The role of Ag in the pre-precipitation process of an Al-1.9Cu-0.3Mg-0.2at%Ag alloy was investigated with regard to the interaction between quenched-in vacancies and Ag atoms. Positron annihilation methods, coincidence Doppler broadening of positron annihilation radiation and positron lifetime spectroscopy, and transmission electron microscopy were used. In the as-quenched state, quenched-in vacancies (V) in the Al-1.9Cu-0.3Mg-0.2at%Ag alloy were associated with Ag atoms as well as Mg atoms (V-Mg-Ag), while V-Mg complexes were formed in an Al-1.9Cu-0.3at%Mg alloy. The recovery of the vacancies after 15s aging at 180C was suppressed by the existence of Ag atoms. These results indicated that the V-Mg complexes were stabilized by the associated Ag atoms, which promoted the co-clustering of Ag and Mg atoms by aging rather than by the formation of dislocation loops.

Coincidence Doppler Broadening Study of the Pre-Precipitation Stage of an Al-Cu-Mg-Ag Alloy. Y.Nagai, T.Honma, Z.Tang, K.Hono, M.Hasegawa: Philosophical Magazine A, 2002, 82[8], 1559-72