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In automotive industries, pulsed laser welding has been gaining importance for joining of thin sheet materials for various reasons, e.g., no use of any filler material, precise control over heat input, penetration depth, molten pool shape and short welding cycle. However, improper choice of heat input can lead to the development of weld defects. Hence, the current study is aimed to comprehend the influence of heat input (32.5, 56.25, 72.22 and 92.22 J/mm) on the weld thermal cycle, microstructural evolution and tensile deformation behavior of Nd:YAG pulsed laser-welded dual-phase (DP 780) steel joints in butt configuration. The effect of pulsation on the weld thermal cycles and the corresponding microstructural changes has been studied. It is estimated that the temperatures in the fusion zone (FZ) ranges from 1759 to 1891 K for 32.5 J/mm heat input and 1964 to 2116 K for 72.22 J/mm heat input welds. Depending on heat input microstructures in the FZ containing martensite, bainite and ferrite are changed due to change in the peak temperatures and the cooling rates. Due to softening of FZ and heat-affected zone by tempering of martensite and because of ferrite grain coarsening the yield strength, tensile strength and uniform elongation decreased with an increase of heat input. All welded joints failed in the softened heat-affected zone, and it was found that the amount and distribution of tempered martensite altered the void nucleation mechanism during the tensile deformation. [ABSTRACT FROM AUTHOR]

Pulsed laser beam welding is primarily used to join thin-walled components. The use of 6xxx group aluminum alloys is characterized by good mechanical properties but these alloys are prone to hot cracking during solidification, i.e., requirements regarding strength and tightness, as increasingly important for electromobility related applications, cannot be fulfilled. The solidification rate has been identified as dominant factor in pulsed conduction welding which can be adjusted by the pulse shape, i.e., by varying the beam power over time for a single pulse.Pulse shapes with different, linear ramp-down slopes were studied to describe the interaction between beam power and resulting solidification rate for spot welds. Based on rotationally symmetric conditions of the spot welds, the solidification rate can be measured in radial and vertical directions. The welding process of EN AW 6082 alloy was examined by in situ high-speed synchrotron X-ray imaging at the European Synchrotron Radiation Facility (ESRF) for this reason. Frame rates up to 120,000 Hz and subsequent image analysis allowed in-depth analysis of the solidification processes, their dependence on different spatial directions, and the resulting effects on hot crack formation.

To achieve high quality welding of an AZ31 magnesium alloy sheet, butt experiments are conducted using an Nd:YAG pulsed laser welder to weld the AZ31 magnesium alloy (1 mm). The influence of preheating temperature on the microscopic structure and mechanical performance of AZ31 magnesium alloy pulsed laser welding is studied. Experimental results show that with the rising of preheating temperature, the grain size of an equiaxed crystal in the weld center and columnar crystal at the fusion boundary (FB) first decreases and then increases and reaches the minimum values of 18.89 ± 0.45 and 32.09 ± 1.52 μm, respectively, when preheated at 200 °C. The maximum force and tensile strength increase first and decrease and reach the maximum of 2.32 kN and 193.3 MPa, respectively, when the preheating temperature is 300 °C. Above all, the welds with excellent mechanical performance can be obtained at the preheating temperature of 300 °C. [ABSTRACT FROM AUTHOR]

In this study, thin films of CuInSe2 (CIS) are expeditiously fabricated within 1 s utilizing the pulsed laser welding (PLW) technique. Preceding the PLW process, thin films of InSe (500 nm) are coated with Cu nanosheets of 60 and 120 nm thicknesses using vacuum coating systems. The optimal PLW parameters leading to the formation of CIS films include a pulse width of 1.0 ms, a spot diameter of 2.0 mm, and a repetition frequency of 10 Hz. The resulting CIS films exhibited a well‐crystalline cubic structure with lattice parameters of 5.265 Å. Surface morphology analyses revealed the preferential formation of porous films with varying stoichiometry, a characteristic that can be manipulated by adjusting laser welding parameters. The energy band gap and room temperature electrical conductivity display values of 1.80 eV and 2.06 × 10−5 (Ωcm)−1, respectively. Cu‐rich samples exhibit a wider energy band gap of 1.94 eV and lower electrical conductivity values of 4.78 × 10−7 (Ωcm)−1. The CIS film demonstrates n‐type conductivity attributed to the formation of donor levels centered at 0.24 and 0.10 eV. This study presents an ultrafast method for fabricating CIS films with physical properties compatible with those produced using traditional methods. [ABSTRACT FROM AUTHOR]

Herein, PtInx nanosheets are fabricated by the pulsed laser welding technique (PLW) in an argon atmosphere within seconds from stacked layers of Pt (150 nm) and In (150 nm). Pt/In stacked layers coated by thermal evaporation under a vacuum pressure of 10−5 mbar are exposed to pulsed laser irradiation. During the welding process, the pulse width, repetition frequency and arc voltage of the laser are all varied. It is observed that the formed PtInx alloys are highly sensitive to the laser welding conditions. A new phase of PtInx alloys, referred to as PtIn4, is obtained and shown to favor a monoclinic crystal structure. PtIn4 displayed a high microwave cutoff frequency exceeding 100 GHz and negative capacitance effect. Modeling of the capacitance spectra in accordance with the Drude–Lorentz approach for ac conduction showed that converting stacked layers of Pt/In into thin films of PtIn4 form by PLW improves the electrical conductance and the drift mobility of the films. A 900-fold enhancement in mobility is achieved via the PLW technique. The characteristics of the produced PtIn4 thin films, including the negative capacitance (NC) effects and the cutoff frequency values, make the films attractive candidates for use as the active layer to produce NC thin film transistors and as band filters suitable for 6G technology. [ABSTRACT FROM AUTHOR]

