Effect of Aging Treatment on Ultra-Fine Grains and Si-Phase in Al-0.5%Si Alloy Fabricated by ARB Process

Abstract

Using TEM observation and Vickers micro-hardness measurements, this study investigated microstructural changes resulting from aging treatment of ultrafine-grained (UFG) Al-0.5%Si alloy fabricated with a six-cycle accumulative roll-bonding (ARB) process, which includes severe plastic deformation. Results show that the mean grain size of the UFGed Al-0.5%Si alloy produced by the ARB was 253 nm. The hardness of specimens aged at 373 K and 423 K decreased monotonously with increasing aging time in the initial stage of aging. The hardness value of the specimen aged at 373 K then became higher than the value of the specimen aged at 423 K after 10 ks. TEM observation revealed that the mean grain size of the UFG specimen aged at 373 K was less than that of the specimen aged at 423 K. Moreover, results confirmed that Si phase precipitates on the {111} planes on the matrix in the UFG specimen aged at 373 K and 423 K. The mean size of Si-phase in the UFG increased with aging time. The Si phase formation in the UFG specimen aged at 373 K is less than that of 423 K in long-term aging. However, the formation of Si phase on the grain boundaries is more conspicuous than in UFG specimens aged at 373 K and 423 K. These results suggest that restraint of the growth of UFG with aging resulted from Si phase precipitation on the grain boundary and lowering of the aging temperature. Moreover the formation of Si-phase in the UFG suggests precipitation hardening in the ARB-processed Al-Si alloy.