Controlled atmosphere brazing (CAB) of aluminium relies on the use of components on which a clad layer of braze alloy is present. Assembled parts require a flux coating before entering the CAB process. New opportunities are now possible, based on inorganic fluoride salts capable of providing both the braze material and the flux needed to effect the brazing of pre-coated parts Selection and blending of different salts provides the opportunity for enhancement of corrosion resistance and design against corrosion for the brazed heat exchanger. Specification of the binder system, in order to ensure the adhesion of the brazing salt to the aluminium surface is essential. A further requirement of the binder is that it should not degrade the controlled atmosphere during brazing. The study describes braze trials with different flux salts. The flux coated aluminium strips were assembled by sandwiching corrugated aluminium fin material used for radiator manufacture and, hence without any braze cladding on the surface. All sample pieces brazed successfully in the trial. In all cases, generous braze fillet sizes were obtained indicating that the actual silicon coating weight could have been much lower than previously anticipated. In fact a silicon content in braze metal of only 1 % was seen to be perfectly adequate. Clad-less brazing, utilising fluoride salts containing silicone is realistically feasible. Binder systems can be developed to meet adhesion and pyrolysis requirements for successful CAB operations based on pre-coated aluminium without the need for clad aluminium products to be included in designs.
Cladless brazing of aluminium
Löten von unbeschichtetem Aluminium
2002
10 Seiten, 6 Bilder, 5 Quellen
Aufsatz (Konferenz)
Englisch
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