Characterization of the intermetallic compounds in aluminium and copper friction stir spot welds

Dissimilar metal joining techniques are necessary for the manufacturing of a number of structures and parts in the industries. The spot welds of aluminium and copper were produced using two different tool geometries, different rotational speeds and tool shoulder plunge depths. This paper presents the characterization of the intermetallic compounds using X-Ray diffraction (XRD) and Energy Dispersive Spectroscopy (EDS) techniques in the Stir Zone (SZ). Furthermore, the microhardness test was performed to investigate the effect of the intermetallics on the microhardness values. The XRD results showed that, the most common intermetallic compounds formed in the spot weld samples were Al₄Cu₉, Al Cu₃, Al₂Cu₃ and Al₂Cu, which also showed low peaks intensity. Moreover, the Energy Dispersive Spectroscopy (EDS) analysis also revealed the presence of intermetallic compounds in the Stir Zone and which correlated to the X- ray diffraction analyses. Higher microhardness values were obtained in the stir zone for all the welds due to the smaller grains present in this region resulting from the frictional stirring of the tool. The high hardness values correlated to the high peaks of the intermetallics formed at the interface.