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Provision of a thin layer of zinc on aluminium to provide the fillets during brazing has been described previously [1]. The process for zinc coating of the extruded aluminium multiport tubes has been further enhanced by utilisation of the zinc layer to carry flux for subsequent brazing operations, thereby making it possible to produce brazed heat exchanger assemblies utilising the thin zinc layer, without the need for a separate fluxing operation prior to brazing. The flux is applied directly onto the molten zinc coating where it becomes mechanically locked in position when the zinc freezes. Because of this action, the flux cannot be easily dislodged, unlike other techniques where powdered flux has been sprayed directly upon the aluminium tube surface or a fused flux has been applied to the tube surface. The prefluxed product can readily be handled and subjected to simple forming operations without dislodging the flux.

Provision of a layer of zinc on aluminium to provide the fillets for soldering is well established but this usually necessitates a thick layer of zinc (>30μm) and soldering at temperatures below 450°C. New technology has been developed to enable sound joints to be made on aluminium heat exchangers using a much thinner layer of zinc (4 to 8 μm typically) on the aluminium component to provide the joint. By the correct combination of flux and zinc coating thickness, joints have been obtained over a wide range of heating conditions. Preferred temperature cycles are similar to those used by the industry today for brazing of Aluminium:Silicon braze-clad aluminium components which should facilitate tranfer by industry to the new technology.