Summary for brushed nickel 356 aluminum Discussion
Brushed nickel 356 aluminum parts with porosity are causing trouble in a corrosion-resistant finishing process. Dave Gruenwald says the hollow permanent-mold castings need an excellent finish and must pass 200 hrs CASS, but PVD is bringing out blisters and the current copper/nickel/chrome plus PVD stack is costly. In response, Guillermo Marrufo suggests the blistering may not be caused by PVD itself, but by heating during the process that drives out entrapped liquids trapped in pores from earlier plating steps. He recommends trying to heat parts before PVD to confirm the source, but cautions that if the pores are the issue, the real fixes are improving casting quality or using a dry pre-process that seals the pores. The thread implies there is no simple low-cost substitute if the porosity remains.
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.
Dave Gruenwald
– Oshkosh, Wisconsin, USA
2003
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.
Guillermo Marrufo
Monterrey, NL, Mexico
2003