Outstanding mechanical properties of ultrafine-grained Al7075 alloys by high-pressure torsion

High frictional die and continuous rotation during high-pressure torsion provide not only a large shear strain but also a large amount of frictional heat that facilitates the generation of complex microstructural changes, including grain refinement, dynamic recovery, and solute migration. Since metallic alloys with low melting temperatures are sensitive to heat energy, the mechanical properties and microstructural evolution of highpressure torsion-processed aluminum 7075 alloys are investigated in this study. The large shear strain resulting from high-pressure torsion induces both grain refinement and dislocation cell formation, leading to strength enhancement and ductility degradation of the alloy. The deformation and frictional heat become a driving force for solute migration, including brittle intermetallic compound dissolution and nano-sized precipitation generation in the matrix. These solute migration activities contribute toward enhancing both the strength and ductility by inducing precipitation hardening and dissolution of the brittle phase simultaneously. Consequently, both the strength and ductility of the high-pressure torsion-processed aluminum 7075 alloy become larger than that of the initial state. This result shows that the microstructural changes of the severe plastic deformation-processed lowmelting-temperature metallic alloys induce a significant mechanical property enhancement of nanocrystalline materials.