Suspension Finishes

[MJinCO]

I'm going to be building some new front suspension control arms this winter and would like to know how people are finishing them. I'm changing from the original Spitfire upright modified to have a lower ball joint apparently from a '60's Cooper to a bottom 5/8" rod end so will be making some new control arms to fit. The control arms will be 7/8" 4130 tubing with rod ends, my current control arms and some old uprights appear to be Cadmium plated and am curious how newer ones are finished.

[Rick Kirchner]

Vintage car? Nickel. Electroplated if you can get it, electroless if you can't

[MJinCO]

Yes, very vintage 1971 Ocelot, thanks for the info.

[10rmotor]

We used bright nickel plating on our Amac DSR suspension pieces. It seemed pretty durable even after many years of use. One of the nice things about that finish is if you needed to weld on it there were no issues with contamination.

[jrh3]

Hopefully someone will jump in with a discussion of embrittlement.
Electroless, electroplated nickel and cadmium as well as need for post plating baking of mild and higher strength steel.

[Rick Kirchner]

I did not think electroless experienced hydrogen embrittlement.

Regardless, if you do electroplating on racing parts its best to find a plater that does it to mil-spec, and then ask them to follow the process (but you don't really need the certs $$$$)

[Lee Johnson]

Hopefully someone will jump in with a discussion of embrittlement.
Electroless, electroplated nickel and cadmium as well as need for post plating baking of mild and higher strength steel.

Hope it is not too detailed & abstract: the following paper from Fastenal Corp. has some good layman-level info on the topic of hydrogen embrittlement --

https://www.fastenal.com/content/fed...rittlement.pdf

The paper is focused on fasteners, but much of the info also applies to other steel parts. Some excerpts from the paper include--

1) "In general, if the hardness of the fastener is less than 35 HRC [Hardness, Rockwell C-scale], there will probably be little difficulty with hydrogen embrittlement. However, if the fastener has hardness above 40 HRC, problems are more likely to occur."
2) "Coating processes such electroplating can introduce hydrogen during the acid cleaning stage."
3) "If electroplating is still desired, ensure that the plater uses the proper procedures and bakes the fasteners
correctly based on the hardness of the fastener....ASTM F1941 has a hydrogen embrittlement relief requirement for coated fasteners made from steel heat treated to a hardness of HRC 40 or above, case hardened fasteners, and fasteners with captive washers
(SEM screws) made from hardened steel. The exact time and temperature of the bake is not specified, but times between 2 and 24 hours at temperatures between 350 and 450°F are listed as suitable depending on type, size of fastener, geometry and other variables." [Note that these temperatures can be achieved in a kitchen oven, only if SWMBO ("she who must be obeyed") agrees of course!]
4) I've read elsewhere that electroless plating processes directly to the part are less prone to inducing hydrogen embrittlement than electroplating processes, but can't quickly find a reference.
5) A Wikipedia article also mentions the possibility of creating hydrogen embrittlement due to improper welding: "A common case of embrittlement during manufacture is poor arc welding practice, in which hydrogen is released from moisture, such as in the coating of welding electrodes or from damp welding rods.^[22][31] To avoid atomic hydrogen formation in the high temperature plasma of the arc, welding rods have to be perfectly dried in an oven at the appropriate temperature and duration before use. Another way to minimize the formation of hydrogen is to use special low-hydrogen electrodes for welding high-strength steels."
Link ==> https://en.wikipedia.org/wiki/Hydrogen_embrittlement

Lee

[Rick Kirchner]

I've seen welding rod ovens but had no idea that was why.

There certainly are a lot of acids involved in Electroless. Besides the usual cleaning methods, after the part is catalyzed with tin-plated palladium particles, you dip the part in hydrofluoric acid to strip the tim from the palladium and then go right into the nickel bath.

At least, that's how we did it in 1986. Hopefully they've come up with a way that's less dangerous. HF is freaking scary.

[DanW]

Suspension parts made of low carbon C1030 mild steel and even normalized 4130 are really not subject to hydrogen embrittlement. As the Fastenal tutorial states, steels @ <35 Rockwell C are not sensitive to HE.

Some of our turbine parts made of 4340HT to Rockwell 50C were hard chrome plated for wear resistance. The plate shop we used would bake our parts just after coming out of the tank before doing the finish grinding.

[Jerry Kehoe]

Years ago I found the simple browning finish as used on some guns works very well to create good looking and rust-free treatment for most steel parts. This is available at any gunsmithing supply place and all you do is heat the part to a couple of hundred degrees, wipe it on, as many times as you like until it is uniform and as dark as you like. After that simply wipe with WD40 from time to time to keep a great finish. If you have to weld the part simply lightly sand it, complete your repair and retreat. I believe it is a form of the bluing done on guns in reality. Costs very little, looks great on brackets, etc as well. Anyone who saw my March/BMW saw the results over the years. It is merely some kind of an oxidation that minimizes development of rust.

