In recent years, the friction stir welding process becomes advantageous due to its application to join aluminium alloys and dissimilar metals. The friction stir welding (FSW) process is initially explored by Wayne Thomas. In this welding process two dissimilar metal sheets are joined by passing rotating tool through adjoining edges of sheets. During passing of tool, the friction heat generation is responsible for welding. The key parameters in friction stir welding are speed of rotation of tool, tool shoulder diameter speed of welding, tool pin diameter, length of tool pin. Tool used in FSW have many geometries like hexagonal, square, rectangular and triangular shapes.