Mechanism of stress aging in Al-Cu(-Mg-Ag) alloys

The effect of stress aging on the nucleation and growth of precipitates in Al-3 .88%Cu and Al-3.87%Cu-0.56%Mg-0.56%Ag alloys was investigated by electric res istivity measurement and transmission electron microscopy observation. The resul ts indicate that external stress promotes the formation of clusters of solute at oms or GP zones,but retards the growth of θ′ and Ω phases. A critica l phenomenon that the microstructural evolution will be modified at a certain ex ternal extress value is found in Al-Cu-Mg-Ag alloy. The applied external stre ss during aging induces preferentially oriented precipitations of θ′ and Ω in Al-Cu and Al-Cu-Mg-Ag alloys,respectively. The origin of stress- induced orientation effect is understood by analyzing interaction between extern al stress and misfit strain by Eshelby elastic inclusion theory.