Welding of dissimilar magnesium alloys and aluminum alloys is an important issue because of their increasing applications in industries. In this document, the research and progress of a variety of welding techniques for joining dissimilar Mg alloys and Al alloys are reviewed from different perspectives. Welding of dissimilar Mg and Al is challenging due to the formation of brittle intermetallic compound (IMC) such as Mg₁₇Al₁₂ and Mg₂Al₃. In order to increase the joint strength, three main research approaches were used to eliminate or reduce the Mg-Al intermetallic reaction layer. First, solid state welding techniques which have a low welding temperature were used to reduce the IMCs. Second, IMC variety and distribution were controlled to avoid the degradation of the joining strength in fusion welding. Third, techniques which have relatively controllable reaction time and energy were used to eliminate the IMCs. Some important processing parameters and their effects on weld quality are discussed, and the microstructure and metallurgical reaction are described. Mechanical properties of welds such as hardness, tensile, shear and fatigue strength are discussed. The aim of the report is to review the recent progress in the welding of dissimilar Mg and Al to provide a basis for follow-up research.

Based on the idea of alloying welding seams, a series of Zn–xAl filler metals was calculated and designed for joining Mg/Al dissimilar metals by gas tungsten arc (GTA) welding. An infrared thermography system was used to measure the temperature of the welding pool during the welding process to investigate the solidification process. It was found that the mechanical properties of the welded joints were improved with the increasing of the Al content in the Zn–xAl filler metals, and when Zn–30Al was used as the filler metal, the ultimate tensile strength could reach a maximum of 120 MPa. The reason for the average tensile strength of the joint increasing was that the weak zone of the joint using Zn–30Al filler metal was generated primarily by α-Al instead of MgZn_2. When Zn–40Al was used as the filler metal, a new transition zone, about 20 μm-wide, appeared in the edge of the fusion zone near the Mg base metal. Due to the transition zones consisting of MgZn₂- and Al-based solid solution, the mechanical property of the joints was deteriorated.

The dissimilar material of AZ31 Mg alloy and TA15 Ti alloy were welded by resistance spot welding. The influence of welding current on the interface of nuggets is studied. The microstructure, hardness, tensile strength and fracture surface of joints are analysed. The results indicate that when the electrode pressure and welding time are determined, the failure load of the joint can be improved by the increase in the welding current; however, excessively high welding current will cause cracks near the interface. Under the welding current of 14.5 kA, the electrode pressure of 0.22 MPa and the welding time of 200 ms, the maximum failure load of the joint can reach 4.79 kN, which is almost the same as the shear strength of AZ31B magnesium alloy base metal.

The welding of Mg/Al dissimilar materials with different filler metal was investigated, and the quantities and kinds of intermetallic compounds were discussed. In addition, the matching degrees between base metal and intermetallic compounds were defined and calculated, and the effect of different quantities of each intermetallic compound on the property of welded seam was investigated. The results indicated that the welded seam was composed of Al₃Mg₂ and Al₁₂Mg₁₇ by Mg/Al directly gas tungsten arc butt welding, and only one intermetallic compound of MgZn₂ formed in the welding seam using Zn and Zn– xAl filler metal. The tensile strengths of the joints increased with the increase of the matching degrees between the intermetallic compounds and the base metal when the welded seam contained different intermetallic compound. Meanwhile, the tensile strengths of the joints are decreased with the increase of intermetallic compound content when the welded seams contained the seam intermetallic compound.

Dissimilar welding between aluminum and copper poses significant challenges, primarily due to differences in their thermal and mechanical properties, resulting in brittle intermetallic compounds, limited joint strength, and high electrical resistivity. This study aims to overcome these issues by employing Ag-18Cu-10Zn filler material and optimizing laser power with a focus on improving joint strength and electrical conductivity. The results indicate that the incorporation of silver and zinc enhances the phase composition and microstructure of the weld. By forming solid solution phases such as Ag₂Al and Cu₅Zn₈, the brittle Al₂Cu phase commonly found in traditional Al/Cu welding is replaced. This not only promotes the heterogeneous nucleation of fine silver-rich grains but also restricts the excessive growth of silver-poor grains, resulting in a uniform distribution of fine grains throughout the weld. These modifications contribute to both fine-grain strengthening and dispersion strengthening. At an optimal laser power of 750 W, joint strength reaches 109 MPa, while joint resistivity decreases to 3.19 μΩ·cm, 12.6% lower than that of the aluminum alloy base material. This study proposes a process for achieving highly conductive, reliable Al/Cu dissimilar metal joints, potentially impacting the aluminum–copper connections in battery modules for new energy vehicles.