Cu-Al-composite braze metals

With the aluminum bronzes copper alloys are known, which have a good temperature strength and a high corrosion and oxidation resistance. However, these alloys cannot be used as braze metals in furnace processes e.g. for brazing CrNi steels, since the high oxygen affinity of the aluminum leads to a passivation of the braze metal preventing it from wetting the steel surface. To solve this problem braze metal composites consisting of an aluminum core and a copper capping layer are used, wherein the braze alloy composition is adjusted by the ratio of the material thicknesses used. The desired copper-aluminum braze alloy is formed then "in situ" during the melting process of the composite. The composite geometry and the temperature control during furnace brazing then determine within wide limits the braze metallurgy and thus the technological properties of the resulting brazed joint. Objective of the project is to investigate these dependencies and to develop suitable aluminum-copper composite brazes and appropriate furnace brazing processes. The braze metal composites can be produced both as wires and as sheets, making them suitable for a variety of brazing applications. Both suppliers of braze materials and producer of brazed assemblies made of CrNi steels, which are required in automotive construction, in heating and air-conditioning technology or in apparatus construction in a wide variety of shapes and designs, can benefit from this.