Porosity & Zinc Die Casts
Q. A number of platers have told us that porosity on zinc diecasts can be reduced by plating with a heavy copper layer and then buffing to cover the pores. Is this a viable method or should we consider a different approach to solving this problem? N. M.
A. I am not a big fan of using the buffing approach to fill in pores in zinc diecasts. If you think about it for a minute, you will probably would understand why. If your base material has a porous surface, when it is plated you will trap plating solution underneath the plate. This trapped solutions “wants out!” Very soon after this, you will start seeing blistering from the trapped plating solution.
If the parts are porous when they come in the door to your shop, they should be rejected flat out. The diecast probably had a bad day and as result turned out faulty porous parts.
If you are buffing the diecasts prior to plating, you must be very careful not to cut through the skin to open up the porous layer beneath the skin.
Some platers have had some success by plating multiple layers of copper over the initial cyanide copper strike. This can be a rather costly process and does not guarantee that you will not have the blistering later on.