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Tuesday, May 15, 2007 - 11:30 AM

Study on Cold Spraying of Al-Based Brazing Alloys

L. Zhao, F. Ernst, J. Zwick, Surface Engineering Institute, RWTH Aachen University, Aachen, Germany; E. Lugscheider, K. Bobzin, Surface Engineering Institute (IOT), RWTH Aachen University, Aachen, Germany

The cold spray process has two special properties which can be very useful for depositing brazing alloys. These are the little oxidation of spray materials and the destruction of oxide scales on the surfaces of the substrate and spray particles during deposition. In our study, the effect of these properties was investigated. Two Al-based brazing alloys (an AlSi and AlSiCu brazing alloy) were sprayed using the cold spray process onto Al alloys. The influence of the spray parameters on the particle velocity was investigated by means of the online particle monitoring device DPV 2000. The deposition behaviour of the particles was studied using splat tests and coating tests. The influence of spray parameters on coating build up and coating microstructure was investigated by means of optical microscopy. Some coated samples were selected to be heat-treated at 500 and 600 °C to investigate the possible diffusion processes and wetting behaviour of the brazing alloys. Some coated samples were brazed under controlled argon atmosphere using a flux or without fluxes. The results show the process gas temperature, gas flow rate and spray distance all can strongly influence the particle velocity and correspondingly, influence clearly the deposition of the powders and the coating microstructure, especially the coating porosity. Due to the destruction of the oxide scales, the braze alloys wetted well on the substrates. The brazed samples show a very good bond between the substrate and the braze alloys. Thanks to the cold spray process, it is even possible to braze the Al alloys under controlled atmosphere without fluxes.

Summary: Al-based brazing alloys could be deposited onto Al alloys by cold spraying. The spray parameters influenced significantly the coating build up and coating microstructure. The deposited brazing alloys showed a good wettability on Al alloys. The brazed samples showed a very good bond between the substrate and the braze alloys.