[Lee Johnson]

I'm going to be building some new front suspension control arms this winter and would like to know how people are finishing them. I'm changing from the original Spitfire upright modified to have a lower ball joint apparently from a '60's Cooper to a bottom 5/8" rod end so will be making some new control arms to fit. The control arms will be 7/8" 4130 tubing with rod ends, my current control arms and some old uprights appear to be Cadmium plated and am curious how newer ones are finished.

Here is a link to the AWS website tips on welding 4130 (it has frequent mentions of our "stuff") --

https://app.aws.org/forum/topic_show.pl?tid=32391

Tips #6 (Heat treating...?) & #10 (Cooling the weld...?) are worth paying attention to. One implication of #10 is getting unexpected hardness through rapid cooling-- this would also possibly result in increased hydrogen embrittlement sensitivity.

Also note some tips (#3 - #5) relating to filler material and modest pre-heat (#2) to drive away any residual H2O (that can disassociate at welding arc temps and result in dissolved hydrogen in the weld pool --> hydrogen embrittlement!).

[patman]

The primary concern for hydrogen embrittlement during welding is from the flux on certain stick electrodes (7018) which absorbs water from the air. Nearly all race car welds should be made using a TIG process where there is no such concern.

There is a concern with embrittlement in the heat effected zone due to rapid cooling of alloy steel, although our most common alloy 4130 doesn't have quite enough carbon to make this a major problem. A common misconception is that this cooling is heat transfer to the air: generally the heat transfer to the surrounding metal is several orders of magnitude higher. A good rule of thumb for 4130 is to preheat anything thicker than 1/8".
Side note: steel does not absorb moisture. Preheat is for reducing heat transfer, not drying anything. The moisture you see on steel when heating with a torch is actually coming from the torch as a byproduct of combustion....

That said be very careful welding to hardened steels, especially high grade fasteners, as it can both embrittle them and leave large internal stresses, leading to sudden and complete failures.

Not that any of that has anything to do with plating. I am with Ted on this one- nickel plating looks and works nice and is easy enough to do.

[Lee Johnson]

The primary concern for hydrogen embrittlement during welding is from the flux on certain stick electrodes (7018) which absorbs water from the air. Nearly all race car welds should be made using a TIG process where there is no such concern.

There is a concern with embrittlement in the heat effected zone due to rapid cooling of alloy steel, although our most common alloy 4130 doesn't have quite enough carbon to make this a major problem. A common misconception is that this cooling is heat transfer to the air: generally the heat transfer to the surrounding metal is several orders of magnitude higher. A good rule of thumb for 4130 is to preheat anything thicker than 1/8".
Side note: steel does not absorb moisture. Preheat is for reducing heat transfer, not drying anything. The moisture you see on steel when heating with a torch is actually coming from the torch as a byproduct of combustion....

That said be very careful welding to hardened steels, especially high grade fasteners, as it can both embrittle them and leave large internal stresses, leading to sudden and complete failures.

Not that any of that has anything to do with plating. I am with Ted on this one- nickel plating looks and works nice and is easy enough to do.

All good points about welding 4130. Patman!

The AWS article I included a link to (reply #7) identifies ERS80-S2 as one suitable filler alloy for 4130. It notably has even lower carbon content than 4130 base material to minimize the chance of weld zone embrittlement tthru the rapid heat conduction out of the weld zone into the base material. ERS80S2 = 0.08% Carbon (nominal) vs 4130 = 0.30% C (nom.). Another similar filler alloy is ERS70-S2 (0.07% C with slightly lower yield strength, but greater elongation than ERS80-S2). Spec sheet links --

https://arc-zone.com/content/pdf/ER8...Spec-Sheet.pdf
https://arc-zone.com/content/pdf/ER7...Spec-Sheet.pdf

[pacratt]

JUST. DON'T. CHROME. (bright OR hard)

That's all I'll say.

Glenn (Machinist / Machine-Builder for 35+ years)

[MJinCO]

Since this is and always will be a low budget car I'm going to use the gun blueing method. I'm going to use 4130 which is readily available from Aircraft Spruce and I haven't found a reliable source for any DOM small tubing as it is all 1008 seam welded. I worked in a tube mill for a couple of years so UTS is not an issue to me , just the quality control involved. An extra $25 for 4130 is not a problem. I won't be doing the welding.

The uprights are Spitfire origin with a ball joint on the top into a solid arm and a ball joint on the bottom supposedly of '60's era Cooper origin. This suspension has upper trailing control rod and leading lower rod rather than fabricated wishbones. The current plan is to use a Spitfire upper ball joint adapted into a solid arm (obviously rod end on the other end) cost wise about $20 vs the $135 from Chapman Racing and a 3/4" rod end on the bottom as a very slight extension is needed to maintain geometry. So new upper and lower main control arms are needed. BTW a '68 Corvette tie rod end will fit the Triumph upright with a thick washer on the nut and is threaded 5/8-18.

[jrh3]

You might check Wicks Aircraft for 4130 prices

[Max.Brass]

I believe Swift used to use Black Oxide to finish suspension components. It's inexpensive, can even be done at home, and when wiped down with WD40 looks quite good.

Just a thought . .

Max