Analysis of the Interaction of NH 4 Cl-Doped Process Gases with Zinc-Coated Surfaces with Regard to Aluminum Brazing with Zn-AlSi Duplex Braze Metal Coatings

This paper reports on the development of a braze metal coating and a brazing process for joining aluminum alloys at temperatures was determined, a value that matches the values stated in the literature. The order of reaction n was found to be significantly lower than 1, which is consistent with gas solid reactions at microscopically fissured interfaces. An in-situ zinc chloride formation rate of 3 µg/(min cm 2 ) at 400°C and 200 vpm hydrogen chloride concentration was obtained from the measured data, which may be sufficient for triggering the flow of braze metal. Experimental brazing tests showed, that when the reaction time was long enough to permit the formation of zinc chloride and this is followed than by a brazing process at 560°C to 570°C in subsequently hydrogen chloride-free nitrogen atmosphere, a liquid ternary AlSiZn braze metal is formed from the dublex coating enabling a wetting and brazing of the contacting join partner.