Galvanic Corrosion

I get questions from techs in the field about galvanic corrosion regularly. This article discusses where we should look for corrosion when installing auto glass and what we can do to prevent it.

Wikipedia defines galvanic corrosion (also called bimetallic corrosion) as an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte.

Short of going into long scientific explanations of how galvanic corrosion occurs, let’s simply put it like this: When two dissimilar metals make contact, the possibility of galvanic corrosion is likely. Galvanic corrosion is not like the “rust” we are used to seeing. Instead of looking like rough orange flaking metal, it appears like a white powder that eventually eats away at the weaker metal.

We as techs rarely think about the ramifications of two dissimilar metals touching when doing an installation, but we should. If a steel screw is used to attach a chrome molding to an aluminum vehicle, we will eventually have problems. The aluminum will eat away, and the molding will come loose. Worse yet, the aluminum could undermine the bond, and the windshield will not perform properly in a collision.

We have heard in the past not to use normal polyurethane on an aluminum vehicle due to the possibility of galvanic corrosion. We were told that if normal, conductive carbon black urethane was used on aluminum pinchwelds, the result would be corroded metal. The possibility of galvanic corrosion, along with the diffusion of an electrical circuit, were the two main reasons for the introduction of non-conductive urethanes. Galvanic corrosion, although still an issue, has taken a back seat since the introduction of the aluminum Ford F-150 and the use of normal urethane with non-conductive primers and protective paints.

However, we still need to pay attention to other situations where this type of corrosion may occur. A good example is the Toyota Camry with riveted side moldings. There are plastic grommets inserted in the same holes in which the aluminum rivets are placed and crimped. By removing the rivets, many times the grommets are damaged. Did all of you replace those damaged grommets to prevent the aluminum rivets from making contact with the steel “A” pillar?

Stop and look carefully as you disassemble any vehicle for glass replacement. You will find many more times when there are protective grommets, washers, fasteners and/or retainers that separate the many metals found on the modern-day vehicle. Don’t ignore them. All of them are there for reason, and it is our job to make sure we don’t shorten the life of our customers’ vehicle. Also remember, with the drive to increase fuel efficiency in future cars, that there will be many more lightweight metals used. We, as professionals, have to be observant and act on what we see.

Bob Beranek is the president of Automotive Glass Consultants Inc.