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NiTi Shape Memory Alloy (SMA) finds wide applications in high-performance engineering industries such as medical devices, micro-electrical and electronic components, aerospace, aircraft structure, and so on, to name a few. This is owing to its superior properties like shape memory effect (SME), superelasticity, and biocompatibility. However, getting a proper joining of NiTi alloys is hard considering its unique characteristics. Therefore, joining this alloy has been a domain of great attention for scientists. The current research work investigates the weldability of NiTi wires using Laser spot welding. The microhardness and the tensile strength of the weld joint are acquired according to Taguchi's design of experiment. The significance of the control factors (laser power, scan speed, and focal length) is identified through ANOVA, and an ideal factor setting for optimum individual responses is established. Moreover, simultaneous optimisation of multi-performance characteristics is also attempted through Grey Relational Analysis (GRA) method. From the GRA, 300 W laser power, 1 mm/sec scan speed, and 0.5 mm focal position are found to be giving optimum results for both the responses. The result from the confirmation runs showed that the predicted optimal welding parameters improve the individual as well as the multiple performance characteristics. [ABSTRACT FROM AUTHOR]

Quenching and partitioning (Q&P) steels are among the most critical third-generation steels for realizing vehicle weight reduction and improving safety performance. It is critical for the structure durability to have an excellent fatigue life of the welds. In this study, Q&P1180 steel was laser spot welded (LSW) in order to evaluate the microhardness, mechanical properties, and fatigue behavior of its joints, which were compared with resistance spot welding (RSW). In both types of joining methods, the welded zone is composed of lath martensite with high microhardness value. Due to the martensite tempering, the sub-critical heat affected zone of Q&P RSW welds was soften, resulting in a decrease of 52 HV of microhardness than the LSW joint. The presence of stress concentration in the boundary influenced tensile strength and all-welded samples failed in the boundary. Furthermore, the fatigue limit of the RSW joint (1.139 kN) was about 91.5%t of the LSW joint (1.245 kN). Fatigue specimens of the LSW joint failed between the fusion zone and heat-affected zone because of their higher sensitivity to stress concentration than the RSW joint, resulting in double eyebrow failure and pull-out failure. Fatigue crack originated from the specimen surface and propagated through fatigue striations together with secondary cracks. In addition, it was found that the strength of the base metal has inconsequentially affected the fatigue life of the welds when these welds were produced by the same welding method and have similar geometries.

The laser-spot welding process of aluminum alloy 1050A with a limited thickness is observed with the x-ray phase contrast method to investigate the melt dynamic especially when the melt penetrates the material. The laser-spot welding is investigated with two different wavelengths of the laser beam source: 515 and 1030 nm to investigate the influence of the absorptivity. The melt progressively penetrates the material during the spot-welding process until reaching the bottom side of the material and when the melt penetrates the lower side of the material, the so-called "lens-like" melt appears at the lower side due to the surface tension. At a comparable beam intensity value, the oscillation of the "lens-like" melt at the lower side of the material is driven by the expansion of vapor capillary. This expansion occurs inside of the material and directly above the "lens-like" melt. The shape of the expanded vapor determines the volume as well as the geometry of the resulting melt volume. Furthermore, the transition from the heat conduction welding mode to the keyhole welding mode is investigated by defocusing the laser beam for the beam source with a 515 nm wavelength. At a given variation, a clear difference between either mode is observed with the x-ray phase contrast method. [ABSTRACT FROM AUTHOR]

The purpose of the experiment was to study the influence of the laser beam in pulse mode on metallic foils in order to obtain a spot weld. The welding process was carried out using the overlap weld method, using spot welds in various quantities. The Nd - YAG BLS 720 pulsed laser was used to conduct the experiment. The impact of the number of spot welds on the value of force needed to break the sample was examined. A number of measurements were carried out to determine the best process parameters. Butt welding and overlap welding were also performed using a continuous weld consisting of spot welds. Weld strength tests were performed to select the most appropriate parameters for the process under consideration.

