Diffusion brazing of Al-alloys for hybride structures

Abstract

The concept of diffusion brazing is an interesting approach to overcome several principal problems when joining high-performance engineering materials. Typical obstacles are low wettability and low melting ranges of the substrate materials, intensive metallurgical interactions or the build-up of thermally induced stresses. In many cases commercially available filler alloys cannot be employed. However, it is crucial to have adequate joining technologies available in order to realize modular design concepts of hybride structures.
The objective of the research is to employ diffusion brazing techniques to join temperature sensitive Al-base alloys. Based on fundamental thermodynamic considerations regarding interfacial phase transformations and corresponding diffusion mechanisms appropriate diffusion couples have been selected. Those materials have been deposited by PVD-processes onto the base materials. Subsequently, the components to be joined are placed into a vacuum furnace and are exposed to a temperature regime significantly below the melting range of the substrates. An additional force guarantees that the joint is in intimate contact and diffusion mechanisms can form a temporary liquid phase which solidifies isothermally during the brazing process. Apart from the materials selected the dwell time is the key parameter that controls the joint quality as well as interfacial precipitations.
A broad set of experiments have been conducted using diffusion bonding agents in the system Al-Cu and Al-Si-Cu. Variations of dwell time and jacking force help to develop a deeper understanding of the underlying diffusion mechanisms which is the basis for further optimization of Al-based diffusion brazements.