Labrat

Re: Hydrogen embrittlement

I have a customer that needs 300 microinches min of zinc, followed by either clear, yellow, or black chromate depending on the order. They also need to verify that the parts have no hydrogen embrittlement. They do this by snapping the clips onto a small diameter rod (drill blank) that places stress on the clip for 24 hours. If no hydrogen - parts remain attached to the rod. If hydrogen is present, the parts break. These are the most delicate parts I have ever dealt with in zinc plating! The only way I can pass this spec is to:

Alkaline soak clean / 30% Muriatic Acid to remove heat scale / bake at 400 degrees F for 5 hours / quick immersion in dilute muriatic acid / zinc plate / bake at 400 degrees F for 5 hours / reactivate / chromate

The reason for this lengthy process is that the following methods have failed:

If I alkaline soak clean / immerse in 30% muriatic acid / zinc plate / bake majority of zinc flakes from parts

If I alkaline soak clean / 30% muriatic acid / bake / quick immersion in dilute muriatic acid / zinc plate / chromate parts do not pass rod test from hydrogen embrittlement; parts break

If I alkaline soak clean / 30% muriatic acid / bake / quick immersion in dilute muriatic acid / zinc plate / chromate / bake parts extremely discolored (cannot distinguish between clear and yellow chromated parts).

I have even tried  alkaline soak clean / 30% muriatic acid / electroclean / copper flash (100 microinches) / 10% sulfuric acid / zinc plate / bake majority of zinc flakes from copper

Do you have any suggestions as to an alternative process? The parts seem to have perfect adhesion (crimp test) until I bake them. 

Labrat

skelton

Re: Hydrogen embrittlement

Labrat-
Music to the metal finishers ears....by the way......it was great to have finally met you in Cleveland.....I am going to give you a shout out tonight at the show.

This specific problem that you are dealing with, has been in so many ways....a thorn in many platers sides. My first question to you is.....what substrate are you plating over? I can assume that this is a heat treated spring steel, but do not want to assume until you have told me differently.

I like the fact that you shared with us what does work for you....Colonel Sanders wouldn't give away the Original Recipe....but Labrat is like me, he wouldn't wish this headache on anyone that is experiencing the same issues....good job again Labrat.

I digress now.....
Regarding your adhesion issue....I can only emphasize the cleaning of the substrate, which I realize you know....In this case, maybe you are overcleaning.....this can happen and can be overlooked very easily....and due to the size of the parts....visual inspection is nearly impossible. Reverse/Direct electrocleaning can be of some assistance in removing any surface dirt, heat treat, oils, etc. Minimizing the pickling process in the dilute Muriatic Acid will also be helpful. And lastly, you may consider a good proprietary acid salt from one of your metal finishing proprietary vendors.

As for you hydrogen embrittlement process/bake....this can be done prior to chromating after zinc plate. Plate, rinse, dry, bake. Activate zinc plate in nitric pre-dip, then chromate. This can help with appearance.

This is all I have got for right now. We can take to PM or email, or I can come  and visit you and we can take a look at it together, I will be glad to do so.

Thanks for the post. Keep the post(s) coming.......I am OUT.


Skelton, hOST
FinishingTalkLive
www.finishingtalklive.com

eboireau

Re: Hydrogen embrittlement

You've got yourself in a real "pickle" there Labrat.

Sorry I had to.:D

I think whenever i bake parts I know there is going to be some discoloration in the finish. The 1% Nitric Predip to reactivate the zinc ussually helps me in many of my cases.

good luck bud!

Eric Boireau
H. LaRosee & Sons Inc.
Hudson MA

skelton

Re: Hydrogen embrittlement

Don't be sour at me labrat......i did post a quick reply and as I was discussing the post, realized that you did bake after plate prior to chromate......I may have been a bit baked myself when addressing this brittle topic......ttyl


Skelton, hOST
FinishingTalkLive
www.finishingtalklive.com