Synthesis and properties of a highly reactive inorganic salt-based solder paste for 1060 aluminum alloy soldering

• A novel inorganic flux system is developed, enabling reliable soldering on aluminum by effectively disrupting the tenacious oxide layer. • A synergistic mechanism is revealed where tin chloride initiates oxide breakdown while zinc chloride enables sustained interfacial bonding. • Unique reaction products including zinc-hydrazine complexes are identified as key intermediates governing the flux activity. • The optimized formulation produces superior joint strength through formation of a graded interface with zinc-aluminum and copper–aluminum intermetallic compounds. Aluminum alloy liquid-cooled plates are the most widely used heat management technology in high-end servers and aerospace thermal control systems. Due to the natural oxidation layer, welding and effective connection of aluminum alloys are still difficult, which greatly limits the performance and lifespan of welded components. In this study, highly active ZnCl 2 -SnCl 4 inorganic salt-based fluxes are prepared in three different proportions and mixed with SnAg3Cu0.5 alloy powder to obtain environmentally friendly solder pastes (LG-1, LG-2, LG-3). The viscosity, acidity, physical stability, and copper plate corrosion of the fluxes meet the standard requirements specified for high-quality soldering, and the three solder pastes had low wetting angles on the 1060 aluminum alloy. LG-3 exhibits the best mechanical properties, reaching a maximum tensile stress and tensile strength of 740.22 N and 38.01 MPa, respectively. Nanoindentation tests were conducted on the aluminum substrate, soft solder paste, and interface, and the results showed that LG-3 had the highest hardness. SEM and FIB-TEM reveal that the solder pastes and aluminum alloy are connected by an intermetallic compound layer. LG-3 has a relatively high ZnCl 2 content, which penetrates the Al grain boundaries during welding and generates Zn-Al IMCs, thus enhancing the mechanical performance of the welded joints.