GALLUMINIUM

The main objective of the project GALLUMINIUM is the technical and scientific evaluation of a new assembly process of aluminium named diffusion-brazing process using gallium. This project associates a component supplier for aeronautics, a university laboratory dedicated to processes and materials and a supercapacitor manufacturer. The standard aluminium brazing process is a difficult and expensive industrial operation. It needs either furnaces under high vacuum or under inert atmosphere, or corrosive chemicals based on fluorine: all these technical steps don't avoid a delicate preparation of the surface and an accurate temperature control. These economical and technical limitations are crucial for many industrial fields like the manufacturing of heat exchangers, for example. In this application field, thin light-alloy pieces are brazed together. The standard manufacturing process needs a long discontinuous step in brazing furnace. The welding process of aluminium is also a complex and expensive operation especially when the welding zone shall not excess a determined temperature or when only one of the two pieces is mechanically accessible. These constraints forbid the use of standard welding processes (TIG, MIG, resistance). Generally, only laser welding and electron beam welding are applicable: it is the case of supercapacitor manufacturing. In one hand these welding processes are complex and highly energy consuming. In the other hand, the mechanical shape of the pieces has to be highly accurate in order to limit the welding zone. The project GALLUMINIUM proposes a new welding technology avoiding the aforementioned disadvantages. This new process of diffusion-brazing of aluminium is characterised by : • the use of a low quantity of gallium (< 1mg.cm-2), • the heat of pieces to braze at a temperature lower than 500°C under air, • the uselessness of corrosive chemicals, • the high speed of the brazing compared to the standard processes (few seconds). It has been shown that first assemblies made during studies were mechanically strong. First electromechanical ageing tests were also performed and are promising. However it is necessary to validate the quality of brazing process through ageing, thermal and mechanical tests and to develop an industrial process. This project proposes a study of materials and process in order to : - Elaborate and characterize the assemblies brazed by the gallium-assist process. The characterization will be mechanical, thermal and electrical. The performances will be compared with the numeric simulations. - Define an innovative and clean process to the industrial scale. - Study the technical economical feasibility of the new developed process.