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
