Improvement of Strength and Ductility of Al-Mg-Si Alloy Containing Excess Fe and Si by Severe Plastic Deformation under High Pressure

The process of severe plastic deformation under high pressure through high-pressure torsion (HPT) was applied to an Al-Mg-Si alloy containing excess Fe and Si, which was designed as a model alloy for aluminum recycling. It was shown that the tensile strength exceeded 500 MPa with a total elongation to failure more than 20% after HPT processing under 2 GPa for 1 revolution. Microstructure observation was carried out using transmission electron microscopy for grain size and dislocations. Three dimensional image analyses were also carried out using high-energy X-rays in SPring 8 of JASRI for pores and intermetallic particles. Strain rate change tests were further performed for the evaluation of strain rate sensitivity (m). It was found that the m value increases with the imposed strain (the number of HPT revolution). This increase in the m value is attributed to a significant decrease in the activation volume through a reduction in mobile dislocation segments and/or their gliding distances along with the reduction in the grain size to the submicrometer range.