EN on Magnesium

Question:

We just started plating electroless nickel on magnesium. We are not having much luck. We use a zincate at 135-150°F and a cyanide copper strike at the same temperature. We then use a nickel strike with fluorides at 180°F. We are having problems with patterns and blisters. Any help would be appreciated. F. P.

Answer:

Plating on magnesium is not a “slam dunk” by any stretch of the imagination. To start with, 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
0.5-2.0 min

— Rinse
— Zincate using the following solution

Zinc sulfate, four 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 (depends 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 two minutes followed by 10–20 asf for an additional 2–5 minutes.

— Rinse
— Nickel strike using a bath containing fluoride
— Rinse
— Electroless nickel plate