Thoughts on Aluminum Panel (Galvanic?) Corrosion Mitigation

[jebiruph]

Picture one looks like the bolts on that door hinge have been removed due to the paint being disturbed. Picture two looks like the bolts have not been removed because the paint is not disturbed.

The top hinge was replaced for the corrosion issue, the bottom hinge is original. I was just trying to show what the washers looked like installed.

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[ShadowsPapa]

Why use zinc? Has anyone looked inside water heaters where the supply pipe enters and the hot water pipe exist? PLASTIC.
Plumbing fixtures don't use zinc. That's sacrificial and the zinc will eventually be eaten away.
Plastic would insulate the parts from each other.
A while back I saw hinge kits with plastic shims or insulators that went between the hinge and the door skin.

If you want to look at it that way, then you need to look at the surface area exposure ratio of the dissimilar metals, which plays a lot into galvanic corrosion. There is a LOT of aluminum and very little steel. This doesn't support the assumption of galvanic corrosion. Don't read anything into what you think 'FCA' is doing.

Anyhow, you state there are redesigned hinges and zinc shims. Tell us more about the redesign and shims. What's different about the hinges? New part numbers? Are the zinc shims bare and not painted? The only way they will be effective is if they are not painted prior to assembly.

IF they are actually using zinc shims, then my bet is that they are trying to use the zinc shims to create galvanic corrosion, effectively saving the aluminum hinges and doors from corrosion by sacrificing the zinc shims. But, it's still going to be a complete sh!t show once the zinc starts corroding.

Bingo - glad I read your post prior to continuing as indeed the surface area, and the amount of the metal matters. It's like people freaking out over a screw of one type being used in a metal of another. There's a lot more to it.
And IMO, the zinc idea is dumb. Look at plumbing pipes - galvanized - ZINC - and what happens?
The zinc is sacrificed and the other metals react.
Experts in design state that yeah, zinc will protect the aluminum until it won't.......... that may be a long time, depending on how thick the zinc is, but the zinc will corrode and then what?

This is the answer -

Otherwise, when talking fasteners, a large anode-to-cathode surface ratio minimizes the risk or problem.

On the JL and JT, the hinges are aluminum and so are the doors. So, just wondering, where are the dissimilar metals?

And yes - if you've been in this type of discussion before, you've seen my other posts on this, explaining a lot of what's being seen is NOT galvanic corrosion at all. That takes place exactly at the joint - not out a ways. So the front edge of a hood, the surface of a hinge, etc. is not galvanic corrosion. That happens at the joint, not away from it.
When people see corrosion on aluminum it's not always galvanic reaction.
People freak when I talk of using stainless steel screws in aluminum and yet it's totally acceptable - there's a large anode-to-cathode ratio (large surface area of aluminum, small surface of the screw)
Maybe in marine applications, constant water, salts, etc. - not a good thing, but for other things, it's fine.

 

[jac04]

Here's a link to a post with the TSB. I'll admit that I am assuming that there is galvanic corrosion causing the problem when it may be it's only the fix for the problem. But it's such an extensive problem that it seems more like a design problem and not a paint quality problem. If your not aware of the extend of the problem, peruse the thread with the TSB a bit and you will get an idea of the extent of the problem.

I don't see the link to the "latest TSB". Can you post it again, or provide the TSB number?

I remember seeing a TSB with information on fixing the corrosion, but nothing about the redesigned hinges and new zinc shims you mention that the latest TSB covers. I'm really curious about these new parts.

Anyhow, I'm aware of the extent of the problem - I've seen a bunch of corrosion posts on the JK and JL forums as well as here on the JT forum.

It is a shame that the internet forums simply perpetuate the claim that galvanic corrosion is the cause.

 

[jac04]

... a lot of what's being seen is NOT galvanic corrosion at all. That takes place exactly at the joint - not out a ways.

For bare metals, yes, galvanic corrosion takes place at the joint. But, coatings play an important part in where the corrosion takes place. For example, if bare aluminum and bare steel are joined together and then the external surfaces are only locally painted at the interface, then the area of aluminum corrosion will be 'shifted' away from the joint to the unpainted area.

 

[jebiruph]

I don't see the link to the "latest TSB". Can you post it again, or provide the TSB number?

I remember seeing a TSB with information on fixing the corrosion, but nothing about the redesigned hinges and new zinc shims you mention that the latest TSB covers. I'm really curious about these new parts.

Anyhow, I'm aware of the extent of the problem - I've seen a bunch of corrosion posts on the JK and JL forums as well as here on the JT forum.

It is a shame that the internet forums simply perpetuate the claim that galvanic corrosion is the cause.

Here's the link https://www.jlwranglerforums.com/forum/threads/bubbles-in-paint-at-door-hinges.32756/post-2276124 I also added to the earlier post

 

[jebiruph]

Here's one of my hinges that has been replaced due to corrosion. The corrosion paint bubble (arrow) starts where the aluminum meets the steel flange of the pin insert and this is the same for the other 6 hinges I've had replaced so far. The body of the steel pin extends into the aluminum up to the 5 (other arrow). That seems to be a significant amount of steel touching aluminum, but whether this is regular or galvanic corrosion really doesn't make a difference. Either way, wouldn't a zinc washer sacrificial anode on the door nut help mitigate the corrosion of the aluminum?

 

[jebiruph]

The real cause of the corrosion is that water/moisture gets 'trapped' at all the hinge/door/bolt/bushing interfaces that are not sealed against moisture. Seal these areas against moisture and the problem goes away.

I noticed that where the corrosion occurs is where the paint is thick enough to completely cover (and seal) the gap between the pin flange and the hinge. The gap is clear on the back of the hinge and there's no visible corrosion. That does seem to indicate that it's water/moisture getting trapped behind the paint being a major factor in this specific hinge pin area corrosion.

The gap is open in the back.

The arrow points to where the gap gets covered with paint.

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