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

E. Avtokratova, O. Mukhametdinova, O. Sitdikov, M. Markushev


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 recrystal-lized structure, processed by warm equal-channel angular pressing with the effective strain of e~3. In this alloy, the fine-grained compo-nent was represented by a “mantle” of new preferably equiaxed grains with size of about 1-2 mm, whose volume fraction did not exceed 30%. Meanwhile, the remnant fragments of original grains, having the size of 10 though 50 mm, contained a well-defined substructure with the subgrain size of about 1mm. The alloy with such bimodal structure exhibited the highest elongation to failure ~ 2570 % at the initial strain rate of 1.4 × 10-2 s-1 and the temperature of 520 ºC. Subsequent rolling, carried out at ambient temperature to e~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 test-ing 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 ~ 3030 % was recorded at the initial strain rate of 1.4 × 10-2 s-1 and the temperature of 520 ºC.

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