Inert Atmosphere Fluxless Brazing of Aluminum Heat Exchangers

Long Manufacturing uses a novel fluxless brazing process for the production of aluminum heat exchangers. Unlike more established vacuum brazing methods, the Long process does not depend on the use of a magnesium promoter. Instead, Al-Si clad brazing sheet is pretreated with a thin nickel alloy coating. This nickel coating reacts exothermically with the aluminum surface during brazing, to accomplish oxide penetration. Small amounts of lead are co-deposited with the nickel to improve wetting.

The nickel coating inhibits oxidation during preheat, permitting brazing to be accomplished in an inert gas furnace. This offers furnace cost and process reliability benefits in comparison to conventional vacuum brazing.

This paper describes the mechanisms of nickel brazing, in comparison to established models for vacuum brazing. Practical process control implications are also described.