Development of a chromium-free pretreatment system for aluminum bodies

A chromium-free surface treatment method was developed for aluminum bodies. By adding fluorine ions and iron complex compounds to the current zinc phosphate pretreatment bath, an improved zinc phosphate film is formed on aluminum. Also, increasing the manganese in the pretreatment bath improves the alkaline resistance properties of the zinc phosphate film. As a result of these changes, the zinc phosphate film has improved secondary adhesion after water conditioning and improved filiform corrosion resistance without using a chromium rinse. Therefore, chromium can be eliminated from the paint process of aluminum bodies. This, in turn, reduces environmental burdens previously posed. (C) 2002 Society of Automotive Engineers of Japan, Inc. and Elsevier Science B.V. All rights reserved.