Influence of Residual Flux Level on the Corrosion Behaviour of Brazing Sheet Materials

摘要

The Nocolok~(TM) Brazing process (NB) is now well established for the manufacture of aluminium radiators for both passenger car and truck applications, additionally, the NB process is being used increasingly for the brazing of evaporators units for air conditioning systems. Since the introduction of the NB process there has been an increasing trend to the reduce flux loadings used in both radiator and evaporator applications. Whilst the potassium aluminium fluoride flux complex is described as non-corrosive, this is a direct reference to it's behaviour compared with the previously used chloride-containing fluxes which, if not rinsed off thoroughly, would initiate corrosion of the aluminium substrate. However, in practice it was observed that the residual flux layer remaining after brazing gave improved air-side corrosion protection. This paper will describe the effect of varying the flux levels used during brazing and the impact on corrosion resistance of standard 3003 type alloys and the high strength long-life alloys i.e. X900. The corrosion behaviour will be assessed by using conventional salt spray testing (SWAAT) and a novel method, employing interrupted sputtering by Glow Discharge Optical Emission Spectroscopy (GDOES), that allows electrochemical measurements to be made accurately at pre-determined levels through the flux/cladding/core interfaces. All tests were conducted using conventional Nocolok flux at levels between 2 to 20 g m~(-2) and the work will also cover characterisation of these layers after the brazing cycle.