Paint Adhesion to Electroless Nickel Plating Problem

A. What electroless nickel (EN)? Look at the ASTM B733 spec and they now specify 5 grades from low to high phosphorous. They're all very different and for each "grade" there are different brighteners (including metallic brighteners such as CADMIUM) and stabilizers (like LEAD) that when co-deposited can result in various properties unlike other electroless nickels (not to mention RoHS, WEEE or ELV compliance issues! ).

In the 60's when EN was either high phos or bright mid-phos, it was a bit easier to simply state "electroless nickel." In the modern age when there are a plethora of formulations for specialty purposes, it needs further description! Find out specifically what bath your plater is using -- most platers use one or two or more. My firm runs SEVEN! To complicate the situation even more, ask the plater how old the bath was? If a new bath takes 20 gallons of the nickel bearing A-component, when the initial 20 gallons has been depleted and another 20 gallons added back, this is described as "1 metal turnover" or 1 MTO. Typical EN baths last for 5 - 10 MTO's -- new baths look as would likewise paint differently than a bath with 8 MTO's, for example.

A. EN coatings are very passive, like stainless steel, and getting paint to stick is difficult. However, if you treat the electroless nickel deposit with a solution of 30 g/L of sodium or potassium dichromate at 85°C for a minute, you will usually get enough adhesion to hold the paint.

If you immerse the EN coating in a 30 g/L solution of sodium or potassium dichromate at 85 °C for 30 to 60 seconds prior to coating, you should get adequate adhesion of the powder coating.

Q. Follow up question. Can you use the same process for EN-Phosphorus coating?

SIDEBAR QUESTION: And what is a good method for cleaning Tin plating over Aluminum 6060-T6 before Powder Coating.

Thank you,

A. Hi, Rich. Most EN plating is EN-Phosphorous, so yes, Ron's answer applied to your coating.

SIDEBAR ANSWER: Letter 29546 may be helpful for cleaning the tin. But it may depend on the situation -- if there are only a few parts, scrubbing with pumice and a tampico brush is straightforward. Good luck.

Regards,

A. Hi, Gareth. Could you please tell us your situation to make the question a bit less abstract? It's possible to sand blast the electroless nickel for tooth, chromate it, then apply a self-etching primer and get some adhesion. But not knowing how old the EN is, whether this is one old item or production of thousands of new ones, thus what steps you are willing and unwilling to do, or it is practical to do, or how good the adhesion needs to be, it's hard to help you very much. Thanks!

A. I agree with Ted. Anyhow, here's an abstract answer. It is possible if you prepare the surface properly. Even so, the adhesion will generally be less than with carbon steel.
G. Marrufo-Mexico

Q. Sorry, my apologies for not providing more information. To put my request into context:

I have a halligan tool that has its working ends made from high alloy steel that has been heat treated for maximum strength, then permanently press fitted and pinned to a 1 in. stress proof or high strength lightweight aluminium bar. The whole thing has a very tough and durable electroless nickel finish.

I found out to my cost that after much cleaning, priming and painting of the bar, the paint layers did not adhere very well as there is no 'key' on the surface. Subsequently even knocking it slightly chips off the paint I applied. Hence my question if powder coating will apply to such a surface and if it will remain durable. I imagine that as well as stripping off the paint I applied, the electroless nickel will also need to be stripped for the best results?

A. Hi, Gareth. Electroless nickel is a combination of nickel and phosphorous that creates a passive and almost a glass-like alloy. It's corrosion resistant, wear resistant, and slippery. It's often used as a mold surface because things tend to not stick to it. Yes, it is difficult to paint, especially a tool that will be so deliberately banged around. If you can get down to the aluminum, either with a chemical stripper made for electroless nickel (contact a plating shop) or by sandblasting, then you should be able to apply an etching primer to the aluminum and paint it. But I think I'd leave it electroless nickel plated instead of painting it :-)

Good luck.

Regards,

A. You should switch to anodize (not hardcoat or water sealed) for the aluminum and Zinc Plating on the steel. Also if RoHs is not an issue, Sherwin Williams P60G2/R7K44 works as a metal prep for any substrate.

A. Hi Glenn,

You should be able to paint over electroplated surfaces, should be able to get good adhesion. If you use a wet system, rather than powder coat I'd suggest you start with a good etch primer (sometimes called a wash primer) to key to the surface, followed by a normal primer.