Superplasticity in Ultrafine Grained Magnesium Alloy AZ31 Prepared by Accumulative Roll Bonding
In this paper, an ultra-fine grained AZ31 magnesium alloy sheet with grain size less than 3μm was generated by three-run accumulative roll bonding of as cast alloy at a deformation temperature of 350°C and a reduction of 80% for each pass. The microstructures on the different ARB stages were observed and superplasticity examination in the ultrafine grained AZ31 alloy were carried out at a fixed temperature of 300°C and varied strain rate ranging from 10-4 to 10-1 s-1. It is indicated that significant grain refinement was mainly achieved in the first run and gradual uniformity of grain size in the next by continuous dynamic recrystalization. Besides, a superplastic deformation with a moderate elongation-to-fracture of 316% was obtained at a strain rate of 10-2 s-1 indicating a low temperature and high strain rate superplasticity, while a maximum elongation-to-fracture of 562% at10-4 s-1. The strain rate sensitivity exponent as high as of 0.34-0.41 implies the dominant role of grain boundary sliding in superplastic deformation at strain rate ranging from 10-3 to 10-2 s-1. The results indicate a possible approach to produce magnesium alloy sheet with fine grain and excellent deep drawing workability.
Q. F. Wang et al., "Superplasticity in Ultrafine Grained Magnesium Alloy AZ31 Prepared by Accumulative Roll Bonding", Materials Science Forum, Vols. 551-552, pp. 249-254, 2007