Herein, MgSe alloys with different compositions are fabricated using laser welding techniques within a couple of minutes in an argon atmosphere. The optimum laser welding parameters, which reveal the correct compositional ratios, are determined by varying arc voltage, pulse width, welding frequency, and laser beam diameter. The structure of the MgSe alloy is monoclinic. Additionally, scanning electron microscopy studies have shown that MgSe alloys are least porous and have a layered structure. The electrical resistance of the welded alloys depends on the Mg content in the samples. Measurements from impedance spectroscopy have shown that the alloys can function as band filters, displaying cutoff frequency values of ≈16 GHz for AC signals propagating at a driving frequency of 1.0 GHz with an amplitude of 0.10 V. The properties of the MgSe alloys make them attractive for use in 5G/6G technology applications as band filters. [ABSTRACT FROM AUTHOR]

Abstract We consider an optimal control problem for a single-spot pulsed laser welding problem. The distribution of thermal energy is described by a quasilinear heat equation. Our emphasis is on materials which tend to suffer from hot cracking when welded, such as aluminum alloys. A simple precursor for the occurrence of hot cracks is the velocity of the solidification front. We therefore formulate an optimal control problem whose objective contains a term which penalizes excessive solidification velocities. The control function to be optimized is the laser power over time, subject to pointwise lower and upper bounds. We describe the finite element discretization of the problem and a projected gradient scheme for its solution. Numerical experiments for material data representing the EN AW 6082-T6 aluminum alloy exhibit interesting laser pulse patterns which perform significantly better than standard ramp-down patterns.

Herein amorphous WO3 thin films prepared by the thermal evaporation technique under a vacuum pressure of 10−5 mbar are treated via pulsed laser welding technique (PLW) in an argon atmosphere. An induced crystallization process within one second for a spot of diameter of 2 mm is achieved via this technique. The crystalline films exhibited hexagonal structure and showed cuboid grains of dimensions of (length × width) 4.6 × 1.1 (μm)2. In addition, the PLW treated tungsten oxide thin films exhibited enhanced light absorbability reaching 90 times at 3.09 eV. Moreover in addition to the existing indirect energy band gap (3.50 eV) of WO3 films, the PLW treatment resulted in formation of another direct energy band gap of value of 1.92 eV. The pulsed laser welding of the WO3 films increased the optical conductivity of the films by 66 times and shifted the plasmon frequency from 0.19 to 6.99 GHz. The free charge carrier density also increased by two orders of magnitude. On the other hand, the impedance spectroscopy studies have shown domination of negative capacitance effect in samples treated with PLW technique. The conversion of the structure of the films from amorphous to polycrystalline that is associated with enhanced light absorption and improved optical conduction which is achieved within 41 s for a large area of 1.25 cm2 of the films is accounted as a smart new approach for improving the physical properties of thin films. [ABSTRACT FROM AUTHOR]

Herein, stacked nanosheets of Au (50 nm) and MgSe (100 nm) are fabricated by the thermal evaporation technique and welded by pulsed lasers of wavelengths of 1064 nm within few seconds. Au/MgSe (AMA) and welded Au/MgSe (PLW) interfaces are coated with another Au point contact and employed as microwave resonators. It is observed that both AMA and PLW devices are of amorphous structure. The laser welding technique resulted in formation clusters composed of very dense grains of Mg1.37AuSe1.18 and other clusters composed of Mg1.16Se. In addition, the impedance spectroscopy measurements on these nano-thick devices have shown their novel ability to perform as negative capacitance sources and as band-stop filters. The pulsed laser welding of these microwave resonators increased their ac conductivities by increasing the hopping sites in the devices. The density of localized states near the Fermi level is increased by ~ 21% and the scattering time constant between hopping sites is shortened via laser welding. As microwave resonators, the pulsed laser welding process shifted the notch frequency from 1.0 to 2.16 GHz, improved the negativity of the capacitance, increased the return loss values and lowered the voltage standing wave ratios to 1.0. The features of the AMA microwave resonators before and after the pulsed laser welding nominate them for use as band-stop filters and as negative capacitance sources. [ABSTRACT FROM AUTHOR]

We consider an optimal control problem for a single-spot pulsed laser welding problem. The distribution of thermal energy is described by a quasilinear heat equation. Our emphasis is on materials which tend to suffer from hot cracking when welded, such as aluminum alloys. A simple precursor for the occurrence of hot cracks is the velocity of the solidification front. We therefore formulate an optimal control problem whose objective contains a term which penalizes excessive solidification velocities. The control function to be optimized is the laser power over time, subject to pointwise lower and upper bounds. We describe the finite element discretization of the problem and a projected gradient scheme for its solution. Numerical experiments for material data representing the EN AW 6082-T6 aluminum alloy exhibit interesting laser pulse patterns which perform significantly better than standard ramp-down patterns. [ABSTRACT FROM AUTHOR]

