Phosphate Uniformity of Aluminum Closure Sheet

Uniform phosphate deposition over the entire outer surface of automotive exterior body panels is necessary in order to optimize surface appearance after painting and to ensure long term corrosion performance. Non-uniformity of phosphate deposition can result from many factors, most of which are related to the processing parameters on the particular cleaning and phosphating line. In this study the phosphate uniformity on AA6111 body sheet material was examined. Phosphating was carried out on sheet metal in the as-annealed condition and after acid cleaning treatment. Phosphate deposition was rated both visually and by SEM analysis. Changes in oxide thickness and chemistry were evaluated by XPS methods. The effects of phosphate non-uniformity on paint adhesion and corrosion performance were also examined.