Resistance spot welding of die-cast and wrought aluminum alloys: the influence of experimental setup-dependent heat field manipulation on weld spot quality when joining EN AC-42.400 to EN AW-6082

Welding aluminum castings is known for a high sensitivity for hydrogen-induced weld porosity. Research has shown that the porosity detected in mixed material resistance spot welds between die-cast and wrought aluminum is predominantly classified as solidification porosity. But, nugget penetration depths into the wrought aluminum alloy are low. In this work, the effect of a forging electrode force during welding current time ti or after the welding current is shut off on weld spot characteristics is investigated, when resistance spot welding (RSW) mixed material joints between EN AC-43500-T6/T7 and EN AW-6082-T6. A current cut-off test based on a welding profile according to VDA 238–401 reveals a welding current time ti between 60 ms ≤ ti ≤ 80 ms as relevant for porosity detection in cross-section analysis. Based on this, different welding profiles are tested, and resulting weld spot characteristics are analyzed when applying chisel tests, cross-section analysis, quasi-static shear tensile tests, and scanning electron microscopy. The application of a forging electrode force reduces weld spot porosity in RSW significantly, while a current downslope leads to an increase. Further, the application of a forging electrode force during welding current time leads to a significant decrease in the standard deviation of s = 1.07 kN to s = 0.08 kN in shear tension force, although the mean shear tension force is increased marginally from 7.07 kN to 7.15 kN. Yet, an increase in weld penetration depth ≥ 20% into EN AW-6082-T6 is only achieved when reducing the initial electrode force to 5 kN and initiating forging electrode force during ti.

Characteristics of shunting in resistance spot welding for dissimilar unequal-thickness aluminum alloys under large thickness ratio

Resistance spot welding (RSW) is an economic, robust welding process, which is easy to automate and widely used in automotive industry. In this work, the resistance spot weldability of die-cast aluminum alloys EN AC-AlSi7MnMg, EN AC-AlSi9Mn and EN AC-AlSi10MnMg-T6/T7 to wrought aluminum alloy EN AW-AlSi1MnMg-T6 is investigated when applying the standard welding profile as recommended in VDA 238-401 considering main challenges in welding aluminum die castings, for example, porosity and inhomogenities. Weldability is best for EN AC-AlSi10MnMg-T6/T7, but the results show limited applicability of VDA 238-401 in general, especially for high total sheet thicknesses, because of invalid electrode force favouring spatter formation and weld spot irregularites. Still, all spot welds between die castings and 2 mm wrought aluminum sheets reach the recommended shear tension forces for spot diameter dw of 5·√t (2 mm: 5.95 kN; 3 mm: 8.96 kN; according to DIN EN ISO 18595), although being afflicted with solidification porosity and liquation cracking. Gas porosity is not observed and solidification porosity is only found to be significant for weld spot failure when being located close to the joining level, which is observed at welding depths of approximately 50% into the wrought aluminum sheet. Here, a failure path across the nugget is found. Weld porosity apart from the joining level is less significant and failure path is found along the fusion line between nugget and wrought aluminum. Instead, hardness difference between nugget and HAZ is the main reason for weld spot failure. Although the applied welding current profile is not suited best for RSW of mixed joints between aluminium die castings and wrought aluminium alloys, the results confirm its potential, for example, a significantly reduced gas porosity compared to applied fusion welding processes.

Effect of adhesive on fatigue property of Aural2 to AA5754 dissimilar aluminum alloy resistance spot welds

Experimental and numerical investigations on built-up cold-formed steel beams using resistance spot welding

A comparative study on resistance spot and laser beam spot welding of ultra-high strength steel for automotive applications

On some fundamental problems in ultrasonic welding of dissimilar metals: Gencsoy, H.T., Adams, J.A. and Shin S. Welding journal, 46, no. 4, p. 145-s (1967)

Effect of ultrasonic welding parameters on microstructure and mechanical properties of dissimilar joints

Efforts to reduce vehicle weight and improve crash performance have resulted in increased application of advanced high strength steels (AHSS) and a recent focus on the weldability of these alloys. Resistance spot welding (RSW) is the primary sheet metal welding process in the manufacture of automotive assemblies. Friction stir spot welding (FSSW) was invented as a novel method to spot welding sheet metal and has proven to be a potential candidate for spot welding AHSS. A comparative study of RSW and FSSW on spot welding AHSS has been completed. The objective of this work is to compare the microstructure and mechanical properties of Zn coated DP600 AHSS (1·2 mm thick) spot welds conducted using both processes. This was accomplished by examining the metallurgical cross-sections and local hardnesses of various spot weld regions. High speed data acquisition was also used to monitor process parameters and attain energy outputs for each process. Results show a correlation found among microstructure, failure loads, energy requirements and bonded area for both spot welding processes.

