| 摘要 |
PURPOSE:To prevent the generation of filiform corrosion by subjecting Al or Al alloy to an anodic electrolytic treatment in an aq. phosphate soln. CONSTITUTION:The Al or Al alloy is subjected to the anodic electrolytic treatment in the aq. phosphate soln. such as sodium pyrophosphate or sodium tripolyphosphate. The concn. of the phosphate in the aq. soln. is made about 0.1-1wt%, more preferably, 1-5wt% and the pH about 3-12, more preferably, about 6-10. At least one kind among a titanium compd., tin compd., zirconium compd. and chromate compd. may be added thereto so as to be incorporated therein at 50-10,000ppm if necessary. The anodic electrolytic treatment is executed at 1.0-3,000 Coulomb/100cm<2>, more preferably 15-240 Coulomb/cm<2> quantity of electricity in the case of constant current supply. The filiform corrosion of the Al or Al alloy is thus suppressed and since the quantity of the electricity to be supplied is small, the reduction in the size of the installation is made possible.
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