The vacancy-trapping model to explain aging retardation in Al-Cu-Sn alloys had been examined by the present authors and the conclusion obtained was that the model had been inadequate and not acceptable. The present study, therefore, was attempted to further examine the same subject in the Al-Cu-Cd system.
Two sorts of alloy systems with 3 and 4wt.% Cu were used. In each alloy system, the Cd content was care-fully varied from 0wt.% to 0.37wt.%.
The results obtained were as follows:
(1) When specimens were of one-phase at the solution temperature, the retardation of aging was not observed at low temperatures. However, the retardation was clearly seen in two-phase specimens as the Cd content increased.
(2) It was found that the retardation in this alloy system was also caused by the decrease of solid solubility of Cu in the α phase at solution temperatures, as in the Al-Cu-Sn alloys.
(3) The theory based on the vacancy-trapping model to explain the aging retardation was again proved to be erroneous in the present study.