hood corrosion Q

So I'm in the midst of repairing the common hood corrosion on my 2011 GT and I've seen the Ford TSB talking about galvanic corrosion and iron particle contamination at the factory, as well as some of the tons of posts on this over the years. But it occurs to me, if iron contamination is such a big deal during painting and assembly, and can cause this type of galvanic corrosion, isn't the aluminum hood just directly contacting the steel (iron) body 24/7 via the hood mount points and the hood latch?

So (all this sanding and prep work to repaint my hood is giving me lots of time to think), would it make sense to better isolate the hood, perhaps with some type of rubber membrane where the hood latch attaches to the body, and where the hood support hinges attach to the hood, so as to separate the aluminum and steel and thus prevent the galvanic corrosion problem?

But then I figure all the engineering power of Ford wouldn't miss such an easy fix with something like 20 years of history on this problem over multiple models.

Can one of you engineer types explain what I am missing? How is the hood not subject to galvanic corrosion every day, being bolted to the steel body? Thanks!

I am not a paint and body guy, however, I too had the hood corrosion starting on mine. All I can tell you is it started on the underside of the hood where the outer panel is folded over the hood reinforcement. Much like any other part of any car, corrosion starts at edges of panels and not in the middle.

IMO it was just poor prep and lack of proper corrosion inhibitors is the real cause.

I saw it starting well before it wrapped around the leading edge and became visible. With a wire wheel, I knocked off the lose stuff and spraybombed it under there.

Luckily, my previous explorer was still under warranty when it happened. Dealership replaced the entire hood and had it painted locally at a body shop.

From what I read, it is the iron particles embedded into the aluminum panel before the paint has been applied. That is why you have to replace the panel, rather than remove the corrosion and repaint it. It will just keep coming back or occurring on other parts of the hood, no matter how many times you paint it.

There are a few class action lawsuits pertaining to this.

If I remember correctly, galvanic corrosion between dissimilar metals still needs an electrolyte to complete the circuit. How does that occur if the iron is stuck to the aluminum and sealed from the atmosphere?
If galvanic corrosion is the problem wouldn’t bolting a sacrificial anode to the body solve it?

I took mine to a reputable local body shop and they would not touch the factory hood. They said they could not warranty their work because the panel itself is flawed and would bubble again in a few years. So i took it to Ford and they told me the same thing and recommended i buy a new hood and then have it painted. So i did, bought a fiberglass hood from Amerihood.

I'm certainly no expert but that is what I'm wondering. Isn't the aluminum hood, which is bolted to the body, essentially acting as a sacrificial anode relative to the steel chassis? There is all this talk and Ford's TSB about not letting iron contaminate or come in contact with the aluminum hood during assembly or painting, but then the aluminum hood is bolted directly to the steel body and also comes in contact with it through the latch mechanism.

Yes if you live in a perfectly dry environment there would be very little electrolyte, but for the rest of us why isn't having the aluminum hood bolted to the steel chassis making the normal corrosion that much worse?

I'm not trying to argue, I just don't understand it to be honest.

You guys are over thinking it.
Think of it more like a sliver that festers
over time.
Galvanic corrosion from the exposure of the aluminum
to the iron happens over a long time period and it is not a simple Ox-Redox reaction. That is part of the reasn why the auto manufacturers over a decade to finally realize that you can't just repaint a contaminated panel and geounding it will make no difference.
The engine heat has been thought towork as a catalyst to speed up the reaction and that is why hoods are usually yhe first part to bubble.
It is now widely known in the bodyshop industry that you need to have a separate set of tools for working on aluminum because tools that have previously been used on regular steel will contaminate an aluminum panel.

I agree dedicated tools for aluminum and steel are required just as working stainless and steel requires separate tools but I don’t buy for a minute that an aluminum hood can’t be striped and painted successfully. There are adhesion promoters and primers specifically for that task.

Midlife Crises said:

I agree dedicated tools for aluminum and steel are required just as working stainless and steel requires separate tools but I don’t buy for a minute that an aluminum hood can’t be striped and painted successfully. There are adhesion promoters and primers specifically for that task.

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And yet, ford themselves failed at it from back in the early 2000's when they first stared using aluminum hoods until they finally realized it couldn't be done in 2017. I'm sure that more than one PhD. in Chemistry took a stab at solving it and still couldn't do it in a cost effective manner.
This is a piece of stamped aluminum, not something whittled down from a block of billet stock.

And now Ford has aluminum bodies on the trucks and vans, not just hoods. Are they going to get the same bubbling on all aluminum panels?

