Painting the bare metal underneath Hinges?

[JTGuy]

I have the 7 year extended warranty. In 29 when it's over, I'll be over the JT.

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[ShadowsPapa]

My guy at the dealer this morning explained that the aluminum pieces that make up the doors and hinges are made from dissimilar aluminum alloys. The new process includes a dielectric between hinges and door skin, that new process Jeep has been using to stop the corrosion. He also explained that two of my four doors have to be replaced because the corrosion has went to deep into the skin and door frame structure. Might be an interesting idea to pull one door apart and coat it, reassemble it and watch, especially if your past the paint warranty.

The problem with their theory is that the two alloys won't be far enough apart in the list of metals in order of how noble they are to cause problems in a short time without a lot of water exposture. There are other metals making contact with each other that are farther apart in that list - without issue.
Magnesium, zinc, galvanized steel (duh, zinc) and then aluminum.
And the alloys of aluminum aren't all that far apart in that list.
(Anodized bare aluminum actually resists corrosion when exposed to salt water.)
So - is that hinge REALLY aluminum, or some alloy of magnesium or similar?

We also have pics of the paint issues well away from other metals - some have shown tailgate paint issues, inches away from anything else, inches away from the edge.

Zinc is also a stupid solution. You still have not isolated the metals electrically.
Zinc and aluminum oxides are non-reactive. That's why once a thin film of aluminum oxide forms on aluminum, it's protected unless said film is damaged. You can leave bare aluminum out and it instantly forms an oxide that's pretty much clear, and prevents further oxidation.

All they need is anything at all to isolate the two parts "electrically" and that could be a really thin film of plastic.
Galvanic action, from dissimilar metals, happens where the two parts contact each other and requires the presence of water.

I have rolls of zinc - and I could actually passivate it in the passivate baths I have in my shop. I can do the zinc in clear, yellow or "black".
Ideally, you'd cut the zinc smaller than the footprint of the hinge by a bit.
On the other hand, I won't be doing that if mine ever has an issue - I'll be making up a better, non-metallic solution. It can be extremely thin, as long as there is no direct contact AND water present, they'd be fine.

 

[Tank555]

They just replaced my hood and all four doors, all under warranty. And the paint match is perfect, I can't even tell. But I had to take it to a dealer that had their own body shop. I called Jeep and they told me which dealer to go to. Took about two weeks.

 

[Minty JL]

I need to take my '19 JLUR in........can't wait to see that epic fail. I had to replace a front fender and the body shop had a hell of a time matching the color; but they nailed it in the end. Mojito! green is apparently of a shade of several other Mopar greens like the Snakeskin that was used on the Viper, BUT not the same.

 

[Badunit]

If the zinc piece isn't a solution, why do you think they did it? Why go with what is probably a more expensive zinc shim if a thin plastic shim or a layer of paint (which could have been painted on the backside of the hinge for the TSB) would be better?

 

[ShadowsPapa]

If the zinc piece isn't a solution, why do you think they did it? Why go with what is probably a more expensive zinc shim if a thin plastic shim or a layer of paint (which could have been painted on the backside of the hinge for the TSB) would be better?

That's a good question.
Only thing I can figure is that the hinge is actually a magnesium alloy and not aluminum. If both door skin and hinge body were aluminum alloys, there'd be no real problem.

Magnesium is highly anodic and will corrode when in contact with almost any other metal, including aluminum, steel, and copper.

Ironically, AMC bolted their aluminum bumpers to the steel bumper supports with steel bolts. Apparently there was enough paint involved or some coating on the aluminum at that point. Their bumpers are hard to strip to repaint.

In any case, the idea is to prevent direct contact from the two metals that are enough apart in the charts to be a problem with each other. Any form of contact prevention, prevent the flow of electrons, etc. will do it.

Looking at this - if you used aluminum and zinc together, the aluminum should go first.

Zinc is used to protect steel as the zinc is anodic to steel and will sacrifice itself before the steel.

 

[jebiruph]

That's a good question.
Only thing I can figure is that the hinge is actually a magnesium alloy and not aluminum. If both door skin and hinge body were aluminum alloys, there'd be no real problem.

Magnesium is highly anodic and will corrode when in contact with almost any other metal, including aluminum, steel, and copper.

Ironically, AMC bolted their aluminum bumpers to the steel bumper supports with steel bolts. Apparently there was enough paint involved or some coating on the aluminum at that point. Their bumpers are hard to strip to repaint.

