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

Low concentration additions of silver to Al-Cu-Mg alloys can lead to the formation of platelike precipitates, designated n , is formed on { 11 1 ] planes. Although the morphology of these precipitates has been extensively studied, little information exists about the chemistry of the n 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 n and 8' precipitates in an Al-Cu-Mg-Ag alloy. The n precipitates are found to be richer in magnesium and silver than the e' precipitates, but are found to have a lower copper content. Studies of coherent interfaces of then precipitates suggest that there is no preferential segregation of magnesium or silver to these interfaces.