Thoughts on Aluminum Panel (Galvanic?) Corrosion Mitigation

[jebiruph]

(Cross posted on the Wrangler forum) https://www.jlwranglerforums.com/fo...anic-corrosion-mitigation.110847/post-2301791

This post is based on my degree in galvanic corrosion from YouTube university. Please feel free to point out any inconsistencies or inaccuracies.

The latest hinge corrosion TSB includes the use of zinc shims behind the door hinges which indicates that FCA sees this as a galvanic corrosion issue (or at least an issue with a galvanic corrosion fix). For those that don't know, galvanic corrosion results from the direct contact of dissimilar metals. This contact creates an electrical pressure that promotes the loss of electrons into the atmosphere of the less noble metal. Corrosion is the result of the loss of electrons. In the galvanic corrosion world, metals are rated from more noble to less noble, where the more noble metal will cause corrosion in the less noble metal. Since zinc is less noble than aluminum (which is less noble than steel), zinc is used as a sacrificial anode and will corrode (give up it's electrons) in place of aluminum.

Another factor needed for the corrosion to form is the ability for the electrons to be absorbed into the atmosphere. This requires an electrolyte which is typically moisture or. A lack of moisture or water is why metal will corrode less in a dry atmosphere.

So either avoiding contact with dissimilar metals, implementing a sacrificial anode, preventing contact with the atmosphere or any of the above should help mitigate galvanic corrosion. To that end, here's what I've thought of so far.

The zinc shim currently being used by FCA as a sacrificial anode will be great when they are available, but as an alternative how about a zinc washer on the door hinge. Time (or opinions) will determine the effectiveness of this.
Here's what a m10 washer with a 20mm outside diameter looks like on the door nut.

Here's one with black permanent marker around the edge so it doesn't show as much.

All of my door hinge corrosion has started at the pin, which I attribute to that being the connection to the dissimilar metal in the rest of the Jeep and also to damage done to the paint from opening and closing the door. My plan is use these Delrin hinge liners to replace the metal hinge liners to both electrically separate the hinge from the body and to also provide a more paint friendly surface for the hinge to pivot on.

And since access to the atmosphere with the presence of moisture or water is also needed for galvanic corrosion, my thought here is to apply strips of paint protection film around the lower edges of the panels to help isolate these corrosion prone areas from moisture and the atmosphere. No pictures of this yet.

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[Gvsukids]

All of my door hinge corrosion has started at the pin, which I attribute to that being the connection to the dissimilar metal in the rest of the Jeep and also to damage done to the paint from opening and closing the door.

Why even keep the pin in?

 

[DailyMoparGuy]

At work, we use zinc anodes on plastic gas distribution pipe for similar reasons. I like your idea with the washer (can’t confirm if it’ll work lol)…it kind of reminds me of an insulating gasket that I’ve seen in process piping when carbon steel pipe connects to stainless.

 

[MrJeep]

Staying tuned to this, my buddies orange JL has the corrosion around the entire hinge assembly bad.
This also reminds me that the single biggest pain in the butt project I have ever done on a jeep, and this is saying a lot, is removing the old Delrin hinge inserts in my TJ last year to replace them.

 

[fourfa]

Just a note; if those are hardware store washers, they’re plain steel with only an atomic-scale zinc plating on it. I wouldn’t expect that much zinc to last long

On the other hand it’s not hard to get solid zinc sheet and make washers out of it. There’s probably a whole marine industry devoted to this already (and maybe that’s where your washers are from)

 

[jebiruph]

Staying tuned to this, my buddies orange JL has the corrosion around the entire hinge assembly bad.
This also reminds me that the single biggest pain in the butt project I have ever done on a jeep, and this is saying a lot, is removing the old Delrin hinge inserts in my TJ last year to replace them.

What brand Delrin hinge inserts and why did they need removed?

 

[jebiruph]

Just a note; if those are hardware store washers, they’re plain steel with only an atomic-scale zinc plating on it. I wouldn’t expect that much zinc to last long

On the other hand it’s not hard to get solid zinc sheet and make washers out of it. There’s probably a whole marine industry devoted to this already (and maybe that’s where your washers are from)

They are hardware store washers. They are easy replace if they dont last long, but I'll keep an eye out for solid zinc washers. I didn’t have any luck finding them on Amazon.

 

[jac04]

The latest hinge corrosion TSB includes the use of zinc shims behind the door hinges which indicates that FCA sees this as a galvanic corrosion issue. For those that don't know, galvanic corrosion results from the direct contact of dissimilar metals.

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

 

[jac04]

And, while I'm thinking about it, you need uncoated surfaces exposed to the electrolyte for galvanic corrosion to take place between dissimilar metals. Everything is coated with paint. The only area suspeptible is the hinge to door interface, which is primed but not coated with body paint, BUT they are similar metals. So, that should rule out galvanic corrosion.

