One of the challenges with yellow hexavalent chromates is the temperature of the chromate film cannot go above 150 F without losing all of its corrosion protection.
EPi now has two solutions for the zinc finisher that result in long-lasting corrosion protection and slightly change color during the baking process. See before and after pictures below.
Process Steps using Hexavalent Yellow:
1) Zinc Plate part
2) Unrack parts
3) Bake parts for hydrogen embrittlement
4) Rerack parts flash zinc plate
5) Yellow hexavalent chromate
Ultra Yellow after baking for 24 hours at 375F.
Process Steps for using Ultra Yellow or E-PASSivation Yellow Red:
1) Zinc Plate parts
3) Bake Parts at 375 F for 4-24 hours
E-PASSivate Yellow Red after baking or 24 hours at 375F.
A zinc finisher now can save labor costs and time for parts that have to be baked. Listed below are the salt spray ASTM B-117 corrosion results before/after baking for 24 hours at 375 F.
Ultra Yellow 150 hours 300 hours
E-PASSivate Yellow Red 250 hours over 350 hours and still going strong in the salt spray chamber at the date this blog was written.
Stay tune to the final results. We would be happy to provide a sample or do small parts in our lab.