Patent ID: 7314671

Claim:
A conversion layer comprising chromium(III), said conversion layer being chromium(VI)-free, said conversion layer being a substantially coherent conversion layer on zinc or a zinc alloy, said conversion layer presenting a corrosion protection of about 100 to 1000 h in the salt spray test according to DIN 50021 SS or ASTM B 117-73 until first attack according to DIN 50961 Chapter 10, said conversion layer having across the conversion layer thickness an average chromium content of more than approximately 5 weight % based on only zinc and chromium up to a depth where the Cr content is 1 weight % based on only zinc and chromium, said conversion layer having a chromium index greater than approximately 10, wherein the chromium index is defined as said average chromium content, expressed as content by weight of Cr divided by the sum of contents by weight of Cr and Zn, multiplied by said depth in nm, wherein said conversion layer is free from the presence of silicate, cerium, aluminum, and borate, is clear or substantially colorless, and further comprises one or more anions and one or more metal compounds selected from the group consisting of 1- to 6-valent metal compounds.