Hot-extruded AZ80Mg was multi-directionally forged (MDFed) at decreasing temperature conditions from 623 K down to 433 K to a cumulative strain of ΣΔε = 5.6 at maximum. Homogeneous microstructures with having various average grain sizes from 0.7 μm to 26 μm were prepared. Tensile strength and hardness increased with decreasing grain size. The MDFed Mg alloys were further extruded at temperatures between 453 K and 523 K at an initial strain rate of 3.0 × 10^-3 s^-1 to form plates and tubes. Even at such relatively low temperatures, extrusion of the ultrafine-grained Mg alloys was successfully carried out. At some conditions, the values of strain rate sensitivity of loading stress became more than 0.3 indicating of occurrence of superplasticity. This result suggested that effect of grain-boundary sliding enabled the warm temperature extrusion of the ultrafine-grained Mg alloys. In such conditions, where lower strain rate, higher temperature and ultrafine-grained structure, slight gain coarsening was also observed. However, the decrease in the strength was quite limited or sometimes further strengthening in contrast took place. This should be due to following effects; i) the employed extrusion temperature was much lower than the conventional one to cause grain coarsening and softening, ii) sharp basal texture evolution for strengthening, iii) dynamic age hardening and iv) work hardening during warm extrusion.
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