Laser spot welding method was employed to fabricate AlSi coated press-hardened steel (PHS) joints in overlapped configuration. Al and Si segregate at the notch root of a laser spot weld of AlSi coated PHS resulting in pre-mature cracking and weakening of the joint strength. The thickness-oriented δ-ferrite strips induced by the Al and Si segregation was mainly responsible for the mechanical deterioration though the dispersive δ-ferrite in the fusion zone also contributes. A supplemental annular stirring with beam oscillation is proposed to break up the segregation. With the annular stirring, the lap-shear peak load and energy absorption increased 57% and 80% respectively, which is attributed to the removal of δ-ferrite strips and the reduction in the fraction of dispersive δ-ferrite. Thermo-fluid numerical simulations suggest that the annular stirring promoted the melt flow and extended the duration of the melt pool, which accelerated and prolonged the diffusion of Al and Si atoms into the fusion zone, thus preventing the segregation of Al and Si and formation of δ-ferrite strips. Meanwhile, the prolonged melt flow pulled additional dissolved Al onto the molten pool surface forming the Al oxide film, resulting in further reduction of Al content and fraction of dispersive δ-ferrite.

During laser spot welding of an Al-Fe alloy, there is a size difference in welding spots under the same sheet-surface condition and the same welding parameters. The microstructures of the surface of the Al-Fe alloy sheet before and after laser welding are analyzed by means of a light microscope (LM) and electron probe microanalysis. It is found that, compared with small welding spots, at the micro-zone where the welding spots are larger, the content of intermetallic compounds (IMCs) is higher before the welding and the contents of Fe and Mn, which constitute IMCs, are also higher after the welding. The results show that the distribution of IMCs in the sheet surface affects the size of laser-welding spots. The difference in the distribution of IMCs at the micro-zone of the sheet surface causes the difference in the size of the welding spots. [ABSTRACT FROM AUTHOR]

To prevent zinc vapor–induced spatter, pre-scanning was proposed as a means to evaporate the zinc coating prior to the welding process. This paper studied the effectiveness of various pre-scanning parameters such as beam defocusing distance, beam power, scanning velocity, and geometric scanning path. The gap conditions during pre-scanning were also studied in regard to outgassing of zinc vapor during pre-scanning. To complement the experimental testing, a thermomechanical numerical model was developed and validated by comparing the size of the predicted versus the physical fusion zone. The effectiveness of the pre-scanning process was evaluated by examining the temperature distribution at both the top and faying surfaces of the stack-up under the condition that the temperature at the faying interface is greater than the zinc boiling point through the entire pre-scanning process to prevent condensation of the zinc vapor back onto the faying interface. The study found that no gap at the faying interface should be allowed with the use of pre-scanning to ensure an effective heat conduction across the faying interface. When the pre-scanning path is spiral or circular, the beam translation should initiate at the center and work outward towards the periphery. The line energy is suggested to decrease as the radius increases to avoid excessive accumulation of heat in the path center. [ABSTRACT FROM AUTHOR]

One of the primary objects during the treat Industry 4.0 is providing a higher energy efficiency through Energy Management execution. In the context of that study, related ISO Standards in the field Energy, Quality and Environmental Management Systems are referred. Followingly, the welding process, handled in that study, is a conventional primary production method applied with the incorporated automation systems of Industry 4.0. So, as a Finite Element Thermal Analysis sub-model, a 'Laser Welding Case' has been selected. Followingly, the whole Industry Process Idea is reached step by step from an incipient manufacturing unit, according to the basic principles of Industry 4.0 including a general performance investigation in the aspect of energy management. Also, that bottom up method can be described as 'an approach over an inverted hierarchy pyramid-like logic' as well. [ABSTRACT FROM AUTHOR]

Effects of initial/tail of the pulse waveform on coupling efficiency and surface morphology of AZ31 magnesium alloy laser spot welding is investigated. Research shows that initial ramp-up waveform can improve the laser spot welding absorptance, but with limited effect (0.88 → 0.9), and melting time of ramp-up waveform is longer than rectangular for equal pulsed energies, making the welding energy coupling efficient and diameter larger. The ramp-down waveform can extend duration (9 ms → 12 ms) of molten pool above melting point temperature (630 °C), increase Marangoni number (R 1 : 29.29, R 2 : 32.11, R 3 : 23.70, R 4 : 26.62), slow down cooling rate (3 × 106 °C/s → 1 °C/s) and recoil pressure (R 3 : 52.90 P 0 → 12.16 P 0 , R 4 : 95.95 P 0 → 20.58 P 0) of instantaneous closure of rectangular waveform, reduce the sensitivity of welding defects such as overfill, undercut and spatter, and improve the surface morphology of laser welding spots. • Initial/closing pulse shaping affects the welding morphology and coupling efficiency. • Coupling efficiency and welding diameter can be improved by ramp-up pulse. • Sensitivity of laser welding defects of Mg can be reduced by ramp-down pulse. • Morphology of welding spots are optimal with Ramp-up + Rectangle + Ramp-Down. [ABSTRACT FROM AUTHOR]

