Effect of cold/warm rolling following warm ECAP on superplastic properties of an Al 5.8%Mg-0.32%Sc alloy

摘要

Commercial extruded rod of 1570 aluminum alloy (Al 5.8%Mg-0.32%Sc) was subjected to equal channel angular pressing (ECAP) at a temperature of 325 ºC with an effective strain of ~8 and subsequent isothermal rolling at the same or ambient temperature up to strain of about 2.0 and 1.6, respectively. The mechanical behaviour in a wide temperature – strain rate range and consequent structure transformations were examined to evaluate an effect of the rolling temperature on the alloy superplastic response. It was found that the warm rolling significantly improved the homogeneity of the ultrafine-grained (UFG) structure formed by ECAP, resulting in near uniform UFG structure with 90-95% of grains having average size of about 1 µm. Such structure demonstrated high thermal stability and elongations to failure more than 2000% with the volume fraction of cavities not exceeding ~1.5% under tension at the strain rates of about 10-1s-1 in the temperature range of 450-475 ºC. In contrast the cold-rolled alloy provided much poorer superplastic behaviour with maximum elongations less than 350% due to low structural stability and intense cavitation. The nature of the alloy structure evolutions under static and dynamic annealing conditions, and superplastic parameters obtained in the as-ECAPed and warm / cold isothermally rolled alloys are discussed.