Low-temperature superplasticity in aluminum alloys processed by equal-channel angular pressing

摘要

Equal-channel angular pressing (ECAP) was applied to achieve grain refinement of Al - 3 mass%Mg alloys containing 0.2 mass%Sc, 0.2 mass%Fe or 0.1 mass%Zn The thermal stability of the fine-grained structures was examined by conducting static annealing experiments. The fine grain Si/CS produced by ECAP were essentially retained up to a temperature of 523 K for the Fe-containing and Zr-containing alloys and up to a temperature as high as 773K for the Sc-containing alloy. The three alloys with Sc, Fe and Zr additions were pulled to failure in tension at 523K corresponding to 0.59T{sub}m, where T{sub}m is the absolute melting point of the alloy, and maximum elongations of ～640%, ～370% and ～390% were obtained at an initial strain rate of 3.3 × 10{sup}(-4) s{sup}(-1), respectively. Such elongations resulted in more than three times or approximately twice the elongation achieved in a binary Al-3%Mg alloy. It is shown that either Fe or Zr may be used as an alternative element in place or Sc to attain low temperature superplasticity. Tensile testing was also conducted on the Sc-containing ternary alloy at a temperature as low as 473K corresponding to 0.54T{sub}m. A maximum elongation of ～420% was attained at an initial strain rate of 3.3 × 1O{sub}(-4)s{sup}(-1). This appears to be the lowest homologous temperature reported to date for superplasticty of Al-based alloys.