| 摘要 |
PROBLEM TO BE SOLVED: To enable brazing by the use of a smaller amount of flux by providing an extruded tube which is brazed by the use of a flux containing silicon powder and has a composition consisting of specific amounts of Si and the balance Al with inevitable impurities. SOLUTION: The amount of Si contained in the extruded heat-exchanger tube is regulated to 0.4 to 1.0 wt.%. Si addition is done to prevent the diffusion of excess Si which does not contribute to the reaction of formation of a brazing filler metal with Al, from a silicon powder in a flux into the inner part of a tube material and to form all the silicon powder into brazing filler metal alloy, by which the amount of brazing filler metal alloy to be formed in a brazing stage can be increased. As a result, the amount of the flux used can be reduced and also the electric potential of the tube can be raised and the potential difference between the tube and a fin can be increased to provide corrosion resistance. By adding <=0.1 wt.% Cu, the electric potential of the tube can be raised to a further extent and corrosion resistance can be improved. At this time, >=50 mV potential difference between the tube and the fin suffices to provide the tube with corrosion resistance over a practical period.
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