PROCESS FOR FORMING CORROSION PROTECTION LAYERS ON METAL SURFACES

摘要

The invention relates to a process for producing a corrosion-inhibiting coating for substrates having a surface consisting of zinc, magnesium, aluminium or one of their alloys, wherein the surface to be treated is brought into contact in direct succession with two aqueous treatment solutions containing chromium(III) ions, metal ions of the substrate surface to be treated and at least one complexing agent. The first treatment solution has a pH in the range from 1.0 to 4.0, while the second treatment solution has a pH of from 3.0 to 12.0. The process of the invention produces a smaller amount of wastewater polluted with heavy metals.