International Journal of Materials Science and Applications
Volume 7, Issue 3, May 2018, Pages: 75-84
Received: Dec. 14, 2017;
Accepted: Jan. 26, 2018;
Published: Apr. 23, 2018
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André Langohr, Institute of Materials Science, Gottfried Wilhelm Leibniz Universität Hannover, Hannover, Germany
Sarah Groß-Bölting, Department of Physics, Technische Universität Dortmund, Dortmund, Germany
Ulrich Holländer, Institute of Materials Science, Gottfried Wilhelm Leibniz Universität Hannover, Hannover, Germany
Kai Möhwald, Institute of Materials Science, Gottfried Wilhelm Leibniz Universität Hannover, Hannover, Germany
This paper reports on the development of a braze metal coating and a brazing process for joining aluminum alloys at temperatures < 570°C without applying a flux before brazing. This is achieved using a duplex braze metal coating made of an aluminum-silicon alloy and zinc as top layer in combination with the use of hydrogen chloride doped nitrogen as process gas. Here hydrogen chloride deoxidate the surface of the zinc coating and form zinc chloride flux in-situ. Defined hydrogen chloride partial pressures between 100 vpm (volume parts per million) and 300 vpm in nitrogen were produced by thermal decomposition of solid ammonium chloride. Reaction kinetics of hydrogen chloride with the zinc coating was investigated by detecting the generation of reaction heat at different hydrogen chloride concentrations and temperatures. An activation energy of
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 cm2
) 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.
Analysis of the Interaction of NH4Cl-Doped Process Gases with Zinc-Coated Surfaces with Regard to Aluminum Brazing with Zn-AlSi Duplex Braze Metal Coatings, International Journal of Materials Science and Applications.
Vol. 7, No. 3,
2018, pp. 75-84.
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