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Copper Plating on Bronze Has Poor Adhesion

Quickstart:
     It is one thing to use electroplating to simply move metal from the anode ⇦ huh? to the workpiece, but achieving a truly satisfactory deposit is quite another thing.
     One of the usual principle requirements of an electroplated finish is excellent adhesion to the substrate, and this always requires good cleaning and activation because, for proper adhesion, electroplating must be done onto raw metal, not onto a layer of tarnish.
     Electroplated deposits are usually stressed to some degree (the electroplated metal wanting to expand or contract, but unable to because the substrate won't), but excessive stress causes adhesion problems.
     Read on, join in ...

"Electroplating and Electroless plating of Copper and Its Alloys"
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Q. Hello, I work for a jewelry electroplating shop, and we've recently encountered an adhesion issue during a job where we're also trying to level or repair the surface with a combination of plating and sanding.

We've noticed the copper strike layer delaminates or peels off the bronze substrate (90% copper, 10% tin). We suspect it only happens on certain areas of the part, and we only notice it when we sand the plated layer to level off surface imperfections.

The area where this occurred also had a patch-welding repair using 655 bronze sheet (1-4% silicon), so we suspect we're not activating the surface properly.

Our activator or acid dip is Acidsalt FL Wet from Haviland: sodium bisulfate, sodium fluoride mix.

Our copper strike is copper cyanide base, run for 2 min, and we then run acid copper to bridge superficial defects on the part for 2 hours.

We then pull the part out and sand with up to 800 grit, which is where we notice the delamination, usually starting with a blister. It seems to take some mechanical work to delaminate or make the adhesion issue apparent.

The copper that peels off is also spring loaded, seems like it is stressed, but I'm not too familiar with what is a normal amount of plating stress.

Question:
Given this information of our electroplating and repair process, what could be causing the delamination of the copper layer over both the substrate and welded material?

"The Hull Cell"
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"Art of Coppersmithing"

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Thank you Ted for your response. The purpose of sanding these pieces was to level/cover severe porosity. It just so happens that this particular piece had a patch-welding repair. This is actually the first time we tried to address surface porosity by "rebuilding" the piece through a combination of acid copper plating and sanding the top layer off-done several cycles we eventually managed to level the surface and cover the porosity. I'm not sure if this is common practice so hopefully this makes sense. Or if you have another less time intensive way of covering porosity through electroplating/sanding, as we are new to these types of repairs. We run hull cells on this acid copper bath pretty regularly, and we did not notice anything out of the ordinary. The low current density end has some haze, but most of the panel is bright. What are hull cell signs that too much brightener was added? I bent a corner of the panel (high end) and didn't hear the plated copper splinter or delaminate. We have a theory that the significant time we are sanding the copper layer is causing the plated layer to harden and stress, and that is what is eventually causing the delamination. Have you ever heard of this happening? thank you Joseph Rodriguez [returning] shop employee - Albuquerque A. Brass and bronze alloys are frequently loaded with lead to facilitate machining. Look with a 20X magnifier at the surface for splotches of lead, or ask your supplier. If the bronze is "leaded", then the sulfate you use makes an insoluble lead compound, so use fluoboric acid. Robert H Probert Robert H Probert Technical Services Garner, North Carolina

Q. The bronze alloy does not contain any lead, but it's possible to have a trace amount.

A. Hi again.

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I'm a bit puzzled that the actual part apparently has a highly stressed deposit on it while the Hull Cell panel doesn't -- so maybe you are right that the sanding is hardening it -- copper is known to quickly harden with working. I'm not sure if annealing would have any practicality in your circumstance.

You use the term "sanding" wheres the term "buffing" is more often used in the auto restoration and copper-nickel-chrome plating fields. Is it possible that a somewhat different technique, using buffing, might get you the leveled surface you need more surely and easily than by sanding and replating? I have heard some buffers use the term "mush buffing" not to refer to the softness of the buffs, but to a reputed technique of mushing some copper into low spots.

I don't know if it actually works, or its exact limitations if it does, but it seems to me that, regardless, buffing is a better approach and it might be doable on jewelry and small items with a Dremel. Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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