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The study aims to provide firsthand knowledge on finite element simulation (FES) of double-side laser welded (LW) stainless steel 304 (SS-304) thick plates used for automobile application. Double-side welding technique is an idea of achieving complete penetration with minimal heat input. The microstructural evaluation revealed the presence of dendritic growth that results in the enhancement of tensile strength (TS) for the welded sample. There is a slight increase in the delta ferrite content in weldment. The change in microstructure is due to thermal history during solidification. The TS of base metal (BM) was $542\pm 5.1$MPa whereas the welded sample exhibited strength of $554\pm 2.3$MPa. FES was successfully employed to simulate TS with error percentage less than 1.

The alloy aluminum of 5000 series will have relatively high strength through solid solution strengthening of Mg. However, when laser welding the 5000 series aluminum alloys, the Mg is selectively evaporated by welding heat due to its low melting and vaporization points, resulting in a reduction in the strength of welds. Therefore, laser welding application is difficult because of such a reduction in strength${}^1,2$ [M. Peel, A. Steuwer, M. Preuss and P. J. Withers, Acta Mater. 51, 4791 (2003); A. Haboudou, P. Peyre, A. B. Vannes and G. Peix, Mater. Sci. Eng. A 363, 40 (2003)]. In this paper, welding experiments were carried out using laser and laser–arc hybrids on aluminum alloy 5083 with 8-mm thickness. Tensile testing, scanning electron microscopy (SEM) analysis and electron probe microanalyzer (EPMA) analysis were carried out on specimens on which the laser and laser–arc hybrid weldings were performed. According to the tensile test results, the tensile strength during laser–arc hybrid welding was greater than 85% of the parent metal. In addition, EPMA analysis showed that the strength of the laser–arc hybrid welds was maintained by supplementing the optional evaporating Mg element, since they use the filler wire.

The protective coatings on laser-welded joints of Zr–1Nb alloy were prepared by the micro-arc oxidation (MAO) process. The morphology, microstructure and phase composition of MAO coatings at different regions of Zr–1Nb alloy laser-welded joints were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion behaviors of the coatings. The MAO coatings at the fusion zone (FZ) and heat-affected zone (HAZ) were smooth with some small holes, while MAO coatings at base metal (BM) were relatively rough with large holes. The cross-sectional topography at FZ coatings was quite dense with less distribution of pores and cracks, which can effectively improve the protective properties of the coatings. HAZ coatings were divided into outer loose layer and inner dense layer. The BM coating layer possessing many holes was a typical sparse layer structure. The phase compositions of welded joints treated by MAO were diverse at different zones of the joints, but all of them consisted of the monoclinic ZrO₂ and tetragonal ZrO₂ phases. The coatings of FZ had the best corrosion resistance, compared with HAZ and BM. The results of EIS indicated that the thickness and defects of the inner compact layer played a key role in improving the corrosion resistance of the MAO coatings on the surface of the Zr–1Nb alloy laser-welded joints.

In this paper, stainless steel was welded by active flux-aided laser welding method. The effects of single active flux (Cr₂O₃, SiO₂ and TiO₂) and composite active flux on laser welding were studied. In the welding process, laser plasma behavior was recorded by a high-speed imaging system. The results show that, with the addition of active flux, the absorption of laser energy and melting efficiency increase. In the laser power of 750 W, effects of active flux on weld depth to width ratio are given by the order: composite active flux $>$ SiO${}_2>$ Cr₂O${}_3>$ TiO₂. The effect of composite active flux is the most significant and it can increase the weld depth to width ratio to 85%. Active flux can restrict the laser plasma. With the addition of composite active flux, the projected area of laser plasma obtained obviously reduced, and it can be reduced by 41.39%. Active flux cannot obviously change the main components in weld zone, but can change the grains of austenite and ferrite.

Laser welding has the benefit of hardly causing welding deformation as it requires less heat input than existing welding methods. The heat input is determined by the laser output and welding speed, and the penetration depth, bead width, joining length, and bead shape are varied depending on these two welding parameters. In this study, bead and lap welding were performed on a thin pure titanium plate with a thickness of 0.5 mm using a disk laser with a maximum output of 3.3 kW. Weldability was evaluated by observing the penetration depth, bead width, joining length, and bead shape for different laser outputs and welding speeds. Results show that a weld zone with excellent joining length can be obtained for an output of 1.1 kW and speed of 2.5 m/min, as well as for an output of 1.3 kW and speed of 3.5 m/min in lap welding. Tensile-shear test was conducted with the specimens under these two conditions to investigate their mechanical characteristics.

