Effect of aluminum on microstructural evolution during hot deformation of TX32 magnesium alloy


The effect of Al (0.4 and 1 wt%) addition on the hot deformation behavior of the Mg–3Sn–2Ca (TX32) alloy has been studied with the help of processing maps generated in the temperature and strain rate ranges of 300–500 °C and 0.0003–10 s−1. The deformed specimens have been examined as regards changes in texture and microstructure using electron back scatter diffraction and transmission electron microscopy, respectively. The map for the TX32 base alloy exhibited two dynamic recrystallization (DRX) domains in the temperature and strain rate ranges: (1) 300–350 °C and 0.0003–0.001 s−1, and (2) 390–500 °C and 0.005–0.6 s−1. While 0.4 wt% Al addition to TX32 did not result in any significant change in the processing map, the map for the alloy with 1 wt% Al (TX32-1Al) exhibited four domains in the ranges: (1) 300–325 °C and 0.0003–0.001 s−1, (2) 325–430 °C and 0.001–0.04 s−1, (3) 430–500 °C and 0.01–0.5 s−1, and (4) 430–500 °C and 0.0003–0.002 s−1. In the first three domains, DRX has occurred, whereas in the fourth domain, grain boundary sliding takes place causing intercrystalline cracking in tension. In Domain 1 for all the alloys, DRX has occurred predominantly by basal slip and recovery by climb as confirmed by the resulting basal texture and tilt type sub-boundary structure. In Domain 2 of the base alloy and Domain 3 of the alloy with 1 wt% Al, second-order pyramidal slip dominates associated with cross-slip which randomizes the texture, and forms tangled dislocations and twist type sub-boundaries in the microstructure. The addition of 1 wt% Al causes solid solution strengthening and results in Domain 2 of the map of TX32-1Al alloy and in this domain basal+prismatic slip dominate.
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