COMPOSITION FOR FORMING ZINC PHOSPHATE COATING OVER METAL SURFACE

摘要

An acidic aqueous zinc-containing coating solution containing about 0.08 to about 0.2 weight percent of zinc, about 0.8 to about 3 weight percent of phosphate, about 0.05 to about 0.35 weight percent of chlorate, about 0.001 to about 0.1 weight percent of nitrite, and a complex fluoride ion having the following concentration: 0.4> y >0.63x - 0.042 wherein x is the concentration of the zinc in weight percent and y is the concentration of the complex fluoride ion in weight percent. The coating solution is useful for forming on metal surfaces zinc phosphate coatings that exhibit excellent alkali resistance, good adhesion to a paint film, and good corrosion resistance after painting when used as an undercoat for the cationic electrodeposition of a paint film.