Abstract
The mechanisms of metal corrosion by recurrent water spots containing ppm concentrations of corrosive ions such as chloride ions were studied using uncoated and chromate conversion coated 6061-T6 aluminum alloys. Temperature cycling between −65 and 131 F (−53 and 55 C) or between −65 and 160 F (−53 and 71 C) drastically reduced the corrosion resistance of the coating to the recurrent water spot corrosion. The test results are presented in terms of the pit initiation cycles and the rate of pit nucleation. The theoretical analysis of the recurrent water spot corrosion indicates that two corrosion mechanisms, the bulk concentration effect and the peripheral concentration effect, were responsible for the observed corrosion patterns, which were quite different from those caused by the differential aeration reaction.
