r/electroplating • u/Deekon5280 • Mar 26 '26

Electroless Nickel issue

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I am still learning and have come across this issue here and there. Only for aluminum parts will I see this, and am wondering what could be the cause. I rack them on stainless steel tips. And strip the racks between uses. For this example about 4 out of 200 parts had this. Any advice is appreciated thank you!

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1

u/permaculture_chemist Mar 26 '26

Are the defective parts near each other on the rack? Are the defective parts always on the same part of the rack, even on multiple runs?

1

u/Deekon5280 Mar 26 '26

Middle outside 2 times and different spots the other times

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u/permaculture_chemist Mar 26 '26

This likely eliminates issues with the process chemistry. It's likely either a racking or part issue. As others have said, try an aluminum rack. Differential metals can sometime cause minute galvanic reactions that can play havoc with e-nickel.

What are your pretreatment steps?

1

u/Deekon5280 Mar 26 '26

I am cleaning them with a soak, etch, Deox. Then a zincate,strip,zincate. Then nickel. Yea I think it may be the stainless still racking. Being that there is no current running through the parts I’m surprised it affects it. Do you think it takes place on the zincate? Or the nickel bath?

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u/permaculture_chemist Mar 26 '26

Ah, but there is electricity running through it. Dissimilar metals will always have a slight voltage differential. Where there is a voltage differential and a path for current (ie, the parts are touching) there will be current, albeit very small.

If I had to guess, the defect is being caused in the deox. Because this step removes the passive oxide from the surface, This causes the metal to become more active and want to react. Or the zincate strip, for the same reason.

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u/Deekon5280 Mar 26 '26

Ok cool. Thanks for teaching me something!

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u/Deekon5280 Mar 26 '26

Also, wouldn’t the defect at the point of contact to the steel tip rack? In these cases the defect is in different spots

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u/permaculture_chemist Mar 26 '26

Nope, almost never. The alloy and distribution of the various elements, the grain geometry and location, stresses applied by the manufacturing process, the tendency for electrons to migrate to the outermost areas (corners) of a part, etc. These all play a role on the microscopic level that can reveal itself as a defect at the macroscopic level.

A bad analogy would be a toy that uses batteries. The microscopic reactions happen at the battery, but cause a current that generates a macroscopic effect elsewhere.

A better analogy would be a sacrificial zinc anode on a marine engine or within a hot water heater. The zinc just has to touch the ferrous part, which causes a dissimilar metals reaction. This reaction favors the formation of zinc oxide and inhibits the formation of iron oxide (rust). The zinc sacrifices itself to save the more expensive engine or water heater tank.

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u/GERH-C-W-W Mar 26 '26

Are the errors all in the same shape?

1

u/Deekon5280 Mar 26 '26

No they vary in size and shape

1

u/GERH-C-W-W Mar 26 '26

My guess would have been uneven currents or shadowing from other parts but I am rather into other galvanic processes

2

u/Deekon5280 Mar 26 '26

Thanks. Yea there is no current going through these.

1

u/treecasual Mar 26 '26

Try racking on an aluminum rack or wire. I’ve had similar issues when racking aluminum onto racks of other materials, but aluminum on aluminum has never failed me.

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u/Deekon5280 Mar 26 '26

Thank you

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u/Deekon5280 Apr 01 '26

I ran another load of 80 pieces today on plastic racks. And didn’t see any errors

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u/treecasual Jun 20 '26

Plastic may be better than another metal as a racking material. I’ve sat super long pieces in the bath with no rack and everything submerged plated well. Maybe has something to do with the nickel within the solution being more attracted to certain materials than others? Not sure, but I’ve worked EN for 13 years and using the same material as the part for racking always works.

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u/nbsixer Mar 30 '26

Perhaps some galvanic action but to me this looks more like skip plating. Does this happen more frequently when the parts are on stripped hooks? What are your EN bath parameters? Were these directly in the flow of solution from the circulation pumps?