Aging behaviour of Al2O3-particle-dispersed (20vol%) Al-3.96%Cu and Al-4.09%Cu-1.58%Mg alloy composite materials was investigated by means of microvickers hardness, electrical resistivity measurements and transmission electron microscopy. In a case of an Al2O3/Al-3.96%Cu composite materials θ' phase precipitates on subgrain boundaries at an early stage of aging at 423K. After a prolonged agings an increased number of θ' precipitates are seen inside grains. While GP zones form normally in an Al-3.96%Cu alloy at this aging condition, no GP zones precipitate in the Al2O3/Al-3.96%Cu composite material and age-hardening does not take place. On the contrary, age-hardening is clearly observed in an Al2O3/Al-4.09%Cu-1.58%Mg composite material aged at 423K. In this composite material, both GP zones and θ' precipitates are found inside grains, being different from GPB zones and S' intermediate phases normally formed in an Al-4.09%Cu-1.58%Mg alloy.
