Using a broad-range pH indicator, the corrosion of Al and Al alloys in chloride-containing agar gels was studied. Distinct changes in pH were observed at low-pH anodic sites and at high-pH cathodes. There was a definite edge effect that occurred when gels were placed directly on the metal, which dominated the pattern of corrosion. Wet-abraded surfaces initially showed a general type of corrosion, whereas dry-abraded surfaces showed localized corrosion under the gel. Pure Al, AA1100 (UNS A91110), AA2024 (UNS A92024), and AA5052 (UNS A95052) all showed pitting in contact with agar gels when the edge effect was prevented. Abraded AA7075 (UNS A97075) exhibited a filiform type of corrosion caused by high concentrations of corrosion product initiating corrosion ahead of the growing site.

Subject
Pits, Abrasion, Tape, Metal surfaces, Sodium chloride, Wiring, Convection, Acidity, Corrosion products, Cathodic sites, Color, Pitting, Concentration cells
Keywords:
AA1100, AA2024, AA5052, AA7075, aluminum, chloride, localized corrosion, pH
NACE International
2000
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