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If base metal is shotpeened before plating, must it be shotpeened again if plating is reworked?

April 11, 2012

Q. We have a few cases of faulty chrome and need to replate the part. The base metal was shotpeened as a requirement prior to plating. My question is do you have to reshotpeen prior to replate?

Wilson Canupin
Senior Quality Inspector - Richmond, BC, Canada

April 13, 2012

A. Hi Wilson,

It really depends on your stripping method as to whether you need to peen again. Anything that removes depth will facilitate a need to re-shot peen.

One other thing to note is that every time you strip and re-plate chrome there is a reduction in the fatigue life of the steel, shot peening will not mitigate the whole effect. If the item is highly stressed (and as you are having the part shot peened one has to assume it is) you should get a stress engineer to look at the potential fatigue effects of the strip and re-plate.

Brian Terry
Aerospace - Yeovil, Somerset, UK

April 17, 2012

Q. We chemically strip faulty chrome on steel part using a 6-8 oz/gal of sodium hydroxide and 50 oz/gal of chromic acid for aluminum parts. Is there a changes for this to etched base metal if all parameters as correct?

We also stress relieve the part after chrome strip per AMS2759 [affil. link]. Thanks for your experienced opinion, We are preparing a sample for lab analysis.

Wilson Canupin
aerospace - Richmond, BC, Canada

April 20, 2012

A. Hi Wilson,

I would suggest that you should not need to re-shot peen after the stripping methods you are employing; they should not be removing any base material. Stress relief after stripping is also the right thing to do.

If there is any doubt about the shot peen surface then you should re-peen, this will not adversely affect the surface and as you know will help to mitigate the effects of the induced tensile stresses from the chrome plating process.

Brian Terry
Aerospace - Yeovil, Somerset, UK

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