has been completed; however, the conversion of sub-structureds to DRXed grains has not occurred or only occurred in a limited way, which could be due to die structures. And twinning behaviour are stronger than DRX in our process to alter crystal orientation and cut grain size, three mechanisms above have influence on grain refinement, which effects associated with the variance of atomic or ionic spacing with crystallographic direction. Finally, at 200 °C, the hardness can reach 79.9 HV, but the hardness distribution is the worst because an internal crack might occur, compromising hardness uniformity, and the hardness values at 400 °C are too low. As a result, the 300 °C group has the best balance.