Understanding the effect of interlayers on the interfacial temperature during laser brazing for the use of higher melting braze materials

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In contrast to welding, the base materials are not melted during the brazing process but joined together by the braze material melt. Today laser brazing of galvanized steels by copper based braze material is established in serial production in the automotive industry. The laser beam is a suitable tool to realize braze joints with high quality due to the possibility of targeted energy input. One limitation is the strength of the brazing materials. Since nowadays only brazing materials can be used, which have lower melting temperatures than the base materials to be joined, the achievable strength is often material-specific limited. For example, the desire for high-strength aluminum-based braze materials exists in the laser brazing of aluminum alloys. However, the liquidus temperature of aluminum-based brazing material is only slightly or not below the solidus temperature of the aluminum base material, so that there are currently no sufficient process windows. Previous efforts have investigated the possibility of reducing the melting temperature of the braze material by adapting the composition. In contrast, this project pursues the extension of the process window in laser brazing to braze materials that are equal or higher melting than the base materials. The project is based on the hypothesis that intermediate layers can limit the interfacial temperature between braze and base material via their enthalpies of fusion and evaporation as well as due to fluid-dynamic effects in terms of wetting and spreading behavior, so that a sufficient process window is created when a suitable laser process is applied.