Microstructural characterisation and mechanical properties of friction stir welded joints of aluminium alloy to copper

Good appearance and defect free friction stir welded joints of aluminium alloy to copper were obtained in a narrow range of welding conditions. The weld nugget (WN) consisted mainly of Cu(Al) solid solution, Al and several intermetallic compounds (IMCs), including CuAl(2), CuAl, Cu(9)Al(4) and Cu(3)Al although the maximum peak temperature measured in the weld was 422 degrees C. Intercalation was a typical structure distributed widely in the WN and consisted of many parallel alternate lamellae. At the WN/Cu interface, the intercalations were characterised by flat or bended feature and composed of CuAl+Cu(9)Al(4), Al+CuAl(2)+Cu(Al) and Cu(Al) laminae. The formation mechanisms for these intercalation structures and IMCs were attributed to the intense stirring action of the tool pin and the short circuit diffusion caused by extreme deformation respectively. The fracture surface exhibited some IMCs, including Cu(9)Al(4) and CuAl(2), which should be responsible for the limited tensile strength. The hardness profiles were consistent with the variation in the structures within the WN, and lower tool rotation rate resulted in higher peak hardness.