Inducing the Effect of a Ga2O3 Nano-Particle on the CsF-RbF-AlF3 Flux for Brazing Aluminum to Carbon Steels

In this study, a Ga2O3 nano-particle was added into CsF-RbF-AlF3 flux to develop a highly active flux for brazing aluminum alloy to steel, and the spreadability and wettability of Zn-Al filler metal that matched the CsF-RbF-AlF3 flux-doped Ga2O3 nano-particle on the steel were investigated. The results showed that the spreadability and wettability of the CsF-RbF-AlF3 flux-doped Ga2O3 nano-particle could be remarkably improved when matching Zn-Al filler metals on both aluminum and low-carbon steel, for which the optimal content is in the range of 0.001−0.003 wt.% of Ga2O3. An investigation and analysis on the mechanism of reactions among CsF-RbF-AlF3-doped Ga2O3 nano-particle flux and filler metal or base metals showed that the Ga2O3 nano-particle is selectively absorbed by the interface of molten Zn-2Al filler metal and base metal, which released the surface-active element Ga to enrich the molten Zn-2Al filler metal and decreased the interfacial tension, so as to promote the enlargement of its spreading area during the brazing process. It was concluded that adding a trace amount of Ga2O3 nano-particle into CsF-RbF-AlF3 flux is a meaningful way to improve the activity of flux for brazing aluminum to steel compared with adding ZnCl2, which poses the risk of corrosion on aluminum.