OBRABOTKAMETALLOV Vol. 27 No. 3 2025 technology arc welding (GTAW), and riveting, include the possibility for full process automation and integration into robotic production lines. The main challenges limiting the application of RSW for aluminum alloys are: 1) limited service life of contact electrodes. The surface of aluminum alloys is characterized by the presence of an oxide film (Al₂O₃) with high electrical resistance and non-uniform thickness [1, 2, 12–16]. When the sheets are compressed by the electrodes, the oxide film deforms unevenly, resulting in current concentration at localized contact points. The high current density in these areas causes intense heating, localized melting, and fusion between the copper electrode and aluminum, leading to erosive wear of the electrode’s working surface [1, 2]. Changes in the geometry and composition of the electrode surface during operation cause instability in welding parameters and reduce weld strength [12–15]. 2) high welding current requirements. To ensure the formation of high-quality welds in aluminum alloys by RSW, significantly higher welding currents are required compared to steels. This factor diminishes the potential energy efficiency advantages of aluminum alloys related to their lower density compared to steels [3, 4, 17, 18]. Existing studies on resistance spot welding (RSW) of aluminum alloys are predominantly focused on thick materials [19–21]. Thin-sheet aluminum alloys require separate consideration because differences in contact areas, thermal regimes, and electrical characteristics necessitate adjustments in welding parameters, including electrode force and current density [1, 2, 20–22]. Both alternating current (AC) and direct current (DC) power sources with varying frequencies are used for RSW [1, 2, 23–29], affecting energy transfer modes and optimal welding period for both stationary and portable equipment [1–3, 22, 28, 30, 31, 31–36]. Welding quality is also significantly influenced by external factors such as surface condition (roughness, contamination) [2–8], assembly accuracy [9], electrode condition (wear) [9–14], and the precision of positioning the welded parts (axial and angular misalignment) [20–22]. Aluminum alloys are highly sensitive to oxidation under environmental exposure. The oxide film formed on the surface (Al₂O₃) exhibits high electrical resistance, which leads to increased heat generation at the contact zone during welding. Insufficient surface preparation aimed at oxide film removal can cause aluminum adhesion to the electrode material, accelerated electrode degradation, and poor-quality welds [1–5, 36–38]. Some studies have investigated the surface characteristics of aluminum alloy welds produced by RSW [3–8]; however, only a few reports document a significant decrease in hardness within the weld zone [1–4] for various aluminum alloy grades. Several works address the reduction in weld joint strength relative to the base metal and analyze the fracture behavior in the central weld nugget zone [29, 39]. This study aims to investigate the influence of resistance spot welding (RSW) parameters on the microstructure and mechanical properties of weld joints made from Al-5 Mg aluminum alloy. The objectives of this work are: 1) to evaluate the applicability of resistance spot welding (RSW) for joining Al-5 Mg aluminum alloy; 2) to determine the effect of key RSW parameters on the microstructure and mechanical properties of the weld joint. Materials and experimental procedure The RSW process cycle diagram and the lap joint configuration used for tensile shear testing are shown in Figs. 1 and 2, respectively. For welding, 2.5 mm thick sheets of Al-5 Mg aluminum alloy (GOST 21631-2023) were used. Surface preparation of the sheets included the following steps: preliminary degreasing, followed by etching in a 4 % sodium hydroxide (NaOH) solution for 10 minutes, and subsequent treatment in a 2 % nitric acid (HNO₃) solution for 5 minutes to remove the oxide film. Welding was performed on a stationary resistance spot welding machine MTN-100.01. The RSW process scheme and cycle diagram are presented in Fig. 2. Shear tensile tests were conducted on a universal electromechanical testing machine Instron at room temperature, with a constant traverse speed of 1 mm/min until complete joint failure. The weld nugget diameter was measured on the fracture surface after the shear tensile test. Load values at shear and nugget diameter were calculated as the arithmetic mean of five measurements for each test series.
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