Cadmium Plating: Brightness = Embrittlement?
A discussion started in 1998 & continuing through 2017(1998)
Q. I've been puzzled by high-strength threaded fasteners I've been evaluating from a potential new supplier. They are to be cadmium plated and chromate treated per QQ-P-416 [link by ed. to spec at Defense Logistics Agency, dla.mil] . They are very bright and shiny. The specification does not prohibit a shiny appearance, but it does prohibit the use of brighteners in order to avoid hydrogen embrittlement. The supplier's tests show no embrittlement, and they have specifically stated that no brighteners were used.
The problem is that I consult with a plating expert who has stated that such uniform brightness (including in thread roots and a head recess) is almost impossible to achieve without using brighteners - he is very skeptical. Applying my own limited experience (with cyanide-free caustic zinc plating) to the question, I would tend to agree.
Should I be skeptical? Any opinions/facts would be welcome.
(For those not familiar with QQ-P-416, it does not specify the type of cadmium bath to be used, but I assume it is a cyanide process).
Thanks for your help.John Ullman
A. I have seen Cd plating on aerospace bolts very bright, the cadmium could be getting polished in the chromate step. I don't know how bright is bright, but perhaps even the dragin of some surfactants from the post plate treatment would be enough to brighten the deposit a bit. What a hoot! Nosireee, we don't add a drop of brightener, we just drag cleaner into the tanks once in a while, and old Homer over there chews tobacco, and ooweee, you know, they keep moving that spittoon closer and closer to that Cd tank, one time he even lost his false teeth down in that tank. Parts sure looked pretty for a while after that:-0
How about a test for carbon in the deposit. There is some test where you convert all the carbon in a sample to CO2 and get a reading that way. Maybe you will see a difference in C content in bright and not so bright deposits. I would like to see some work done in that area, since I fly around in those big planes too.
A. Any plating or etching is going to put SOME embrittlement into the part. What he probably means is that it does not fail the pull test.
Lea Ronal has a non cyanide process out that uses a very low metal content (probably a fluoborate) that does not use a brightener.
I also do not believe that you can get a full bright without the intentional or unintentional use of a brightener. Some specific metallic contamination or drag in could be brightening the bath.
Brighteners do contribute to embrittlement. Unfortunately the mil spec does not consider that the etch step can have a far larger effect than the plating. The lady in charge of that revision was not even aware that there was an acid cad bath. She also evidently was not aware that there was a low hydrogen embrittlement spec that should have been called out rather than prostituting QQ-P-416.James Watts
- Navarre, Florida
Q. The consensus of (2) respondents seems to be that there must be a brightening agent, either intentionally added or a contaminant, which is causing the brightness I'm seeing. Mr. Watts also seems to be saying that QQ-P-416 shouldn't have been revised (prohibiting brighteners) in order to allow it's use on high strength fasteners - other Cd plating baths such as fluoborate types should be used. Any further comments along these lines?John Ullman [returning]
A. John, I think that you misunderstood my comment. When they revised QQ-P-416 eliminating brighteners, it was done for embrittlement reasons. I had several letters and phone conversations with the people. Rather than pointing out that there was another specification available, specifically LHE Cad, they made this one more restrictive. High strength fasteners should be done to the LHE spec, not to prostitute the basic cad spec.
The navy office responsible had little knowledge. They took any proposed change and sent it out to about 50 people for comments and tended to go with a consensus opinion.
Fact, You can put more embrittlement into a part with the acid etch than you can with a cyanide cad bath. An acid cad bath plates so much faster, it introduces far less embrittlement. 416 does not even acknowledge the existence of the acid bath. The lady in charge did not even know that they existed.
We used knoch bars that were very significantly higher strength than the minimum required and never had a failure!
