Superplastic deformation mechanisms in fine-grained Al–Mg based alloys

The superplastic deformation behaviour at elevated temperatures and constant strain rates of two fine-grained AA5083 type aluminium alloys was investigated. The first alloy with chromium contains Al6(Mn,Cr) particles and the second alloy without chromium has Al6Mn particles. The effective activation energy of superplastic deformation and the activation parameters for the grain boundary relaxation was calculated. The microstructure evolution and contributions of grain boundary sliding, intragranular deformation and diffusion creep to total superplastic deformation were studied by SEM, EBSD, FIB, TEM techniques. Low values of grain boundary sliding and permanent continuous formation of sub-grain boundaries were found in both alloys. Significant dynamic grain growth during superplastic deformation and large value of intragranular deformation were found in the alloy without chromium. Intragranular deformation is not significant and the superplasticity is primarily a result of diffusion creep in the chromium containing alloy with Al6(Mn,Cr) particles.