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 use Boeshield at all these interfaces. I apply with a dropper, and it wicks into all the interfaces. If you try it, it is quite surprising how much liquid will wick into these interfaces. I did this to my 2014 JK (aluminum hinges with steel doors) when brand new and I did it to my JT when it was new. No issues so far with either vehicle.

 

[chorky]

And, while I'm thinking about it, you need uncoated surfaces exposed to the electrolyte for galvanic corrosion to take place between dissimilar metals. Everything is coated with paint. The only area suspeptible is the hinge to door interface, which is primed but not coated with body paint, BUT they are similar metals. So, that should rule out galvanic corrosion.

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 use Boeshield at all these interfaces. I apply with a dropper, and it wicks into all the interfaces. If you try it, it is quite surprising how much liquid will wick into these interfaces. I did this to my 2014 JK (aluminum hinges with steel doors) when brand new and I did it to my JT when it was new. No issues so far with either vehicle.

Are you talking about this?
https://www.amazon.com/BOESHIELD-Co...keywords=boeshield&qid=1679700905&sr=8-2&th=1

Looks a lot like Amsoil HD metal protect
https://www.amsoil.com/p/heavy-duty...ln3CJCXgCk7ZPhYNhbgGOTAuvcK1oGBEaAqllEALw_wcB

 

[jac04]

Are you talking about this?
https://www.amazon.com/BOESHIELD-Co...keywords=boeshield&qid=1679700905&sr=8-2&th=1

Looks a lot like Amsoil HD metal protect
https://www.amsoil.com/p/heavy-duty...ln3CJCXgCk7ZPhYNhbgGOTAuvcK1oGBEaAqllEALw_wcB

Yes, but I bought the gallon jug of Boeshield because I use it for other things as well.

It is much 'thinner' (less viscous) than the Amsoil product, and it takes longer to dry. This allows it to penetrate and creep into joints and hard-to-reach areas.

 

[jebiruph]

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

The bolts that hold the aluminum hinges on are steel and they connect to steel. But I'm mostly relying on FCA's redesigned door hinges and zinc shim combo as evidence of galvanic corrosion.

 

[jac04]

The bolts that hold the aluminum hinges on are steel and they connect to steel. But I'm mostly relying on FCA's redesigned door hinges and zinc shim combo as evidence of galvanic corrosion.

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.

 

[BGlad]

This post is based on my degree in galvanic corrosion from YouTube university. Please feel free to point out any inconsistencies or inaccuracies.

The latest hinge corrosion TSB includes the use of zinc shims behind the door hinges which indicates that FCA sees this as a galvanic corrosion issue. For those that don't know, galvanic corrosion results from the direct contact of dissimilar metals. This contact creates an electrical pressure that promotes the loss of electrons into the atmosphere of the less noble metal. Corrosion is the result of the loss of electrons. In the galvanic corrosion world, metals are rated from more noble to less noble, where the more noble metal will cause corrosion in the less noble metal. Since zinc is less noble than aluminum (which is less noble than steel), zinc is used as a sacrificial anode and will corrode (give up it's electrons) in place of aluminum.

Another factor needed for the corrosion to form is the ability for the electrons to be absorbed into the atmosphere. This requires an electrolyte which is typically moisture or. A lack of moisture or water is why metal will corrode less in a dry atmosphere.

So either avoiding contact with dissimilar metals, implementing a sacrificial anode, preventing contact with the atmosphere or any of the above should help mitigate galvanic corrosion. To that end, here's what I've thought of so far.

The zinc shim currently being used by FCA as a sacrificial anode will be great when they are available, but as an alternative how about a zinc washer on the door hinge. Time (or opinions) will determine the effectiveness of this.
Here's what a m10 washer with a 20mm outside diameter looks like on the door nut.

Here's one with black permanent marker around the edge so it doesn't show as much.

All of my door hinge corrosion has started at the pin, which I attribute to that being the connection to the dissimilar metal in the rest of the Jeep and also to damage done to the paint from opening and closing the door. My plan is use these Delrin hinge liners to replace the metal hinge liners to both electrically separate the hinge from the body and to also provide a more paint friendly surface for the hinge to pivot on.

And since access to the atmosphere with the presence of moisture or water is also needed for galvanic corrosion, my thought here is to apply strips of paint protection film around the lower edges of the panels to help isolate these corrosion prone areas from moisture and the atmosphere. No pictures of this yet.

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.

 

[jebiruph]

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.

Here's a link to a post with the TSB. https://www.jlwranglerforums.com/forum/threads/bubbles-in-paint-at-door-hinges.32756/post-2276124
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.

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