Mechanistic Aspects of the NOCOLOK Flux Brazing Process

NOCOLOK^(R)*, Alcan's non-corrosive flux brazing process is rapidly increasing in acceptance for the manufacture of brazed aluminium heat exchangers. In common with all other fluxes for aluminium, the action of NOCOLOK flux is to remove the tough, persistent oxide film from the metal surface and promote filler metal wetting and flow. Although the practical applications of the NOCOLOK process itself have been well documented, little or no published information exists regarding the mechanism of operation of the flux.

It has been found using a hot stage environmental cell fitted to a light microscope that NOCOLOK flux (a mixture of potassium fluoro-aluminates) operates at brazing temperatures by melting, spreading and dissolving the oxide film. In contrast, chloride salt based fluxes work by melting followed by penetration and separation of the oxide film from the metal substrate.