Journal of Welding Science

In this research, copper/silver-silicon carbide Cu-Ag-SiC composite was prepared by the friction stir processing (FSP). For this purpose, nanometer and micrometer SiC particles were used as reinforcing particles. In order to evaluate the microstructural properties, X-ray diffraction (XRD) analysis, scanning electron microscope and optical microscope were employed. Evaluation of mechanical properties through microhardness measurement, tensile test and pin on disc test were utilized to evaluate the wear behavior of the composite. The results of X-ray analysis revealed the presence of two phases of CuAg solid solution along with SiC particles, which indicated the formation of Cu-Ag-SiC composite. The addition of nano-particles led to a significant decrease in the intensity of peaks compared to micro-particles. This indicated a decrease in the grain size of the CuAg matrix. Using the FSP in the presence of reinforcing particles and without it led to a decrease in the crystal size and average grain size compared to the sample without FSP. So that the grain size of the sample without FSP and the FSPed sample without reinforcing particles and with nano-reinforcing particles were found to be about 46.3, 19.2 and 3.6 µm, respectively. The wear mechanism in the sample before FSP was adhesive wear due to its soft nature of the matrix, and after FSP in the sample without reinforcing particles, the adhesive wear decreased and due to the addition of silicon carbide micro and nano- particles reinforcement, the wear mechanism in entirely altered to abrasive wear. Overall, it can be stated that the addition of silicon carbide nanoparticles by FSP leads to the fabrication of  Cu-Ag-SiC composite with high mechanical properties.

In this study, the effect of friction stir welding on the microstructure and mechanical properties of Fe-24Ni-4Cr austenitic steel was investigated. For this purpose, a sheet with a thickness of 1 mm was subjected to friction stir welding using a WC-5%Co tool at a traverse speed of 100 mm/min and a tool rotational speed of 450 rpm. Electron backscatter diffraction (EBSD) analysis revealed that this process led to grain refinement and an increase in high-angle grain boundaries in the stir zone, attributed to dynamic recrystallization during welding. Phase maps indicated an increase in the BCC phase fraction in the stir zone compared to the base metal. Given the high strain rate and the presence of stabilizing elements, this phase was primarily strain-induced martensite. Mechanical property assessments showed a significant increase in the tensile strength of the stir zone (450 MPa) compared to the base metal (350 MPa). Moreover, the yield strength of the stir zone (388 MPa) was substantially higher than that of the base metal (145 MPa), which can be attributed to grain refinement, an increase in high-angle grain boundaries, a higher dislocation density, and martensite formation. However, the ductility of the stir zone decreased due to higher stress concentration and dislocation density in this region. These findings suggest that friction stir welding can be an effective method for enhancing the strength and hardness of austenitic steels, but process conditions must be carefully controlled to prevent reductions in toughness and ductility.

Wire-arc additive manufacturing (WAAM) is a prominent technique for producing large metallic components due to its high deposition rate. Utilizing austenitic stainless steels in this process not only reduces production costs but also provides greater design freedom. Among these steels, SS310, known as heat-resistant steel in the industry, offers excellent oxidation resistance and high-temperature performance. However, it is highly susceptible to hot cracking during welding and additive manufacturing processes. In this study, the microstructure and mechanical properties of SS310 fabricated using WAAM with Cold Metal Transfer (CMT) and Gas Metal Arc Welding (GMAW) processes were compared. The results revealed that the CMT process, due to its lower heat input, effectively reduces the susceptibility of SS310 to hot cracking compared to the GMAW process. These findings emphasize the importance of selecting an appropriate process to achieve high-quality components and minimize structural defects.

This research looks at how microstructure and mechanical properties change in resistance spot welds of QP980 advanced high-strength steel. It specifically focuses on the effects of zinc coating and how it influences weld nugget formation, mechanical properties, and fracture behavior. The study involved microscopic examinations, mechanical tests, and finite element simulations to determine the thermal history of different weld zones. A key finding was that rapid cooling during the welding process led to the formation of, metastable phases, such as martensite, in both the weld nugget and the heat-affected zone. A finite element model of the welding process was used to simulate heat distribution and analyze the microstructure in various weld regions. This model showed that reaching the peak temperature during four-pulse resistance spot welding is delayed. This delay, along with proper hold times, helps prevent the formation of voids. The simulated thermal history and the rapid heating/cooling conditions effectively predicted the evolution and transformation of the microstructure in different weld areas. It was found that the presence of a zinc coating, and the resulting reduction in electrical contact resistance, delayed the formation of the weld nugget at lower welding currents. However, at higher currents, the primary source of heat generation shifted from contact resistance to bulk resistance within the steel sheet. This led to larger weld nuggets in coated samples compared to uncoated ones. While uncoated samples showed higher weld nugget hardness (512 Vickers) and greater tensile-shear strength (with a maximum load-bearing capacity of 28.1 kN in uncoated samples versus 24 kN in coated samples), coated samples were able to achieve the critical weld nugget size for a change in fracture mode at lower welding currents (9 kA compared to 9.5 kA).

