Search Results (230)

Climate concerns are driving the automotive industry to adopt advanced manufacturing technologies that aim to improve energy efficiency and reduce vehicle weight. In this context, lightweight structural materials such as aluminium alloys have gained significant attention due to their favorable strength-to-weight ratio. Laser welding plays a crucial role in assembling such materials, offering high flexibility and fast joining capabilities for thin aluminium sheets. However, welding these materials presents specific challenges, particularly in controlling heat input to minimize distortions and ensure consistent weld quality. As a result, numerical simulations based on the Finite Element Method (FEM) are essential for predicting weld-induced phenomena and optimizing process performance. This study investigates welding-induced distortions in laser butt welding of 1.5 mm-thick Al 6061 samples through FEM simulations performed in the SYSWELD 2024.0 environment. The methodology provided by the software is based on the Moving Heat Source (MHS) model, which simulates the physical movement of the heat source and typically requires extensive calibration through destructive metallographic testing. This transient approach enables the detailed prediction of thermal, metallurgical, and mechanical behavior, but it is computationally demanding. To improve efficiency, the Imposed Thermal Cycle (ITC) model is often used. In this technique, a thermal cycle, extracted from an MHS simulation or experimental data, is imposed on predefined subregions of the model, allowing only mechanical behavior to be simulated while reducing computation time. To avoid MHS-based calibration, this work proposes using thermal cycles acquired in-line during welding via infrared thermography as direct input for the ITC model. The method was validated experimentally and numerically, showing good agreement in the prediction of distortions and a significant reduction in workflow time. The distortion values from simulations differ from the real experiment by less than 0.3%. Our method exhibits a slight decrease in performance, resulting in an increase in estimation error of 0.03% compared to classic approaches, but more than 85% saving in computation time. The integration of real process data into the simulation enables a virtual representation of the process, supporting future developments toward Digital Twin applications. Full article

An ultra-high-strength press-hardening steel (PHS) and a high-strength dual-phase steel (DP) were butt-joined by the gas metal arc welding (GMAW) process, aiming to assess the effects of a high heat input welding process on the structure-property relationship and residual stress. The post-weld microstructure, the microhardness profile, the tensile behavior, and the experimentally obtained residual stresses (by x-ray diffraction) of the steels in dissimilar (PHS-DP) and similar (PHS-PHS, DP-DP) pair combinations have been analyzed. Results indicated that the ultimate tensile strength (UTS) of the dissimilar pair PHS-DP achieves a similar strength to the DP-DP joint, whereas the elongation was similar to that of the PHS-PHS weldment. The failure location of the tensile specimens was expected and systematically observed at the tempered and softer sub-critical heat-affected zone (SC-HAZ) in all welded conditions. Compressive residual stresses were consistently observed along the weldments in all specimens; the more accentuated negative RS were measured in the PHS joint attributed to the higher volume fraction of martensite; furthermore, the negative RS measured in the fusion zone (FZ) could be well correlated to weld restraint due to the sheet anchoring during the welding procedure, despite the presence of predominant ferrite and pearlite microstructures. Full article

This research provides a detailed investigation into the mechanical properties and microstructural evolution of heat-resistant steel P92 subjected to both initial (i) welding procedures and simulated (ii) repair welding. The study addresses the influence of critical welding parameters, including preheating temperature, heat input, and post-weld heat treatment (PWHT), with a particular emphasis on the metallurgical consequences arising from the application of repair welding thermal cycles. Through the analysis of three welding probes—initially welded pipes using the PF (vertical upwards) and PC (horizontal–vertical) welding positions, and a PF-welded pipe undergoing a simulated repair welding (also in the PF position)—the research compares microstructure in the parent material (PM), weld metal (WM), and heat-affected zone (HAZ). Recognizing the practical limitations and challenges associated with achieving complete removal of the original WM under the limited (in-field) repair welding, this study provides a comprehensive comparative analysis of uniaxial tensile properties, impact toughness evaluated via Charpy V-notch testing, and microhardness measurements conducted at room temperature. Furthermore, the research critically analyzes the influence of the complex thermal cycles experienced during both the initial welding and repair welding procedures to elucidate the practical application limits of this high-alloyed, heat-resistant P92 steel in demanding service conditions. Full article

