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Abstract No.: |
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Scheduled at:
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Tuesday, June 21, 2022, Saal Brüssel 2:00 PM Advanced filler alloys
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Title: |
Development of copper-aluminum composite brazing wires for brazing stainless steels
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Authors: |
Ulrich Holländer / Leibniz University Hannover, Germany Maurice Schmieding* / Leibniz University Hannover, Germany Kai Möhwald/ Leibniz Universität Hannover / Institut für Werkstoffkunde, Germany Hans Jürgen Maier/ Leibniz Universität Hannover / Institut für Werkstoffkunde, Germany
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Abstract: |
Aluminium bronzes have excellent high temperature strength and scaling resistance. However, these alloys cannot be used as brazing materials in inert gas furnace processes because the extremely high oxygen affinity of the aluminium in the alloy causes oxidation of the brazing alloy, which prevents flow of the liquid braze metal and wetting of the joint surfaces. The solution to this problem is the use of brazing composites consisting of an aluminium core and a copper cladding, where the target composition is determined by the ratio of the material thicknesses used. The desired brazing alloy is formed "in situ" only during the melting process. The composite brazing geometry and the temperature control during brazing then determine to a large extent the brazing metallurgy and thus the technological properties of the resulting brazed joint. The task of the project was to investigate these relationships and to develop suitable aluminium-bronze composite brazing alloys and brazing processes. As a result, the Cu-Al composite brazing wires developed offer significant progress compared with the state of the art: their processability in furnace brazing of CrNi steels is comparable with that of pure copper brazes; in the much faster induction brazing under inert gas, the wetting and flow behavior on CrNi steels is still clearly superior to that of copper. The resulting brazed joints are - in contrast to copper brazes - still scale-resistant even at 650°C in air. The shear tensile strengths of the connectors made with Cu-Al composite reach up to 350 MPa and are thus significantly higher than those of the comparative samples brazed with pure copper wires.
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