Team Metal Finishing

Team Metal Finishing · 2008-04-04 12:27:58

A customer writes:

We are plating 6061 T651 aluminum alloy with electroless nickel to a thickness of .0003".. Note that 6061 T651 has essentially the same composition as the more common 6061 T6 but has been stress relieved for use as tooling plate. Our goal is to have a plated surface with the smoothest surface possible. The two attached files illustrate the problem as seen under a microscope at a magnification of 500X. The nodules on the surface have a diameter range of .0001 to ..0005". In addition there are occasional fissures and pits. The goal is to eliminate all those defects. At this time we are polishing the surface after plating but this is very labor intensive. One of our plater has never heard of nodule formation. Our other one is aware but has much difficulties doing something about it.

We have found that the manufacturer of aluminum memory disk for computers are using EN plating with a requirement for an extremely smooth surface. Perhaps you might be familiar with the process that is used for this application. Does your company have the capability to control the surface defects described above?

Team Metal Finishing · 2008-04-15 08:30:06

Looks like there may be some contamination of some sort within the plating bath. "Roughness" is common in some electroless nickel shops that do no segregate the types of substrates that the plate in individual tanks.

I am curious as to what shape the substrate was in prior to EN plating.

I recieved the new piece from this customer, and magnified the surface 60X and took a photo. This is what the mirror polished surface showed.

This is a very smooth surface (<25 RMS) but as you can see it retains some slight inclusions, and voids in the surface.

We will be plating this part, to see if the results are comperable.

Team Metal Finishing · 2008-04-17 11:03:31

And the results are in.. The following photos are labeled as such.

This is under a 200X magnification, I am hoping that I will be forwarded the 500X magnification drawings soon.

and the other side is

now this is the unpolished surface as plated:
Notice the many imperfections and inclusions in the surface. (this resembles the raw surface of the mirror polished area)

This is the mirror polished surface as plated
a significant difference from the raw state. the Nickel has bridged most of the minor inclusions. The "bright spots" you see will more than likely be substrate showing through the plating. I am able to conclude that there are in fact nodules at only 200X magnification. notice the little sporadic bumps all over the part.

this is Groove 3 edges
Very smooth surface leading up to the edge, Minor Bright spots on the left hand side are detectable at 200X

This is Groove 3's base (deepest point)
Spectacular finish in the base, Nice even coating with Minor bright spots detectable at 200X

Here is Groove 2 edges
Smooth plating up to the edges, Minor bright spotting again on left hand side very smooth finish otherwise.

Here is groove 2's base
Many bright spots detected in the base of groove 2

Here is groove 1's edges and base (the shallowness of the cut allowed for a single photo)

Minor bright spotting.

And finally the As machined surface.
There are a few brightspots but I suspect this may be the substrate showing through the plating.

Concluding that the nodules are contamination is almost finite. The advanced filtration that we use on site catches everything in the bath llarger than 1 micron.

Ryan Cook · 2008-05-14 14:13:57

Photo DSCN0993
This is the "unpolished" section of the sample. This area was in fact sanded before being plated in an attempt to remove machined marks. The machined marks were removed but the surface was left relatively rough. The plating seems to make the surface even rougher, There are also many nodules in various stages of formation. Some seem perfectly round while others seem to be in the process of growing out of the surface. Surface contamination might have also contributed to the roughness and nodules.

Photo DSCN0994
This is the "polished" section of the sample. Diamond polishing compound was used to minimize the machined marks. A mirror surface resulted but was not as reflective as the "as machined " surface. There are not as many nodules and they are smaller than in the "unpolished" area. The surface features are also much smoother.

Photo DSCN0995
This is the "Groove 3" area. The surrounding area is about the same as the "Unpolished"area. Note the erosion along the groove's left edge.

Photo DSCN0998
This photo show by far the most impressive results. This surface was first prepared by milling with a CNC machine to a roughness of about 6 microinches and produced a surface with some mirror qualities. After plating the mirror quality of the surface increased dramatically as shown in the "as machined" photo of the forum. The microscope photo of the plated surface is almost featureless. The nodules are almost absent and the machined marks are smoothed over by the plating.

Conclusions: Surface preparation is one of the important factor in obtaining a smooth surface free of nodules. To minimize nodules a surface with mirror qualities without contamination is very important.

*this post was submitted by a 3rd party not affiliated with Team Metal Finishing for whom this technical write up was produced for, and wished to remain anonymous*

I would like to thank R.R. for working with me on this technical writeup, and look forward to bringing the information gathered in this project into practice to take our processes to the next level.

Last edited by Ryan Cook (2008-05-14 14:17:22)

Team Metal Finishing

Announcement

#1 2008-04-04 12:27:58

Nodules in Electroless Nickel coating under magnification.

#2 2008-04-15 08:30:06

Re: Nodules in Electroless Nickel coating under magnification.

#3 2008-04-17 11:03:31

Re: Nodules in Electroless Nickel coating under magnification.

#4 2008-05-14 14:13:57

Re: Nodules in Electroless Nickel coating under magnification.

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