In-process penetration monitoring of the pulsed laser welding process remains a great challenge for achieving uniform and reproducible products due to the highly complex nature of the keyhole dynamics within the intense laser-metal interactions. The main purpose of this study is to investigate the feasibility of acoustic emission (AE) measurement for penetration monitoring based on acoustic wave characteristics and deep learning. Firstly, a series of laser welding experiments on aluminum alloys were conducted using high-speed photography and AE techniques. This allowed us to in-situ visualize the complete keyhole dynamics and elucidate the generation mechanism of acoustic waves originating from pressure fluctuations at the keyhole wall. Then, an adaptive time-frequency technique namely VMD (Variational Mode Decomposition) was proposed to characterize the acoustic energy distribution among the nine subsignals with low-frequency and high-frequency components under different welding penetrations. Lastly, a novel hybrid model combing CNN (Convolutional Neural Network) and LSTM (Long Short Term Memory) was designed to deeply mine the spatial and temporal acoustic features from the extracted frequency components. Extensive experiments demonstrate that our proposed approach yields a remarkable classification performance with a test accuracy of 99.8% and a standard deviation of 0.21, which obtains a high recognition rate. This work is a new paradigm in the digitization and intelligence of the laser welding process and contributes to an alternative way of developing an efficient end-to-end penetration monitoring system. [ABSTRACT FROM AUTHOR]

Herein lead selenide crystals are fabricated by the pulsed laser welding (PLW) technique within 2 min. The effect of the pulse width on the crystallinity, surface morphology, structural parameters, compositional stoichiometry, electric resistivity and dielectric constant is considered. It is observed that the PLW technique allowed the growth of the crystals in a short period of time. The grown PbSe crystals are mostly cubic containing tetragonal SeO2 as a minor phase. Selenium oxide presented due to the surface oxidation of PbSe after exposing the crystals to air. Remarkable decreases in the electrical resistivity and increase in the dielectric constant by more than two orders of magnitude are achieved as the pulse width increases from 10 to 50 ms. It is observed that the optimum pulse width revealing the highest dielectric constant value is 30 ms. For these samples, a negative capacitance effect is observed for ac signals of frequencies larger than 700 MHz. In addition, analyzing the microwave cut-off frequency spectra for an imposed signal of low amplitude displayed cut-off frequency values larger than 100 GHz at the point where negative capacitance dominates and ac conductance shows a maxima. The features of the PbSe crystals which are prepared in 2 min nominate them for use as negative capacitance sources and band filters suitable for 6G technologies. [ABSTRACT FROM AUTHOR]

Herein, AgMn alloys are prepared by the pulsed laser welding technique in an argon atmosphere. The effect of the laser pulses width and stoichiometric composition of the alloys on the structural, compositional, morphological, and electrical properties are investigated. In contrast to the traditional preparation techniques which reveal cubic structure of AgMn alloys, the pulsed laser welding technique reveals the orthorhombic phase of the alloys. The lattice parameters of the orthorhombic phase of AgMn are α=13.0250Å,b=15.7768Å,c=2.6728Å$\alpha = 13.0250\ \text{\AA} ,\ b=15.7768\ \text{\AA} ,\ c=2.6728\ \text{\AA} $. It is observed that pulse widths of 50 ms are the optimum from preparing these alloys. From an electrical point of view, the AgMn alloys exhibit negative dielectric constant and negative conductance effect in the microwave frequency domain. The impedance spectroscopy analyses in the frequency domain of 0.01–1.80 GHz have shown that AgMn alloys can be employed as band filters with return loss value of ≈16 dB. The features of the AgMn alloys which are achieved by the pulsed laser welding technique nominate them for use as negative capacitance and negative conductance transistors. These devices are suitable for noise reduction and parasitic capacitance cancellation. [ABSTRACT FROM AUTHOR]

• Joining of thermoplastic additive manufactured parts to glass. • Use of nanosecond IR pulsed laser for the development of the glass to PLA joints with an intermediate sacrificial aluminum layer. • Mechanical characterization and Weibull analysis of the joint's shear strength. • Shear strength comparison of laser welded and adhesively bonded lap joints. We present an adhesive free, low-cost and effective solution for joining of thermoplastic additive manufactured parts to glass using an industrial nanosecond IR pulsed fiber laser. We demonstrate the potential of the method by means of laser joints of glass to Polylactic Acid (PLA). The glass to PLA joints are realized via Laser Transmission Welding (LTW) and Laser Direct Welding (LDW) using an intermediate sacrificial thin layer of aluminum. The laser joints are compared with adhesive glass to PLA joints. The mechanical testing involves a thorough strength evaluation by using block shear test method, demonstrating the superior performance of laser-welded joints over conventional adhesive alternatives. The results of these shear tests reveal a remarkable 565 % improvement in shear strength in comparison to the adhesive joints (maximum shear strength of laser bonds: 9.57 MPa). Furthermore, a Weibull statistical analysis is applied to assess the reliability of the joints, disclosing a very high survival probability of the samples under a loading of 4.5 MPa as well as a σ 0 (stress for which the 1/e (37 %) of the samples survive) of 8.15 MPa. [ABSTRACT FROM AUTHOR]

Aluminium alloys exhibit eco-friendly aspects related to global environmental issues, such as almost unlimited recyclability. Nevertheless, some intrinsic characteristics are challenges to explore all their benefits. In the welding process, the high thermal conductivity and low melt point require high control of heat input. Alternatively, the pulsed laser mode provides a sharp beam focus with precise control enabling regulating the energy delivered. In this sense, this present work analysed the effect of pulsed laser welding parameters on 3-mm-thick AA5083 aluminium alloy sheets. Trials targeted to develop sound welds with minimum defect and high penetration depth adopting statistical methods. The optimum parameter arrangement was achieved by varying peak power, spot diameter, and pulse duration. Finally, the best parameter combination was applied using different pulse shapes to mitigate crack formation and pores. As a result, the pulse shape with step-down at the end of each pulse generated crack-free spot welds. [ABSTRACT FROM AUTHOR]

