Subgrain formation and evolution during the deformation of an Al-Mg-Sc alloy at elevated temperatures

The microstructure and mechanical properties of a commercial Al-6Mg-0.3Sc (Russian Al 1570) were characterized. The presence of Sc results in the uniform distribution of fine L1₂ precipitates which stabilize the grain substructure/structure in the alloy. At an intermediate temperature of 350°C, subgrains are formed and they are stable even under a dynamic condition (i.e. under stress). The deformation of Al 1570 at this temperature is controlled by solute drag on gliding dislocations. Thus, the strain rate sensitivity value is about 0.33. At a high temperature of 475°C, fine subgrains are still preferentially formed under static conditions (i.e. without stress). But, under a dynamic condition the low-angled subgrain boundaries quickly convert into high-angled grain boundaries and lead to extensive grain boundary sliding. Therefore, the dominant deformation mechanism of the alloy at 475°C is grain boundary sliding, and the alloy exhibits a strain rate sensitivity value close to 0.5.