Hot deformation behavior and microstructural evolution of as-homogenized Al–6Mg–0.4Mn–0.25Sc–0.1Zr alloy during compression at elevated temperature

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Hot compression tests of homogenized Al–6Mg–0.4Mn–0.25Sc–0.1Zr alloy were carried out on Gleeble-3500 testing system in the temperatures range from 300°C to 450°C and strain rates range from 0.001s−1 to 10s−1. To evaluate the hot workability of this alloy, the processing maps at strains of 0.3 and 0.5 were established on the basis of dynamic material model and Prasad’s instability criterion. The related microstructures were studied by optical microscopy, scanning electron microscopy and transmission electron microscopy. The results show that flow behavior and microstructural evolution of the alloy are significantly affected by deformation temperature and strain rate. The peak flow stress decreases with increasing deformation temperature, but increases with increasing strain rate. Stable deformation mainly occurs at high temperature with low strain rate due to the softening effect of dynamic recovery and dynamic recrystallization. The volume fraction of new dynamic recrystallized grains increases with increasing temperature and/or decreasing strain rate. These grains are prone to coarsen at elevated deformation temperatures. But thanks to the resistance of Mn-containing particles and nano-scale Al3(Sc,Zr) dispersoids, the coarsening of grains are restrained efficiently. Flow instability mainly occurs at high strain rates because of shear bands, brittle β-phases and initiation of micro-cracks along grain boundaries. According to the processing map at strain of 0.5 and microstructural observation, the optimum processing parameters of the alloy are deformation temperature of 380–430°C with the strain rate between 0.001s−1 and 0.3s−1.