Microstructural evolution and orientation-correlated origin of the coarsening behaviors in Au–Sn eutectic alloys

Abstract

Au–Sn eutectic alloys are widely used in lead-free sealings and solders. Hot rolling, a process of the combination of deformation and heat, remains an attractive method to thin the solder strips for bulk ingots of Au–Sn eutectic alloys, but the mechanisms governing the hot rolling process of Au–Sn eutectic alloys is not yet clear. Solder strips thinning is thus not reached easily. In this study, the heat induced coarsening origin and spheroidization mechanisms in Au–Sn eutectic alloys were uncovered in terms of the microstructural evolution and orientation relationship. Microstructure evolution of lamellar colony of Au–Sn eutectic alloy revealed that the initiation sites of coarsening occurs at the boundary of the lamellar colony structure and the end of the lamellar fault inside the colony structure. Termination migration was found to dominate the origin of coarsening mechanism of Au–Sn eutectic alloy, with involving large scale nano-lamellae, paired lamellar faults and a large number of coarsening structure. And another new coarsening mechanism, lamellae splitting, was proposed based on “groove” morphology, interface structure and crystallographic orientation relationship, to create massive lamellar faults for termination migration. The mechanisms will provide a new insight into coarsening origin. And the results pave the way of hot rolling Au–Sn eutectic alloys in terms of parameter selection, microstructure evolution and coarsening mechanisms.