I have worked with LHE CN baths, regular CN baths, acid cad and homemade fluoborate cad. None of them were "full Bright",without brightener, especially on the valleys of a threaded fastener. I therefore say that something is brightening it.James Watts
- Navarre, Florida
A. Just to kick a dead horse, if the deposit is bright it is being processed with brighteners. The roots of threads, nor recesses will not have enough current density to brighten that area, nor would they be polished.I hesitate to say, this is common :-)Ward Barcafer, CEF
aerospace - Wichita, Kansas
Q. OK, so the majority of respondents think there are brighteners in the bath when the thread roots are bright. By the way, I shared the first three responses with my consultant, and he said anyone who saw these bolts would have no doubts. Next question: if this situation is as common as has been suggested, how should it be handled? We are an ISO 9000 company and we want to "say what we do and do what we say", not to mention there are still a few of us who want to do what's right just "because". Should there be a revision to QQ-P-416 to allow the use of brighteners as long as testing proves that embrittlement hasn't occurred?John Ullman [returning]
A. We are the largest cadmium plating job shop on the West Coast and have been doing cadmium for over 30 years. The QQ-P-416 does not let one put high strength parts into an acid cleaning bath. This is where much of the hydrogen embrittlement can be introduced but--- it is very difficult to clean a heat treated part without some acid. If the part is cleaned and plated properly, even using brighteners, and baked afterwards using proper procedures there should be no occurrence of embrittlement.Andy Scheer
A. All of the above comments are interesting. Has anyone considered the possibility that a brightener was used and post process embrittlement relief achieved prior to embrittlement testing. Some embrittlement relief occurs over time at ambient temp. Baking the parts at 375+ °F degrees will achieve embrittlement relief. QQ-P-416 is a mil spec that allows for embrittlement relief processing.Glenn Stover
We also are having a problem with QQ-P-416. We are required to cad plate without the use of brighteners according to this spec. However, many of our customers (and our QA inspectors) will not accept cad plated parts that our dull in appearance. A big dilemma.
In regards to the comment by Glenn: I think the theory with the use of brighteners in Cad plating is that the bright Cad prohibits the diffusion of Hydrogen from the base metal even with the 375 °F bake for embrittlement relief - thus the restriction on brighteners.Greg Haataja
helicopters - Fort Worth, Texas
I am from India and I do not know what is QQ-P-416. Regarding Cadmium plating and embrittlement, I would like to state that use of Fluoborate based electrolyte keeps your Cadmium plated components, out of all embrittlement problems.
We are manufacturers and suppliers of Cadmium Plating solution. Our solution is currently being used for plating many components with Cadmium in Indian Defence Factories.K.Ajith kumar
- Trichy-10, TN, India.
Well hello folks.. I'm new here and have been working in the Cadmium plating process for 6 weeks, but know a few things.. From what I have learned, the parts may have been dipped in peroxide, which I find brightens cad parts very well.. But to do many small parts, like fasteners, using a basket, or even a barrel, could blacken them very fast, like 1 second fast. So there is really no use of a chromate, but peroxide... Hope that helps...
I crave more knowledge of this business, and remember, it's technique...
Have a good day!
- Erie, Pennsylvania, USA
August 25, 2008
A. I myself cad plate and know for a natural fact that if your cad is bright you have brighteners in your tank. In my shop we have tanks with brighteners and tanks with none.
The tanks with no brightener are dull which is why we call it the dull cad tank.
- Puyallup, Washington
March 12, 2011
A. I myself Plated Cad both bright and non-bright on aerospace and no-cert jobs. depending on the size of the parts, nuts, bolts and hardness if you want them to be brighter in a non-bright bath, for example LHE cyanide bath, the best way to get the parts brighter would be using a tumbler.Oz Sanchez
February 1, 2017
Q. I am looking for chemical brightener additives, chemicals/addition agents that could be used to enhance brightening and grain refining of Cadmium plating bath. Need some one to guide and suggest chemicals. Thanks.Ahmed Manzoor
- B-174 LalaRukh Wah, Pakistan
^- Privately contact this inquirer -^
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