In situ brazing is a powerful method for understanding dynamic material behavior during joining process, enabling real-time observation of melting, wetting, and interfacial reactions. The present study investigates the influence of aluminum alloy chemical composition on wetting behavior and interfacial phase formation during soldering with a Sn78Cu22 alloy. The experiments were performed inside a large-chamber scanning electron microscope (LC-SEM) to monitor heat-induced deformation, melting, melt propagation, elemental segregation, and solidification. Microstructural and compositional analyses were carried out using SEM/EDX and TEM, supported by thermodynamic calculations using Thermo-Calc. Despite the low melting point of Sn78Cu22, solder reactions could only be initiated at significantly higher temperatures, namely 466 °C for EN AC-42,100, 500 °C for EN AW-5083, and 600 °C for EN AW-3003, due to the presence of stable surface oxide films. The Si-rich EN AC-42,100 alloy exhibited early filler deformation and formation of Al–Cu and Cu–Sn intermetallic compounds, namely Cu6Sn5, Cu2Sn, while Sn wetting was limited by a Si diffusion barrier. In contrast, the EN AW-5083 and EN AW-3003 alloys showed delayed wetting caused by MgO and MgAl2O4 oxide layers, respectively. For EN AW-5083, Mg reacted with Sn to form Mg2Sn within the filler and at the interface, accompanied by Al–Cu formation. For EN AW-3003, Al–Cu interdiffusion led to the formation of Cu-rich Al4Cu9-type intermetallics with shallow Sn penetration. These results demonstrate that aluminum alloy chemistry critically governs wetting kinetics and interfacial reactions during soldering with Sn78Cu22.
Khatami et al. (Thu,) studied this question.