plating, anodizing, & finishing Q&As since 1989
Alternative to Chromium Passivation for Zinc Plating
Methode Electronics (Malta) Ltd. is involved in the manufacture of automotive switches and as part of the manufacturing process, the contact terminals of the switches are electroplated using either zinc or silver plating.
We are currently encountering a problem with our zinc electroplating process. The post treatment used for the zinc plated parts (the bath used is an alkaline non-cyanide one) is yellow and blue passivation using hexavalent chromium solutions. We are aware that chromium is an environmentally undesirable material. As a result, we are looking for alternatives for the post treatment process utilising more environmentally friendly materials. However, we do not know whether these do in fact exist and whether they would produce the same type of finish and electrical properties obtained with the chromium passivation.
We would appreciate any advice on this matter.
electronics - Mriehel, Malta, Europe
Back in 1991, there was an article in Metal Finishing called "Corrosion prevention and chromates : the end of an era?", it's in the september and october issues. It covers extensively your question, it shows many possible alternatives, but as chrome plating is still prevalent, I suppose the era is not over yet.
I've heard of Gardolene VP 4683, it featured in the May issue of Finishers' Management (1990), apparently it contained no chromium and gave corrosion resistance equal to that of chromium. It could be used on zinc, aluminium and phosphated steel, why this hasn't cornered the market I don't know but would be very interested in hearing from anyone that used or still uses it. Hope this helps.Ian Brooke
university - Glasgow, Scotland
Ed. note: A lot has changed in the years since this letter was posted. Hexavalent-free chromates are now a commonplace, widely available from suppliers, and in wide use in plating shops. However, these often involve a topcoat which may not offer proper conductivity for electronic applications; anyone specifying chromates for their components who requires good conductivity is urged to investigate the situation before the situation causes field problems.