A novel ultrasonic vibration assisted (UVA) wire arc additive manufacturing (WAAM) was used to fabricate Cu-8Al-2Ni-2Fe-2Mn alloy in this study. The effect of different interpass temperatures with and without ultrasonic vibration on the microstructural evolution and mechanical properties of the fabricated part were investigated by optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), nanoindentation, and mechanical tensile testing. The results showed that reduction of the interpass temperature without UVA treatment cannot prevent the columnar dendrites directionally growing along the deposition direction. Under the UVA treatment, the coarse columnar dendrites were broken at the interpass temperature of 400 °C, and formed a fine cellular structure with an interpass temperature of 100 °C, owing to the acoustic streaming effect and cavitation effect. In addition, globular κ_II phase was based on Fe₃Al and lamellar κ_III phase was based on NiAl distributed in the interdendritic region, whereas κ_IV phase (rich-Fe) were precipitated in the α-Cu matrix. The improvement of microstructural characteristics caused by UVA treatment further improved the tensile properties and nano-hardness of WAAM fabricated parts. Eventually, it is experimentally demonstrated that WAAM fabricated Cu-8Al-2Ni-2Mn-2Fe alloy can obtain high-performance at UVA process under an interpass temperature of 100 °C.

Friction stir spot welding (FSSW) of Al to Ti alloys has broad applications in the aerospace and automobile industries, while its narrow joining area limits the improvement of mechanical properties of the joint. In the current study, an Al-coating was prepared on Ti6Al4V alloy by hot-dipping prior to joining, then a Zn interlayer was used during friction stir joining of as-coated Ti alloy to the 2014-Al alloy in a lap configuration to introduce a brazing zone out of the stir zone to increase the joining area. The microstructure of the joint was investigated, and the joint strength was compared with the traditional FSSW joint to confirm the advantages of this new process. Because of the increase of the joining area, the maximum fracture load of such joint is 110% higher than that of the traditional FSSW joint under the same welding parameters. The fracture load of these joints depends on the joining width, including the width of solid-state bonding region in stir zone and brazing region out of stir zone.

Friction stir lap welding of 1.5-mm thick 6082-T6 aluminum alloy to 2-mm thick galvanized DP800 steel (Zn-coated) was carried out. Optimal welding conditions were obtained aiming to defect-free joints with good mechanical properties. The interfacial intermetallic compounds (IMCs) at the stir zone and hook zone were characterized under different revolutionary pitches. With a revolutionary pitch of 1.0 mm/rev, maximum joint strength reached 71% of that of the aluminum alloy. In the meantime, the average thickness of IMC layer is less than 1 μm; Al_3.2Fe in the Al-rich side and Al₅Fe₂ in the Fe-rich side at the interfaces of stir zone while Al₆Fe and nanocrystalline close to Al_3.2Fe at the interface of the hook zone. At a relatively lower revolutionary pitch (0.5 mm/rev), Zn was found with the aggregation of Si and Mn at the hook-zone interface, leading to the generation of Al-Fe-Si phase thus decreasing the thickness of the IMC layer. In the stir zone, the revolutionary pitch has a significant influence on the interfacial microstructures. The interfacial IMC layer at 1.0 mm/rev is simple and flat, but the one at 0.5 mm/rev becomes thicker and more complex. Stir zone aluminum under different revolutionary pitches is similar in microhardness and tensile behavior. The mechanical response of joints was modeled based on linear mixture law with an iso-strain assumption and neglection of the IMC layer. The modeling results are in good agreement with the experimental ones indicating the resultant interfaces act as good as the good boundaries between dissimilar Al/steel joints.