The high energy density beam welding techniques, such as laser and electron beam welding process, have been widely used in industrial applications. In this study, the butt structures of Ti-6Al-4V alloys with the thickness up to 8 mm are successfully joined by the laser welding process. The macromorphology and microstructures of the welded joints are investigated by a scanning electron microscope (SEM). The penetration increases from 5.91 mm to 9.37 mm with the decrease of welding speed from 1.2 m/min to 0.8 m/min under the condition of equal laser power. The acicular ${\alpha }^{\prime }$ is formed in the fusion zone, resulting from high cooling rate during the process. The metallurgical porosity formation is proposed by investigating the distribution of Al and H elements around the pores. It is concluded that the pores in the weld bead are induced by aluminum vapor and hydrogen gas from the molten pool. The diameter of metallurgical pore has a tendency to increase with the decrease of welding speed.

A 4 mm thick heat-treated aluminum alloy AA 6061-T6 has been butt welded in 1 G position using a 12-kW disk laser. A novel high magnesium content filler rod ER 4943 belonging to the 4xxx series of aluminum alloys has been used to investigate its effects on microstructure, mechanical properties and alloying elements segregation in the fusion zone. The results have also been compared with an autogenous laser butt welded joint case. A solidified microstructure has been analyzed by EBSD. It was found that additional solute content brought by filler rod into the molten pool caused a higher proportion of equiaxed grain zone after solidification due to an enhanced constitutional supercooling ahead of solid/liquid interface. For an autogenous butt welded joint, the columnar morphology sustained for a longer period and a narrower equiaxed grain zone were observed. Point analysis by an EDS revealed a higher retention of magnesium and silicon inside the solid solution with filler rod welding. In addition, the area map of magnesium also observed a denser distribution of magnesium inside the fusion zone. Both hardness and tensile strength of filler rod welded joint were higher than without filler rod welding. It is believed that a higher proportion of equiaxed grains and additional solute content within the solid solution are the primary causes of higher mechanical properties owing to hampered dislocation motion. The much desirable results obtained in terms of microstructure and mechanical properties could be of great significance to the welding industry.

This paper investigates the impact of heat input and post-weld aging behavior at different temperatures on the laser paper welded maraging steel grade 250. Three different levels of heat inputs were chosen and CO₂ laser welding was performed. Aging was done at six different temperatures: 360${}^{\circ }$C, 400${}^{\circ }$C, 440${}^{\circ }$C, 480${}^{\circ }$C, 520${}^{\circ }$C and 560${}^{\circ }$C. The macrostructure and microstructure of the fusion zone were obtained using optical microscope. The microhardness test was performed on the weld zone. Tensile tests and impact tests were carried out for the weld samples and different age-treated weld samples. Fracture surfaces were investigated by scanning electron microscopy (SEM). Microhardness values of the fusion zone increased with increasing aging temperature, while the base metal microhardness value decreased. Tensile properties increased with aging temperature up to 480${}^{\circ }$C and reduced for 520${}^{\circ }$C and 560${}^{\circ }$C. This was mainly due to the formation of reverted austenite beyond 500${}^{\circ }$C. XRD analysis confirmed the formation of reverted austenite.

In this work, attempt is made to carry out post weld heat treatment (PWHT) on NiTinol samples using laser power source. Initially, 1mm thick NiTinol sheets were welded in butt joint position using Ytterbium: Yttrium aluminum garnet (Yb: YAG) laser power source. Laser welding was carried out in continuous mode, and the quality of the weld was assessed with respect to phase transformation temperatures, microhardness, tensile strength, and corrosion resistance. To improve the quality of the welded samples, PWHT was done by passing a laser beam over the welded samples. It was found that PWHT had a significant effect on the phase transformation temperatures, microhardness, tensile strength and corrosion behavior of the welded NiTinol joints.

In this paper, an effort is made to determine the optimized parameters in laser welding of Hastelloy C-276 using Artificial Neural Network (ANN) and Genetic Algorithm (GA). CO₂ Laser welding was performed on a sheet of thickness 1.6mm based on Taguchi L27 orthogonal array. Laser power, welding speed and shielding gas flow rate were chosen as input parameters and Bead width, depth of Penetration and Microhardness were measured for assessing the weld quality. ANN was applied for modeling the welding process parameters i.e. heat input, welding speed and gas flow rate. Various learning algorithms such as Batch Back Propagation (BBP), Incremental Back Propagation (IBP), Quick Propagation (QP) and Levenberg–Marquardt (LM) were comprehensively tested for estimating the output parameters and a comparison was also made among them, with respect to prediction accuracy. BBP method was found to be the best learning algorithm. Experimental validation test was performed based on the ANN and GA predicted optimized responses and this welding input parameters provided satisfactory weld metal characteristics in terms of penetration depth, bead width and microhardness.

