超微細粒、強ひずみ加工、Al-Si-Ge合金、時効硬化
Using Vickers hardness measurements and TEM observation, this study investigated the aging behavior of ultrafine-grained（UFG）Al-0.5%Si-0.5%Ge alloy fabricated using six-cycle ARB processing. The hardness of the starting specimen of ultrafine-grained Al-0.5%Si-0.5%Ge alloy is about 2.3 times higher than that of the coarse-grained specimen. 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 after long-term aging at 473 K, 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 the maximum value. 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 it has many elongated ultrafine grains. Many fine Si-Ge precipitates formed inside grains of the UFG specimen aged at 373 K in long-term aging.