• The effect of laser pulse shapes on Al-Cu dissimilar metals mixing. • Relationship between metals mixing and IMCs formation. • The effect of laser pulse shapes on mechanical and electrical properties of Al-Cu joints. The Nd: YAG laser is utilized to weld 1060 aluminum (Al) and 110 copper (Cu) with a thickness of 0.4 mm. The effect of different pulse shapes on the microstructure, mechanical and electrical properties of Al-Cu lap joints are investigated by using of the optical microscopy, scanning electron microscope (SEM), tensile test device and micro-resistance tester, respectively. This investigation provided a detailed understanding of how the different pulse shapes influence the metal mixing and the formation of intermetallic compounds (IMCs). The results indicate that the pulse shape with an initial preheating phase improved the laser absorption efficiency. Additionally, this pulse shape resulted in less dissimilar metal mixing compared to the pulse shape that maintained the maximum power throughout. Furthermore, the pulse shape in which the laser power was linearly increased and then maintained at maximum power reduced the formation of IMCs at the joint interface. As a result, the joint exhibited mechanical strengths up to 92 % of the Al base material and similar electrical conductivity. The study provides theoretical guidance on how to utilize pulse shape modulation in laser welding to achieve optimal mechanical and electrical properties in typical joints between Al tabs and Cu busbars. [ABSTRACT FROM AUTHOR]

This paper has proposed a parameter estimation method for a laser welding process inherently highly nonlinear as a result of the highly nonlinear inputs and outputs of the system. Hence, a nonlinear system identification method was developed for the laser welding process using the wavelet network nonlinear autoregressive exogenous (ARX) model. The advantage of ARX over the standard nonlinear models is that it not only considers the delayed input and output regressors but also uses nonlinear functions for mapping, thus making ARX a better candidate for the prediction of nonlinear behaviors. In total, nine available datasets for the training and test phases at pulse durations, pulse frequencies, focal lengths, currents, and welding speeds were considered. Five inputs including pulse duration, pulse frequency, focal length, current and welding speed, and temperature as one output were considered. The first eight datasets were utilized for the training phase and one was used for the testing phase. The results showed that the ARX model had an acceptable performance in training and test phases, and it was capable of identifying the nonlinear and time-variant phenomenon of the laser welding process examined in this paper. For instance, most fitness values for austenitic and ferritic steel samples in the training time histories were 97.13 and 97.95, respectively. [ABSTRACT FROM AUTHOR]

In the present study, the optimization of pulsed Nd:YAG laser welding parameters was done on a lap-joint of a 316L stainless steel foil in order to predict the weld geometry through response surface methodology. For this purpose, the effects of laser power, pulse duration, and frequency were investigated. By presenting a second-order polynomial, the above-mentioned statistical method was managed to be well employed to evaluate the effect of welding parameters on weld width. The results showed that the weld width at the upper, middle and lower surfaces of weld cross section increases by increasing pulse durationand laser power; however, the effects of these parameters on the mentioned levels are different. The effect of pulse duration in the models of weld upper, middle and lower widths was calculated as 76, 73 and 68%, respectively. Moreover, the effect of power on theses widths was determined as 18, 24 and 28%, respectively. Finally, by superimposing these models, optimum conditions were obtained to attain a full penetration weld and the weld with no defects.

Tn order to obtain a 0.2 mm-thick NiTi shape memory alloy (NiTi-SMA) welded joint with a small difference in phase transformation temperature between the welded metal and the base metal, it will meet the needs of practical applications. Tn this paper, the Nb element is introduced into the weld by adding welding wire, and the welded joint is aging treated after welding to realize the control of the weld metal phase transition temperature, so that it can reach a level similar to that of the base metal. The results show that the weld metal of NiTi joint with Nb wire is mainly R2 phase, R1 S'phase, NbTi phase, Nb phase and (NiTi，Nb) solid solution, and Ni4Ti3 phase precipitates from weld metal after PWHT at 600°C. Through the compound method of "adding 0.1 0mmNb wire+ PWHT at 600 °C"，weld metal with As and Ms very close to that of NiTi base metal was obtained. [ABSTRACT FROM AUTHOR]

Lithium-ion cell based battery storages are indispensable in many fields of application such as electromobility and stationary energy storage devices. Cylindrical 18650 cells are regularly utilized and connected by cell connectors made of nickel plated steel. Since this setup suffers from high electrical losses and a poor heat removal during operation, copper connectors are demanded more often. For joining the cells and the connectors, laser beam welding offers great potential due to its low energy input and high flexibility. However, challenges arise, as copper materials show a strong reflectivity for infrared wavelengths. Experimental investigations for the contacting of 18650 cells and copper connectors using a spike pulse welding strategy combined with green laser radiation are presented within this study. [ABSTRACT FROM AUTHOR]

Joining metallic alloys can be an intricate task, being necessary to take into account the material characteristics and the application in order to select the appropriate welding process. Among the variety of welding methods, pulsed laser technology is being successfully used in the industrial sector due to its beneficial aspects, for which most of them are related to the energy involved. Since the laser beam is focused in a concentrated area, a narrow and precise weld bead is created, with a reduced heat affected zone. This characteristic stands out for thinner material applications. As a non-contact process, the technique delivers flexibility and precision with high joining quality. In this sense, the present review addresses the most representative investigations developed in this welding process. A summary of these technological achievements in metallic metals, including steel, titanium, aluminium, and superalloys, is reported. Special attention is paid to the microstructural formation in the weld zone. Particular emphasis is given to the mechanical behaviour of the joints reported in terms of microhardness and strength performance. The main purpose of this work was to provide an overview of the results obtained with pulsed laser welding technology in diverse materials, including similar and dissimilar joints. In addition, outlook and remarks are addressed regarding the process characteristics and the state of knowledge.

