Abstract
Aging phenomena of Al-4%Cu alloys containing Mn up to 0.5% were studied. Two types of solution treatments, normal treatment at 520°C for 2 hr and special treatment at 520°C for 1 hr after annealing at 560°C for a week, were made. Specimens were aged mainly at 200°C. The initial aging rate and age-hardenability of the ternary alloys normally treated reduce with increasing Mn content. This fact is well understood basing on the fact that the density of dislocation loops acting as nucleation sites for θ' phases decreases, because dispersed insoluble phases as sinks of excess vacancies form. The initial aging behavior of the ternary alloys up to 0.3%Mn specially treated is nearly the same as in the binary alloy resulted from disappearance of the insoluble phases. The aging rate of the ternary alloys is considerably retarded after prolonged aging with increasing Mn content accompanying by asharp suppression in the growth rate of θ' phases. The mechanism is discussed in relation to Mn atoms having extremely low diffusion coefficient in the aluminium matrix.
