Galvanic Corrosion

Aluminum is generally considered a "corrosion-proof" material for building bicycle frames, and it certainly resists corrosion in the sense that it does not rust like steel does. What is common with aluminum frames, however, is the process of galvanic corrosion. The problem with aluminum frames is that the frame is often in contact with a dissimilar metal, such as steel or even different aluminum alloys. The two metals have two different electric potentials, with the possibility of a tiny electrical current flowing between them. The presence of water and an electrolyte (both of which are found in the rider's sweat) facilitates this current flow, and ions begin to flow between the metals. The problem lies in the fact that the metal which loses ions begins to corrode much more quickly that it otherwise would.

Below are two examples of galvanic corrosion occuring on the same frame. The first photo shows a steel ferrule that has been in contact with the aluminum frame for a very long period of time, and has also been exposed to a lot of sweat. The steel ferrule has corroded and gotten stuck in the frame. Luckily, this is an example where the frame has not been affected, only the ferrule.















The second photo shows an area of the frame that has been in contact with another aluminum part, and also has been exposed to the rider's sweat for some time. In this example, the frame is the part that has been corroded by the process. You can see that the edge of the cable exit hole in the frame has begun to be eaten away. The other part involved is not pictured, but has not been affected.

















The solution to the problem of galvanic corrosion lies partly in proper preparation of the parts before assembly, and partly in rider maintenance. A layer of grease between to dissimilar metals will act as an insulator, and is very effective at preventing the problem. However, it is not a substitute for regular cleaning of the bike. This is especially true in the off season when the bike is on a trainer. Because the rider does not have wind current to aid in evaporation of sweat, more of it ends up in contact with the bike. This makes it especially important to try to keep the bike covered when riding on a trainer (we can get you the Safe-T-Net from Minoura or other similar models) and one must remember to clean the bike after workouts. Replacement of cables and housing once a year will also ensure that the insulating layer of grease between parts is there to insulate the two parts.