Influence of magnesium on grain refinement and ductility in a dilute Al-Scalloy

Experiments were conducted to determine the influence of magnesium addition s on grain refinement and tensile ductility in an Al-0.2% Sc alloy Processe d by equal-channel angular pressing (ECAP). The experiments show ECAP reduc es the average grain size to within the range of similar to0.70 to similar to0.20 mum for alloys containing from 0 to 3% Mg but the as-pressed grain s ize increases to similar to0.3 Pin in an alloy with 5% Mg because it is the n necessary to use additional annealing treatments during the pressing proc ess. The ultrafine grains introduced by ECAP are stable to high temperature s in the alloys containing from 0 to 3% Mg: in all alloys, the average grai n size is <5 mum after annealing for I It at temperatures up to similar to 750 K. High superplastic ductilities were achieved in the alloy containing 3% Mg but alloys containing 0.5% and 1% Mg exhibited the enhanced ductiliti es generally associated with conventional Al-Mg alloys. The results suggest the addition of similar to3% Mg is optimum for achieving superplastic elon gations at rapid strain rates in the Al-0.2% Sc alloy. (C) 2001 Acta Materi alia Inc. Published by Elsevier Science Ltd. All rights reserved.