Ultra-high strength steel (UHSS) contributes significantly to lightweight design, environmental compatibility and lower fuel consumption. However, it is essential to maintain excellent mechanical properties in terms of structural integrity, strength and ductility after the applied welding process. In this study, the effect of post-welding heat treatments on the welding of UHSS S1100MC was investigated in order to compensate for the deterioration in toughness that occurred as a result of joining by electron beam welding. Electron beam welding (EBW) provides high energy density and therefore relatively low heat input compared to arc welding. However, the narrow fusion zone (FZ) and heat-affected zone (HAZ) may have insufficient toughness values due to rapid cooling of the joint. In order to protect the relationship between strength and toughness, both the material and the joint were subjected to heat treatment at 500, 650 and 750 °C temperatures for 2 h and were cooled in the furnace. Microstructural characterization and mechanical testing, namely hardness, Charpy impact and tensile tests, were performed to correlate the influence of post-weld heat treatment on the microstructural formation and the corresponding mechanical properties. While the material and the joint maintained their hardness values at 500 °C of around 412 ± 15 HV_0.2, there was an approximately 8% decrease in hardness to 378 ± 18 HV_0.2 at 650 °C. At 750 °C, it dramatically lost its high hardness properties, resulting in a low 178 ± 9 HV_0.2. However, direct quenching from the austenitic temperature resulted in fresh martensite, which provided both the required strength and toughness values in the EBW joint. With a hardness of 437 HV_0.2, a tensile strength of 1345 MPa and a fracture elongation of more than 9%, superior mechanical properties could be achieved. Full article

This investigation explores the application of supervised machine learning regression approaches to predict various responses, including penetration, bead width, bead height, hardness, ultimate tensile strength, and percentage elongation in autogenous TIG-, A-TIG-, and TIG-welded joints of SS304H, which is considered as an advanced high-temperature resistant material. The machine learning (ML) models were constructed based on the data gathered from 50 experimental runs, considering eight key input variables: gas flow rate, torch angle, filler material, welding pass, flux application, root gap, arc gap, and heat input. A total of 80% of the collected dataset was used for training the models, while the remaining 20% was reserved for testing their performance. Six ML algorithms—Artificial Neural Network (ANN), K-Nearest Neighbors (KNN), Support Vector Regression (SVR), Random Forest (RF), Gradient Boosting Regression (GBR), and Extreme Gradient Boosting (XGBoost)—were implemented to assess their predictive accuracy. Among these, the XGBoost model has demonstrated the highest predictive capability, achieving R² scores of 0.886 for penetration, 0.926 for width, 0.915 for weld bead height, 0.868 for hardness, 0.906 for ultimate tensile strength, and 0.926 for percentage elongation, along with the lowest values of RMSE, MAE, and MSE across all responses. The outcomes establish that machine learning models, particularly XGBoost, can accurately predict welding characteristics, marking a significant advancement in the optimization of TIG welding parameters. Consequently, integrating such predictive models can substantially enhance the precision, reliability, and overall efficiency of welding processes. Full article

