Effect of alumina particle size on aging in Al2O3/Al-Cu-Mg composite materials.

Effect of particle size on aging in alumina particle dispersed composite materials has been investigated by transmission electron microscopy. Age-hardening curves of composite materials containing larger alumina particles ranging from 8 to 15μm, were quite similar to those of mother alloy. In these composites, aging processes started with the formation of GPB zones and were followed by the precipitation of S' intermediate phases. While in the composite materials containing smaller alumina particles ranging from 1 to 3μm, the hardness under peak aging condition was lower than that of mother alloy. The electrical resistivity just after solid solution treatment had also lower values than that of mother alloy. Their aging processes started with the formation of GP zones and were followed by the precipitation of θ' intermediate phases. The dissimilarity of these aging processes depending on size of alumina particles caused by the decrease of magnesium content in the matrix due to the formation of spinels on alumina particles.