Abstract
Aluminum alloy three-layered brazing sheets, clad with sacrificial anode alloy on one side of them, have widely been used for the tube of radiators for automotive in which cooling water circulates. Inner pitting corrosion resistance of the tube has been excellent both in acidified and in neutral corrosive aqueous solutions by the effect of sacrificial anode. On the other hand, it has been reported that the sacrificial anode does not work effectively in alkaline solution, and perforation by pitting corrosion occurs in earlier testing period of time. In this report, localized corrosion characteristics in alkaline solution were investigated by immersion corrosion tests and electrochemical measurements. Based on the experimental results, new corrosion mechanism was proposed in terms of solution environment formed on cathode surface. Pitting corrosion of the core alloy grew not with the attack by the alkaline bulk solution, but with accelerated dissolution by strong alkaline solution derived from the electrochemical cell formation between sacrificial anode and cathodic core alloy. Corrosion products formed in the pit were effective for maintaining strong alkaline environment on the core alloy surface.
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