Multi-wire welding has received much attention in the machinery industry due to its high efficiency. The aim of this study was to investigate a novel pulse gas metal arc welding (GMAW) that has circular triple-wire electrodes. The effect of the pulse phage angle on arc stability was particularly studied. Research showed that for typical phase angles the arc stability from low to high is 180°, 0°, and 120°, and the arcs are very stable at 120°. The triple-wire welding was used to weld a 9 mm thick Q960E steel, which is typically used for the arm of construction machinery. When the welding heat input was controlled at 1.26–1.56 kJ/mm, the weld zone was dominated by acicular ferrite, and the coarse-grained zone of the heat-affected zone was a mixed structure of lath martensite and lath bainite. The tensile strength of the welded joint reached 85% of the base metal and the impact toughness was above 62 J, which can meet the requirements of construction machinery. This indicates that the triple-wire welding has great potential to achieve efficient and high-quality welding for the construction machinery.

No abstract

The main purpose of this work was to investigate the microstructure and mechanical properties of spray-formed 2195-T6 Al-Li alloy welding joints produced by tungsten inert gas (TIG) with Al-Cu and Al-Si-Cu filler wires, so that they can be better used in space vehicle tanks. The porosity analysis indicates that the porosity area of the weld seam with the Al-Si-Cu filler wire is approximately 7.989 times larger than that of the Al-Cu filler wire. Furthermore, the microstructure and microhardness results indicate that the Al/Cu eutectic near the fusion line distributes more at the grain boundaries, while more dispersed Al2Cu phase is found inside the grain, which improves the strength of the joint when using Al-Cu filler wire. However, when using the Al-Si-Cu filler wire, more Si, Cu, and Ti elements are segregated at the grain boundaries, forming a brittle-hard network Al/Cu/Ti eutectic, which reduces the performance of the joint. Additionally, the tensile strength and elongation of the weld joint are about 68.6% and 89.9% of the base metal (BM) when using the Al-Cu filler wire, and can approach the level of friction stir welding (FSW). However, the tensile strength and elongation are only about 56.8% and 39.9%, respectively, of the BM in the weld joint when using the Al-Si-Cu filler wire. Lastly, the fractures both occur on the fusion line and the fracture morphology of the weld joint shows that it is a mixed fracture mode dominated by plastic fracture when using Al-Cu filler wire, while it is mainly a quasi-cleavage fracture mode when using Al-Si-Cu filler wire. Therefore, the joint strength when using Al-Si-Cu filler wire with high strength matching is not as good as that of Al-Cu filler wire with low strength matching.

Since heat affected zone (HAZ) is the weak area of welded joints, this article proposes a method to predict the HAZ microstructure and hardness for the triple-wire gas metal arc welding (GMAW) process of Q960E high strength steel. This method combines welding thermal simulation and numerical simulation. The microstructures and hardness of Q960E steel under different cooling rates were obtained by thermal simulation and presented in a simulated HAZ continuous cooling transformation (SH-CCT) diagram. The cooling rate in HAZ were obtained by numerical simulation with ANSYS software for the triple-wire welding of Q960E thick plates. By comparing the cooling rate with the SH-CCT diagram, the microstructure and hardness of the HAZ coarse-grained region were accurately predicted for multiple heat input conditions. Further, an ideal heat input was chosen by checking the prediction results. This prediction method not only helps us to optimize the welding parameters, but also leads to an overall understanding of the process-microstructure-performance for a complex welding process.

No abstract

The weld joints of sprayed 2195-T6 and cast 2195-T8 aluminium–lithium alloy were created using tungsten inert gas with filler wire. The microstructures and mechanical properties of the weld joints were examined. The results of the microstructure analysis showed that the width of the equiaxed grain zone (EQZ) and the amount of the second phase θ’(Al2Cu) was greater in the weld joint of the cast 2195-T8 Al–Li alloy than that of the sprayed 2195-T6 Al–Li alloy. Tensile testing indicated that failures occurred in the EQZ and partially melted zone (PMZ) for both weld joints. The tensile strength and elongation of the weld joints of the sprayed 2195-T6 and cast 2195-T8 Al–Li alloys were about 68.2%, 89.7%, and 50.7% and 28.3% those of the base metal in the joint, respectively. The cast 2195-T8 Al–Li alloy joint had more pores and cracks, resulting in lower tensile strength and elongation than those in the sprayed alloy. Further, the tensile fracture surface morphology indicated that the fracture mode of the sprayed 2195-T6 Al–Li alloy was a mixed fracture mode dominated by plastic fracture and that of the cast 2195-T8 Al–Li alloy joints was a mixed fracture mode dominated by brittle fracture.

High-efficiency and high-quality welding has always been the focus of welding research. This article proposes a novel double-pulse, triple-wire MIG welding process for the welding of 6082-T6 aluminum alloy. The process characteristics of welding arc and droplet transfer were studied, and the performances of weld formation, morphology, hardness, and tensile strength were tested for the 1 Hz, 3 Hz, and 5 Hz double-pulse welding and normal-pulse welding. It was found that in the welding process, the pulsed arc steadily alternated among three welding wires without arc interruption, and the arc length changed periodically with the double-pulse frequency. The droplets transferred with a stable one-pulse-one-drop mode. Besides, a proper double-pulse frequency, e.g., 3 Hz in this case, was conducive to forming good welds with regular fish-scale patterns and no pores. The tensile strength of the joint could reach 64% of the base material’s tensile strength, and its fracture belonged to plastic fracture, which occurred in the HAZ. This new welding method will have great potential in aluminum alloy welding.

High-strength aluminum alloy fabricated using spray deposition technology possesses many advantages, such as fine crystal grains, low component segregation, uniform microstructure, and small internal stress. In this study, spray-deposited 2195 Al-Cu-Li alloy in forged state was used and welded using the gas tungsten arc welding (GTAW) process to test and verify the features of the fusion joint. Quantitative analysis was carried out to evaluate the relationship between the local microstructures and performances of the fusion joint, which was composed of four zones: weld metal, fusion zone, heat-affected zone, and base metal. The characteristic quantities of each zone, including recrystallized grain fraction, grain sizes, grain misorientation angle, and Vickers hardness, and their distributions were considered as the key factors affecting the performance of the joint because of welding thermal cycle impact on the fusion joint. To recognize the metallurgical characteristics of spray-deposited alloy 2195, a statistical algorithm based on the concept of the Hall–Petch relationship was proposed to validate the actual test results, which include the correlation effects of both the filler wire and welding process. The correlation between the microstructures and performances of several characteristic quantities were evaluated by integrating the above characteristic information of the fusion joint under the strong coupling of multiple factors. Thus, the advantages of weldability of spray-deposited alloy 2195 using GTAW could be understood in detail.