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Hydrogen embrittlement in zinc plating of auto parts from the 1960's

Q. Q. In order to restore a 1967 GM muscle car, I sent out nearly every original nut/bolt and larger parts including control arms, etc. to my local commercial plater to have zinc plated. Mostly clear but some black zinc. Never even heard of hydrogen embrittlement at that time. The plater did not heat treat anything before or after.

Did I ruin all of these parts?

Thank you for your expertise.


Bob Benson
- Simi Valley, California
February 23, 2022

A. Hi Bob. Although plain, soft, mild steel does not suffer from hydrogen embrittlement, hardened steel unfortunately does -- and yes your parts may be ruined :-(

This issue is a perennial problem. The customer is likely to say, as you did, that they've 'never even heard of hydrogen embrittlement -- the shop should have told me that plating and/or plating without baking would be a problem'. And the shop is likely to say 'How are we supposed to know that a customer's parts are hardened steel and they shouldn't be plated, or should at least be baked, if he didn't tell us?'.

Although strangers like myself don't like to get in the middle of a contract dispute, especially after hearing only one side of the story, I think a plating shop ought to recognize forged hard components like steering linkage, and caution the customer that they shouldn't be electroplated or will require embrittlement relief; they shouldn't take a contract to plate them without baking unless the customer specifically disclaimed it.

2nd opinions from other readers are always welcome.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey
February 2022

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