Magnetic pulse welding (MPW) is a promising solid-state joining process that utilizes electromagnetic forces to create high-speed, impact-like collisions between two metal components. This welding technique is widely known for its ability to join dissimilar metals, including aluminum, steel, and copper, without the need for additional filler materials or fluxes. MPW offers several advantages, such as minimal heat input, no distortion or warping, and excellent joint strength and integrity. The process is highly efficient, with welding times typically ranging from microseconds to milliseconds, making it suitable for high-volume production applications in sectors including automotive, aerospace, electronics, and various other industries where strong and reliable joints are required. It provides a cost-effective solution for joining lightweight materials, reducing weight and improving fuel efficiency in transportation systems. This contribution concerns an application for the automotive sector (body-in-white) and specifically examines the welding of AA6082-T6 aluminum alloy with HC420LA cold-rolled micro-alloyed steel. One of the main aspects for MPW optimization is the determination of the process window that does not depend on the equipment used but rather on the parameters associated with the physical mechanisms of the process. It was demonstrated that process windows based on contact angle versus output voltage diagrams can be of interest for production use for a given component (shock absorbers, suspension struts, chassis components, instrument panel beams, next-generation crash boxes, etc.). The process window based on impact pressures versus impact velocity for different impact angles, in addition to not depending on the equipment, allows highlighting other factors such as the pressure welding threshold for different temperatures in the impact zone, critical transition speeds for straight or wavy interface formation, and the jetting/no jetting effect transition. Experimental results demonstrated that optimal welding conditions are achieved with impact velocities between 900 and 1200 m/s, impact pressures of 3000–4000 MPa, and impact angles ranging from 18–35°. These conditions correspond to optimal technological parameters including gaps of 1.5–2 mm and output voltages between 7.5 and 8.5 kV. Successful welds require mean energy values above 20 kJ and weld specific energy values exceeding 150 kJ/m². The study establishes critical failure thresholds: welds consistently failed when gap distances exceeded 3 mm, output voltage dropped below 5.5 kV, or impact pressures fell below 2000 MPa. To determine these impact parameters, relationships based on Buckingham’s π theorem provide a viable solution closely aligned with experimental reality. Additionally, shear tests were conducted to determine weld cohesion, enabling the integration of mechanical resistance isovalues into the process window. The findings reveal an inverse relationship between impact angle and weld specific energy, with higher impact velocities producing thicker intermetallic compounds (IMCs), emphasizing the need for careful parameter optimization to balance weld strength and IMC formation. Full article

The automotive and aerospace industries increasingly rely on lightweight, high-strength materials to improve fuel efficiency, making the joining of dissimilar metals such as aluminum and steel both beneficial and essential. However, a major challenge in these joints is the formation of brittle intermetallic compounds (IMCs) at the interface, even when using low heat-input solid-state welding methods like friction stir welding (FSW). Furthermore, IMC growth at elevated temperatures significantly limits the service life of these joints. In this study, an intermediate layer of stainless steel was deposited on the steel surface prior to FSW with aluminum. The resulting Al–Steel joints were subjected to heat treatment at 400 °C and 550 °C to investigate IMC growth and its impact on mechanical strength, with results compared to conventional joints without the intermediate layer. The intermediate layer significantly suppressed IMC formation, leading to a smaller reduction in mechanical strength after heat treatment. Joints with the intermediate layer achieved their highest strength (350 MPa) after heat treatment at 400 °C, while conventional joints exhibited their highest strength (225 MPa) in the as-welded condition. At 550 °C, both joint types experienced a decline in strength; however, the joint with the intermediate layer retained a strength of 100 MPa, whereas the conventional joint lost its strength entirely. This study provides an in-depth analysis of the role of IMC growth in joint strength and demonstrates how the intermediate layer enhances the thermal durability and mechanical performance of Al–Steel joints, offering valuable insights for their application in high-temperature environments. Full article

This study explores the friction stir welding (FSW) of thin aluminum sheets, focusing on alloys 1050 and 5754. FSW, a solid-state joining technique, offers advantages like minimal deformation and high joint strength, but optimizing welding parameters is crucial for sound welds. In order to investigate the optimum welding parameters, the Taguchi method was employed, in which key parameters such as rotational and welding speed were optimized to enhance tensile strength and weld quality. The tensile testing of the welded specimens revealed that the optimal combination—1000 RPM rotational speed and 250 mm/min welding speed—produced the highest tensile strength and weld quality. The results highlight the importance of parameter optimization in ensuring strong, stable welds, with rotational speed having the most significant influence. Additionally, excessive rotational speeds were found to weaken welds due to excessive heat input, while a slower welding speed contributed to greater weld stability. Full article