In this study, laser direct deposition was employed to fabricate a functionally graded transition between 17‑4PH stainless steel and Stellite 6. Specimens were designed and produced such that the chemical composition varied incrementally from 100% 17‑4PH to 100% Stellite 6, with each step involving a 25% decrease in the 17‑4PH content and a corresponding 25 % increase in Stellite 6. Microstructural evolution and elemental distribution were characterized by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS), while mechanical properties were assessed via Vickers microhardness testing and uniaxial tensile tests. The microstructural analysis revealed a needle‑like martensitic matrix in the substrate, which transformed into cellular dendrites upon reaching the 25% Stellite 6 layer. As the Stellite 6 fraction increased, along with corresponding rises in Cr and W content, grain boundaries broadened and carbides accumulated within interdendritic regions. At the 50% composition, oriented columnar dendrites became prominent, and at higher Stellite 6 levels the dendritic structure refined further, ultimately evolving into an equiaxed morphology. Microhardness measurements showed a continuous increase from approximately 300 HV in the 17‑4PH substrate to 490 HV in the pure Stellite 6 layer. Tensile testing demonstrated that both yield strength (σᵧ) and ultimate tensile strength (σᵤ) remained within 1102–1159 MPa across all compositions, with no evidence of brittle phases or manufacturing defects. Elongation increased from 7% in pure Stellite 6 to 19% in pure 17‑4PH, with the 50%–50% gradient exhibiting an optimal balance of strength and ductility (14.5% elongation).

This study investigated the effects of pulsed current and constant current on the microstructure and mechanical properties of Hastelloy X superalloy welds produced by Gas Tungsten Arc Welding (GTAW), using ERNiCrMo-2 filler metal. Key microstructural parameters, such as elemental segregation, dendrite refinement, and weld metal uniformity, along with changes in weld strength and hardness, were examined and compared between the two welding modes. Microstructural evaluations were conducted using optical microscopy, Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD) for phase identification. Pulsed current welding resulted in a finer microstructure with more equiaxed dendrites, reduced elemental segregation, and a more uniform distribution of M₆C carbides. Furthermore, this process led to significant improvements in hardness, impact toughness, and tensile strength of the weld metal compared to constant current welding. Fracture analysis confirmed ductile fracture behavior in all specimens, consistent with the microstructural and mechanical findings. The results of this research highlight the importance of using pulsed current in GTAW as an effective method for controlling the microstructure and enhancing the mechanical properties of Hastelloy X alloy joints. 

The friction stir spot welding (FSSW) process is a solid-state welding technique recognized as one of the most significant advancements in metal joining over the past decade. In this study, the effects of rotational speed and tool contact time, with a unique design different from previous research, on the microstructure and mechanical properties of 5754 series aluminum alloy were investigated. The workpiece was clamped using a specialized fixture on a radial drilling machine, and welding operations were performed using a FSSW machine at different rotational speeds and various tool contact times. Subsequently, the microstructure, microhardness, and tensile-shear strength of the welded spot region were evaluated. The results showed that increasing the tool rotational speed and prolonging the tool contact time led to an improvement of approximately 105% in the tensile-shear strength. According to statistical analyses, the factors of rotational speed and tool contact time significantly affected the shear strength with a confidence level greater than 95%; however, statistical analyses revealed different results regarding the relationship between rotational speed, contact time, and hardness.

In this study, an AA5083/Al12Mo surface composite containing approximately 10 vol.% of pre-synthesized molybdenum aluminide particles was fabricated using Friction Stir Processing (FSP) under optimized conditions, including six passes, a rotational speed of 1000 rpm, and a traverse speed of 52 mm/min. Multiple FSP passes reduced the particle size from about 20 µm to nearly 1.7 µm and improved their distribution uniformity, while simultaneously refining the matrix grains and enhancing the strain-hardening capability. These microstructural improvements led to a ~16% increase in tensile strength compared to the unreinforced FSPed alloy and ~20% relative to the as-received base metal, along with ~50% and ~63% hardness enhancement in the 4-pass and 6-pass samples, respectively. Quantitative analysis of the strengthening mechanisms revealed that strain hardening contributed the most to the overall strength increment, and the presence of reinforcing particles delayed the onset of the Portevin–Le Chatelier (PLC) serrated flow. Fractography indicated a mixed fracture mode consisting of particle fracture, particle–matrix decohesion, and matrix rupture. Furthermore, corrosion tests demonstrated a decrease in corrosion resistance, mainly due to the discontinuity of the protective aluminum oxide layer and the formation of defects at particle–matrix interfaces caused by severe plastic deformation.