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Is there standard test method for electronic Measurement for Hydrogen Embrittlement for Zinc Chromate plating?

September 11, 2008

I have a current product that is Zinc Chromate plated, Alkaline bath .0003" thk.
Is there a procedure standard using a Hydrogen detection instrument ?
Or is there a need using Alkaline to do a bake @ 200 °C for 4 hrs ?
Looking forward to your response,
Chet

Chester Fijor
- Chicago, Illinois

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Chester,

Depends on the customer specification, but if the material is over 38-42 Rockwell it is prone to embrittlement and needs baked. I'm not familiar with an instrument test. The standard test I use is a notched bar test (see ASTM F519).

Trent Kaufman
electroplater - Galva, Illinois
September 16, 2008

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September 17, 2008

Trent,
I would like to discuss your answer and some more with you. Are you using Hex or Tri ?
At this moment, my present supplier is barrel plating TRI with alkaline. I heard from one source, that if there is a Alkaline base then there is no need even for bake. The present process , is causing me to inspect 100 % incoming due to dinging.
Is there a cost alternative ( besides rack ) in the plating world that can withstand 77 hrs to white and 122 to red in salt spray?

Chester Fijor
- Chicago, Illinois

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Chester,

I am currently plating hex and trivalent over acid chloride and alkaline non-cyanide zinc. 77 hours to white shouldn't be a problem with any of the above. To the best of my knowledge the chloride bath should be less prone to embrittlement because it is pretty much 100% efficient and generates very little hydrogen as opposed to an alkaline bath which is much less efficient (i.e., more gassing). That being said, it is my opinion that the pretreatment (acid dip) has a much larger contribution of hydrogen. You will need to bake if the part is anywhere at or above the 38-42 Rockwell hardness. Mechanical plating might be a bit more cost effective and that as far as I know isn't prone to embrittlement as long as the pretreatment steps aren't too aggressive.

It will be pretty hard to beat zinc plating with a hex chromate coating when it comes to your cost. One simple way to test your process is to run one of the ASTM 519 tests at a reputable lab.on the process and see if they pass or fail.

I hope this helps.

Trent Kaufman
electroplater - Galva, Illinois
September 22, 2008