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 resistivity measurement and transmission electron microscopy observation. The results indicate that external stress promotes the formation of clusters of solute atoms or GP zones, but retards the growth of theta' and Omega phases. A critical phenomenon that the microstructural evolution will be modified at a certain external extress value is found in Al-Cu-Mg-Ag alloy. The applied external stress during aging induces preferentially oriented precipitations of theta' and Omega in Al-Cu and Al-Cu-Mg-Ag alloys, respectively. The origin of stress-induced orientation effect is understood by analyzing interaction between external stress and misfit strain by Eshelby elastic inclusion theory.