Journal of Welding Science

This study investigated the influence of resistance spot welding current intensity on the formation of liquid metal embrittlement (LME) cracks in galvanized advanced QP1180 steel. Galvanized steel sheets with a thickness of 1 mm were welded at currents of 6.5, 7, 7.5, and 8 kA. The results revealed that increasing the current significantly enlarged the weld nugget size, molten volume, electrode indentation, and the likelihood of LME crack formation. Microstructural analysis, elemental distribution, and crack characterization were conducted using optical and electron microscopy. The findings indicated that the weld zone microstructure primarily consisted of martensite, while the non-uniform distribution of zinc along grain boundaries facilitated the initiation and propagation of LME cracks. Cracks were predominantly observed at the periphery of the weld pool indentation and in the electrode-sheet contact area. This study demonstrates that controlling welding current intensity is a key factor in mitigating LME and improving the mechanical properties of joints in galvanized QP1180 steel. Optimizing welding parameters, particularly limiting current intensity, can prevent molten metal-induced cracking and enhance the durability and safety of automotive structures. Hardness profiling revealed peak hardness in the weld zone, followed by a gradual decrease toward the heat-affected zone (HAZ).

This study experimentally investigates the repair of surface grooves on pure magnesium samples using the surface friction stir processing (SFSP). Grooves with depths of 0.5, 1, and 1.5 mm were created and subsequently repaired under constant parameters of 1400 rpm rotational speed and 40 mm/min travel speed. The results revealed that the stir zone (SZ) exhibited fine equiaxed grains due to complete dynamic recrystallization, leading to significant improvements in tensile strength and hardness compared to the base metal. The highest ultimate tensile strength of 66.1 MPa and hardness of 60 HV were achieved in the 1 mm groove sample. Additionally, partial dynamic recrystallization was observed in the thermo-mechanically affected zone (TMAZ), and complete elimination of grooves was confirmed in all samples. These findings demonstrate that the SFSP is highly effective for localized repair and enhancement of mechanical properties in magnesium components, offering a promising solution to extend the service life of damaged magnesium parts.

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.

The weldability of the superalloy Inconel 738LC is compromised by its susceptibility to heat-affected zone (HAZ) liquation cracking, a consequence of its high gamma-prime (γ') precipitate strength and the formation of low-melting-point eutectic phases. This study investigates the impact of Gas Tungsten Arc Welding (GTAW) current mode—comparing continuous current with pulsed current—on the microstructure, mechanical properties, and overall weldability of IN738LC. Through room-temperature tensile testing, Vickers hardness measurements, and microstructural analysis via optical and electron microscopy, it was demonstrated that pulsed current, particularly at higher frequencies, substantially mitigates liquation cracking and improves joint integrity. The pulsed technique introduces controlled thermal fluctuations that reduce the effective heat input, promoting a transition from columnar to equiaxed dendritic solidification, minimizing interdendritic segregation, and refining the distribution of MC carbides. Consequently, the weld metal exhibits enhanced tensile strength, ductility, and hardness. These findings establish pulsed GTAW as an effective strategy for suppressing cracking and improving the performance of IN738LC welded joints.

The Ti-6242 alloy is of particular significance in additive manufacturing due to its high thermal resistance. However, components fabricated from this alloy using the electron beam powder bed fusion (EB-PBF) process often exhibit poor surface quality, primarily resulting from the layer-by-layer fabrication nature and and the presence of partially melted powder particles. In this study, laser polishing was employed to enhance the surface characteristics of EB-PBF fabricated Ti-6242 specimens using three laser powers (195, 260, and 325 W) and two scanning speeds (4.5 and 3 mm/s). The effects of these parameters on surface roughness, microstructure, and mechanical properties were evaluated through surface profilometry, metallography, hardness, and wear tests. The results indicated that the average surface roughness decreased by up to 93%, from 9.36 µm to 0.61 µm. Moreover, the initial α and β phases transformed into a fine, martensitic α′ phase within the polished layer, leading to a 33% increase in hardness—from 380 to 506 HV—and a significant improvement in wear resistance. Consequently, optimal adjustment of laser polishing parameters can simultaneously reduce surface roughness and enhance the mechanical performance of Ti-6242 components.

