Jeep Wrangler Galvanic Corrosion Issue

[DKAwildcat]

thread108-501244
I dropped my 2018 Jeep Wrangler at the body shop to have the galvanic corrosion repaired before the 5-year warranty expires. The galvanic reaction occurs due to the steel door, hood, and tailgate hinges being in direct contact with the aluminum panels prior to painting. Jeep’s solution (per Technical Service Bulletin 23-020-23) to prevent this from happening again is to place a thin zinc shim between the steel hinges and the aluminum panels. I assume the zinc shim will mow act as the sacrificial anode. Does anyone know what this will look like in time? Is it a reasonable fix?

 

[TugboatEng]

According to the table of nobility zinc is slightly sacrificial to aluminum. With that said, you don't want your shim wearing out as that will loosen things up. In reality it probably performed more as a gasket than an anode. If you seal the joint you won't have galvanic corrosion issues.

They are painting this after it's installed?

 

[MintJulep]

On its face, this seems like a terrible solution.

Zinc is sacrificial to both aluminum and steel.

Zinc is farther away from steel than aluminum.

So, with no other changes, it seems that the zinc will corrode, and will corrode faster than the aluminum in the original joint.

As Tug noted, as the zinc shim corrodes it will somehow change volume, thickness and stiffness, all will possible bad side-effects on the mechanical integrity of the joint.

 

[DKAwildcat]

TugboatEng: The TSB isn’t clear as to whether the galvanized shim is painted, but I would assume it would be to match in color.

MintJulep: It doesn’t seem like a good solution to me either, but this is their current “fix”. I always thought you were suppose to separate two different metals with a non-conductive material.

 

[TugboatEng]

The shim itself doesn't need to be painted, the assembly needs to be encapsulated in paint.

Aircraft are built from assemblies of aluminum and titanium, one of the most galvanically dissimilar couples available. The key is the prep on the aluminum. Paint doesn't stick well to aluminum, crevice corrosion exacerbates the problems. Chromate conversion coatings are common in the aircraft industry to prep the metal for paint. Once properly painted galvanic corrosion becomes less of a problem.

 

[Daryl_Automotive]

I agree with most of what has been mentioned, including that this sounds like a poor fix. The use of a sacrificial 'isolator' will do its job, but the key word is sacrificial. It will corrode and return you to corroded appearance and worse, a loose joint.

Galvanic isolation is better but also easier said than done. Paint is a good start but the screw will actually still become a galvanic bridge between the parts. There are some greases that can mitigate this, but you are still subject to the chaos of it perfectly isolating the galvanically active metals. Also, if the joint should loosen, even in a micro state, the paint can be abraded and now the joint subject to fretting corrosion.

And, not to pile on, but some of these joints could see road/environmental salts, which is like adding gas to the galvanic fire.

If you want to take care of it yourself, forget the sacrificial part and use a good epoxy paint between and over the joint. Use the dielectric grease and a 'Loctite' thread locker capable of grease applications.

 

[TugboatEng]

Consider making the shim out of Garolite G-10.

 

[Comcokid]

So, what are they using to connect steel hinges to aluminum body? Steel bolts?

Oldsmobile in the 80's changed from using a cast iron intake manifold on their V8s to an identically shaped aluminum one. But they kept the same die-cast thermostat housing and steel bolts. The bolts were indirectly exposed on the water/antifreeze by seepage through the thermostat gasket. What it meant was when you went to change the thermostat, the steel bolts would break-off in the aluminum. The oxidized aluminum around the bolts would swell effectively permanently locking the bolt threads in place. And thread-breaker penetrate would not soak through the oxidized aluminum with rust mixture. it's a lot of fun trying to hand drill out a steel bolt without the drill bit drifting into the soft aluminum.

 

[Factoter]

What are they using . . . Steel bolts! (Comcokid)

Yes, pictures look like zinc plated steel; here is the part number 68297680AF

TSB disallows replacement unless visible corrosion present, parts painted prior to install
No provision for treatment of panels or body corrosion

https://static.nhtsa.gov/odi/tsbs/2023/MC-10234479-9999.pdf

 

[TugboatEng]

Zinc plated bolts are not common in automotive anymore. Most fasteners use an inorganic zinc/aluminum coating. Dacromet is a common brand.

 

[enginesrus]

Easy fix, recall and replace all the aluminum bodies with the good old steel of years past. Oh and paint it good with good paint not water colors.

 

[TugboatEng]

Aluminum performs better than steel if you can resist the urge to paint it. See vintage Airstream trailers.

Enginesrus, remember steel is used for body panels because it is cheap. There is no other reason. There are tons of materials out that that can perform better. Personally, I think the Cybertruck should have been done in Monel. I don't mind a but of verdigris in extreme environments.