Under the action of pressure, the relative motion between the welding contact end faces is used to generate frictional heat and deformation heat at and around the friction surface under constant or increased pressure and torque. The range is close to but generally lower than the melting point, the deformation resistance of the material is reduced, the plasticity is increased, the interface oxide film is broken, and the solid welding method is formed through the interface under the effect of upsetting pressure, plastic deformation and flow accompanying the material, molecular diffusion and recrystallization, To achieve welding. Friction welding usually includes the following four steps: mechanical energy is converted into heat energy; plastic deformation of material; thermoplastic forging pressure; intermolecular diffusion and recrystallization. The difference between the friction welding stage, the temperature of the traditional fusion welding metal is increased energy does not reach the melting point in the entire welding process, that is, the metal forging solid phase connection to achieve a thermoplastic state.
Welding materials have expanded from traditional metal materials to powder alloys, composite materials, functional materials, refractory materials, and new materials such as ceramics and metals, and have been applied in different material fields.
Friction surface atoms produce frictional heat and plastic displacement due to rotation or relative motion between workpieces.
Friction stir welding is an emerging welding technology that has been widely used in the automotive industry due to its advanced, environmentally friendly, safe and reliable process characteristics. It is an important direction for new energy vehicle welding in the future. Friction stir welding is a method that uses the heat generated by the movement of the end faces of the workpieces to rub each other to make the end faces reach a thermoplastic state, and then quickly forges to complete the welding. Friction welding can easily connect the same or different materials, including metals, some metal matrix composites, ceramics and plastics.
The geometric dimensions of the welding workpiece limit or increase productivity, such as phase friction welding, radial friction welding, linear friction welding, etc., but there are few practical applications. The temperature during friction stir welding is relatively low, so the residual stress or deformation of the structure after welding is also much smaller than that during fusion welding. Especially in the process of welding aluminum alloy sheets, the out-of-plane deformation of the structure is very obvious. Whether it is non-deformation welding technology or post-weld hot and cold calibration technology, it is very troublesome and increases the manufacturing cost of the structure.
As a new multidisciplinary method, friction stir welding can develop longitudinal seam welding, girth welding, welding, keyless hole variable partial welding, self-supporting double-sided welding, space three-dimensional curve welding, friction stir spot welding, and backfilling. Methods and techniques, such as various types of spot welding, friction stir welding surface modification treatment, friction stir welding superplastic material processing.