Volume 7, Issue 3, May 2018, Page: 75-84
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
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
Received: Dec. 14, 2017;       Accepted: Jan. 26, 2018;       Published: Apr. 23, 2018
DOI: 10.11648/j.ijmsa.20180703.12      View  896      Downloads  31
Abstract
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.
Keywords
Aluminum Brazing, In-Situ Fluxing Agent, Reaction Kinetics
To cite this article
André Langohr, Sarah Groß-Bölting, Ulrich Holländer, Kai Möhwald, 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. doi: 10.11648/j.ijmsa.20180703.12
Copyright
Copyright © 2018 Authors retain the copyright of this article.
This article is an open access article distributed under the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Reference
[1]
Swidersky, H.-W.: Aluminium brazing with non-corrosive fluxes – state of the art and trends in NOCOLOK flux technology, conference transcript of “Löt 2001”, 6th International Conference on Brazing, High Temperature Brazing and Diffusion Bonding, 8-10 May, Aachen, DVS-Reports, Vol. 212.
[2]
Wielage, B.: Entwicklung eines Controlled Atmosphere Brazing (CAB) Verfahrens zum Fügen von Aluminiumguss- und Aluminiumknetlegierungen, research report for the project of the same name, AiF Project No. 13.788 N.
[3]
Belt, H.-J.; Swidersky, H.-W., Wielage, B., Martinez, L.: Aluminium brazing at 500°C – characteristics of ZnAl-joints, conference transcript of “Löt 2001”, 6th International Conference on Brazing, High Temperature Brazing and Diffusion Bonding, 8-10 May, Aachen, DVS-Reports, Vol. 212, pp. 214–217.
[4]
Bach, Fr-W.; Möhwald, K.; Holländer, U.; Ditz, R.: Flammlöten von Aluminiumschmiedeteilen, in: conference transcript of the 10th Material Technology Colloquium – WTK Chemnitz, 2007.
[5]
Bach, Fr.-W.; Möhwald, K.; Holländer, U.; Langohr: Niedrig schmelzende Aluminiumhartlote aus dem System Al-Si-Zn, Schweissen und Schneiden Vol. 62, No. 11, pp. 632-637, 2010.
[6]
Langohr A.; Swider M. A; Möller F.; Wulf E.; Möhwald K.; Hassel T.; Maier H. J. (2013): Development of flux free filler metals and processes for brazing of aluminum, In: Brazing, high temperature brazing and diffusion bonding. Printed as MS, Düsseldorf: DVS Media (DVS-Reports, 293), 2013, pp. 205–211.
[7]
Wielage, B.; Hoyer, I.; Weis, S.: Entwicklung niedrig schmelzender Al-Lote für hochfeste Al-Legierungen, conference transcript of “Löt 2010”, International Conference on Brazing, High Temperature Brazing and Diffusion Bonding, DVS-Verlag GmbH, Düsseldorf 2010, pp. 366-370.
[8]
Engelbert, Peter et al.: Method for soldering aluminum, Patent EP 1485224A1.
[9]
Nigel, F. C. et al.: Tin- and zinc-based solder fillers for aluminium body parts and methods of applying the same, Patent GB 2387347A.
[10]
Hoffmann, R.: Fluxless brazing method and compositions of layered material systems for brazing aluminum or dissimilar metals, Patent WO 03/045618A1.
[11]
Childree, D. L: Aluminium filler alloy containing sodium for fluxless brazing, Patent WO 01/98019A1.
[12]
Palmer, S.: High temperature aluminium alloy brazing sheet and manufacturing and uses therefor, Patent WO 02/070189A2.
[13]
Berkowicz, P.: Method for joining parts of aluminium or aluminium alloys, Patent EP 1030760B1.
[14]
Wielage, B., Trommer, F., Hielscher, H., Mücklich, S.: New developments on ultrasonic brazing technologies, conference transcript of “Löt 2001”, 6th International Conference on Brazing, High Temperature Brazing and Diffusion Bonding, 8-10 May, Aachen, DVS-Reports, Vol. 212, pp. 236–239.
[15]
Engelbert, Peter et al.: Soldering flux for soldering aluminum, Patent US 7481894B2.
[16]
Barin, I.: Beiträge zur Kinetik der Chlorierung von Metalloxiden, post-doctoral thesis, RWTH-Aachen, 1976.
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