Friction stir welding of aluminum alloy and copper dissimilar pipes of thin wall and small diameter

Friction stir welding (FSW), a promising and developing solid state joining technique for welding dissimilar metals and alloys, has been successfully applied to produce joints of aluminum alloys and copper with good mechanical properties in previous studies. However, almost all works focused on friction stir butt or lap welding of aluminum sheets and copper sheets. In this study, effective joints of thin-wall (Al: 1.5 mm; Cu: 1 mm) and small-diameter (19 mm) 3003 aluminum alloy pipes and pure copper pipes were obtained via FSW. Varying macro-/micro-structure was observed along the circumferential weld seam, which can be divided into 4 characteristic regions. Very different tensile strength, ductility and fracture modes were found in these regions. Evidenced by the welding temperature field, such varying macro-/micro-structure was in turn attributed to the significant heat accumulation during welding, which is an important feature for FSW of small-diameter pipes.