Prediction of Pitting Probability on 1050 Aluminum in Environmental Conditions Available to Purchase

A new mathematical treatment for the pitting corrosion of aluminum is proposed. Pit depth relative frequency data (P) are related to exposure time (t) by a bilogarithmic law: log P = a + b log t. Both terms a and b were defined dependent on sulfur and chloride compounds levels, on time of wetness, and on one independent term, enclosing the environmental, mechanical, and metallurgical variables not explicitly considered. The equation outlined is fitted to the experimental data by a multiple linear least-square regression (r = 0.90). This equation allows us to predict the probability of a defined depth pit to be formed when aluminum is exposed to known atmospheric conditions. The physical meaning of the terms was recovered at the end of the mathematical treatment. During the first month of exposure, the treatment predicts a constant influence of sulfur compounds on the pits formation and growth, whatever the pit depth was. Chloride ions have a preferential influence on the pit formation and on the deepening of the deepest pits. For longer times, the term b predicts a synergistic influence of sulphur and chloride compounds on the deepening.