Co-segregation behavior and weakening effect of the major elements in Al-Zn-Mg-Cu series alloys on Al Σ3(111)[110] symmetrical tilt grain boundary: a first-principles study

Abstract

This study comprehensively investigated the co-segregation behavior of Mg, Zn, and Cu atoms at the Al Σ3(111)[110] symmetrical tilt grain boundary (GB) and its strengthening effect on the GB strength by first-principles calculation. The atoms of the three elements had a strong tendency to segregate at the GB based on the calculation of the segregation energy. The order of their co-segregation was Mg, Zn, and Cu, respectively. The change of the bond lengths between atoms near the GB increased/decreased the charge density attributed to the different atomic radii of the elements. The separation energy and tensile strength of the Al Σ3(111)[110] GB decreased with the preferential segregation of Mg first, then continued decreasing with the co-segregation of Zn, and finally increased with the co-segregation of Cu, decreasing overall. These results suggest that the co-segregation behavior of Mg, Zn, and Cu atoms at the Al Σ3(111)[110] symmetrical tilt GB embrittles the GB and reduces the mechanical properties of the alloy. Besides, O and H atoms further reduce the strength of the GBs co-segregated by Zn, Mg, and Cu.

Keywords

• Co-segregation
• Grain boundary
• Al-Zn-Mg-Cu
• Strengthening
• Embrittlement
• First-principles calculation