On Vacancy and Solute Co-Segregated η1 Interface in Over-Aged Al-Zn-Mg Alloys

Abstract

We represent a combined first-principles and scanning transmission electron microscopy (STEM) study of the η1A1 interfaces in an over-aged Al-Zn-Mg alloy. As one of the major η-MgZn2 precipitate phase variants, η1A1 tends to form highly coherent interfaces with Al matrix, along with various unique solute segregation patterns on its interfacial layers. The interface phase diagram suggests either an Mg-rich or a Zn-rich interface, depending on the chemical potential range of Zn. Further segregation calculations, however, strongly suggest the STEM Z-contrast imaged interface to be a vacancy and solute co-stabilized Mg-rich structure that is favored at relatively low Zn chemical potentials. Based on our experimental and calculation results, the profound thermodynamics origin of the η1A1 interface and its intricate segregation behavior were clarified and described using a generalized structure model. The η1A1l interface structure and segregation at higher Zn chemical potentials were also predicted for future experimental validation.