This study investigated the effects of average power and pulse duration of pulsed laser welding on weld dimensions, microstructure, microhardness and pitting corrosion resistance of 21% Cr ferritic stainless steel. Optical microscopy and scanning electron microscopy (SEM) were used to observe the microstructure of the fusion zone. Microhardness tests and electrochemical measurements were carried out to study the mechanical and pitting corrosion properties, respectively. Results show that the depth of welds dropped firstly and then increased with the pulse duration. The grain size in the fusion zone and heat affected zone (HAZ), and the width of HAZ all increased with the average power, but changed little with the pulse duration. The microhardness of welds decreased with the average power but almost kept constant when the pulse duration was lower than 5 ms. The pitting corrosion resistance of welded joints was weakened with the increase of pulse duration. [ABSTRACT FROM AUTHOR]

The Nd: YAG pulsed laser welding process with different speed and shielding gas was applied on 2205 duplex stainless steel. The effects of different parameters on the microstructural evolutions and mechanical properties were investigated. Four different zones with different secondary austenite contents were observed in the weld microstructure. By changing the shielding gas from argon to nitrogen, the secondary austenite percentage was not significantly varied. The secondary austenite fraction was showed about 38% reduction with increasing the welding speed. The weld penetration depth decreased with changing the shielding gas from argon to nitrogen (about 26% and 14% reduction at speed of 3.8 and 8.3 mm/s, respectively) and increasing the welding speed (about 43% and 34% reduction under shielding gas of argon and nitrogen, respectively). The variations in microhardness values along the weld line were correlated to the microstructural characterizations. Changing the welding speed had no significant effect on the microhardness variations, but changing the shielding gas from argon to nitrogen caused a significant increase of microhardness. [ABSTRACT FROM AUTHOR]

Pulsed laser welding have a wide application in welding of thin sheet because of high intensity of its localized heat source. In the current study, 3 experimental tests with low, medium, and large level of energy and also, the 3D finite element simulation of Nd:YAG pulsed laser welding in thin sheet AISI316L have been done. Thermal analyzes were done with ABAQUS software in transient heat transfer. In order to increase the accuracy of thermal model, heat losses were considered as convection, radiation, and thermal conduction. 3 thermal models with different heat flux distribution as Gaussian surface, Gaussian volume, and conical volume were used. The main aim of this study is the selection of best thermal model between 3 mentioned thermal models to estimate the melt pool geometry with high accuracy. In addition, with defining and applying the shape factor in 3 thermal models, the finite element analyses were carried out in order to enhance the precision of estimated melt pool geometry. After thermal analysis, the melt pool geometry dimensions are extracted for each of the mentioned thermal models and compared with experimental results. Results show that thermal analysis with Gaussian surface model have the melt pool geometry accurately just in welding with low energy. Also, the conical model could estimate the melt pool geometry in all levels of energy with acceptable accuracy. Therefore, the pyramidal thermal model can be selected as the most suitable model for simulating pulsed laser welding in thin steel sheets. [ABSTRACT FROM AUTHOR]

Highlights • The source mechanism for AE generation is the recoil force and thermal vibration. • The AE signals contain valuable information about plasma plume. • AE signals shows the energy characteristics of plasma plume. • AE signals are valuable to evaluate the plasma plume and the weld penetration. Abstract The acoustic emission (AE) signals were detected in real-time during the process of pulsed YAG laser welding. Some characteristic analysis methods, including AE count statistic, root mean square (RMS) waveform calculation and power spectrum distribution, were used to analyze the AE signals. According to the AE signals, the characteristics of plasma plume and penetration of weld bead were studied. The results showed that the source mechanism for AE generation was the recoil force and thermal vibration generated by the plasma plume acting on molten pool. The AE signals detected in welding contained a lot of valuable information about plasma plume. AE count, RMS waveform and power spectrum of AE signals showed the energy characteristics of plasma plume in time and frequency domain. Therefore, AE signals detected in pulsed laser welding had clear correlations with plasma plume, which were valuable to evaluate the plasma plume and the penetration of weld bead. [ABSTRACT FROM AUTHOR]

Welding by laser beams is one of the essential parts of production process in automobile manufacturing used for joining plates. In this paper, for the first time, simulation of pulsed laser welding process of joining stainless steel to low carbon steel was carried out. For this purpose, at first, thermal analysis was carried out by finite element method and with exact definition of thermal resource; temperature profile and the dimensions of the melting area was gained as results. This was followed by mechanical analysis. The thermal analysis results were stored in a mechanical element as history to obtain the thermal conditions of the material. As results of this analysis, the strain of elastic and plastic as well as the amount of residual stress was obtained. The results show that low carbon steel passes through higher range heat in cooling process, because of higher thermal conductivity. Also, low carbon steel saves more residual stress due to higher yield stress. For validation of simulated model, two plates of 304 stainless steel with similar parameters with the simulated model were welded by laser welding. Comparing the results obtained from the experimental model with the simulated model shows a very good agreement. [ABSTRACT FROM AUTHOR]

