Effect of Cu element addition on the interfacial behavior and mechanical properties of Sn9Zn-1Al2O3 soldering 6061 aluminum alloys: First-principle calculations and experimental research

In this study, Sn9Zn-1Al2O3-xCu (x = 0, 1.5, 4.5, 6 wt %) composite solder is used to investigate the effect of Cu element and Al2O3 particles addition in soldering 6061 aluminum alloys. First-principle calculations were performed to explore the interface structure, interfacial energy, contact angle, and electronic properties of the Al2O3/Sn9Zn interface. Wettability, microstructure, interface morphology, hardness and mechanical properties of Sn9Zn-1Al2O3-xCu soldering 6061 aluminum alloys were examined in experimental section. In the calculation part, Sn9Zn-1Al2O3-4.5Cu and Sn9Zn-1Al2O3-6Cu show stable structures. For experiments, when the content of Cu element is 4.5%, a large amount of fine Cu5Zn8 phases appear in the soldering seam, and the Al4Cu3Zn solid solution layer is the thinnest and flattest. Meanwhile, using Sn9Zn-1Al2O3-4.5Cu solder, the wetting area and shear strength are increased by 27.12% and 75.6% respectively compared with the original Sn9Zn-1Al2O3 solder, which was attributed to a second phase of Cu5Zn8 strengthening mechanism. The Cu5Zn8 phases can generate obstacle for the dislocation at the grain boundary.