The research and related tests aimed to investigate the effect of different heat inputs on the microstructure and properties of the joint when using laser-backing welding for X80 steel, with the purpose of guiding a reasonable adjustment of heat inputs to obtain a sound and high-quality joint, and ultimately laying the foundation for the engineering application of laser-backing welding. The fiber-laser-backing welding is performed on a 22 mm thick X80 steel, before which a groove is prepared and assembled; joints were obtained under different heat inputs (162, 180, 210, 270 J/mm) with orthogonal combinations of laser power and welding speed. The microstructure and properties of the joints were characterized by using an optical microscope, scanning electron microscope, and microhardness tester. According to this investigation, the morphology of the joint is directly affected by the heat input, and insufficient heat input (<180 J/mm) will lead to an unacceptable weld profile. The width of the weld and heat-affected zone gets bigger as the heat input increases. The hardness nephograms of the joints under different heat inputs show that the weld has the highest hardness, followed by the coarse-grain heat-affected zone and the fine-grain heat-affected zone, sequentially. The less heat input, the lower the joint hardness; when the heat input increases to 270 J/mm, the coarse-grain zone near the fusion line shows obvious hardening. In addition, heat input also affects the impact toughness of the weld. The grain size of X80 steel with a lower content of niobium easily becomes coarse under excessive heat input (270 J/mm), resulting in the degradation of the grain-boundary slip ability; hence, the impact toughness of the joint deteriorates. The optimal heat input of 210 J/mm was identified, achieving a grain size of nearly 14 µm and providing a balanced combination of lower strength and higher impact toughness. Full article

This study investigates the effects of molybdenum (Mo) and boron (B) on the microstructures and impact properties in the coarse grain heat-affected zone (CGHAZ) of a low-carbon V-Ti-N steel. The results demonstrate that, at a heat input of up to 75 kJ/cm, the addition of Mo alters the microstructure of the CGHAZ, transforming it from a polygonal ferrite (PF) + degraded pearlite (DP) composition to a granular bainite (GB) + a small amount of acicular ferrite (AF). This transformation increases the impact energy from 20 J to 35 J. Furthermore, with the Mo/B composite addition, the CGHAZ microstructure was refined due to the formation of a large number of acicular ferrites, and the mean equivalent diameter (MED_MTA≥15°) decreased from 7.9 μm to 4.2 μm. Consequently, the impact toughness of the CGHAZ increased from 35 J to 111 J. The correlation between the Mo/B elements, microstructure and impact toughness was investigated in detail. The findings of this study have the potential to generate novel ideas for the advancement of steel materials in the context of high heat input welding. Full article

Aiming at the requirement of high stress ratio reinforcement in space steel structures, a novel method for enshancing the load-bearing capacity of casings through indirect welding to produce a reinforced steel pipe is introduced. To investigate how the mechanical properties of steel pipe members change when reinforced using this method, a series of welding reinforcement axial compression tests were designed, incorporating local reinforcements at various positions and with different initial stress ratios. By comparing the reinforced specimens with those left unreinforced, we obtained insights into the failure modes, ultimate bearing capacities, and strain data of the steel pipes. To further validate the findings, 236 finite element models were developed. These models allowed for a comprehensive analysis of the numerical results alongside the experimental data, taking into account the thermal effects of welding. Quantitative analyses were performed to assess the impact of the initial stress ratio, initial defects, welding heat effects, slenderness ratio, the area ratio between the reinforcement and the pipe, and the length of the reinforcement on the ultimate bearing capacity of the reinforced members. The findings indicate that residual stresses resulting from the welding process have a minimal influence on the ultimate bearing capacity. The method maintains over 75% of its efficiency even at initial stress ratios up to 0.8. Additionally, the study elucidates the rules governing the impact of localized reinforcement on the mechanical properties of loaded steel pipe members. Combining the theoretical calculations with numerical simulations, an empirical formula for estimating the ultimate bearing capacity of the reinforced pipe specimens was derived. The relative error of the formula is less than 10% with the experimental outcomes and the finite element analysis results thereby offering a reliable tool for engineering applications. Full article

