Brushed Nickel 356 Aluminum with Corrosion Resistance

Q. We are trying to get a brushed nickel finish on 356 permanent mold castings that are hollow. The castings have some porosity, apparently caused by the sand core. These castings, once finished, must have excellent corrosion resistance (200 hrs CASS test).

PVD seems to bring out blisters. We are currently electrolytically plating with copper, nickel, chrome then PVD. Is there another way? PVD is extremely costly.

A. Have you tried to heat some parts before entering the PVD process? Most likely the blisters are not directly related to PVD itself, but to any kind of heating above boiling point and they come from entrapped liquids in the pores during the previous plating processes. If this is the case there is very little you can do but to improve the casting quality or change to a dry pre-process that seals off the pores.