An evaluation of superplasticity in aluminum-scandium alloys processed by equal-channel angular pressing

An Al-0.2%Sc alloy and an Al-3%Mg-0.2%Sc alloy were subjected to equal-chan nel angular pressing to a strain of similar to 8 to produce grain sizes of similar to 0.7 and similar to 0.2 mu m, respectively. Because of the presen ce of some areas of subgrain boundaries in the Al-3%Mg-0.2%Sc alloy, additi onal samples of this alloy were subjected to ECA pressing to a strain of si milar to 12. In both alloys, the grain sizes were reasonably stable up to a nnealing temperatures above 700 K. Tensile specimens were machined from the as-pressed samples for testing at elevated temperatures. The Al-3%Mg-0.2%S c alloy pressed to a strain of similar to 12 exhibited exceptional ductilit y with elongations up to a maximum of similar to 1560% at 673 K at the high strain rate of 3.3 x 10(-2) s(-1). By contrast, the Al-0.2%Sc alloy failed under all conditions at elongations < 400%. The difference in behavior bet ween these two alloys is attributed to the nature of the deformation mechan ism which serves to accommodate the superplastic process.