Guest Editorial                                                  

 Don Baudrand, Don Baudrand Consulting,   e-mail:donwb@tscnet.com

Adhesion of Electro and Electroless Deposits onto Aluminum

In 1979 I dug out of the literature numerous methods of preparing aluminum for electroplating or electroless nickel plating. I tried each one in my laboratory. What I found then was that there were a few of the processes that produced good adhesion that were not involving zincate processes. However, most of these produced good adhesion only on 1100 series (virtually pure aluminum) or cast aluminum. At that time, only one process worked on virtually all alloys and castings. That one was zincating.

Many years later I studied the zincate process to try to find the best way to use zincate. What I found was that the thinner the second zincate, the better the adhesion. So I asked why. The answer came from Dr. Stephen Armynov of the Institute of Physical Chemistry in Sofia Bulgaria. Dr. Armynov found that if the zinc is dissolved in the electroless nickel solution, leaving no zinc on the surface, the adhesion was the highest. He was using only electroless nickel, and a special one at that. One that started slowly, allowing complete dissolution of zinc.

I got busy and tested a number of variations on EN, copper plating and electroplated nickel. Low and behold I found that his proposition worked. The best adhesion was when all or most of the zinc was gone.

Conclusions:
1. Use the double zincate process for all but 1100 series and castings (it is even used for 1100 Al and cast Al)
2. Don’t over etch in the preparation cycle. Etching in alkaline cleaners or alkaline etch formulas leave alloying constituents behind that can cause capillary spaces that entrap the solution. It is difficult to impossible to rinse out the trapped material. The left over material will bleed out in the hottest solution (usually the electroless nickel solution0
3. Mild acid etching is somewhat better because there is more attack on the alloying constituents.
4. Non etch or very light etch cleaning works well for most applications.
5. A very important part is use the shortest possible time in the second zincate solution that will give complete coverage so as to allow thorough rinsing before entering the plating solution/ (the first zincate will etch sufficiently for most applications.)

What is new?

I have seen favorable results from a mildly acid nickel immersion process that seems to give good adhesion. I intent to pursue this avenue. I believe that it is possible, out there somewhere, is a better than zincate process.