Vacuum brazing of aluminum: Auger studies of wetting and flow characteristics

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Abstract
Fluxless vacuum brazing has become a commercially feasible process for the high-volume, low-cost production of aluminum heat exchangers. With an Al–Si–Mg filler metal, excellent joint quality is obtained without requiring the use of a flux. A limited understanding of the wetting and flow characteristics of the filler alloy and the role of the magnesium promoter in the vacuum process, however, have hampered efforts to optimize control of the vacuum process. Auger electron spectroscopy and vaporization methods have been used in studying the mechanism of brazing to elucidate the characteristics of the oxide film barrier and magnesium promoter. With these methods it is possible to follow the distinctive variations in surface composition and magnesium vaporization rate that occur in the braze sheet as a function of its temperature. The mechanistic details of the wetting and flow processes in this commercially important material are delineated in the results.

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