Critical grain size for change in deformation behavior in ultrafine grained Al–Mg–Sc alloy

Experimental evaluation of critical grain size for the change in deformation behavior from strain hardening to strain softening in ultrafine grained (UFG) Al–Mg–Sc was carried out. UFG alloy was processed using friction stir processing (FSP). Two different average grain sizes were obtained by changing the FSP parameters. UFG alloy with grain size larger than the subgrain size showed sufficient strain hardening during tensile testing, whereas smaller grain size material exhibited strain softening.