• He can more effectively suppress the inverse bremsstrahlung absorption. • He can improve the transmittance rate of laser energy. • He can improve the absorption efficiency of materials to laser energy. • A larger gas flow can suppress the electron density and the IB absorption. According to the theory of plasma sheath layer, the charge-voltage of plasma was measured by the principle of plasma probe to investingage the effect of shielding gas on the plasma plume in bead-on-plate welding by pulsed laser. The electron temperature, electron density, IB linear absorption coefficient of plasma and transmittance rate are interrelated and important parameters to estimate the energy absorption mechanism in laser welding. The results showed that Helium atmosphere suppresses the plasma eruption in laser welding more effectively than the Argon atmosphere, which is shown to reduce the electron temperature of plasma and shorten the duration of plasma eruption. Compared with the suppressing effect of Argon atmosphere, Helium atmosphere can more effectively suppress the inverse bremsstrahlung absorption effect of plasma induced in laser welding, improve the transmittance rate of laser energy, so as to improve the absorption efficiency of materials to laser energy, which is conducive to higher welding efficiency. In addition, a larger shielding gas flow can also suppress the increase of electron density and the inverse bremsstrahlung absorption effect of plasma, and increase the transmittance rate of laser energy. So, a larger shielding gas flow in laser welding is beneficial to suppress the plasma eruption either in Helium atmosphere or in Argon atmosphere. [ABSTRACT FROM AUTHOR]

• Pulsed laser welded joints with and without filler strip were achieved respectively. • Filled strips reduced the cooling speed and temperature gradient of the molten pool. • Element segregation and precipitated phase affect the mechanical properties of the joint. • The tensile strength of weld joint is 310.56 ± 2.88 MPa, about 72.3% of the base metal. Al-Li alloy has excellent specific strength and corrosion resistance, which shows a wide application prospect. However, its further application is hindered by the high crack sensitivity. In this work, the 2195 Al-Li alloy sheet filled with strips was welded by pulsed laser. The results showed that the weld joint with nearly no cracks was obtained after the filling of strips. The temperature gradient and cooling speed of the molten pool were reduced by nearly 50% and 42%, respectively. The Cu was segregated at the grain boundaries of the weld joint. The eutectics of the weld were T 1 -Al 2 CuLi and T 2 -AL 6 Cu (Li, Mg) 3 phases. The combination of element segregation and the reduction of the strengthening phases in the weld joint were the main reasons for the decrease of the mechanical properties. The tensile strength of the weld joint could reach 310.56 ± 2.88 MPa. The weld joint was intergranular fracture, belonged to mixed fracture mode. [ABSTRACT FROM AUTHOR]

Abstract The results of joining quasidissimilar NiTi shape memory alloys (i.e. whereas one component is initially in martensite state and the other one is in austenite state at room temperature) in analyzed in view of the possible use of the combined superelastic and shape memory properties in particular devices with application in the biomedical, automotive or aerospace industry. Alloys with the diameter in the range of 400 µm, were welded using Nd:YAG pulsed laser with 25 or 50% overlap for a spot size of 400 µm. The resulting joints were characterized by tensile testing at RT and at temperatures in the transition range of the shape memory alloy wire. The tensile strength of the joint is in the range of 70–75% of the components. It is also shown that the thermomechanical characteristics of both alloys are preserved in the joint and are influenced by the temperature. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

Flow behavior determines the formation and evolution of porosity and other defects in laser welding, but the existing investigations of liquidity of molten pool are restricted by qualitative analysis methods, so it is of great significance to quantitatively characterize the flow patterns and flow characteristics of the pulsed laser welding for understanding the porosity suppression mechanism. A series of welding experiments was carried out by using 1.5 kW slab CO2 laser under a variety of pulse parameters, and the images of molten pool and keyhole were captured by using a high-speed camera during welding. Porosity rate was also obtained by image processing of x-ray inspection of weld joints. The flow characteristics of molten pools including speed and vortices from these images were extracted and analyzed quantitatively. Effects of different pulse frequency and duty ratios on penetration depth, weld width, and flow characteristics of the molten pool were investigated and compared with each other. A three-stage flow pattern of molten pool for pulse laser welding and the respective characteristics of each stage were revealed. The analysis result shows that the velocity at the starting time in a pulse impact phase is about three times of that in the steady-state phase and the primary mechanism for suppression of pores lies in the impact and stirring on molten pool in pulse laser welding. The other suppression mechanisms of pores for welding joints are also discussed. [ABSTRACT FROM AUTHOR]

Pulsed laser welding is a powerful technique especially suitable for joining thin sheet metals. In this study, based on experimental data, pulsed laser welding of thin AISI316L austenitic stainless steel sheet has been modeled and optimized. The experimental data required for modeling are gathered as per Central Composite Design matrix in Response Surface Methodology (RSM) with full replication of 31 runs. Ultimate Tensile Strength (UTS) is considered as the main quality measure in laser welding. Furthermore, the important process parameters including peak power, pulse duration, pulse frequency and welding speed are selected as input process parameters. The relation between input parameters and the output response is established via full quadratic response surface regression with confidence level of 95%. The adequacy of the regression model was verified using Analysis of Variance technique results. The main effects of each factor and the interactions effects with other factors were analyzed graphically in contour and surface plot. Next, to maximum joint UTS, the best combinations of parameters levels were specified using RSM. Moreover, the mathematical model is implanted into a Simulated Annealing (SA) optimization algorithm to determine the optimal values of process parameters. The results obtained by both SA and RSM optimization techniques are in good agreement. The optimal parameters settings for peak power of 1800 W, pulse duration of 4.5 ms, frequency of 4.2 Hz and welding speed of 0.5 mm/s would result in a welded joint with 96% of the base metal UTS. Computational results clearly demonstrate that the proposed modeling and optimization procedures perform quite well for pulsed laser welding process. [ABSTRACT FROM AUTHOR]

