Microstructure evolution of accumulative roll bonding processed pure aluminum during cryorolling

The microstructure evolution and mechanical properties of ultrafine-grained (UFG) Al sheets subjected to accumulative roll bonding (ARB) and subsequent cryorolling was studied. Cryorolling can suppress the dynamic softening of UFG Al sheets subjected to ARB at room temperature. After the third ARB pass, the grains are slightly refined as the number of ARB passes increases. However, the grains are significantly refined further during cryorolling. The grain size of 460 nm achieved after the third ARB pass is reduced to 290 nm after two cryorolling passes with total reduction ratio 80%. Sheets subjected to ARB + cryorolling show improved mechanical properties compared to only ARB-processed sheets due to a change in the fraction of high-angle boundaries and elongated grains. The deformation mechanism for ultrafine grains at room temperature is determined by grain boundary sliding or dislocation-based recovery, while it is governed by dislocation glide at cryogenic temperature.