Effects of microalloying with Cd and Ag on the precipitation process of Al-4Cu-0.3Mg (wt%) alloy at 200°C

The present work investigates the effects of individual and combined additions of Cd and Ag on precipitation processes in an Al-4Cu-0.3Mg (wt%) alloy. Analytical scanning transmission electron microscopy revealed that microalloying with Cd stimulates nucleation of θ′ phase on (001)_α planes and that Cd-rich particles form on the rim and broad facets of the θ′ platelets. We interpret these observations to suggest that Cd nucleates heterogeneously at the θ′-α interface and that θ′ can also nucleate heterogeneously at the Cd-α interface. In the quinary alloy, it was observed that Ag and Cd additions seem to work independently resulting in a fine and uniform dispersion of both Ω and θ′. Furthermore, the hardening effect of the (111)_α Ω phase appears to be more potent than other precipitates formed in this system since the hardness of the quinary alloy was intermediate between the Al-Cu-Mg-Ag and the Al-Cu-Cd alloys.