Hexa chrome free passivation — Experience as part of ELV Implementation 2008-28-0076
Hexavalent chromium Cr(VI) is recognized as a known human carcinogen via inhalation. This is banned to be used in Corrosion Protective Coatings as per End Life of Vehicle regulation (ELV) 2000/53/EC effective July'07 in EU. Traditionally all automotive metallic components which are Zinc plated are passivated with a thin Chromate layer to add to its brightness and protect it from premature corrosion. These Chromate coatings (or passivation) are generally Hexavalent chromium based and available in four grades: clear, yellow, olive drab, and black.
Alternatives in the form of Trivalent Chromium Cr(III) are now available. By nature, both these passivations have different properties. Trivalent chromium has high temperature resistance but low wear resistance thus does not possess self healing properties. Also, its cost is significantly higher compared to hex chrome solutions. Most importantly, strict process controls like control of temperature, pH, concentration etc are necessary for Trivalent passivation. Failing this, SST (Salt Spray test) performance goes down. Further aggravating the situation is the fact that plating industry in India is highly unorganized in form of small job makers. Here Process control requirements as stipulated for Trivalent Passivations are extremely difficult.
This paper highlights Maruti's experience in Implementing Hex chrome free passivations for its zinc plated parts. Technical Partnership were undertaken with various chemical suppliers pooling in ideas to bring small yet effective process improvements at Plater site ensuring supply of consistent and quality Trivalent Passivation.