Microstructure and Mechanical Properties of Al-4Mg-0.3Cu Alloy after HPT and Postdeformation Annealing

The effects of different strain levels applied through high-pressure torsion (HPT) deformation following annealing on the microstructural evolution, thermal stability, and mechanical properties of Al-4Mg-0.3Cu alloy were investigated. The results reveal that Cu-segregated grain boundaries (GBs) were generated in the ultrafine-grained Al-4Mg-0.3Cu alloy with high angle grain boundaries. By contrast, the phenomenon of Cu segregation was not found in micron-scale and submicron-scale grains with low-angle grain boundaries. The mechanism of Cu segregation in ultrafine-grained Al-4Mg-0.3Cu alloy was discussed. After heat treatment, Cu segregation induced the precipitation of the dense Al2CuMg phase at GBs, which strongly inhibit grain growth and improve thermal stability. Stress-strain curves of as-cast, 5-turn, and 10-turn HPT samples showed that fracture strength significantly increased, attributed to grain size refinement, dislocation density increase, and Cu segregation at GBs. After heat treatment, 5-turn and 10-turn HPT samples demonstrate an enhanced elongation to fracture with a slight reduction of fracture strength.