NOCOLOK® Sil Flux brazing is a technique, which eliminates the need for clad brazing sheet or conventional Al-Si filler metal. Sil flux brazing uses filler metal generated in-situ to effect brazing. The mechanism for creating this filler metal in-situ is described below:
One of the surfaces to be joined is coated with a mixture of NOCOLOK® Flux and metallic Si powder. The coated assembly is then heated in the same fashion as in conventional furnace or flame brazing techniques.
As the temperature rises, the flux melts at 565°C, dissolving the oxides on both the Al substrates and the Si particles.
The bare Al surface is now in contact with metallic Si, and in the absence of oxides, allows solid-state inter-diffusion of Al and Si. Very quickly the composition near a Si particle reaches that of the Al-Si eutectic (Al-12.6% Si).
As the temperature increases beyond the eutectic reaction temperature of 577°C, the formation of a liquid pool is established. The formation of the liquid leads to rapid dissolution of the remaining Si through liquid diffusion. The pool of liquid continues to grow, consuming Al, until all of the Si is consumed in the melt. In the presence of a joint, the liquid pool is drawn to the joint by capillary action.
Upon cooling, the liquid layer solidifies to form a metallurgical bond between the components.