Microstructure and Mechanical Properties of Al–Zn–Mg–Ni–Fe Alloy Processed by Hot Extrusion and Subsequent Radial Shear Rolling

The evolution of the microstructure and mechanical properties of Al–5.76Zn–1.77Mg–0.33Fe−0.45Ni (wt pct) alloy bars produced by hot extrusion (HE) followed by radial shear rolling (RSR) and heat treatment (quenching + aging) has been studied. The results show that the suggested thermomechanical treatment (TMT) allows one to produce a specific type of microstructure. HE provides for defect-free deformation of the initial cast structure, while RSR leads to the formation of a fine microstructure due to unique temperature–strain conditions. During deformation, insoluble Al₉NiFe eutectic phase crystals are refined to a size of about 100 nm. These crystals are localized along the grain and subgrain boundaries and act as effective barriers to the migration of high-angle and low-angle grain boundaries. As a result, the formation of a deformed structure with an extensive network of low-angle grain boundaries (especially in the near-surface region where the equivalent strain is about 15) is observed in the central part and in the near-surface region of the obtained bars. The formation of a structure with an average characteristic subgrain size (~ 2 to 3 μm) comparable to that of grains produced by severe plastic deformation processes provides for a favorable combination of mechanical properties (UTS ~ 416 MPa, YS ~ 293 MPa, δ ~ 8.4 pct), which are comparable to the mechanical properties of a similar alloy after equal channel angular pressing.