The lightweight construction of automotive car bodies is the more important to reduce the fuel consumption and costs. High-strength steels and aluminium alloys are suitable for achieving these aims. Recent car bodies contain both materials, therefore necessary to make reliable joints between them. The resistance spot welding (RSW) can be used for joining of car bodies and it is applicable for aluminium/steel hybrid joints, too. High cycle fatigue (HCF) test results can be rarely found in the literature while HCF loading basically determines the lifetime of hybrid joints. 5754-H22, 6082-T6, and DP600 base materials were used for similar and hybrid RSW joints and HCF tests were performed. Number of cycles to failure values, failure modes, furthermore brittle intermetallic compound (IMC) layers were studied and analysed. In both aluminium/steel hybrid joints, the HCF test results showed better endurance limit like concerning aluminium/aluminium similar joints, but worse than steel/steel joints. For 5754-H22 alloy the endurance limit values are 648 N, 939 N, and 1285.5 N, for similar aluminium, hybrid, and similar steel joints, respectively. For 6082-T6 alloy these values are 513 N, 625.5 N, and 1285.5 N, respectively. In case of similar joints only base material fracture happens, but hybrid joint specimens show different failure modes. Base material fracture and shearing after partial base material fracture were typical failure modes in case of 5754-H22/DP600 and 6082-T6/DP600 hybrid joints, respectively. The full and partial plugging as a failure modes appeared for hybrid joints, too. The IMC layer characteristics showed opposite results in cases of hybrid joints, both the layer thicknesses of the shared and plugged joints and the thickness differences between the inner and outer parts of the joints were different.

Materials for lightweight vehicle structures play an increasingly important role in both economic and environmental terms; high-strength steels and aluminum alloys are suitable for this role. Resistance spot welding (RSW) and conventional clinching (CCL) methods can be used for joining vehicle bodies and can also be applied for aluminum/steel hybrid joints. Whereas vehicle structures are subjected to cyclic loading, damages can occur due to high-cycle fatigue (HCF) during long-term operation. Systematic HCF test results are rarely found in the literature, while HCF loading basically determines the lifetime of the hybrid joints. The base materials 5754-H22, 6082-T6, and DP600 were used for similar and hybrid RSW and CCL joints, and HCF tests were performed. The number of cycles-to-failure values and failure modes were studied and analyzed. Based on the experimental results, HCF design curves belonging to a 50% failure probability were calculated for all cases, and the curves were compared. Clear relationships were found between the failure modes and fatigue cycle numbers for both joining methods. Considering the steel/steel joints as a base, the load-bearing capacity of the hybrid joints is lower (48.7% and 73.0% for RSW, 35.0% and 38.7% for CCL) and it is even lower for the aluminum/aluminum joints (39.9% and 50.4% for RSW, 31.7% and 35.0% for CCL). With one exception, the load-bearing capacity of the CCL joints is higher than that of the RSW joints (156.1–108.3%).

Some welding tasks can be difficult to solve with conventional arc welding processes, due to the applied high heat input, thus the different welding machine manufacturers have developed different processes and process variants. One such development was the CMT (cold metal transfer) process variant. The process is based on a short-circuit version of gas metal arc welding (GMAW) process, but the main difference is, that during the CMT process, the droplet deposition is controlled by the retraction of the wire, which also has the advantage of providing a joint with almost no spatter. Subsequently, several different process variants of the CMT have appeared in recent years, which have other beneficial properties. Therefore, the aim of this paper is to summarize the CMT process variants and the different types of them and their potential applications.

Hardfacing is a widely used technique to create wear-resistant layer on the base material to ensure good durability and performance under harsh operating conditions. However, despite its effectiveness in improving wear resistance, hardfaced layers can sometimes exhibit softening phenomena during welding, compromising their mechanical properties and overall performance. In this research, the effect of heat input was investigated in case of Fe-based hardfacing material with high Cr content. 4 different heat inputs were applied with gas metal arc welding and significant differences were determined in hardnesses, which can be influential to the lifetime of hardfaced parts. Hardness drop happens in the heat-affected zones between the hardfaced layers and the highest heat input causing the most significant softening (20% hardness drop).