High strain rate superplasticity of an 1570C aluminum alloy with bimodal structure obtained by equal-channel angular pressing and rolling

Using as-cast homogenized aluminum alloy 1570C, the feasibility has been demonstrated to reach enhanced parameters of high-strain-rate superplasticity with elongations to failure more than 2000 % in the alloys of the Al-Mg-Sc-Zr system having the partially recrystallized structure, processed by warm equal-channel angular pressing with the effective strain of e similar to 3. In this alloy, the fine-grained component was represented by a "mantle" of new preferably equiaxed grains with size of about 1-2 mu m, whose volume fraction did not exceed 30 %. Meanwhile, the remnant fragments of original grains, having the size of 10 though 50 mu m, contained a well-defined substructure with the subgrain size of about 1mm. The alloy with such bimodal structure exhibited the highest elongation to failure similar to 2570 % at the initial strain rate of 1.4x10(-2)s(-1) and the temperature of 520 degrees C. Subsequent rolling, carried out at ambient temperature to e similar to 1.6, resulted in replacement of the bimodal structure described above by a heavily deformed one, consisting of the areas of high density dislocations developed in both coarse and fine grained regions; that further improved the alloy superplastic characteristics. So, the interval of the testing parameters, corresponding to optimum superplasticity, was extended toward the higher strain rates and simultaneously, the maximum elongation was significantly increased. The highest elongation to failure of similar to 3030 % was recorded at the initial strain rate of 1.4x10-2s-1 and the temperature of 520 degrees C.