Electroless Nickel on Magnesium

Q. We are trying to plate electroless nickel on magnesium. So far we have not had much success. We use a zincate bath at 135-150°F and a cyanide copper strike at the same temperature. We then use a nickel strike with fluorides at 180°F. The main problems are blisters and patterns on the surface. Any help would be appreciated.

A. Any type of plating on magnesium can give you “indigestion” and electroless nickel is no exception. Different magnesium alloys may require slightly different preparation/cleaning cycles. The proper application of the zincate and copper strike is also critical.

The following general sequence is one that should work for you:

-Process Step

-Degrease

-Rinse

-Cathodic electroclean, 75 – 130 ASF, 185°F

Activate in the following solution:

-Phosphoric acid, 20%

-Sodium or potassium bifluoride, 14 oz/gal

-60 – 100°F

-0.5 – 2 min

-Rinse

-Zincate using the following solution

-Zinc sulfate, 4 oz/gal

-Tetrasodium pyrophosphate, 16 oz/gal

-Sodium fluoride, 0.7 oz/gal

-Sodium carbonate, 0.7 oz/gal

-PH, 10.2 – 10.4

-Temperature, 175-185°F

-Time, 3 – 6 min (depending on the alloy)

-A commercial zincate solution can be used if it is formulated for use with magnesium-based alloys.

-Rinse

-Repeat the zincate step by repeating the activation and zincating step a second time.

-Rinse

-Copper strike; enter the strike bath live

-Plate at 45 - 90 ASF for 2 min followed by 10 – 20 ASF for an additional 2 - 5 min.

-Rinse

-Nickel strike using a bath containing fluoride

-Rinse

-Electroless nickel plate

Originally published in the August 2015 issue.