Effect of welding energy on interface zone of Al–Cu ultrasonic welded joint

Abstract

Ultrasonic welding is attracting increasing attentions in joining of dissimilar materials. The effect of welding energy on joint strength, failure behaviour and microstructure of Al-Cu ultrasonic welded joint has been experimentally investigated. The results showed that joint strength increased with welding energy initially and reached its maximum at 1000 J, then dropped significantly instead. Meanwhile, the failure mode changed from interfacial debonding to nugget pullout, and then back to cleavage failure. Various microstructures with different morphologies and properties were also observed at the interfacial region. At lower energy, the joint was only partly bonded by numbers of dispersed microbonds. A swirl-like structure appeared at the weld interface and led to a mechanical interlocking between the materials at higher energies (y1000 J). However, cavity defects and intermetallic compound (IMC) were more likely to form under excessively high energies. A 0?5 mm thick IMC layer with dominant phase of Al 4 Cu 9 was found in 2000 J joint.

Effects of Vibration Amplitude on Microstructure Evolution and Mechanical Strength of Ultrasonic Spot Welded Cu/Al Joints

“…It was found that the lap shear tensile strength of the Cu/Al joints decreased when the thickness of the intermetallic layer exceeded 1 µm at various amplitudes. Besides, the Cu/Al joint failure always occurred along the interface instead of in a nugget pull-out mode, as previously reported for Cu/Al [3,20]. It was thus more likely that the copper substrate suffered from the higher strain rate deformation than the aluminum substrate.…”

“…For the amplitude of 22.5 µm, the maximum interface temperature at the welding time of 1 s was approximately 633 K, which could not satisfy the requirement of melting the welded coupons. However, it was sufficient to cause a dramatic decrease of the welded coupons' yield stress and generate the intermetallic compound between the base materials [3]. Significantly, the local melting at the periphery of Cu/Al joints was also observed, which will be addressed in the following.…”

“…Moreover, the tensile strength increased with the effective bonded area. The partial mechanical interlocking and a thin intermetallic reaction layer contributed to the improvement of the tensile strength [2,3]. Nevertheless, it is well known that the excessively thick intermetallic layer that is produced during ultrasonic spot welding at the faying interface results in the decreased tensile strength of the Cu/Al joints [2].…”

“…Dissimilar joints between aluminum alloys and copper are widely used in the battery packs and electronics industry because of their higher corrosion resistance and their electrical and thermal conductivities [2,3]. The joining of aluminum alloy and copper is also highly significant in cable systems owing to the lower weight and price of aluminum alloys [4].…”

Influence of Pin Length and Electrochemical Platings on the Mechanical Strength and Macroscopic Defect Formation in Stationary Shoulder Friction Stir Welding of Aluminium to Copper

“…By applying processes like electromagnetic pulse welding [18], ultrasonic welding [19,20], and friction stir welding [21], the IMC formation can be minimized successfully. Friction welding and friction stir welding, which can be defined as heat and forge type processes as described by Gould [22], are especially suitable for dissimilar joints, as the high applied strain under elevated temperature allows the displacement of oxides and containments and rapid bond formation in solid state by recrystallization.…”