In any case, the idea is to prevent direct contact from the two metals that are enough apart in the charts to be a problem with each other. Any form of contact prevention, prevent the flow of electrons, etc. will do it.

Looking at this - if you used aluminum and zinc together, the aluminum should go first.

Zinc is used to protect steel as the zinc is anodic to steel and will sacrifice itself before the steel.

Every list I've seen shows Zinc as less noble than Aluminum. Isn't Zinc used as a sacrificial anode on aluminum boat hulls?

For the hinges, the Zinc shim is electrically insulated from the hinge, so would only be a sacrificial anode for the door. Although I wonder if the purpose of the shim is to stop the corrosion that starts on the hinge from spreading under the paint to the door.

 

[ShadowsPapa]

For the hinges, the Zinc shim is electrically insulated from the hinge, so would only be a sacrificial anode for the door. Although I wonder if the purpose of the shim is to stop the corrosion that starts on the hinge from spreading under the paint to the door.

I've forgotten - is that zinc piece coated on the hinge side?
The corrosion shouldn't spread to the aluminum if the hinge is magnesium alloy. The hinge should be impacted.

I just can't see why, if it's a galvanic reaction thing, and it should not be if both parts are aluminum, even alloys, (which makes me question the composition of the hinge itself) - why don't they simply isolate the two from each other? No zinc needed!
The isolators for plumbing are simply plastic pieces that prevent the two different metals (copper and iron pipes) from touching directly.

Zinc is used in water heaters - where there's no aluminum, only steel (and copper).

 

[Vtur]

The doors skin is probably some 5025 aluminum, highly doubt that the hinges are the same material. I think a 1/16" sheet of Viton rubber would help seperating the two unknown materials.

 

[legacy_etu]

I need to take my '19 JLUR in........can't wait to see that epic fail. I had to replace a front fender and the body shop had a hell of a time matching the color; but they nailed it in the end. Mojito! green is apparently of a shade of several other Mopar greens like the Snakeskin that was used on the Viper, BUT not the same.

I can’t imagine trying to match Mojito. I mean I’m no body guy but if I remember correctly there’s a ton of metallic flake in that color, right?

 

[legacy_etu]

Every list I've seen shows Zinc as less noble than Aluminum. Isn't Zinc used as a sacrificial anode on aluminum boat hulls?

For the hinges, the Zinc shim is electrically insulated from the hinge, so would only be a sacrificial anode for the door. Although I wonder if the purpose of the shim is to stop the corrosion that starts on the hinge from spreading under the paint to the door.

Yes, all boats, not just aluminum ones, use zinc anodes. Even fiberglass boats have them. Also, outboard engines have anodes bolted to them to protect the metal in them. You swap them out every few years. Different situation there though I believe as the anode is meant to attract stray electrical current from poorly wired docks as it was explained to me. Protects the metals on the boat from being attacked from stray current. I could be slightly off in this explanation though so don’t quote me on this, I am no electrical expert by any stretch.

 

[jac04]

The corrosion issues appear simultaneously on the door skins and hinges, which tells us that this isn't a galvanic corrosion issue from dissimilar hinge and door skin materials.

Also, corrosion happens at the bottoms of the aluminum doors and hoods starting at the edge seams. Unless the inner structures for the doors and hoods are a far more noble material than the skins, this also supports the position that this isn't a galvanic corrosion issue.

What all of these places have in common is that they are areas where moisture (along with road salt, acid rain, etc.) can become trapped. When moisture gets trapped in these areas, it will lead to corrosion of the aluminum by itself - a combination of crevice corrosion and filiform corrosion.

 

[RIPLER]

I can’t imagine trying to match Mojito. I mean I’m no body guy but if I remember correctly there’s a ton of metallic flake in that color, right?

Mine's billet silver which has metal flake in it, it took 2 tries and nearly 15K for them to get it right.

 

[Splenda]

I had a 2019 Ram 1500 that the driver's door had white corrosion running down the full length of the seam in the door jamb. I had no idea this was an issue on them until I got my Jeep. I didn't even know the Ram had aluminum doors.

 

[Minty JL]

I can’t imagine trying to match Mojito. I mean I’m no body guy but if I remember correctly there’s a ton of metallic flake in that color, right?

Yes, took my body shop about 7 spray out to get it right and they're the best in town...........They nailed in the end

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