Abstract
The aging behaviors of Al-2%Cu-0.9%Mg alloy have been studied paying attention to the effect of Si addition up to 0.5% by means of hardness, calorimetric and electric resistivity measurements and transmission electron microscopy. Specimens were solution-treated at 505°C, water-quenched and subsequently aged mainly at 200°C.
The hardness of aged ternary alloy was remarkably increased by adding Si, probably due to the change in aged structures that there appeared three sorts of precipitates in Si added alloys in contrast to one sort of precipitate (S') in the ternary alloy. Si addition was effective only when the specimen was water-quenched and not direct-quenched in an aging bath. On the other hand, the Si addition to ternary alloy having higher solute contents, that is, Al-4%Cu-1.8%Mg alloy was found to have a tendency to lower the hardness after aging.
