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High-frequency induction brazing Al/Steel dissimilar metals with different composition Zn Al filler metals was performed. Before the brazing experiment, the wettability of the filler metals on steel and aluminum alloy plates was investigated, respectively. The results shown that the Zn 15Al (wt%) filler metal had the best wettability on the aluminum. The brazing experiment indicated that when the brazing gap was 0.3 mm, the maximum wetting length and best filling performance of the joint were obtained. The most serious dissolution of aluminum in the brazing seam was observed when using Zn 2Al filler metal. The three-layered structures, which were composed of IMCs layer, Zn rich layer (occurred in particular situation) and Zn Al eutectoid structure, were found near the steel interface. Experiments and thermodynamic calculations were applied for analyzing microstructure evolution and elemental diffusion behavior. The highest shear strength reached 81.52 MPa when the Zn 15Al filler metal was used in 773 K for 30 s. The fracture morphology indicating that brittle fracture occurred in all the joints. But partial breaking in filler metal not in the IMCs layer, which means that the Zn Al filler metal improved the shear strength of the joint.

A laser beam joining an Al-on-steel overlap configuration of 5052 aluminum alloy and Q235 steel was conducted with Sn-30Zn filler wire. The influence of processing parameters on weld appearance was investigated. The microstructures and mechanical property of the joints were analyzed. The results show that Sn-Zn filler wire could well wet 5052 aluminum alloy and the steel under heating of defocusing laser. Good weld appearance was obtained by suitable processing parameters. The solid solution interface was formed at the aluminum alloy side and intermetallic compounds (IMCs) interface was formed at the steel side. With increasing laser power, intergranular penetration of the Al side aggravated, and the thickness of the IMCs layer at the steel side increased. It was found that all of the joints fractured in the seam according to the results of the tensile tests. The intergranular penetration and IMCs did not reduce the mechanical property of the joint. The maximum value of fracture load reached 312 N/mm. The fractured surface was characterized as a ductile fracture. The influence of processing parameters on the microstructures and mechanical property was discussed.

Low-temperature high-frequency induction brazing of 5052 aluminum alloy to stainless steel was carried out using Sn-30Zn with reactive-flux 88ZnCl2-10NH4Cl-2NaF wt.%. The influence of processing parameters on microstructures, mechanical property and fracture behavior was investigated. Intermetallic compounds were not observed at the interface of the steel. The brazing seam consisted of Sn-Zn eutectic structures, Zn-rich solid solution and oxide inclusion. The diffusion of Sn and Zn into the aluminum grain boundary led to an intergranular penetration layer. When brazing at 370°C for 30 s, the joint fractured in the brazing seam and the shear strength reached the highest at 87 MPa. The fracture surface of the joint presented ductile characteristics. The diffusion of F− in the flux made the oxide film expand and crack. Zn2+ permeated through the crack of the film and then reacted with Al, which removed the film from aluminum substrate.

The purpose of this paper is to provide the gist for the selection of filler wire during the laser welding-brazing of Al to steel. A comprehensive comparison of laser welding-brazing 5052 aluminum alloy to unbeveled galvanized steel using pure Al, AlSi5, AlMg5, AlCu6, and ZnAl2 filler wires were conducted with varied laser beam offset. The comparison was carried out in terms of weld formation, interfacial microstructures, and mechanical properties. The results show that the fluidity of liquid filler is Pure Al AlMg5 > AlCu6 > ZnAl2 > pure Al. The fracture of the joints all occurred at the brittle intermetallic layers when five different filler wires were used.

Butt joining of 5052 aluminum alloy and Q235 low carbon steel was achieved using laser beam welding with Sn-30Zn filler wire. The weld formation, microstructures, and mechanical property were investigated with varied laser power. The results show that joining of 5052 Al/Q235 steel dissimilar metals in a butt configuration by laser beam welding with Sn-30Zn filler wire is feasible. The solid solution interface formed at the aluminum side and the reaction layer formed at the steel side. With increasing laser power, the joining mode transformed from brazing to welding-brazing due to the melt of aluminum alloy. The thickness of the interfacial intermetallic compounds (IMCs) layer was also increased with laser power. However, when the laser power was 1200 W, the thickness of the interfacial IMCs layer sharply decreased due to the detachment of the IMCs layer. The fracture of the joint occurred at the steel interface and partially through the weld seam on the top surface. The fracture surface was characterized by both brittle and ductile fracture. When the joints were obtained at the laser power of 800 W and 1200 W, the tensile strength reached 79 MPa and 78 MPa, respectively. Furthermore, the formation mechanism of microstructures and its influence on mechanical property was discussed.

To improve interfacial inhomogeneous temperature distribution and weld appearance of butt welding-brazing of steel/aluminum dissimilar metals, a hybrid heat source method combining laser penetration welding with CMT arc was developed. The Ni/Zn double coating was prepared on the surface of steel to improve the interfacial reaction and achieve fluxless process. The welding characteristics of bare steel/aluminum alloy, Ni coated steel/aluminum alloy, and Ni/Zn double coated steel/aluminum alloy were comparatively studied. Transmission electron microscope (TEM), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS) were used to analyze the interfacial microstructures of the joint. The results showed that the fluxless process were implemented by preparing Ni/Zn double coating on the surface of steel. The interfacial reaction between liquid Al and solid steel was obstructed to some extent by Ni/Zn double coating. The thickness of intermetallic compounds (IMCs) was reduced significantly. The interfacial reaction layer consisted of Fe2Al5 near the steel side and Fe4Al13 near the aluminum side. No continuous Ni-Al IMCs were found at the Fe/Al butt interface. The maximum tensile strength of Ni coated steel/aluminum joint was up to 93.4 MPa, which increased by 12% than that of the bare steel/aluminum joint. The maximum tensile strength of Ni/Zn double coated steel/aluminum joint was up to 112.6 MPa, which increased by 35% than that of the bare steel/aluminum joint. On this basis, the fluxless wetting and interfacial reaction mechanisms were revealed.

To investigate the influence of Ni coating layer on the interfacial reaction of Al/steel dissimilar metal brazing, a high-frequency brazing method of Al alloy and steel with/without a Ni coating layer were designed. The steel side interfacial microstructure of the Al/bare steel joint consisted of Fe (Al,Si)3, Al7.2Fe1.8Si. After the preparation of the Ni coating layer on the stainless steel, the interfacial microstructure consisted of Al3Ni, Al3Ni2, and residual Ni coating layer. An ultra-thin Al3Ni2 reaction layer was observed in Al/Ni-coated steel joint by transmission electron microscopy (TEM). With increasing reaction time, the Ni coating layer completely dissolved into liquid filler metal. Interfacial structure transformed into Fe(Al,Si)3/Al7.2Fe1.8Si, which was the same as that of the Al/bare steel joint. The shear strength of the joint with the Ni-coated layer increased first and then decreased with increasing brazing time, which was influenced by the dissolution level of Ni coating layer. The maximum shear strength exceeded 20.3% that of the joint without Ni coating layer. The element diffusion phenomenon in the field of the solid/liquid interface and the dissolution behavior of the Ni coating layer were analyzed by the thermodynamics method. A model of Ni dissolution kinetics was established to optimize the thickness of the Ni coating layer and the processing parameters of the brazing. The effect mechanism of Ni coating layer on the interfacial reaction of the Al/steel dissimilar metal brazing was clarified.