Aluminum panels on vehicles is not new, chances are it was single stamping plant in metro Detroit that had a flawed process or perhaps a couple of employees that did not realize the consequences of something they were doing.
When Ford rolled out the 2015 F150, they likely had a plant with new tooling and won't have that problem.
A lot of GM SUV's have the bubbling paint as well-mostly on the hoods and the hatches.

From a chemistry and galvanic corrosion perspective, how is an aluminum hood that is contaminated with iron dust during assembly or paint any different from an aluminum hood that is physically bolted to a big chunk of steel (iron)?

Aren't you going to get the same galvanic corrosion problem either way, with the noble and less noble metals in direct contact with each other and all the problems that come from that?

I let this go too long and now I am repainting the entire front lip of my hood. It gets really bad if you ignore it.

Body panels are galvanized so that you don't get a reaction between dissimilar metals, the Fe particles that contaminated the hoods, hatches, etc... were not galvanized.

https://galvanizeit.org/design-and-fabrication/design-considerations/dissimilar-metals-in-contact

And again, replace the hood unless you want the disappointment of watching the bubbles return after re-painting it. Yours is one of the contaminated ones and not all of them are contaminated, the majority have not been contaminated.

I have seen this bubbling leading edge on 2005-2010 mustangs. Having a hard time with only a small percentage of hoods were contaminated. Just sayin'.
As for bodyshops not wanting to deal with actually fixing it? When I had my Cervini hood installed, the shop bought my stock hood to fix a deer hit that came in.

I've had it on one out of 6 ford aluminum hooded vehicles that I have owned or had as a work truck and all those models were known to occasionally have this problem. If the one on my mustang does it, I'll go to an aftermarket hood rather than trying to fix it.
Fiat Chrysler stopped replacing hoods after they had found a process for repairing the existing hood. It successfully got a lot of them out of warranty but sounds like many are back to bubbling. Grand Cherokee's and ram 1500's had this problem.

I have used zinc chromate primer on aluminum before. The aircraft industry couldn’t exist without it. Zinc anodes are common in aircraft and boats. Zinc clad aluminum is a common construction material and has been around for a long time. I suspect the corrosion between sandwiched layers, folded and welded can’t be accessed for removal mechanically. There is no way a shop could warranty their work knowing the blister will come back.
Thing is, if an iron pipe and an aluminum pipe are screwed together and sealed inside and out with paint no corrosion will occur. Fill it with water, no corrosion will occur. Scratch the paint, the water becomes electrolyte and corrosion is certain.

RED09GT said:

And yet, ford themselves failed at it from back in the early 2000's when they first stared using aluminum hoods until they finally realized it couldn't be done in 2017.

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What happened in 2017? The hoods are still made of aluminum.

Mi [QUOTE="Juice said:

I have seen this bubbling leading edge on 2005-2010 mustangs. Having a hard time with only a small percentage of hoods were contaminated. Just sayin'.
As for bodyshops not wanting to deal with actually fixing it? When I had my Cervini hood installed, the shop bought my stock hood to fix a deer hit that came in.

Click to expand...

You know, it's really hard to understand how this could continue for over 10 years. Is Ford just sitting on their hands and just hoping the warranties expire before too many people have an issue?

13v6 said:

What happened in 2017? The hoods are still made of aluminum.

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My 2017 explorer sport needed a new hood at less than 2 years of service so they had yet to get it fully sorted. That was my point...

When (not if) mines starts corroding, I'm using it as an excuse to get a sweet fiberglass or carbon fiber hood.

I don't come in here much anymore but i still get notices from this forum.I am going to copy my post that i did a long time ago concerning this topic.I have(had) a 2009 that this has happened to twice.The first time was under the hood right side at the seem and was fixed under warranty.A few months later it appeared again.This time it was under the hood in front and worked it's way on top,spidering the paint.By this time the car was out of warranty.So after contacting ford corporate,it came down to me having to pay a third of the cost(corporate,pays a third,dealer pays a third).Actually the dealer shouldn't have to pay anything,it's not their fault.My dealer has been as good as gold with me on the three and a half years i've owned this car.Anyway come to find out that ford has knowed about this problem since 2004 and hasn't done anything about it,which between that and the clutch issue(that had four tsb's on)ticked me off and what broke the camel's back was the body shop who did a great job repairing it said this problem WILL recurr(i appreciate their honesty).I took the car straight from the bodyshop to a dealer and traded the car off for a corvette and i'm enjoying it.I really liked the 500 but i'm tired of the bs.The next time that hood would start corroding,the whole thing would come out of my pocket....and it's never ending.Btw i didn't like any of the fiberglass hoods that were offered for replacement,but at least the vette won't ever have this problem.PS the fix(second and trade) was on 12/07/12. and btw,i still have the Vette.