ABSTRACT
Chemical pretreatment usually involves application of a conversion coating. In this chapter, phosphating, chromating, anodizing, and titanium-zirconium (Ti/Zr)– based processes and a process based on Cr(III) are briefly discussed. Phosphate conversion coatings are mainly used on steel and zinc, where they are widely used. Chromate conversion coatings were the dominating pretreatment for aluminum, magnesium, and zinc until around 2000. The widespread use was due to their excellent corrosion resistance and coating adhesion. Anodizing is primarily used as a final treatment of aluminum to obtain corrosion and wear resistance, as well as an appealing visual appearance. Conversion coatings based on titanium or zirconium or both were the first chromate-free chemical pretreatment processes on the market with a performance that was comparable to that of the chromate conversion coatings. Conversion coatings from Cr(III)– based chemicals have been commercially available since the early 2000s.
