Electroless Nickel on Aluminum
Question: We want to plate aluminum with electroless nickel.
Question:
We want to plate aluminum with electroless nickel. We require excellent adhesion. How should we do this? D.H.
Answer:
Plating aluminum with electroless nickel is not difficult. The aluminum parts must be cleaned to remove greases, oils and other soils. After this step the parts are treated with an alkaline dip and/or an acid dip, depending on the type of aluminum alloy being used. For example, a common process is to use a 6.5 oz/gal sodium hydroxide solution for 30 sec at a temperature of 120–130F. This step is followed by desmutting in a solution made of 75% nitric acid and 16 oz/gal of ammonium bifluoride. This solution is used at 65–75F for 30–45 sec. Other cleaning/conditioning procedures can be found in the Electroplating Engineering Handbook, 4th Edition, edited by Lawrence J. Durney, Metal Finishing Publications, 914-333-2578.
The next step is critical in the process and involves the zincating of the aluminum surface. Zincating solutions can be formulated from various combinations of zinc oxides, sodium hydroxide and ferric oxides, but I recommend a commercial formulation over a "home brew." Most people use a double zincate process. After the first zincating step the zinc is stripped by using a 50% nitric acid dip and then zincated a second time.
After the zincating step, a cyanide or alkaline copper strike is applied followed by the specified metal deposit. In the case of electroless nickel you can skip the copper strike and apply the electroless nickel directly to the zincated part. For maximum adhesion the parts should be baked at a low temperature.
Related Content
-
3 Tests to Ensure Parts are Clean Prior to Plating
Making sure that all of the pre-processing fluids are removed prior to plating is not as simple as it seems. Rich Held of Haviland Products outlines three tests that can help verify that your parts are clean.
-
How to Choose the Right Coating for Fasteners
Choosing the proper coating for fasteners can help with performance by improving durability and lifespan. In this helpful Ask the Expert article, Mark Schario of Columbia Chemical offers advice for choosing the right fastener coatings.
-
Trivalent Chrome Overview
As the finishing industry begins to move away from the use of hexavalent chromium to trivalent chromium, what factors should finishers consider as they make new investments? Mark Schario, chief technology officer for Columbia Chemical offers a helpful overview of this complicated topic.