Microstructural evolution during superplastic flow in aluminum alloys processed by ECAP

Equal-channel angular pressing (ECAP) was performed at room temperature to achieve grain refinement in two A1-0.2% Sc alloys containing either 0.5% Mg or 1% Mg, respectively. Processing by ECAP was conducted using dies having internal channel angles of either 60° or 90° where these dies give equivalent strains of ∼1.6 and ∼1.1 for each separate pass, respectively. Samples were pressed up to a maximum of 8 passes. Tensile tests were performed on the specimens after ECAP by pulling to failure at a temperature of 673 K. The results show that significantly higher elongations are recorded in the alloy containing 1% Mg but for both alloys the elongations to failure increase essentially linearly with the equivalent strain imposed in ECAP and this increase is independent of the channel angle. Using analytical techniques after tensile testing, it is shown that a texture is present and there are predominantly low-angle boundaries in the non-superplastic alloy with 0.5% Mg whereas there is no texture and a predominance of high-angle boundaries in the alloy with 1% Mg.