Experimental Characterization and First-Principles Calculations of Zn Segregation at the β″-Mg5Al2Si4/Al Interfaces in Al-Mg-Si Alloys

In 6000-series Al-Mg-Si alloys, Zn is commonly added to enhance the aging response for improved properties. However, the segregation of Zn to interfaces and its interaction mechanisms with strengthening phases remain unclear. Combining experiments and theoretical calculations, we systematically investigated Zn segregation behavior at the β″/Al interfaces in Al-Mg-Si alloys. Using a modified β″-Mg5Al2Si4 model, we determined that the interface (100)β″//(130)Al has a slightly smaller formation energy of 1.06 kJ/mol, while (001)β″//(3¯20)Al has a relatively smaller interfacial energy of 116 mJ/m2. HAADF-STEM analysis revealed these interfacial morphologies and atomic distributions, showing that Zn atoms not only enter the β″ phase but are also inclined to segregate at the interfaces by occupying the Si3/Al sites. Furthermore, the stability of the β″/Al interfaces and the Zn segregation behavior are well explained at the atomic scale, with calculations showing that stronger hybridization between Zn-3d and Si-3s orbitals facilitates Zn segregation at the interfaces.