Yellow Zinc Plating
When we talk about "Yellow Zinc Plating", we are actually referring to Standard Zinc Plating and a Trivalent Yellow Passivate or a Hexavalent Yellow Chromate.
So... it is important to understand that there is no such thing as a true "Yellow Zinc Deposit". BUT... through the use of Trivalent Yellow Passivates or Hexavalent Yellow Chromates, we are able to produce a "Yellow" Finish for our Zinc Plated Parts / Components.
The above picture... and the picture below are both nice pictures of Zinc Plated Parts that were processed through a Hexavalent Yellow Chromate Solution...
Zinc Plated Hydraulic Fitting processed through a Hexavalent Yellow Chromate...
As we discussed above, engineers have two options if they wish to "color" their Zinc Plated Parts / Components for a "Yellow Finsih".
Hexavalent Yellow Chromate
For all practical purposes, the Hexavalent Yellow Chromate is DEAD! Hexavalent Yellow Chromate was a great way to get "Yellow Zinc Plating" because it was cheap and it gave good
The Hexavalent Yellow Chromates are known by their defining characteristic of
Probably the first picture on this web page gives you the best idea of this iridescence and the various iridescent colors of reds, pinks, violets, greens, etc...
Trivalent Yellow Passivates
Most trivalent passivates are simply a thin or Thick-Film Passivate with a Yellow Dye added in.
These dye based systems are definitely NOT perfect systems and it takes great effort to maintain a consistent yellow color from day-to-day and week-to-week.
As the Hexavalent Yellow Chromate was defined by iridescence, Trivalent Yellow Dye-Based Passivates are able to create uniform yellow colors ranging from light yellow to deep dark-red brass colors.
It is also possible to create the "Hexavalent Yellow Iridescent" look through the use of Cobalt Containing Thick-Film Passivates. Again, it is very difficult to maintain the same exact color from day-to-day and week-to-week in a production environment.
In addition, most Automotive OEMS have kept away from anything that looks "Yellow"... due to association with "Hexavalent Chromium - Cr (VI)" and switched to the "Silver / Transparent / Iridescent" look of the Thick-Film Passivates... because these Passivates are Cr (VI) - Free AND RoHS Compliant!!!
And one "NON dye-based" trivalent yellow passivate...
There is at least one "Non Dye Based" Trivalent Yellow Passivate that seems to be very popular if engineers are wishing to copy the "Hexavalent Yellow Iridescent" look. ENTHONE's PERMA PASS 5108.