A critical review of material flow investigation in friction stir welding using novel techniques

In modern times, friction stir welding (FSW) has emerged as a cutting-edge technique. It provides an efficient, environmentally friendly, and versatile method for joining robust aircraft-grade aluminum alloys and various other metal alloys, which are often difficult to weld using traditional fusion techniques. Thanks to its unique advantages—such as solid-state bonding, the absence of fusion and melting, and adaptability to diverse work environments and material combinations—FSW has seen significant growth in applications within the automotive and aerospace industries. Producing flawless welds requires a thorough understanding of the complex material flow phenomena that occur during friction stir welding. Achieving the desired material properties in the weld zone also depends on precise measurements of flow characteristics, including velocity, strain, and strain rate. This study focuses on examining material flow behavior across a broad range of metallic and non-metallic materials in the context of friction stir welding. Additionally, it provides a comprehensive assessment of how process variables—such as tool rotation, traverse rates, tool tilt, and contact load—affect weld quality.