Mechanical properties of Bʹ precipitates and fracture behavior of Bʹ/Al interface in Al-Mg-Si alloys: A first-principle calculation study

Abstract

Bʹ is a metastable precipitate in the over-aged Al-Mg-Si alloys, which often coexist with other precipitates such as U1, U2 and βʹ precipitates. In this paper, the properties and tensile behavior of Bʹ precipitate and Bʹ (101¯0)/ Al (5¯10) interface were studied by the first-principles calculations. First, the cohesive energy, enthalpy of formation, and elastic constant and mechanical properties of Bʹ precipitate were calculated. Then the Bʹ (101¯0)/ Al (5¯10) interface models were constructed and their stability was investigated. Finally, the fracture behavior of the B/Al interface was studied by the first principles computational tensile tests. The result shows that due to its brittleness, cracks may be preferentially generated in the Bʹ precipitate. The most stable interface structure is T1-Al, which was obtained by comparing their adhesion works and the interfacial energies. The Si-Al bond plays a key role in interfacial bind strength and toughness. The study of the fracture behavior of the Bʹ (101¯0)/ Al (5¯10) interface shows that cracks are prone to appear in the Bʹ precipitates near the interface, and the destruction of the Al-Mg bond is the source of the cracks.