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Achieving the effective joining between Al alloy and stainless steel with a large cross-section was meaningful in the significant industry field. For this, the Al/steel dissimilar bimetal materials were manufactured by a novelty hybrid technology, named thermo-compensated resistance brazing welding. The effect of the single Zn foil and the deposited Zn coatings with cold spray technology on the bonding interface, interfacial microstructure, and mechanical properties of the final Al/steel resultant joints were systematically investigated by the relevant analysis method. The results revealed that the obvious reaction layer with main components of Al(s.s) was formed at the Al/steel joints with the single Zn foil as the interlayer. Meanwhile, the introduction of the Zn interlayer improved the temperature field of the joint, which enhanced the lap-shear load of the weld. Besides, the Zn coating was deposited at the top surface of the 304ss substrate as the interlayer to increase joint performance further. The advantage of the pre-deposition formed a better metallurgical bond between the coating and 304ss. The subsequent lap-shear load of the weld was improved with the increase of the Zn coating thickness. The maximum lap-shear load of the final joints reached 2087.6N with a Zn coating thickness of 500 μm and the interfacial structure of the joint was changed: Al alloy, reaction layer I, Al(s.s) + Al2O3, and 304ss from top to bottom. The main composition was Al(s.s) at the reaction layer I between Al alloy and coating.

The 6061 aluminum alloy/304 stainless steel dissimilar materials with a certain area were successfully achieved by a novelty welding method, named thermo-compensated resistance brazing welding, in which, the high-resistivity graphite was inserted as the auxiliary electrode. The effect of the welding current and welding time on the temperature field of the graphite, mechanical properties, and the fracture surface of the final Al/steel weld was investigated. The results revealed that the temperature field was generated by Joule heat based on graphite, Al alloy, and stainless steel in the welding process. The generated Joule heat was gradually extended from one point to the entire interface in the whole welding process. The temperature field and tensile-shear load of the joint were also improved with the increase of the welding parameters. The degree of diffusion surface was illustrated at the fracture, indicating the “brazing” feature. There were three diffusion regions A, B, and C on the fracture surface with the steel side of the optimal parameters. The mechanical properties of the weld mainly depended on regions B and C. The effective connection was formed at a local area of the entire interface between Al alloy and 304ss at this parameter. Al(s.s) and Fe2Al5 IMC were generated at the interface. The typical inclined interfacial failure was formed after the tensile-shear test due to the heat generation mechanism. The Al(s.s), Fe(s.s), and Fe2Al5 IMC were presented on the fracture surface, which was consistent with the above contents.

A novel plasma-pulsed GMAW hybrid welding (plasma-GMAW-P) process is proposed for joining 6061 aluminum and zinc-coated steel. The results show that the change in welding heat input has little effect on the microstructure of the joint and the composition of the intermetallic compounds (IMCs) but only changes the thickness of the reaction layer (increased from 5 μm to 12 μm). when the plasma arc current is 20 A and the MIG current is 80 A, the welded joint obtained has the highest tensile-shear force. With the optimal process parameters, the weld strength obtained by filling ER4043 welding wire is the highest, accounting for 65% of the tensile-shear force of the base material. The effect of the plasma arc acting on the joint properties is studied through the microstructure and a tensile-shearing test. The action position of the plasma arc plays a significant role in the Al/steel interface, which directly influences the strength of the welded joints. Regardless of the plasma-GMAW-P style used to obtain the joints, Fe-Al IMCs appear at the interface. When the plasma arc is in front of the welding direction and the GMAW-P arc is in the rear, the tensile-shear force reaches the maximum of 3322 N.

In the magnetically controlled Plasma-GMAW welding process, the composite arc forms a keyhole in the workpiece to be welded. In order to explore the effect of process parameters on arc coupling, weld pool and keyhole, and the behavior characteristics of keyhole, the arc behavior and side weld pool information were collected using a welding arc acquisition system and a high-speed camera during bead-on-plate welding. The arc image is processed by pseudo-color enhancement technology, and the collected molten pool information is analyzed by boundary extraction algorithm and coordinate conversion algorithm, and the molten pool boundary and keyhole entrance width are obtained. It is found that the coupling degree of the two arcs increases with the increase in plasma current, GMAW current and magnetic field intensity. With the increase in plasma current, the size of keyhole inlet increases; with the increase of GMAW current, the size of keyhole inlet decreases, and the wave crest increases. With the increase of magnetic field intensity, the intensity of metal oscillation between the two arcs increases, and so does the wave crest.

The Q235 steel plate butt joint was successfully welded by the laser K-TIG hybrid welding method. The effects of hybrid welding process parameters such as welding current, the distance between heat sources, laser power, laser defocusing amount, and welding speed on the coupled arc profile and welding process stability were studied. The results indicated that the laser deflects the K-TIG arc, and the deflection angle becomes smaller as the arc current increases. After K-TIG generates small holes, if the laser beam acts on the bottom of the keyhole, the welded depth can be further increased; however, the laser power has little effect on the welded depth. The distance between heat sources is the main factor affecting the state of laser-arc coupling. Optical microstructures of welded joints showed that the grains in the arc zone were coarser than those in the laser zone, and there are more columnar crystals in the fusion zone. The microhardness of the weld center is significantly higher than that of the base metal, up to 220 HV. At the same time, the change of tensile strength of the weld under the influence of a single parameter was analyzed, and it was found that tensile properties of the weld first increased and then decreased with the increase of K-TIG arc current I, heat source distance D, and welding speed V, respectively. With the increase of laser power P, it first decreased and then increased, and with the increase of laser defocusing amount δf, it showed a downward trend.

The use of a Zn/Ag–Cu–Zn/Zn multi-interlayer was observed to avoid the formation of Mg–Al binary intermetallic compounds (IMCs), which cause embrittlement and low strength of bonding when dissimilar metals such as Mg/Al are joined using ultrasound-assisted transient liquid phase bonding (U-TLP). The change in the microstructure and mechanical properties of the AZ31B/LY12 joints at 410, 440, and 460 °C with prolonging ultrasonic treatment (UST) time was investigated. The results showed that the diffusion of Ag and Cu was faster into the brazing seam on the LY12 side than that on the AZ31B side with increasing UST and temperature. The IMCs on both sides of the joints were transformed with the diffusion of Ag and Cu. The transformation made the fracture path shift from the AZ31B side (410, 440 °C) to the LY12 side (460 °C), and the maximum shear strength of the joints from 43.3 (410 °C) to 65.7 (440 °C) to 84.7 MPa (460 °C). The IMCs on the surface of the fracture path corresponding to the joints with optimal mechanical properties changed from Mg7Zn3+MgZn2+α-Mg (410 °C) to MgZnCu+Mg7Zn3 (440 °C) to Al2Cu (460 °C).