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topic 2278

Does Zinc Plating Cause Hydrogen Embrittlement?


Does zinc plating reduce the strength of the underlying metal? I have been told that the acid bath introduces hydrogen into steel, reducing its strength. The specific application is bolts used in flanged connections for industrial process piping. How much reduction in strength? Does the same situation occur in hot dipped galvanized steel? Technical articles/references?


John Byrne
design - Richmond, Virginia


Dear John ,

What you should have been told is that Zinc Plating can induce "Hydrogen Embrittlement" in certain steels with a hardness of greater than 30 Rockwell C .

The plating does not lessen the hardness of the steel but it makes it inclined to break from a "Brittle Fracture"

there are ways of lessening the effect of this phenonemon by baking for several hours after plating , the correct procedure is laid out in the ASTM Specifications .

Plating Zinc from Acid Chloride baths is not as likely to cause this phenonemon as these baths approach 95 +% in effeciency whereas a Cyanide Bath which has been in constant operation for a number of years will probably be plating at about 65% effeciency .

There is a process called Mechanical Plating that claims to offer no Hydrogen Embrittlement , it is in use by most of the motor companies on their critical parts in braking assemblies "etc" for this very reason .

Do a literature search under "Hydrogen Embrittlement" and it will turn up the papers you want


John Tenison-Woods
John Tenison - Woods
- Victoria Australia


Thought must also be placed on turned metal parts that are hardened. An issue recently occured where a special self tapping screw being hardened after forming and then plated gave failures due to hydrogen de-embrittlement.

Charles Tones
security systems - Birmingham,England

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