Friction Stir Welding (FSW) is a solid-state joining process widely used for welding metals, especially aluminum and its alloys. Invented in 1991 by The Welding Institute (TWI), FSW uses a non-consumable rotating tool with a specially designed pin and shoulder to generate frictional heat, softening the materials at the joint without melting them. The rotating tool stirs and forges the softened material together, resulting in a high-strength, defect-free weld. FSW is energy-efficient and ideal for aerospace, automotive, and marine applications due to its ability to join dissimilar materials and produce superior mechanical properties compared to conventional welding methods.