Dissimilar Welding

Dissimilar Welding:

Joining dissimilar materials becomes inevitable in engineering industries for both technical and economic reasons. The adoption of dissimilar-metal combinations provides possibilities for the flexible design of the product by using each material efficiently, i.e., benefiting from the specific properties of each material in a functional way. Fusion welding is one of the most widely used methods for the joining of metals. Therefore, continuous efforts are made to apply these methods to the joining of dissimilar-metal combinations, despite the many difficulties encountered. These difficulties include problems associated with metallurgical incompatibility, e.g., the formation of brittle phases, the segregation of high- and low-melting phases due to chemical mismatch, and possibly large residual stresses from the physical mismatch. There are several choices amongst the fusion welding processes, such as common conventional shielded metal arc, gas tungsten arc, gas metal arc, and submerged arc welding. They also include processes characterized by high energy density, such as plasma arc, electron beam, and laser beam welding. In addition to fusion welding, several other types of joining techniques are also available, and may often be associated with less difficulty for producing dissimilar-metal joints. These are solid-state welding e.g., pressure welding, friction, resistance and diffusion welding, as well as brazing and soldering, adhesive bonding, and mechanical joining. Most of these techniques can eliminate the fusion problems because the base metals remain in the solid state during joining. Therefore, they are better than fusion welding in this aspect .
However, the service conditions may make particular processes unsuitable, e.g., for high-temperature applications, soldering and adhesive bonding cannot be candidates, and for leak-tight joints, mechanical joining is not acceptable. Furthermore, the required joint geometry can make processes, such as friction welding, difficult to apply. Diffusion welding often provides superior technical benefits for joining small dissimilar-metal parts, but the process is rather time-consuming. Therefore, solutions relying on high energy density processes, e.g., electron beam welding (EBW) and laser beam welding (LBW), are still of great industrial interest .