The aging behavior of ultrafine-grained (UFGed) Al–0.5%Si–0.5%Ge alloy fabricated using six-cycle accumulative roll-bonding (ARB) processing has been investigated using Vickers hardness measurement and TEM observation.
The hardness of UFGed alloy before aging is about 2.3 times higher than that of the starting specimen without ARB process. The starting UFG specimen showed ultrafine grains with mean size of 156 nm. The hardness of a UFG specimen aged at 473 K decreased monotonously with increasing aging time. From TEM observations of the microstructure of UFG specimen aged at 473 K for long time, results show that the mean size of ultrafine grains increased significantly with increasing aging time. Furthermore, few precipitates exist inside gains, although many coarse precipitates exist at grain boundaries. The hardness of UFG specimen aged at 373 K showed higher value than that aged at 473 K. From TEM observations, results showed many elongated ultrafine grains, with many precipitates formed on the grain boundaries and inside grains of the specimens aged at 373 K.
These results suggest that precipitation hardening strongly affected the hardness in this alloy because many Si–Ge precipitates formed inside grains of the UFG specimen aged at 373 K for long time.