Evaluation of microstructure and mechanical properties of Al-Zn alloy during rolling

Solid solution-treated binary Al-20% Zn alloy was deformed by rolling and accumulative roll bonding in the equivalent strain range of 0.19-12.05 at room temperature. The grain size of the Al matrix decreases with the increase in deformation degree and reaches the nanometre range. The dislocation density initially increased with the deformation degree and then decreased. The Zn-phase particles were dynamically precipitated from the Al-Zn supersaturated solid solution and then coarsened during rolling. Rolling after the strain of 12.05 did not result in full decomposition of the solid solution. The hardness of the Al-Zn was also investigated. Results showed that the value reached up to 119.76 Hv at a strain of 2.92 and then decreased with increasing rolling strain. At the early stage of rolling, the strengthening mechanism of the rolled Al-Zn alloy included work hardening by dislocations, precipitation strengthening by nanosized precipitates and boundary strengthening by grain refinement. When the strain was larger than 2.92, the Al-Zn alloy's consistent softening was attributed to the decomposition of supersaturated solid solution, coarsening of the precipitate phase and annihilation of dislocations during severe plastic deformation.