The resistance welding processes commonly employed for joining aluminum are resistance spot welding, resistance seam welding, resistance roll welding, upset and flash welding for butt joining welding, and high-frequency resistance welding. This article discusses the general factors affecting resistance welding: electrical and thermal conductivities, rising temperature, plastic range, shrinkage, and surface oxide. It reviews the weldability of base materials such as Alclad alloys and aluminum metal-matrix composites. The article describes the joint design and welding procedures for resistance spot welding, as well as the joint type, equipment, and welding procedures for seam and roll spot welding. It concludes with information on flash welding, high-frequency welding, and cross-wire welding.

Flash welding, also called flash butt welding, is a resistance welding process in which a butt joint weld is produced by a flashing action and by the application of pressure. The flash welding process consists of preweld preparation, flashing, upsetting (forging), and postweld heat treatment. This article provides an overview of both flash welding and upset welding and describes the various process and failure origins of flash welding as well as the equipment used. It also explains the characteristics and advantages of solid-state upset welding.

This article describes the mechanism, advantages and disadvantages, fundamentals, capabilities, variations, equipment used, and weldability of metals in solid-state welding processes, including diffusion bonding, explosion welding, friction welding, ultrasonic welding, upset welding, and deformation welding.

Resistance welding (RW) encompasses a group of processes in which the heat for welding is generated by the resistance to the flow of electrical current through the parts being joined. The three major resistance welding processes are resistance spot welding (RSW), resistance seam welding (RSEW), and projection welding (PW). This article addresses the considerations for using these processes to join specific types of materials. It discusses the process variations, applicability, advantages, and limitations of these resistance welding processes. The article provides information on flash welding, high-frequency resistance welding, and capacitor discharge stud welding. It concludes with a discussion on resistance welding of stainless steels, aluminum alloys, and copper and copper alloys.

Upset welding (UW) is a resistance welding process utilizing both heat and deformation to form a weld. A wide variety of shapes and materials can be joined using upset welding in either a single-pulse or continuous mode. This article discusses the advantages and disadvantages of upset welding, as well as the types of welds. The advantages include speed, ease of control, fewer defects, enhanced weld properties, simplicity of equipment, less-strict composition requirements, and ability to join difficult-to-weld materials. The article reviews the role of a homopolar generator as an alternative method for supplying the electrical current for upset welding.