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 422uC. 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 CuAlzCu 9 Al 4 , AlzCuAl 2 zCu(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.

No abstract

No abstract

No abstract

Alclad 7B04-T74 aluminum alloy was friction stir lap welded at different welding parameters. The microstructural characteristics and mechanical properties of the joints were investigated. After welding, the initial Alclad at the faying interface upward migrated and penetrated into the stir zone from the retreating side. This reduced the postweld thickness of the upper sheet and formed a potential crack propagation path in the stir zone during tensile shear testing. During welding, the stirred Alclad was lifted by the probedriven material flow and pressed down by the shoulder-driven material flow. The higher tool rotation speed or the lower welding speed made the redistributed Alclad in the stir zone more disperse. Higher fracture strength of the joint was obtained when the retreating side of upper sheet was loaded. A mathematical relationship between the fracture strength and the welding parameters was developed by applying the BoxBehnken experimental design, and the optimized fracture strength of 749 N/mm was obtained.