Benefit of wider gap at brazing aluminium alloys to stainless steels in the air using the flux containing zinc

摘要

The brazing of aluminum alloys to stainless steel was conducted using the aluminum-silicon brazing filler in the air under the existence of the flux. Aluminum alloys and stainless steel easily form the strong oxide layers on the surface and they are the obstacle to accomplish their dissimilar brazing joint in the air. To remove those oxide layers, the water soluble active corrosion chloride flux including zinc chloride was pasted. In this experiment, Zn simultaneously diffused fast in the aluminum bulk. The EDX mapping showed the diffusion of Zn into Al alloys, on the other hand silicon was condensed in the residual molten brazing filler. The fast isothermal solidification from the Al alloys surface before the breakage of the oxide film on the stainless surface is considered the obstacle of brazing them in the air. The wetting time of the stainless steel surface using the flux with zinc and the aluminum-silicon brazing filler was measured. The numerical simulations on the Fickian diffusion of the Si into aluminum alloys is also conducted to estimate the isothermal solidification time from the Al alloys' surface. Combining the results of the wetting time and the isothermal solidification simulations, the gap width required for accomplishment of the brazing Al alloys and stainless steel was proposed.