An experimental investigation on implications of traverse speed in joining of dissimilar Al–Cu by friction stir welding

Al–Cu joints are used in the electrical industry because of its unique mechanical, thermal and corrosion resistance properties. The present investigation concentrates on understanding the influence of traverse speed on friction stir welded butt joints of 3-mm-thick AA 6061-T6 and pure copper. The welds were produced by varying the traverse speed (30 mm/min, 90 mm/min and 150 mm/min) at a constant rotational speed of 800 rpm. Changes in microstructure and mechanical properties with the change in forces generated during the welding were observed and analysed. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses revealed the formation of AlCu, Al₂Cu and Al₄Cu₉ phases at low and moderate speeds (30 mm/min and 90 mm/min), whereas at higher traverse speed (150 mm/min), iron aluminide phases (Fe₂Al₅ and FeAl₃) formed along with Al–Cu phases. These iron aluminium phases act as initial promoters for fracture. The hardness values for all welding parameters were mapped which show hardness variation due to the inhomogeneous distribution of precipitates within the NZ. This is due to different thermal cycles for aluminium and copper as the tool passes the joint line. The tensile strength was measured and found to be maximum at a traverse speed 90 mm/min.