- Galvanic corrosion occurs when two dissimilar metals come into contact with one another, combined with the presence of moisture or condensation. In most cases, such as two parts being bolted together, the aluminum and steel are kept separate with a polymer shield that prevents them from coming into contact with one another. In welding, however, this is not possible. Therefore, the welded surfaces have to be sealed from moisture or electrical conductivity to prevent galvanic corrosion of the aluminum.
- Gas metal arc welding is primarily used to bond aluminum to steel. This process is facilitated by the application of either a bi-metallic shield between the materials or by coating the steel part in aluminum in a process known as aluminizing. When welding with a bi-metallic shield, you first have to weld the aluminum to the aluminum side of the shield, and then weld the steel to the steel side of the shield. In cases where the steel has been aluminized, arc welding should be directed to the aluminum side of the joint, allowing the weld puddle to work its way downward over the aluminum coating. The steel should not come into contact with the welding arc.
- The welding equipment you need to use is usually GMAW or gas metal arc welding. MIG welding will not work for this type of welding process. In addition, you can braze aluminum to steel using a bi-metallic shield or an aluminized coating with brazing torches and the appropriate brazing rods.
- The strength of the bond between the steel and the aluminum is equal to the weakest material bond used to connect the materials together. Because the process is more complicated than aluminum to aluminum or steel to steel welding, there is a greater likelihood of weld failure due to stress cracks in the material.
Corrosion problems
Welding Processes
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