Effect of annealing treatment on the microstructure and mechanical properties of hot compression Au80Sn20 alloy

Intrinsic fragility is the major bottleneck for expanding the application of the Au80Sn20 eutectic solder. Motivated by eliminating the deformation defects and internal stress, the microstructural evolution and mechanical properties have been studied in a hot compression Au80Sn20 alloy annealed at different temperatures and times. Results show that after annealing treatment, the microstructures of the Au80Sn20 develop from lamellar to equiaxed grains. All the diffraction peaks positions of Au80Sn20 alloy have a right shift revealing an elimination of the deforming residual stress and show a certain degree preferred orientation of (100) AuSn and (012) Au5Sn planes. The indentation depths have a sharp increase at the same load pressure after annealing, meanwhile the hardness and modulus of Au80Sn20 alloy drop evidently. Combining the result of microstructure and mechanical properties evolution, the Au80Sn20 alloy is optimized annealed at 260 °C for 5 h. The stamping performance of Au80Sn20 alloy foil has been significantly improved after annealing and no tearing phenomenon occurs. Our finding not only sheds light on future research on deformation mechanism of fragile metals but also provides practical guidance to the engineers in solder manufacture.