Abstract
The effect of manganese addition up to 0.5wt% on the aging behaviour of an Al-4.2wt%Cu alloy was reexamined. The solubility of manganese in the ternary alloy at the solution treatment temperature was about 0.3wt%, without loss of copper in solution. With further addition of manganese, a gradual decrease of copper in solution resulted. The initial rate of room temperature aging observed by electrical resistivity measurements was not materially affected by the amount of manganese. However, retardation of age hardening occurred with increase of manganese content, and in an alloy containig 0.5wt% manganese no effective hardening occurred during a few weeks.
Within the temperature range of artificial aging at which hardening occurred in two stages, the peak hardness of the ternary alloys was vertually unaffected by the amount of manganese and it was higher than that obtained for the binary alloy with the same copper content, though in alloys with higher manganese content, the retardation of hardening was apparent at the initial stage of aging at all temperatures. As raising the aging temperature to where hardening occurred in a single stage, the peak hardness decreased gradually followed by a marked drop. The higher the manganese content, the lower was the peak hardness. In alloys containig lower manganese content, the age hardening effect was remarkable at 180200°C in comparison with the binary alloy of the same copper content.
