Summary for acid copper over zinc die-cast Discussion
Acid copper over zinc die-cast is the core issue here: the question asks how to rework a buffed area where heavy acid copper was cut through to the zinc base metal, causing blistering at the copper-to-zinc interface around the cut-through rim. The answer explains that acid copper cannot be applied directly to die-cast zinc and that exposed zinc must first receive a cyanide strike. For rework, the advice is to use a thicker-than-usual copper strike, about 100 microinches or more, and then build up with acid copper to the thickness needed for buffing. The responder notes that there will still be a thickness difference at the cut-through area, but careful buffing may make it less noticeable. The discussion also reiterates the broader plating principle that acid copper is simple and bright, but it needs an underlayer on zinc or steel to adhere properly.
Copper plating can be done from an acid copper bath (often called bright acid copper), a cyanide copper bath, or a proprietary bath like copper pyrophosphate. Acid copper is the simplest, cheapest, easiest, and brightest.
Unfortunately, acid copper will not adhere properly directly to die-cast (or steel for that matter). Rather, a thin layer of cyanide copper (or a proprietary copper plating) must be applied before the bright acid copper. Thus, this discussion of acid copper plating on die-cast cannot avoid also mentioning cyanide copper plating.
Q. I would like to know how to process a specific rework of cutting through Heavy Acid copper plating during a copper buff that cuts through to the Zinc die-casting. The specific problem is blistering at the exact interface of the copper plate to the Zinc base metal around the entire rim of the cut through.
Bob Campbell
– Milwaukee, Wisconsin
2003
“Finishing and Electroplating Die Cast and Wrought Zinc”
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A. To rework exposed zinc a cyanide strike must be used. The copper strike should thicker than the usual copper strike, i.e. about 100 micro inches or more, followed by acid copper plate to the desired thickness for buffing. There will be a thickness difference where the cut through occurred, perhaps it can be made not noticeable by careful buffing.
Don Baudrand
Consultant – Poulsbo, Washington
(Don is co-author of “Plating on Plastics”
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A. At the edge you may be seeing poor results due to an immersion deposit of copper. Keep the preps for the zinc as short as you dare, make sure any acid prep is fairly fresh, and if possible use a shower nozzle hose to wash the area as it is removed from each prep tank. Also try going in “live” (power on and a jumper cable on the rack before immersion to the strike) I use to plate custom chrome on diecast, hate the stuff.
Jon Quirt
– Minneapolis, Minnesota
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