In the present study, the effect of parameters of autogenous pulsed Nd: YAG laser welding process on the lap joint of a 316L stainless steel foil with a thickness of 100 µm to be used as bipolar plates of polymeric fuel cell was investigated. For this purpose, the statistical tools, the analysis of variance and the various diagrams were used to analyze the data by response surface methodology. The peak power (130 to 650 W), pulse durability (1.5 to 3.5 ms), and welding frequency (14 to 18 Hz) were considered as input parameters. The mentioned statistical method was able to predict the effect of welding parameters by developing second-order polynomials, so that the total error including the repeatability error and the lack of fit error for shear strength model, weld undercut model, and weld underfill model obtained 2, 8 and 3, respectively. The defects of weld undercut and lack of penetration were identified as most important factors affecting the shear strength. The laser power is as the main parameter in this process and the impact of it on the shear strength of the weld, the weld undercut and the weld underfill is calculated 64, 62 and 66%, respectively. Finally, the maximum shear strength with the value of 522 MPa is achieved at a peak power of 260 W, pulsed duration of 3 ms and welding frequency of 17 Hz. In this case, the weld undercut is determined as 3 micrometers. [ABSTRACT FROM AUTHOR]

Laser - material interactions such as welding, heat treatment and thermal bending generate thermal gradients which give rise to thermal stresses and strains which often result in a permanent distortion of the heated object. This paper investigates the thermal distortion response which results from pulsed laser surface melting of a stainless steel sheet. Pulsed holography has been used to accurately monitor, in real time, the out-of-plane distortion of stainless steel samples melted on one face by with both single and multiple laser pulses. It has been shown that surface melting by additional laser pulses increases the out of plane distortion of the sample without significantly increasing the melt depth. The distortion differences between the primary pulse and subsequent pulses has also been analysed for fully and partially overlapping laser pulses. [ABSTRACT FROM AUTHOR]

Pulsed laser welding was used to weld dissimilar joints in Ti6Al4V/Nb alloys. The effect of heat input on the microstructural characterizations and mechanical properties of the joints was investigated. The experimental results show that underfill defects disappeared in the fusion zone (FZ) as the heat input increased. No intermetallic compounds were formed in the FZ, but a dendritic zone of Ti-rich phases and an island zone of Nb-rich phases were present for all welded joints, indicating that composition segregation occurred in the Ti6Al4V/Nb dissimilar joint. Moreover, the microstructure and mechanical heterogeneity in the FZ of the welded joint increased with increasing heat input. The microhardness of the island area was lower than that of the dendritic zone in the FZ, because it possessed higher levels of Nb. The results of the tensile tests show that the joints fractured at the Nb base metal side, suggesting that the strength of the FZ is higher than that of the Nb base metal. [ABSTRACT FROM AUTHOR]

In this study, the optimization of pulsed Nd:YAG laser welding parameters was done on the lap-joint of a 316L stainless steel foil with the aim of reducing weld defects through response surface methodology. For this purpose, the effects of peak power, pulse-duration, and frequency were investigated. The most important weld defects seen in this method include underfill and undercut. By presenting a second-order polynomial, the above-mentioned statistical method was managed to be well employed to balance the welding parameters. The results showed that underfill increased with the increased power and reduced frequency, it first increased and then decreased with the increased pulse-duration; and the most important parameter affecting it was the power, whose effect was 65%. The undercut increased with the increased power, pulse-duration, and frequency; and the most important parameter affecting it was the power, whose effect was 64%. Finally, by superimposing different responses, improved conditions were presented to attain a weld with no defects. [ABSTRACT FROM AUTHOR]

Pulsed laser welding of TC4 titanium (Ti) alloy to SUS301L stainless steel (SS) has been applied using pure Nb as an interlayer. Microstructures of the joints were analyzed by means of scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Mechanical properties of the joints were evaluated by tensile tests. Based on avoidance of the formation of Ti-Fe intermetallics in the joint, two welding processes for the Ti alloy-Nb-SS joint were introduced. One process was one pass welding involving creation of a joint with one weld zone and a reaction layer separated by remaining unmelted Nb. The weld was formed while the laser was acted on the Ti alloy-Nb interface, and simultaneously, the reaction layer was formed based on interdiffusion and eutectic reaction of Nb and Fe at the Nb-SS interface. The mechanical performance of the joint was determined by the reaction layer at the Nb-SS interface with a tensile strength of 370 MPa. The other was two pass welding involving creation of a joint with two weld zones separated by remaining unmelted Nb, while the laser beam was focused on the Ti alloy-Nb interface and the Nb-SS interface, respectively. At this point, the mechanical performance of the joint was determined by the weld zone formed at the Nb-SS interface with a tensile strength of 171 MPa. [ABSTRACT FROM AUTHOR]

In the present study, the optimization of pulsed Nd:YAG laser welding parameters was done on a lap-joint of a 316L stainless steel foil in order to predict the weld geometry through response surface methodology. For this purpose, the effects of laser power, pulse duration, and frequency were investigated. By presenting a second-order polynomial, the above-mentioned statistical method was managed to be well employed to evaluate the effect of welding parameters on weld width. The results showed that the weld width at the upper, middle and lower surfaces of weld cross section increases by increasing pulse durationand laser power; however, the effects of these parameters on the mentioned levels are different. The effect of pulse duration in the models of weld upper, middle and lower widths was calculated as 76, 73 and 68%, respectively. Moreover, the effect of power on theses widths was determined as 18, 24 and 28%, respectively. Finally, by superimposing these models, optimum conditions were obtained to attain a full penetration weld and the weld with no defects. [ABSTRACT FROM AUTHOR]

