Hydrogen Embrittlement & Plating

So I suspect i learned something yesterday. Fabricated/tig welded a pair of CM suspension arms. Had them post weld heat treated and shot peened. I like powder coating, bit felt a yellow zinc plating prior to powder coating might be the best long term solution, no pun intended. However solution plating in the harder materials has the potential downside of hydrogen embrittlement. The solution then is a prompt after plating 375F 4 hr minimum bake cycle to drive out the trapped hydrogen. One issue in my design, there was lapped gusset reifnorcement that could not by design be welded closed. I was certain it was going to trap liquid , whatever small amount.. My thinking was, with the added bake cycle, no liquid could survive, and it would not be an issue. I was wrong.

What I found out was, the bake cycle is not at the end, but more mid process, as later solution immersions trap later solutions, unbeknownst to me. So I mocked up the part, fitted it, put it on the shelf, for a month and two days ago inspected it and found leakage corrosion around the lapped metals, and then called the plater. and was told about the real sequence of the bake cycle.

Baking after final plating would "blow off" the plating.

Who knew?

I'm not 100% clear on your parts or assembly but it sounds simply like you have coating solution that was trapped and has leached out. This is common but it often ties back to the coating supplier not using an adequate rinse process after conversion coating. Your last sentence is not at all true. I've been dealing hands-on with plating & coating of parts for 35+ years. The bake cycle does not remove coating. However, depending on the process used and if not done properly or if part geometry is not favorable, the coating process will not provide coating in some areas and will often leach coating solution residue over time.

- EM

Unless you're building airplane parts, hydrogen embrittlement shouldn't be a concern. There was once a time when racers of all types chromed everything in sight and didn't have issues. They no longer do that simply because the technology changes too quickly. They were aware of hydrogen embrittlement but weren't concerned about it.

Is my process overkill, yes, is the part a non redundant potentially catastrophic suspension part of the chassis, yes, and to think I resisted additional cyro treatment because I thought that would be a bit much.

Maybe I was exaggerating a bake cycle "blowing off" a plating. Maybe a better description would be the final finish would lose luster and the plater doesn't want to hear complaints about finish color/sheen. Yes the part expectedly trapped one or part of all the solutions after the baking process, leading to the corrosion noticed after time. And yes, I am certain I am not 100% knowledgeable on this process, and why I am here.

Now that I think about it, not sure the 375F? is critical, as maybe a bake cycle at say 250F but for a much longer time might achieve the same beneficial results with no degrading of the final plating. But because of cost/time, the plater may elect for the higher temps to get product out the door. I don't know.
On the chrome plating, I was also under impression another chrome plate downside was, it had the potential to also "cover" initially developing fatigue cracks.

Is it possible to drill a drain hole for the solution that was being trapped?

It was once explained to me that chrome moly can be a problem to put any kind of coating on other than oil simply because the "moly" is actually a lubricant that can't be completely removed. One of the reasons I think most high end race cars these days are left bare metal. If you do see a painted cage, its probably made from mild steel. I'd say build your CM parts then wipe 'em down with WD40 and forget the "pretty".

375 will not affect the plating. I build airplane parts and its not an issue to bake.

Actually on Funny Cars and Dragsters, it's for weight and for ease of inspection for cracks and repair. Pro Stock and most everyone else are painted or powder. I prefer paint for ease of fixing and/or adding stuff (welding) and then fixing the finish. Plus guys are still concerned with appearances.

NHRA hasn't allowed plating (chrome) on cage components for years. Paint and powder only.

http://www.galvanizeit.com/uploads/ASTM-B-633-yr-13.pdf

http://imf-co.com/wp-content/uploads/2015/12/Website-Eliminating-Hydrogen-Embrittlement-per-ASTM-B633.pdfhttp://imf-co.com/wp-content/uploads/2015/12/Website-Eliminating-Hydrogen-Embrittlement-per-ASTM-B633.pdf

At what temp have you found temp to be a problem, and in my case I'm talking yellow zinc?

I have discolored yellow zinc when doing typical powder coat temps.

I only have the platers word to go on here, and the 375F is from my memory , I could be wrong.

And yes, the drain hole if possible is the proper solution, and my part had needed drain holes for other areas.

Electroless nickel is the best plating I've ever used for moly parts.

"A note about electroless nickel and hydrogen

Electroless nickel (EN) generates hydrogen as a part of the deposition reaction. Therefore Hydrogen embrittlement of high-strength steels can occur. What is different about electroless nickel deposits, you ask? Remember that electroplated deposits are crystalline. That is they have grain boundaries from which hydrogen can escape during the baking process. Electroless nickel is virtually amorphous (without grain structure). Since there are no grains, it is very difficult for hydrogen to pass through electroless nickel deposits, particularly thicker deposits where there is little or no porosity."

http://www.plateworld.com/editorial65.htm