Fasteners corrosion

Anti-seize is not a corrosion inhibitor. Anti-seize is a dry film lubricant that has an oil carrier that can sometimes prevent some corrosion. For corrosion protection you would be better off using a water resistant grease.

As for modern vehicle fasteners, they typically have an inorganic zinc coating, Dacromet being an example. This provides good corrosion resistance.

Modern fasteners are coated as TBE says, and even the scuffing from making them up isn't fatal.
There are some thread lubes that have inhibitors in them but they are not used in automotive work.
Over the long term there will be some corrosion, especially in climates where they salt roads.
But having done some undercar work on by 2011 Toyota Avalon I can tell you that the modern treatments are very effective.
A bit of lubrication and some soak time and all fasteners came out fine.
That would not have been the case 20 years ago.


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P.E. Metallurgy, consulting work welcomed

thanks to both of you , my concern is mainly with the internal threads, not so much the bolt itself as that can be replaced easily, the rest is part of the chassis and when there is rust inside, I think is not easy to remove from the threads. I guess to do a perfect job I would therefore have to grease every thread, it seems like a long job

You can also use a low strength thread locker or thread sealant.

In the marine industry it's standard practice to out anti-seize on the pipe threads for tank vent fittings (exposed to salt spray). These require regular removal so the tribe has decided anti-sieze is best. It's always an ordeal come load line inspection time. We switched our fleet to PTFE thread sealant and no longer have problems with removal.

ah, alright, so wanting to really rust proof my car I have to do this job. I could take a PTFE spray grease, is there any type of grease that damages the paint? Idrocarbures, silicon, litium, copper?

Modern cars use EPDM rubber for bushings, seals, hoses, etc... This type of rubber is damaged by petroleum oils. Silicone based oils/waxes would be safest for corrosion protection.

The bigger issue is water getting trapped in the frame sections.
Making sure that these can drain is the biggest help.

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P.E. Metallurgy, consulting work welcomed

Silicone oils can have higher SG than water which means it can displace trapped water. High gravity silicone oil is a bit expensive, though.

Silicone oil or grease are electrical conductive?
Because I think is better to keep conductivity in bolt threads or it doesn’t matter?
What about the blue marine grease?

Silicone oils have high dielectric strength which means they're non conductive. Conductivity is a negative characteristic as it allows for the creation of a galvanic cell if dissimilar metals are present. A class 10.9 fastener threaded in to a weld nut will create some potential for galvanic corrosion.

Blue marine grease is petroleum based so it will damage bushings, hoses, and seals. The petroleum oils will also stain paints and plastics over time.

The blue "marine" grease is one of the worst performing greases I have worked with.

I would avoid soap based grease as they aren't stable and the oil separates from the thickener over time.

Good to know , thanks, I will stick with silicone oil or grease then.
There are really too many grease out there

This company makes the coating GM is currently using on truck frames.

Well shoot, now you've got me going down the rabbit hole of "gelled calcium sulfonate". These products look very promising for some of my applications.

Not very many threaded connections to be found in a modern automotive chassis.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

there are the threads of the front and rear subframe, engine mounts, exhaust, front and rear protective beams, heat shields for the exhaust, doors… not many but not very few. I wonder if this thing I want to do is also necessary where the bolt is painted outside together with the bodywork and inside it has the protective cavity wax, in these cases the air and humidity cannot enter, there will be only the little bit trapped in the thread

I looked at many products but almost all of them seem to have something like it, metals or petroleum, in practice there is only the normal silicone grease, the one that gives on the rubber seals. you say it could go? I also have some cavity wax jut in case.

What about Teflon grease? Is petroleum based? It harden or stay soft?

People like Tef-Gel but the price is quite a bit higher than silicone grease and offers no better protection, only better lubrication.

The other option is Krytox grease.
This is a fluorocarbon grease (short chain Teflon).
And they make versions with corrosion inhibitors.
This stuff is expensive, but totally inert and very slick.

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P.E. Metallurgy, consulting work welcomed

Be careful about fastener choices... the configurations and materials and usage environments and torque settings and locking features, etc... all factor into fastening durability and 'harmony'.

Question to ask... not in any particular ranking/order...

Bolt/nut/washer configurations: what do these parts 'look like' by necessity. Example: hex-head bolts VS 2X-Hex VS Cap Bolts; plain, countersunk, split-lock, star-lock, etc washers; hex or 2X-hex or spanner or castellated etc Nuts... or tap-threaded holes with or without inserts and plain or self-locking, etc features.

Next Bolt, Nut and Washer alloys and corrosion protective finishes need to be considered. Carbon steel, Low alloy steel, stainless steels, heat resistant alloys, super alloys. Types of finishes such as zinc, zinc-nickel, cadmium, with extra chemical treatments such as chromates, phosphates, baked-on solid film lubricants, etc. Also installation lubricants for friction control: none, acetyl alcohol, lube-oil [often common to the vehicle systems], greases, CPCs [corrosion preventative compounds] or anti-seize ['wet' or dry/powdered [MoS2, graphite, etc]. Also Is the fastener install considered 'permanent' [no intention to remove], semi-permanent [remove for rare maintenance]; or an active maintenance remove/reinstall [such as wheels], etc.

CAUTION: Bolt, Washer and NUT alloys/strengths/finishes need to be in harmony with each other, IE: strength-durability-stiffness matching to prevent fastener failures due to 1-miss-matched part... and any materials miss-matches resulting in dissimilarities/corrosion or galling.

What is the environment: hot exposed to engine-oil, or coolant or other fluids, etc; hot-dry-dusty external; hot-humid-moist-salty external; salty-wet/slushy/snow/ice/rain; arctic external; exposed to exhaust/pollutants, etc. Is the fastener experiencing extreme thermal cycles or is it at long-term ambient?

How critical is assembly/re-assembly [long-term] torque-tension requirement? Configuration, alloys, finishes, surface damage, tools, etc all affect torque-tension. Friction increase usually translates to lower tension pre-load to a 'standard torque-value'... and yet increase shear stresses on head-fillets and threads; while reduced friction can result in excessive tension preload for the 'standard torque value' with increased tension load thru the head-filets and threads.

Now... does the fastener installation/assembly require 'locking' or is 'plain' OK. Self-locking parts are rarely re-useable after 10-15 assemblies. IF not self-locking, are they locked with a second/jam-nut, cotter-pins or lock-wire or thread-locking compound or external crimping, etc.

My head hurts and I have to go back to work.

Regards, Wil Taylor
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