POSITION SENSITIVE ATOM PROBE STUDIES OF THE COMPOSITION OF Ω AND θ' PRECIPITATES IN Al-Cu-Mg-Ag ALLOYS

Abstract
Low concentration additions of silver to Al-Cu-Mg alloys can lead to the formation of platelike precipitates, designated Ω, is formed on {111} planes. Although the morphology of these precipitates has been extensively studied, little information exists about the chemistry of the Ω precipitates, and in particular, about local elemental segregation. In this paper we report the results obtained in a series of experiments carried out in the Oxford atom probe laboratory on the microchemistry of both Ω and θ' precipitates in an Al-Cu-Mg-Ag alloy. The Ω precipitates are found to be richer in magnesium and silver than the θ' precipitates, but are found to have a lower copper content. Studies of coherent interfaces of the Ω precipitates suggest that there is no preferential segregation of magnesium or silver to these interfaces.