ABSTRACT
Welding is a metallurgical process-all aspects of a welding process can be, more or less, related to the metallurgy of the materials involved in welding, either the base metal or the electrodes. There are a number of books dedicated speci cally to welding metallurgy.1-7 Although most of them are on fusion welding, the general metallurgical principles are applicable to resistance spot welding (RSW). In this chapter, the metallurgical principles governing the various aspects of RSW are discussed. They are critical in understanding the formation of the structures of an RSW-welded joint, the mechanisms of defect formation, and their impact on a weld’s strength. This chapter is categorized according to the materials most relevant to RSW as workpieces and electrodes. The metallurgical characteristics of steels, aluminum alloys, and magnesium alloys that affect welding processes and weld quality are discussed. In addition to “conventional” materials used in RSW such as steels, magnesium alloys are also included because of their increasing presence in automobile construction for signi cant weight reduction. The impact of electrode material on resistance welding has been widely recognized by the resistance welding community, yet little can be found from the public domain that directly aids the understanding and control of the RSW process. In fact, many processes in RSW are electrode dependent. For instance, resistance heating at the electrode-workpiece interface introduces unwanted changes such as alloying and others, affecting the life and performance characteristics of the electrodes, and the integrity of the weld. Therefore, Cu is included in this chapter as it is the most common material for electrodes. Finally, the metallurgical aspect of cracking is presented. For additional information regarding the metallurgy in resistance spot welding these materials, the reader is referred to the recommended reading listed at the end of this chapter.
