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-4Cu0.3Mg (wt%) alloy. Analytical scanning transmission electron microscopy revealed that microalloying with Cd stimulates nucleation of theta' phase on {001}(alpha). planes and that Cd-rich particles form on the rim and broad facets of the theta' platelets. We interpret these observations to suggest that Cd nucleates heterogeneously at the theta'-alpha interface and that theta' can also nucleate heterogeneously at the Cd-alpha 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 fl and theta'. Furthermore, the hardening effect of the {111}(alpha) Ohm 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. (C) 2001 Elsevier Science Ltd. All rights reserved.