Duplex stainless steel (DSS) welding is critical for producing structures and components in a variety of industries. Because traditional optimization approaches cannot manage the complexity of welding, additional solutions must be investigated. This study addresses the need for a systematic exploration of the welding parameters affecting the quality and performance of DSS butt joints, specifically employing fiber laser welding. This study focuses on butt joints in UNS S32304 and 304L using a fiber laser. Welding process parameters were systematically varied, including laser power, scanning speed, beam diameter, and focal position. To efficiently examine the parameters in the design space, the response surface methodology (RSM) with Box–Behnken design (BBD) was used. The combination of the specific parameter values used in the 7th run (Laser Power: 1600 W, Scanning Speed: 2000 mm/min, Beam Diameter: 1.5 $\mu$m, Focal Position: 30 mm) led to better yield point stress (YPS), maximum tensile stress (MTS), break stress (BS) and reduction in area (RA). ANOVA and lack of fit analysis confirmed the significance of the experiment. In particular, the selected welding parameters significantly influenced all responses. A hybrid machine learning method of deep neural network (DNN) and human eye vision algorithm (HEVA) was used for predicting weld quality during laser beam welding (LBW). The hybrid DNN-HEVA consistently outperformed other optimization methods (RSM-BBD, FNN, CNN, and RNN) across key welding quality parameters. High $R$² values (0.9922, 0.9962, 0.9983, and 0.9907) indicated a strong correlation between predicted and actual values for all calculated responses. Lower RMSE, MSE, and MAE values were also highlighted in the precision of predicted values to the experimental data.

Carbon nanotubes (CNTs) were welded on the surface of thermoplastic polypropylene (PP) substrate by laser irradiation and then manganese dioxide (MnO₂) was deposited on the surface of CNTs by electrochemical method to prepare CNTs/MnO₂ flexible electrodes (L-CM). The microstructure and morphology of CNTs/MnO₂ composites were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The results showed that CNTs were welded on the surface of the substrate, adhering to each other to form a porous network structure. In addition, there were distinct small protrusions on the surface of CNTs, indicating that MnO₂ had been successfully deposited on the surface of CNTs. Cyclic voltammogram (CV), galvanostatic charge/discharge (GCD) and electrochemical impedance spectroscopy (EIS) techniques were employed to investigate the electrochemical performance of the composites. Compared with CNTs/MnO₂ composite prepared via compaction (denoted as C-CM), L-CM composite prepared under the laser power of 0.75W (denoted as L-CM75) showed a larger capacitance of 214.6Fg${}^{-1}$ at the current density of 0.5Ag${}^{-1}$ and displayed excellent bendability, demonstrating capacitance retention of approximately 89.6% after 1000 bending cycles. The excellent performance of L-CM75 may be attributed to the fact that the CNTs welded on the substrate have formed an effective conductive network whose porous structure can facilitate easy access of electrolytes to the electrode, which results in enhancement of the electrochemical performance of L-CM75.

Laser welding is a suitable joining technique for shape memory alloys (SMAs). This paper reports the existence of shape memory effect (SME) on laser welded NiTi joints, subjected to bending tests, and correlates this effect with the microstructural analysis performed with X-ray diffraction (XRD). All welded samples were able to recover their initial shape after bending to 180°, which is a remarkable result for industrial applications of NiTi involving laser welding.

Cellular shape memory alloys (SMAs) are very promising smart materials able to combine functional properties of the material with lightness, stiffness, and damping capacity of the cellular structure. Their processing with low modification of the material properties remains an open question. In this work, the laser weldability of CuZnAl SMA in the form of open cell foams was studied. The cellular structure was proved to be successfully welded in lap joint configuration by using a thin plate of the same alloy. Softening was seen in the welded bead in all the investigated ranges of process speed as well as a double stage heat affected zone was identified due to different microstructures; the martensitic transformation was shifted to higher temperatures and the corresponding peaks were sharper with respect to the base material due to the rapid solidification of the material. Anyways, no compositional variations were detected in the joints.