In this study, the Friction Stir Welding process was employed to repair artificial cracks and grooves in 7075 aluminum alloy. Samples with different groove depths (0.5, 1, 1.5, and 2 mm) were prepared and evaluated through experimental tests, metallographic analysis, tensile testing, and numerical simulation using Abaqus software. The results showed that the Friction Stir Welding successfully repaired the defects without creating voids or surface irregularities. Microstructural observations in the stir zone revealed that dynamic recrystallization led to the formation of fine and homogeneous grains, resulting in improved hardness and tensile strength. The specimen with a 1 mm groove depth exhibited the best mechanical performance, with a maximum hardness of approximately 109 HV and the highest tensile strength among all samples. Conversely, samples with 0.5 and 2 mm groove depths showed void formation and reduced strength due to insufficient or excessive heat input and uneven material flow. Both experimental and simulation results confirmed that a groove depth of 1 mm provides optimal conditions for defect repair in 7075 aluminum alloy.

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.

In this study, the effects of diffusion-bonding temperature and time on the microstructure and corrosion behavior of Al₀.₅CoCrFeMnTi₀.₅ high-entropy alloy coatings applied on A283 plain carbon steel were investigated. The coatings were produced by diffusion bonding using the spark plasma sintering method, in which high-entropy alloy powders were bonded to the substrate at temperatures of 850, 950, and 1050°C for holding times of 10, 15, and 20 minutes. Microstructural characterization performed by field-emission scanning electron microscopy (FESEM) revealed that increasing the diffusion-bonding temperature and time led to reduced porosity and enhanced coating densification. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests conducted in a 3.5 wt.% NaCl solution demonstrated that increasing the bonding temperature and time resulted in higher charge transfer resistance (Rct) and corrosion potential (Ecorr values, along with a decrease in corrosion current density (icorr). The coating produced at 1050°C with a holding time of 20 minutes exhibited the highest corrosion resistance. The improvement in corrosion performance was attributed to the formation of a uniform and adherent oxide film, which effectively inhibited the penetration of corrosive ions into the steel substrate.

In this study, a novel two-step heating strategy was investigated for transient liquid-phase (TLP) bonding of the IN-738LC superalloy. The bonding process consisted of an initial heating at 1150 °C for 5 seconds, followed by holding at 1110–1130 °C for 3 to 40 minutes. The microstructural evolution during the process, as well as the interface morphology, was characterized and compared with conventional TLP joints. This approach significantly reduced the time required to complete isothermal solidification; the width of the central eutectic zone decreased from 45 µm at 3 minutes to 19 µm at 12 minutes, and the eutectic zone was completely eliminated after 40 minutes. Microstructural examinations revealed that the initial step of the two-step heating process produced a cellular–dendritic solidification interface, leading to a non-uniform distribution of porosity along the bond region. Subsequent homogenization removed boride precipitates and resulted in the formation of uniformly distributed γ′ precipitates similar to those in the base metal. These findings provide practical and microstructural insights into the influence of thermal profiles on interfacial evolution and offer a pathway for improving joint quality in nickel-based superalloys.

In the present study, AISI 1030 cast-steel samples were cladded using duplex stainless-steel wire ER2209 by the Gas Tungsten Arc Welding (GTAW) process under different preheating temperatures and varying numbers of passes. The  degrre of dilution of the clad layers,affected by both  of the preheating temperature and the number of passes—was calculated, and was evaluated its influence on the adhesion and bonding integrity of the ER2209 clad layer on the cast-steel substrate. The results showed that by increasing the number of clad layers led to a lower dilution in the samples. Furthermore, a rise in preheating temperature also contributed to an increase in dilution. Among all conditions, the three-pass cladded sample with a preheating temperature of 100 °C exhibited the highest dilution degree. Bending test results demonstrated that the bending angle increased by the number of clad passes. Macroscopic examination confirmed  that complete interfacial continuity between the clad layer and the base metal. Phase analysis and microstructural observations revealed that the base metal consisted of approximately 80% ferrite and 20% pearlite; the heat-affected zone (HAZ) exhibited a ferrite–transformed pearlite structure with similar volume fractions; and the cladded samples in the final pass presented a duplex austenitic–ferritic structure with 10–20 Wt.% ferrite content. Microhardness test indicated that the two-pass cladded sample  that preheated at 200 °C had the highest hardness value, up to 355 HV.

