Segregation of the major alloying elements to Al3(Sc,Zr) precipitates in an Al-Zn-Mg-Cu-Sc-Zr alloy

Solute segregation of Zn, Mg and Cu in and around Al-3(Sc,Zr) precipitates in an Al-Zn-Mg-Cu-Sc-Zr alloy was systematically studied using atom probe microscopy, aberration-corrected scanning transmission electron microscopy and first-principles simulations. Results show that the Al-3(Sc,Zr) precipitates occur as a Sc-rich 'core' and Zr-rich 'shell' structure. Zn segregates to the Zr-rich shell of Al-3(Sc,Zr) precipitates and substitute mainly for the Al atoms, and the Zn segregation intensifies with increasing ageing time. Mg and Cu atoms segregate to the Zr-rich shell during the early stages of ageing, while the Mg atoms prefer the Al-matrix with longer ageing time. Density functional theory calculations demonstrate that such segregation is energetically favored and highlight the diverse role of Al-3(Sc,Zr) in influencing the distribution of the major alloying elements.