Considerations on a new brazing concept for vacuum brazing of aluminium and copper

Abstract

Mixed joints made of aluminium and copper are increasingly important in industrial applications. This type of mixed joint is of interest, e.g. when good electrical and thermal properties, as in power electronics cooling, are required. The joining requirements consist of the formation a metallurgical bond and planar joint between aluminium alloys and copper. The fluxfree vacuum brazing process is considered one appropriate joining technology. When using standard filler metals, formation of brittle phases and erosion of the aluminium base metal occur due to increased copper diffusion at high brazing temperatures. Based on these findings and an energetic consideration of the brazing process, an AlCuSi filler metal with a reduced liquidus temperature has been developed. In fundamental studies the wetting and brazing behaviour of this newly developed filler metal has been investigated. The filler metal is used as a foil and preapplied as a thermally sprayed coating on an EN AW-3003 aluminium base sheet. The formation and the structure of the braze metal as well as observations focused on the interaction between the components involved are discussed.