Aluminum Corrosion at Urban and Industrial Locations

Seven-year exposures of several aluminum alloys, mild steel and zinc demonstrate the excellent corrosion resistance of aluminum in urban and industrial environments. Panels of aluminum-manganese alloys (3000 series) of the types used for siding, roofing and flashing along with the structural aluminum-magnesium silicide alloys (6000 series) showed seven-year corrosion rates which never exceeded 0.151 mpy (mils per year) in even the very severe environment at Widnes, England. In the Chicago area the same alloys had rates less than 0.067 mpy. The atmospheres at Richmond, Virginia, and Manila, Philippine Islands, were relatively mild toward aluminum while that at Phoenix, Arizona, had almost no effect on any aluminum material. By comparison, the corrosion rates of mild steel and zinc were greater than those for aluminum at all locations. The corrosion of the aluminum alloys was predominantly of the pitting type (generally pits were deepest on the skyward side at Manila, Phoenix, and Widnes). Changes in mechanical properties were, in most cases, of a magnitude not to affect the structural strength of the aluminum. Pitting depths never penetrated the panels to a depth greater than 14 mils.