KevinSun

What have you done to prevent galvanic corrosion of the aluminum frame on the C7?

Are there any brass or steel bolts or fasters owners should pay attention to?

RC000E

I talked at length with the engineers in 2013 about this. Interestingly the friction stir welding process that connects the extruded members of the frame, to the cast members actually uses steel fasteners. In a somewhat crude explanation, the machine spins the "screw" we'll call it, at such a high speed, that the heat created welds the members together. My first thought was to ask about the galvanic corrosion aspect, but was told that a coating is in place on the fasteners to prevent it. It was a process developed between GM and the company I suppose they utilize for that process.

I believe we've always seen some element of steel bolts to aluminum members, as these cars have had aluminum suspension components with steel bolts for some time.

I'm always up for more explanation/knowledge, but in case this never gets put forward, I figured I'd offer you that much that I've collected directly from the source.

KevinSun

Thanks for the response RC.

I was starting to think that this thread might not get much interest.

Interesting concept related to welding extruded to cast through friction. I was not even thinking about welds when I asked the question. I was wondering if we have any steel or stainless (Magnesium?) bolts, going through the aluminum frame. I was also wondering if they have done anything to insulate between them to prevent electron transfer. It would be nice to know if they have and where, just to know where to look in 4 or 5 years to see if there is any corrosion happening.

I was doing some reading related to the idea that Aluminium can't rust, but discovered it can corrode and is particularly sensitive to galvanic corrosion.

Hopefully, this thread will turn into a body of knowledge that we can share as forum members to keep our beauties in great shape for a long time.

bjmsam

Excellent question. I am eager to see more discussion on this topic having experienced significant corrosion problems with the BBK installed on my previous (daily-driven in all-seasons) vehicle.

RC000E

Be clear to readers that the pic you posted above is NOT a Corvette part, nor installed on a Corvette, but merely an example of an aftermarket big brake kit that exhibited some corrosion, as reference.

jjv104

Galvanic corrosion may or may not be an issue with steel bolts attached to an aluminum frame. Although aluminum is a more "active" metal than steel, the main reason you don't usually have a problem is due to current densities. When you have a large mass of aluminum bolted with a steel bolt the corrosion will be distributed over the entire surface of the aluminum so corrosion is not much of an issue. Flip that around and use aluminum fasteners on steel and due to the small, by comparison, amount of aluminum and the aluminum will corrode very quickly. This is analogous to the aluminum hats on the Brembo 2 piece rotors shown in the photo. Add the fact that the hats are not bolted tightly to the cast iron rotors leaving a gap where water, especially with road salt, can collect which will form a perfect galvanic cell that will destroy the hats.

The friction stir welding process does not really affect the corrosion rate. The main reason it is used is because it will weld similar or dissimilar metals with almost no distortion. It is commonly used in manufacturing commercial aircraft. The tooling is very expensive so it is normally used only for mass produced parts.

BTW Rust is corrosion but the word rust is reserved for iron bearing materials like steel or iron.

\Boost Monkey/

It all depends on the environment (electrolyte solutions ie water) you put it in more than anything, but there are alot of factors to the rate of corrosion a particular example would experience. It isnt exactly black and white that part X will corrode at X speed per year. You would have to look at each individual example for a corrosion factor.

Also, welding the two metals together, for instance, is much worse than simple surface contact galvanic corrosion. This is why you have to use special welding procedures in industrial applications like 309 wire when welding stainless to carbon for example.

But the last poster is correct, in our case the more active metal is the larger mass (by far) than the noble one, and coupled with the fact that the worst we would have is surface contact galvanic corrosion... I would not worry about this at all (no more than surface corrosion from road salts on carbon steel components that cars have always had).

To be honest... from a corrosion standpoint ill take the aluminum over the carbon steel any day of the week.