In this research, the parameters of pulsed Nd:YAG laser welding on the lap-joint of a 316L stainless steel foil were optimized through the response surface methodology with the aim of enhancing the tensile-shear strength. For this purpose, the effects of peak power, pulse-width, and frequency were investigated. The results showed that the analysis of welding parameters in the form of a simple combination of pulse energy could not completely predict welding properties, and the above-mentioned statistical method could appropriately be employed to balance the parameters by modeling and presenting a second-order polynomial. In this model, with the increased power and pulse-width, the strength first increased and then it decreased, and its maxima occurred at a power of 260 W and a pulse-width of 3 ms. The most important parameters affecting this model have been found to be power and pulse-width with impacts of 65 and 25%, respectively. In addition, microscopic studies showed that decrease in strength was because of the undercut and lack of penetration. [ABSTRACT FROM AUTHOR]

The objective of the present work is to investigate the tensile behavior on laser welded Al-Mg-Sc-Zr in situ nano TiB composite. Al-3.5Mg-0.15Sc-0.075Zr-1TiB composite was melted in a resistance heating furnace. TiB was formed during in situ reaction of KTiF and KBF salt mixture at 750 °C for 60 min. Welding was done using Nd:YAG pulsed laser source JK 600 (GSI make) using a robotic (IRB1410 of ABB) laser set up. The autogenous welding experiments were carried out using some of the significant parameters such as frequency-75 Hz, laser beam energy-8.10 J, pulse width-2.5 ms and welding speed-5 mm/s. It was observed that laser beam power played a major role and lower value of energy with higher repetition rate resulted better and uniform weld bead with full penetration. Five different processing methods were utilized to investigate the mechanical and metallurgical properties namely: (a) as cast (AC), (b) as cast followed by welding (AC + W), (c) as cast followed by aging (AC + A), (d) as cast followed by aging and then welding (AC + A + W) and finally (e) as cast followed by welding and then aging (AC + W + A). The ageing treatment followed was heating the samples at 300 °C for 5 h followed by air cooling. The obtained results infered that apart from the obvious superior properties shown by as cast followed by aging treatment (AC + A: 248 MPa); the AC + W + A specimens showed better properties (235 MPa) along with AC + A + W specimens (226 MPa). The fracture surface analyses revealed the following: (a) the weld region in the laser welded as cast material did not show any TiB in the structure probably due to the fact that temperature experienced during laser welding process might have melted the particles and was dissolved in the solid solution, (b) the interface of the weld-base region showed the presence of few TiB particles which lost their hexagonal shape due to preferential melting along the edges. (c) The fracture morphology of both AC + A + W and AC + W + A specimen's showed typical mixed mode fracture with fine precipitates along the interface. The strength increased in AC + W + A at the expense of ductility due to formation of AlSc precipitates. [ABSTRACT FROM AUTHOR]

Achieving a uniform welding seam with minimum overheating is crucial to obtain high quality joints in laser welding. The classical formula of the overlapping factor for laser pulsed welding was modified by the introduction of empirical corrections from the application of static pulses involving constant energy combinations of laser power and pulse duration. The energy re-allocation in the case of dynamic pulses was studied as a function of the laser displacement speed. Energy optimization criteria aiming the minimization of the energy per length unit or surface unit were introduced. An optimized uniform welding seam with minimum thermal affectation was obtained by means of dynamic pulses. [ABSTRACT FROM AUTHOR]

Pulsed laser welding of TC4 titanium alloy to SUS301L stainless steel with copper sheet as interlayer was studied in this paper. Microstructures of the joints were analyzed by optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The mechanical properties of the joints were measured by nano-indentation test and tension test. Experimental results showed that copper interlayer was helping to decrease the Ti-Fe intermetallics by forming Cu solid solution, CuTi, Cu-Ti, and Cu-Ti in the weld. The composition and microstructure in the weld were uneven, which led to an inhomogeneous distribution of the hardness. The average tensile strength of the joint was 350 MPa, and all the tensile samples fractured in the Cu-Ti layer with a maximum hardness in the weld adjacent to TC4 titanium alloy side. [ABSTRACT FROM AUTHOR]

Pulsed Nd:YAG laser beam welding (P-LBW) and pulsed tungsten inert gas (P-TIG) welding were used to prepare full penetration bead-on-plate weldments of 1.6 mm thick Ti-5Al-2.5Sn alpha titanium alloy sheet. The influence of welding phenomenon on the microstructure, micro-hardness, tensile properties, surface and sub-surface residual stress distribution and deformation and distortion of both the weldments were studied. Higher cooling rate in P-LBW resulted in complete α' martensitic transformation in fusion zone whereas in P-TIG weldment α' and acicular α was formed within equiaxed β matrix due to lower cooling rate. Hardness in fusion zone of P-LBW was higher than that of the fusion zone of P-TIG weldment due to faster cooling rate in P-LBW. The welded zone in both the weldments showed higher hardness and strength than that of the parent metal since a ductile fracture occurred in the un-welded section during tensile testing. Residual stresses in both P-LBW and P-TIG weldments showed similar trend but the distribution was much narrower in P-LBW due to less width of heat affected zone. P-LBW resulted in more nonuniformity in through thickness stress profile because of greater top to bottom width ratio. Less residual stresses, deformation and distortion and superior mechanical properties in P-LBW made the process more feasible than P-TIG for the welding of Ti-5Al-2.5Sn alloy sheet. [ABSTRACT FROM AUTHOR]