The development of clean energy resources, including hydro power, plays an important role in protecting the global environment. Multi-layer bellows are key components and are widely used in hydro power plants. Due to the special multi-layer structures, conventional arc welding is prone to the defects of pores and insufficient fusion when fabricating or repairing such bellows. Precise laser welding with a high energy density and a low heat input has the potential to join multi-layer bellows in a high-quality manner. In this study, a comparative investigation was conducted on the arc welding and laser welding of multi-layer 316L stainless steel sheets and B610CF high-strength steel plates regarding the weld quality, microstructure and tensile properties. The results show that laser-welded joints produced a narrower heat-affected zone and a full weld without visible defects. Compared with arc welding, laser welding had more equiaxed grain regions in the fusion zone and a homogeneous elemental distribution in the heat-affected zone. This led to a more reliable welded joint using laser welding. Full article

The boiling point of metals is dependent on the ambient pressure. Therefore, in laser-based fusion welding and additive manufacturing processes, the resulting process regime, ranging from heat conduction welding to the keyhole mode, is also influenced by the process pressure. While laser welding deliberately uses reduced process pressures to achieve the keyhole mode with a lower laser power input as well as a more stable keyhole, there are no positive findings on the laser powder bed fusion process (PBF-LB/M) under vacuum conditions so far. Furthermore, the literature suggests that the process window is significantly reduced, particularly in the high vacuum regime. However, this work demonstrates that components made of the ferritic steel 22NiMoCr3-7 can be successfully manufactured at low process pressures of ${2 \times 10}^{-2} \mathrm{mbar}$ using a double-scanning strategy. The strategy consists of a first scan with a defocused laser beam, where the powder is preheated and partially sintered, followed by a second scan with a slightly defocused laser beam, in which the material within a single layer is completely melted. To test this manufacturing strategy, 16 test cubes were manufactured to determine the achievable relative densities and tensile specimens were produced to assess the mechanical properties. Metallographic analysis of the test cubes revealed that relative densities of up to 98.48 ± 1.43% were achieved in the test series with 16 different process parameters. The tensile strength determined ranged from 722 to 724 MPa. Additionally, a benchmark part with complex geometric features was successfully manufactured in a high vacuum atmosphere without the need for a complex parameterization of individual part zones in the scanning strategy. Full article

In order to find the optimal heat input for simulating the welding of the coarse-grained heat-affected zone (CGHAZ) of a novel Q690 MPa V-N microalloyed medium and heavy plate, the study investigated the precipitation of V (C, N), microstructural changes, and impact toughness under five different heat inputs (E). The results show that in the CGHAZ, as the heat input increases, the dominant microstructure changes from intragranular acicular ferrite (IGAF) and lath bainitic ferrite (LBF) to polygonal ferrite (PF) and a small amount of IGAF. At the same time, the area fraction of the brittle phase martensite/austenite (M/A) constituents increased from 4.96% to 7.95% as heat input increased, and the microhardness difference between the M/A constituents and the matrix significantly increased. In addition, with the E increases, the fraction of high-angle grain boundaries (HAGBs), which can hinder crack propagation, increases from 59.2% to 62.2% and then decreases from 62.2% to 49.3%. Moreover, the impact toughness of the simulated CGHAZ of the Q690 MPa V-N microalloyed medium and heavy plate first increases from 62 J to 100 J and then decrease to 20 J. Full article

High-strength low-alloy (HSLA) steels have garnered significant attention owing to their widespread applications across various industries, with weldability being a particularly critical aspect. However, the impact toughness of the coarse-grained heat-affected zone (CGHAZ) remains a notable challenge under high-heat-input welding conditions. Despite existing research acknowledging the beneficial effects of micro-alloying elements on steel properties, there are still numerous uncertainties and controversies regarding the specific influence of these elements on the microstructure and impact toughness of the CGHAZ under specific welding conditions. To address this issue, this study presents a comprehensive review of the impact of common micro-alloying elements on the microstructure and toughness of the CGHAZ during high-heat-input welding. The results indicate that elements such as cerium, magnesium, titanium, vanadium, nitrogen, and boron significantly improve the toughness of the CGHAZ by promoting intragranular nucleation of acicular ferrite and inhibiting the coarsening of austenite grains. In contrast, the addition of elements such as aluminum and niobium adversely affect the toughness of the CGHAZ. These findings offer crucial theoretical guidance and experimental evidence for further optimizing the welding performance of HSLA steels and enhancing the impact toughness of the CGHAZ. Full article