Adhesion of a powder coating on a zinc treated surface

I have some problems to get good adhesion of a powder coating on a zinc treated surface. This problem concerns especially the zinc with Cr6-free passivation. What is the difference between the Cr6 and Cr6-free passivation concerning the adhesion of an organic layer? How can I solve my problem? Thanks in advance.

Cr6 is a chrome rinse. Cr6-free is without chrome. So, the difference between Cr6 and Cr6-free passivation on the parts you're trying to powder coat is that the ones that come Cr6-free have not been put through a chrome rinse.

The issue you're seeing with adhesion on the Cr6-free parts is they are probably using some sort of corrosion inhibitor on the parts that is leaving an organic film. That organic film is what causes the adhesion issue with your powder coat.

To solve this issue you can wash the part in a caustic cleaner or a phosphoric acid cleaner. The phos acid cleaners are fairly common for this application especially when people are doing larger parts. Which one you use really just depends on your system. But washing the part with either one will eat through that film and create better adhesion for you.

I can help you troubleshoot further if you need. Just let me know.