Effects of Sn addition on dynamic recrystallization of Mg-5Zn-1Mn alloy during high strain rate deformation

Effects of Sn addition (0-1.5 mass%) on dynamic recrystallization (DRX) of Mg-5Zn-1Mn alloy during high strain rate (ε̇=9.1 s−1) deformation are investigated by hot compression testing. With a higher Sn addition, the strain corresponding to the maximum softening rate and the critical strain corresponding to the onset of DRX decrease at first and then increase, while the DRX fraction is just the reverse. The Mg-5Zn-1Mn-0.9Sn alloy shows the biggest DRX extent. Continuous DRX with twin nucleation is the dominant DRX mechanism for all the alloys. The high density dislocations inside twins gradually evolve into the cellular structures and sub-grains by dynamic recovery, and sub-grains turn into the DRX nuclei. The Sn addition can adjust the nucleation rate and the nucleus growth rate of DRX by regulating the inclination for twinning, adjusting stacking fault energy (SFE) and changing the amount of precipitates. Solute Sn atoms not only promote DRX nucleation by increasing twin density but also stimulate the DRX nucleus growth by reducing SFE. With the higher amount of MgZn2 and Mg2Sn dislocation-induced precipitates, the negative effect on DRX derived from the precipitates becomes effective, including hindering the formation of cellular structures and preventing the rotation and the growth of sub-grains by the pinning effect.