Fatigue Behavior of Dissimilar Aluminum Alloy Spot Welds

Effect of specimen configuration on fatigue properties of dissimilar aluminum to steel resistance spot welds

Lightweight materials such as high-strength steels and aluminum alloys are widely used in automotive components for the purposes of weight reduction and consequent higher fuel efficiency. As new alloys have been developed, magnesium alloys have become attractive for the production of automotive components due to their unique properties, such as high specific strength, damping capacity, and recyclability. In the assembly process of these materials, resistance spot welding (RSW) is used to construct thin sheet structures. Although RSW of steel sheets with high weld quality has already been established, the following problems remain with regard to RSW of magnesium alloys: high welding current, degeneration of electrodes, and blowholes and expulsion in or around the nugget. In this study, RSW with cover plates was applied to magnesium alloy sheets to investigate the performance of spot-welded joints. The weld quality was evaluated based on the tensile shear strength of the joints, the shape and the size of the nugget, and the appearance of blowholes and expulsion. Since RSW with cover plates is similar to conductive heat resistance seam welding (CHRSMW), the results showed that RSW with cover plates enabled the spot welding of a magnesium alloy with a large nugget and high tensile shear strength in the joint. It was also shown that blowhole-free spot welds with a large nugget and high tensile shear strength were obtained for welding currents above 8 000 A with a long down-slope time of welding current and a high electrode force.

Among the AHSS, the dual-phase (DP) steels have been the subject of particular attention owing to their good combination of high strength and ductility and recent study focus on the weldability of these alloys. Resistance spot welding (RSW) is the primary sheet metal lap joining process in the manufacture of automotive assemblies. However, AHSS in RSW has revealed a number of problems that are a concern to the increased adoption of this range of alloys. Friction stir spot welding (FSSW) has been developed as an extension of friction stir welding (FSW). During FSSW, the rotating tool penetrates the sheets being weld and is then retracted producing a stir zone region that comprises a fine dynamically recrystallized microstructure. Solid-state metallurgical bonding was produced using a range of plunge rate, plunge depth, and tool rotational speed. The objective of this work is to compare the microstructure and mechanical properties on DP780 AHSS (1.6 mm thick) spot welds conducted using both process. The hardness, microstructure, failure mode, and bound area were examined. The results show that RSW has higher strength and bound area: the FSSW with decolorized advantage. Based on these results, we can provide the direction to choose the appropriate weld method.

Stainless steel railway car bodies are assembled by joining the outer plates and the pillar materials using resistance spot welding. In recent years, more and more car bodies are being assembled using laser welding in addition to the resistance spot welding. For this laser welding system, we developed a condition monitoring system considering the processes before and after laser welding as a single system, and obtained and put into practical use an appropriate condition that suppresses spatter generation during laser welding. On the other hand, in resistance spot welding, the current, weld time, electrode load, and electrode tip shape are the main factors that determine the welding quality. Therefore, the configuration of the equipment is less complicated than that of laser welding system, and the condition monitoring is easier than that of the laser welding. In this study, by transferring the concept of the condition monitoring system developed for laser welding to resistance spot welding, we achieved a reduction of more than 60% in terms of electricity consumption and improved the appearance of the car body by optimizing the indentation shape. In addition to this technical achievement, we also present in this paper a case study showing the opportunity for innovation by restructuring the technological paradigm of the resistance spot welding in the production of stainless steel car body shells.

This paper presents a review on the resistance spot welding (RSW) of Al/Al alloys, Al alloys/steel, Al/Mg alloys, and Al/Ti alloys, with focus on structure, properties, and performance relationships. It also includes weld bonding, effect of welding parameters on joint quality, main metallurgical defects in Al spot welds, and electrode degradation. The high contact resistance, induced by the presence of oxide layer on the surface of Al alloys, and the need for application of high welding current during RSW of Al alloys result in rapid electrode tip wear and inconsistency in weld quality. Studies have shown that cleaning the oxide layer, sliding of a few microns between sheets, enhancing the electrode force, and the application of a low-current pre-heating can significantly reduce the contact resistance and improve joint quality. For Al/steel dissimilar RSW, the technique of resistance element welding, the use of optimized electrode morphology, the technique of RSW with cover plates, and the use of interlayers such as Al-Mg, AlSi12, and AlCu28 alloys were found to suppress the formation of brittle intermetallic compounds (IMC) and improve the joint quality. The employment of pure Ni foil, Au-coated Ni foil, Sn-coated steel, and Zn-coated steel interlayers was also found to restrict the formation of brittle IMCs during RSW of Al/Mg alloys. Furthermore, the techniques of RSW with cover plates and RSW under the influence of electromagnetic stirring effect were found to improve the weldability of Al/Ti dissimilar alloys.