First-principles calculation of interface binding strength and fracture performance of β’/Al interface in Al–Mg–Si–Cu alloy

Abstract

High strength and high toughness are the key requirements of Al–Mg–Si (6xxx) alloys, and the performance of the precipitate phase directly affect the mechanical properties of the alloys. Among them, the β’ (Mg9Si5) precipitate has the strengthening effect for Al–Mg–Si alloy which has not been systematically studied. Therefore, we explore the essential mechanism of simultaneously enhancing the mechanical strength and fracture resistance of alloy from the perspective of two kinds of orientation relationships (ORs) precipitate/matrix by using density functional method. In this study, we obtain the thermodynamically stable interface structures by the calculation of adhesion work and interface energy. By analyzing the micro-structure and bond charge transfer at the interface, it is found that the Si–Al bond and the Mg–Al bond play a key role in interfacial bind strength and toughness, respectively. Based on the Griffith fracture theory, we point out that the initial fracture in the alloy is related to the element composition ratio, and β′ will not trigger fracture preferentially. An in-depth analysis of the electronic structure of atoms at β’/Al interface indicates that the difference between Si–Al bond and Mg–Al bond interactions mainly lies in the decomposition of bond strength and orbital hybridization. This research extends our knowledge of improving the strength and toughness of Al–Mg–Si alloy.