OBRABOTKAMETALLOV technology Vol. 27 No. 3 2025 Introduction Resistance spot welding (RSW) is widely used in the automotive, aerospace, construction, and energy industries for joining sheet metal components made of steel and aluminum alloys, as well as for creating dissimilar joints between steel and aluminum, aluminum and magnesium, and aluminum and titanium [1– 10]. For example, the productivity of modern automated automotive assembly lines reaches up to 7 million spot welds per day [8, 9]. Aluminum alloys are extensively employed in the aerospace industry due to a combination of properties such as low density, high specific strength, good machinability, and corrosion resistance. Another significant advantage of aluminum alloys is their wide availability. The density of aluminum alloys is approximately one-third that of steel, which allows for a reduction in aircraft structural weight, improved fuel efficiency, and increased payload capacity. For manufacturing critical load-bearing structural components of supersonic aircraft, where high strength is crucial, steel remains the preferred material [11–15]. However, aluminum alloys are widely used for wing panels, fuselage sections, empennage components, exhaust system parts, interior components, and engine turbine parts of modern aircraft. Aluminum alloys constitute between 50 % and 90 % of the mass of modern spacecraft. They have been extensively used in spacecraft such as Soyuz, Progress, space shuttles, satellites, and others [11–15]. Aluminum alloys are classified based on alloying systems such as Al–Mg, Al– Mg–Li, Al–Cu–Li, among others, which are the most common types applied in aerospace and automotive industries for high-strength engineering applications [14–18]. One of the key trends in the automotive industry is the reduction of vehicle weight. This goal is achieved by using materials with low specific weight, such as aluminum and its alloys, which in turn contributes to optimizing production costs [7–9]. Aluminum alloys are suitable metals for automotive applications because they can be easily cast and formed into required shapes and offer promising weight reduction compared to steel. The use of aluminum alloys in manufacturing body parts, cabin panels, wheel rims, and interior trim can reduce vehicle mass by more than 50 % [10, 11]. Owing to their combination of casting and deformation properties along with low specific weight, aluminum alloys stand out favorably compared to steels and are widely applied in the automotive sector. For resistance spot welding of aluminum and its alloys, high-power welding guns are required due to the need for welding currents 2 to 3 times higher than those used for steel. This is caused by aluminum’s higher electrical and thermal conductivity. Meanwhile, the welding period must be reduced to approximately onethird of that used for steel welding [1, 2]. Resistance spot welding (RSW) is a process of joining contacting metallic surfaces through heating generated by the electrical resistance to the current flowing through the parts being welded [1]. The welding process is controlled by three main parameters: mechanical (electrode force), electrical (welding current), and temporal (welding period). An electric current supplied to two overlapping sheets via coaxial electrodes is maintained for a sufficient duration to achieve localized fusion at the interface of the metal sheets. After the current is switched off, pressure is applied to form a strong joint along the fusion line. Subsequently, the molten metal cools down, forming a cast weld nugget within a confined volume. The current density and applied pressure must be sufficient to form a solidified nugget but not so high as to expel molten metal from the weld zone. The welding current duration should be short enough to prevent excessive heating of the electrode surfaces. Electrode force, welding current magnitude, and welding period play a decisive role in the quality of the resistance spot weld. An electronic control unit is used in welding machines to monitor and regulate these welding parameters. The quality and strength of welds produced by RSW are determined by the shape and size of the weld nuggets. Nugget size is a critical parameter that dictates the load-bearing capacity of the joint. There exists a direct correlation between heat generation and the size of the weld nugget during the RSW process. Heat generation, and consequently nugget size, is influenced by the following primary factors: contact resistance between the welded surfaces, welding current density, welding period, and thickness of the sheets being joined. Akey feature of RSW is the absence of the need for filler materials or fluxes. The competitive advantages of RSW over alternative metal joining methods, such as gas metal arc welding (GMAW), gas tungsten
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