Abstract
Al2O3 and SiC particle dispersed Al–4 mass%Cu composites were prepared from mechanically alloyed (MA) and wet-mixed powders (WM). The effects of the kind, size and volume fraction of ceramic particles on aging behaviors of the composites were investigated. There were the regions with high dislocation density in the vicinity of the ceramic particles after solution treatment. The regions were due to the differential thermal expansion coefficient between ceramic particles and the matrix. In the regions, the precipitation of θ′ phases was activated and the time to the peak hardness of aging curves was shortened with increasing dislocation density. The acceleration of aging reaction was, therefore, attributed to the preferential precipitation of θ′ phases on dislocations. The amount of age-hardening was slightly dependent on the nature of ceramics, and remarkably decreased with the volume fraction of particles. In particular, the age-hardening in MA composites was low, because MA composites had many regions of very high dislocation density and grain boundaries where were preferential precipitation sites of θ phase. Present composites were mainly strengthened by the precipitation of θ′ on dislocations during aging and the apparent activation energy of aging in the composites was about 1/2 of that in IM alloy.
