Galvanic Corrosion

[mr_bots]

I was poking around on my truck and noticed there's a lot made out of aluminum, which got the engineer in me thinking: has anyone had a dissimilar metals vehicle before and noticed any galvanic corrosion? Aware of anyone that's released a write-up on steps they took to prevent galvanic corrosion as they all start including more aluminum in designs. Granted, I don't expect to hear of any on this or the JL as new as they are but GM has been using aluminum hoods since 2014 and surely there's more out there to see how they're aging in the real world.

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[OMTBiker]

I had galvanic corrosion on the hinges of my JL in less then 16 months, there are several threads on the JL forum.

 

[ShadowsPapa]

I was poking around on my truck and noticed there's a lot made out of aluminum, which got the engineer in me thinking: has anyone had a dissimilar metals vehicle before and noticed any galvanic corrosion? Aware of anyone that's released a write-up on steps they took to prevent galvanic corrosion as they all start including more aluminum in designs. Granted, I don't expect to hear of any on this or the JL as new as they are but GM has been using aluminum hoods since 2014 and surely there's more out there to see how they're aging in the real world.

I could point to the aluminum bumpers used on the Concord, Spirit and Eagle in the late 70s and through the 1980s, how I have 3 or 4 of them stored under my lean-to, and have multiple cars in my shop with them. They are fine - they also use steel brackets to secure them to the steel frame channels. I never see trouble with the aluminum and they are bolted to steel, and face all the crud the wheels can toss at them.
I could point to the aluminum fuel lines used by some for a few years.
There are many aluminum parts in use for decades. No problem.
Body panels should be no problem.

I also restore starters, alternators, wiper motors, blower motors and other components with aluminum parts, as well as the clutch master and slave cylinders in my Eagles - aluminum bolted to steel with brass fittings.

I notice damage on the steel parts and usually the aluminum parts outlast the steel.

Check all the aluminum parts here (carburetors are zinc allow castings)

 

[ShadowsPapa]

I had galvanic corrosion on the hinges of my JL in less then 16 months, there are several threads on the JL forum.

At what point? Where the bolts are? Was there a hood light or anything electrical on it?

 

[mr_bots]

I had galvanic corrosion on the hinges of my JL in less then 16 months, there are several threads on the JL forum.

I did a quick search and found one that shows some paint bubbling where the hinge mount touches the door panel. That's not where I'd expect it since the doors and hinge mount are both aluminum. I was expecting it to be more of a problem where the hinge mount on the door touches the hinge on the body or at one of the screws since it seems all the screws/bolts are steel.

 

[OMTBiker]

At what point? Where the bolts are? Was there a hood light or anything electrical on it?

The corrosion was on the door skin along where the outside edge of the hinge has a small gap.

 

[OMTBiker]

I did a quick search and found one that shows some paint bubbling where the hinge mount touches the door panel. That's not where I'd expect it since the doors and hinge mount are both aluminum. I was expecting it to be more of a problem where the hinge mount on the door touches the hinge on the body or at one of the screws since it seems all the screws/bolts are steel.

The corrosion/paint bubbling occurred around the edge of the hinge and the door skin, apparently the hinge and door are bare metal where they meet.

 

[ShadowsPapa]

The corrosion/paint bubbling occurred around the edge of the hinge and the door skin, apparently the hinge and door are bare metal where they meet.

I wonder if a ground strap from door to chassis could have helped.
There are a lot of aluminum parts bolted to steel with no issues on other vehicles.
Wonder if they have an alloy issue or electrical potential issue.

 

[mr_bots]

The corrosion/paint bubbling occurred around the edge of the hinge and the door skin, apparently the hinge and door are bare metal where they meet.

That sounds more like a poor paint job leading to paint failure or corrosion crawling up under the paint since the door and hinge are both aluminum.

 

[OMTBiker]

That sounds more like a poor paint job leading to paint failure or corrosion crawling up under the paint since the door and hinge are both aluminum.

The hinges are bolted and aligned before the door is painted, it would make more sense to paint them separately then bolt together but the bolts would have paint chips if painted then installed.

 

[ShadowsPapa]

The hinges are bolted and aligned before the door is painted, it would make more sense to paint them separately then bolt together but the bolts would have paint chips if painted then installed.

Cars and trucks are historically assembled with hood, trunk, doors, etc. then painted. For one thing - the paint between the pieces would lead to trouble as it's compressible and won't allow a tight joint. And like you said - the bolt heads. For metallics and certain other paints you want things painted all at the same time, same batch, and in the same orientation or you can at times see the differences in finish.

 

[93civej1]

Any JT guys having this issue? I was over reading on the JL board and there was 36 pages on one post about this subject.

 

[ShadowsPapa]

The hinges are bolted and aligned before the door is painted, it would make more sense to paint them separately then bolt together but the bolts would have paint chips if painted then installed.

Vehicles have always been painted with body fully assembled. For reasons you mention. It's way too risky to guide parts into place after painting - and deal with scratches, chips and more - and unpainted bolt heads and so on. Imagine them being painted then assembled and they have to move and slide things around to line them up.

The idea is also that the paint seals things.............. And with paint between panels, it can wear away and then you have loose parts.

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