Coupling of highly elliptical laser diode emission into single mode fiber using two spherical ball lenses is investigated and the effectiveness of the mode matching with the circular mode field of the fiber is realized. Coupling efficiency is theoretically analyzed by employing ray and Gaussian beam optics. A 100% coupling efficiency is obtained at an optimum working distance of 3.5 mm. the coupling efficiency is found to be largely affected by the angular, lateral and transversal offsets. It can also be controlled significantly by optimizing the lenses separation distance. The experimental measurements agree with the theoretical calculations. However, the maximum coupling efficiency obtained is around 75% due to some practical limitations regarding the positioning of ball lenses and their separation. From the variations of coupling efficiency with lateral, transversal and angular offsets, the effective mode matching is inferred. Laser welding technique with active alignment facilities have been used in the alignment and attachment of all the coupling components. Laser welding pulse parameters have been optimized for reliable weld yields.

In this paper, comparison of mechanical features of the welded joint in 9Cr-1Mo steel welded by shielded metal arc welding (SMAW), and CO₂ laser welding using Numerical Analysis and Mechanical test, is presented more particularly. The result of residual stress and hardness analyses regarding each welding method shows that CO₂ laser had slightly higher value than SMAW. However, its difference was minute. Charpy impact test on specimens indicated that the impact absorbing energy of CO₂ laser was more than five times higher than SMAW. It has been observed that all specimens in both tensile test and bending test, were fractured in the base metal regardless of welding method

Electron backscatter diffraction (EBSD) was used to study the microstructure and formation mechanism of tailor welded sheet of dissimilar steel. The microstructure of weld zone mainly was matensite, the microstructure of heat affected zone (HAZ) were matensite, bainite and ferrite. The analysis of EBSD showed that the microstructure of weld zone was coarser and it had obvious texture. The microstructure in HAZ consisted of equiaxed grains principally. And there was no obvious preferred orientation. A lot of grain boundary and dislocation improved hardness and reduced plasticity for weld and HAZ. The grains of two kind steels had no significant preferred orientation. A large number of high-angle boundaries made the base metal show good strength and plasticity.

Due to the strict requirements from the government for CO₂ emission of vehicles, Light-Weight design is now one of the most important and popular topic in automotive manufacturing. Therefore, the hot forming steel, as a high strength material, is used for manufacturing of more and more automotive body parts. And the laser is now a mandatory tool in the manufacturing. TRUMPF, as a leader of Laser manufacturing technology, is devoting its effort to improve the existing laser processes, such as 3D laser cutting, laser ablation of Al-Si coating and laser welding of patchwork. Meanwhile, we're also developing new applications for manufacturing of hot forming parts, such as laser softening of the hot forming parts on a certain area for diverse purpose. This paper demonstrates our latest development and new trends of the laser applications for hot forming parts.

Laser welding is widely used for the on-line joining of hot-rolled steel strips for hot stamped steel by steel plants recently. However, the high breaking rate caused by the emergence of hard martensite in weld was a fatal disadvantage. In this paper, the welded joints of hot-rolled strips for 1500 MPa grade hot stamped steel were made through laser filler wire welding and laser welding, and a series of PWHT experiments were further conducted on laser welding joints. The influence of filler wire and PWHT on the microstructure and mechanical performance of welded joints was analyzed. The results showed that weld appearance was refined by wire filling process, while the microstructure of weld was martensite and cupping test results could not meet the requirements still. As for welded joints with PWHT, the microstructure and mechanical performance were not refined when the PWHT temperature was 500 °C. But the cupping test results were much better at 600 °C and 800 °C compared with the as welded states, accordingly, the weld metal microstructure was tempered martensite and ferrite.

In this paper, 0.6mm thick stainless steel plates were welded by YAG pulse laser machine. According to the performance parameters of 304 stainless steel and the preliminary experiments, welding parameters were determined. Laser scanning speed is 36mm/min. After welding, different heat treatment processes were carried out on 304 stainless steel samples. Experimental results show that by water cooling at 1000°C for 60min for welding samples, the microstructure of the weld center is fine and uniform equiaxed grains. The weld edge is columnar crystal that perpendicular to the fusion line and extends to the weld center. The hardness of the weld center is 216.39HV. The tensile strength of welded joint is 375MPa. It is much higher than that of the other heat treatment processes. By the heat treatment process, weld quality of the samples is nice, the interface of the joint achieve metallurgical bonding and has higher mechanical properties.