In this study, the effect of an additional pass using a pinless tool on the microstructure and mechanical properties of friction stir welding (FSW) AA1100 butt joints was investigated. The microstructure was characterized using optical microscopy and scanning electron microscopy (SEM), while the mechanical properties were evaluated by tensile and Vickers microhardness tests. The results indicated that applying additional passes led to grain refinement of the microstructure and a reduction in grain size to approximately 1 µm in the stir zone. Moreover, the microhardness in the upper stir zone increased from about 30 HV in the initial joint to nearly 55 HV in the processed sample. Tensile test results also revealed an improvement in mechanical properties, with the ultimate tensile strength (UTS) increasing from 86 MPa to 101 MPa, corresponding to an enhancement of approximately 17%. This improvement was mainly attributed to grain refinement and the increased grain boundary density.

Nickel-based superalloys are among the most critical materials used in high-temperature components of gas turbines, where their replacement costs and potential turbine damage necessitate effective protection and repair strategies. Optimizing repair methods to enhance efficiency and reduce costs has therefore been a continuous focus. The aim of this study is to improve the repair process of Inconel 738LC superalloy by reducing the susceptibility to liquation cracking. Activated tungsten inert gas (A-TIG) welding was performed on Inconel 738LC using a welding current of 60 A. Titanium dioxide (TiO₂) powder was employed as an activating flux, and weldments with four flux concentrations were examined. The microstructure was characterized using optical microscopy and scanning electron microscopy. The results revealed that flux concentration had a significant influence on penetration depth, with a concentration of 1 g/mL producing the maximum effect. At this concentration, weld penetration increased by 68% and weld pool volume by 63%, while the heat-affected zone width decreased by 12%. Arc imaging and quantitative/qualitative analysis demonstrated a constricted and focused plasma arc column in the presence of TiO₂ flux. Microstructural examinations further revealed suppression of columnar dendrite growth. It was found that TiO₂ flux enhances weld penetration and pool volume by constricting the arc and activating a reversed Marangoni flow, while simultaneously reducing HAZ width. However, the increased weld pool volume also intensified contraction stresses, leading to liquation cracking in the weld with the largest pool volume.

Selective laser melting (SLM) has been considered as a method for manufacturing large and complex industrial parts. Considering that structural defects are generally caused by process parameters, the optimal evaluation of parameter selection to minimize localized defects has been of interest. Therefore, a model was presented to predict the optimal single-pass geometric characteristics based on the main process parameters, namely laser power and scanning speed, to prevent defects in single-pass Inconel 738LC on Inconel 738 casting substrate. An optimal process map was obtained based on the use of linear regression method combined with genetic optimization algorithm with optimal combination parameters (PαVβ). Finally, based on the geometric characteristics of single-passes, an optimal region was identified on the process map. At a power of 325 W and a laser scanning speed of 800 mm/s, due to the decrease in the G/R ratio, the microstructure from the junction to the substrate to the top of the single pass has changed from columnar to coaxial dendritic.

