Evolution of the pitting of aluminum exposed to the atmosphere

The atmospheric attack on 1050 aluminum (UNS A91050) is determined by the measurement of the number and depth of the pits formed. The pit density increases linearly with time. A stabilization at high pit density is found when high levels of pollutants are present. The maximum and average pit depths have a bilogarithmic dependence on the exposure time. The simultaneous presence of sulfur and chloride compounds promotes the most intense attack. In those atmospheres with chloride ions, skyward faces are attacked more. Pit depth frequency distributions for different exposure times at various atmospheres were constructed. Data of pit depth frequency are treated as absolute frequency/cm² and as relative frequency. The advantages of each way of data treatment are discussed.