Dissimilar JointsIt is sometimes necessary to join galvanized or coated steel to other metals or alloys; these are commonly referred to as dissimilar joints. In simple terms the metallurgy is similar to welding mild steel to other metals but it is complicated by the presence of the coating which can lead to porosity, cracking, or embrittlement, plus the generation of fume that may be toxic. Welding galvanized or coated steel to carbon and alloy steels may be carried out using fusion techniques and MMA, MIG, and cored wires may give acceptable results. The consumable used for fusion welding to alloy steel must be compatible with both steels. Preheat of the alloy steel may be necessary depending on carbon equivalents. Welding to stainless steel and nickel alloys is rare but may be carried out using these welding processes but it is necessary to grind back the coating from the weld area or metallurgical problems may arise. Special consumable compositions are required in these applications. If welding coated steel to cast iron is required a Ni alloy consumable would be recommended but grinding back the coating would be essential. The main problem then is the low ductility and poor weldability of the cast iron. Welding to copper or aluminium alloys is not recommended.
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