In this study, the effects of welding current intensity (9 and 10 kA) and holding time (5 and 40 cycles) on the energy absorption and failure mode of a dissimilar joint between DP590 and HSLA440 steels in the resistance spot welding process were investigated. For this purpose, four parameter combinations were prepared, and a tensile–shear test was performed on each sample. The results showed that increasing the current from 9 to 10 kA at a holding time of 5 cycles led to an increase of about 1 kN in strength; however, at a hold time of 40 cycles, changing the current resulted in a decrease of approximately 1.6 kN in strength. Therefore, the role of current is limited and dependent on the saturation of the weld nugget diameter. In contrast, increasing the hold time from 5 to 40 cycles had the most significant effect, increasing the energy absorption by about 217 J. Failure mode analysis also revealed that samples with longer hold times predominantly exhibited pull-out failure (PF), absorbing significantly more energy compared to interfacial failure (IF). Overall, the results indicate that controlling cooling through increasing the holding time is the most effective factor in enhancing absorbed energy and altering the failure mode in DP590/HSLA440 joints.

Wire and Arc Additive Manufacturing (WAAM) is one of the modern methods of fabrication parts by arc welding under shielding gas. In this research, the thin-wall of austenitic stainless steel 316L was fabricated via WAAM based on inter-pulse current; accordingly, a thin-wall was fabricated in 25-layers using two different strategies with a reciprocating torch movement pattern. Considering the equivalent chromium and nickel content in the Scheffler diagram, it was predicted that the microstructure solidification was done in the austenitic-ferritic (AF) state. Microstructural examination by optical microscopy and X-ray diffraction confirmed the presence of austenite matrix phase alongside ferrite dendrites (about 5%). The tensile test results showed that samples extracted in the vertical direction with an average tensile strength of 454 MPa had about 12% higher strain rates than horizontal samples with a tensile strength of 436 MPa. Also, examination of fine and coarse indentations on the fracture surface of tensile test specimens by scanning electron microscopy showed that the fracture of the specimens was of the ductile type. The hardness of the fabricated thin-wall was measured in the range of 200 to 265 Vickers with an average of 234 Vickers.

In this research, the influence of various forge pressure values and also the chemical composition of different carbon steels on rotary friction welding of SS 304 to carbon steels has been investigated. The steel rods of AISI 1015, 1030, and 1045 have been RFWed to SS 304 using 20, 40, and 80 bar forge pressure. Results indicated the 40 bar forge pressure as the optimum value, and by applying pressures below this number, the material flow in the weld interface would be tackled, resulting in improper mechanical values. By exceeding the optimum forge pressure, most of the viscoplastic material inside the weld interface would be rejected from that area in the form of flash, causing the weld to be done at a relatively low temperature. Microstructural investigation has been done by optical and scanning electron microscopes. Results showed that the weld zone is extremely fine due to DRX, and in the interface, a pro-eutectoid ferrite layer is formed, which has an increasing width when the heat input increases. Tensile test results showed that the optimum weld specimen is the RFW of AISI 1030 to SS 304 using 40 bar forge pressure, 40 bar friction pressure, 5s friction time, and 1500 RPM rotational speed. This specimen has shown 116 % joint efficiency and 715 MPa ultimate tensile strength.

Welding is one of the methods of surface repair of cast irons. In this study, surface repair of gray cast iron was first performed by gas metal arc welding method with ER70S-6 welding wire under inter-pulse current, heat input of 393 J/mm and dilution of 17%. Also, to compare the results, two samples were welded with ENi-CI and E6013 covered electrodes. Microstructural studies showed that the microstructure of the interface of the sample is composed of martensite with fine lathes and upper bainite. Despite the presence of cementite (Fe₃C) next to alpha iron (α-Fe) in the interface area, the formation of incomplete mixing zone with bainite lathes in the ferrite zone has led to increased toughness and prevented crack formation. The hardness of the ER70S-6 sample was similar to that of the E6013 sample at the interface, at about 809 Vickers, which is 334 Vickers higher than the hardness of the ENi-CI sample. The results of the open circuit potential and potentiodynamic polarization tests showed that the ER70-CI sample, with a corrosion potential and current of -653 mV and 6.8 μA/cm², had a higher polarization resistance and was more resistant to galvanic corrosion than the ENi-CI sample (-622 mV and 8.9 μA/cm²).