Corrosion Resistance of Aluminum Alloy Plate in Rural, Industrial, and Seacoast Atmospheres

Abstract Stress corrosion and exfoliation corrosion test specimens from aluminum alloy plates have completed five years of a scheduled 20 year exposure program in rural atmosphere at Alcoa Center, PA, industrial atmosphere at Los Angeles, CA, and seacoast atmosphere at Point Judith, RI. The materials being evaluated are 19 mm and 64 mm thick plates of the following nine alloys and tempers: 2024-T351 and T851, 5456-H116, 6061- T651, 7050-T7651 and T7451 and 7075- T651, T7651, and T7351. Test data are presented for 6 months, and 1, 2, and 5 years of exposure. In general, the effects of corrosion were most pronounced in the seacoast atmosphere and least in the rural atmosphere. An exception was more severe stress- corrosion cracking (SCC) of the 7xxx alloys in T7 type tempers in the high N0x industrial atmosphere. In addition, accelerated, laboratory tests to determine resistance to stress- corrosion cracking were conducted in 3.5% NaCl by alternate immersion according to ASTM G44. Likewise, resistance to exfoliation was evaluated by the "EXCO" procedure, ASTM G34, except that the "ASSET" procedure, ASTM G66 was used for the 5456 Al-Mg alloy plates. Results obtained in these laboratory tests are compared with those observed in the natural atmospheres.