Atmospheric corrosion behaviors of aluminum and aluminum alloys were investigated through 18-month field exposure tests. The corrosion rates decreased with exposure time. The corrosion products formed in the first 3 months mainly consisted of basic aluminum chloride, basic aluminum sulfate and aluminum hydroxide. However, phase transformation took place during exposure and the corrosion products were composed of basic aluminum sulfate and aluminum hydroxide after 12-month exposure. The corrosion products played a key role of the suppression of the atmospheric corrosion on aluminum and its alloys. The membrane potential of basic aluminum sulfate in NaCl solutions indicated that this compound had a cation-selectivity. The sulfate-containing corrosion products prevent the penetration of chloride ions to protect the aluminum substrate. This is responsible for the observed decrease in corrosion rates after prolonged exposure to the atmosphere.