The effect of electrical pulsing on the structure and hardness of highly deformed coarse- and ultrafine-grained aluminum alloy 1570C

The study investigates the influence of high-density electropulsing (HDEP) on the microstructure and hardness of non-age-hardenable 1570C aluminum alloy (Al-5.0Mg-0.18Mn-0.20Sc-0.08Zr, wt.%). Interplay between the initial microstructure (coarse-grained (CG) vs. ultrafine-grained (UFG) one), deformation temperature (room temperature rolling (RTR) vs. cryogenic rolling (CR)), and subsequent HDEP was examined. The results demonstrate that cryogenic rolling at −196°C with reduction 80 % provides superior hardening (up to 175 HV for UFG + CR) compared to RTR, due to a more non-equilibrium microstructure with higher dislocation density. Subsequent HDEP-induced softening at current densities (Kj) varied from 0.21 to 1.61×104 A2∙s / mm4 revealed a strong dependence of the microstructure and hardness of alloy on its initial state. The alloy in CG + RTR condition exhibited the highest thermal stability and gradual softening via recovery. In contrast, the alloy in UFG + CR state with the highest stored energy softened most rapidly, initiating recrystallization at the lowest values of energy threshold. A key finding is the formation of a kinetically stable, partially recrystallized bimodal structure in the alloy in UFG + CR state after HDEP, resulting from the competition between a high driving force for recrystallization and the Zener pinning effect of nanoscale Al3(Sc, Zr) dispersoids. After high-energy pulsing, the hardness for all states converged to a level near the initial homogenized condition (≈100 HV), signifying a fundamental shift from deformation-based strengthening back to solid solution and dispersion hardening.

1. Russian Science Foundation - № 23-19-00702
2. The state assignment of IMSP RAS -