Friction Stir Welding (FSW) is a solid-state joining process that uses a rotating tool to create frictional heat between two pieces of metal. This heat softens the material without melting it, allowing the tool to stir the metals together, forming a strong bond as the tool moves along the joint. FSW is particularly useful for joining lightweight materials like aluminum and magnesium, which are commonly used in the aerospace and automotive industries. The process is known for producing high-quality welds with minimal defects, making it an efficient choice for manufacturing applications.