• A thermo-fluid process simulation model was developed to simulate the laser-material interaction. • The zinc vapor pressure as an indicator is put forward to estimate the spatter occurrence. • The spatter is greatly reduced by limiting the zinc vapor pressure with redesigned welding schedule. This paper discusses the unique application of numerical modeling of remote laser spiral spot welding of zinc-coated steels to reduce spatter occurrence. A thermo-fluid process simulation model was developed to simulate the laser-material interaction, material melting, keyhole formation and molten pool dynamics occurring in remote laser spiral spot welding of zinc-coated steels. Based upon numerically calculated thermal profiles during welding, the instantaneous zinc vapor pressure between faying surfaces was estimated. It was found that high vapor pressure points correlated well with spattering events observed in high-speed videos taken of the molten pool during welding. Using the estimated zinc vapor pressure as an indicator of spatter occurrence, the welding schedule was redesigned to limit high zinc vapor pressure and rapid pressure increase for spatter prevention. The revised schedule was verified by physical testing and resulted in greatly reduced spatter. [ABSTRACT FROM AUTHOR]

For comparative fatigue strength analysis of laser spot weld bonding joints and laser spot welding joints for DP590 dual-phase steel, the orthogonal experiment of laser spot welding and laser spot weld bonding was designed for 1. 5 mm thick DP590 using welding power, welding time and defocusing amount as variables. The failure load of the two joints was obtained by the shearing test;the variance analysis of the mechanical properties was carried out to acquire the impact of various factors on the welding quality of the two joints. In order to achieve the load-life curves, the fatigue test was practiced and the fatigue fracture of weld-bonded joints was analyzed. The results show that the failure load and fatigue strength of the weld-bonded joints are higher than those of the spot welded joints. The maximum process parameters for the mechanical properties of the weld-bonded joint and the spot welding joints are the welding power and the welding time respectively. The fatigue cracks of weld-bonded joints mainly originate from the heat-affected zone, and there is obvious fatigue striation in the fatigue crack extension area, and the typical dimples appear in the instantaneous fracture zone. [ABSTRACT FROM AUTHOR]

Laser welding of dissimilar metals (steel and aluminium) was investigated with the aim to increase the maximum tensile shear load of the Fe-Al joints. The increase was achieved by texturing the surface of steel prior to the laser spot welding process which was performed in a lap-joint configuration with the steel positioned on top of the aluminium and with a texture faced down to the aluminium surface. This configuration enabled an increase of the bonding area of the joints, because the molten aluminium filled in the gaps of the texture, without the need of increasing the process energy which typically leads to the growth of the intermetallic compounds. Different textures (containing hexagonally arranged craters, parallel lines, grid and spiral patterns) were tested with different laser welding parameters. The Fe-Al joints obtained with the textured steel were found to have up to 25% higher maximum tensile-shear load than the joints obtained with the untextured steel. [ABSTRACT FROM AUTHOR]

A finite element (FE) approach is developed to investigate the laser spot welding (LSW) of flat-plate solar absorbers and the stress and distortion fields that develop after fabrication and during operation. Numerical calculations at two different levels are carried out. At a microscopic scale, the details of a spot weld are analyzed. At a macroscopic level, a global approach is used to simulate the joining of the pipeline to the absorber plate and the "restoration" (flattening) process of the absorber. The simulated welding-induced distortion is compared with experimental measurements. The thermomechanical behavior of a solar absorber under working conditions is also studied and operational stresses and the critical locations for structural failure are reported. [ABSTRACT FROM AUTHOR]

Process of metal evaporation in laser welding is accompanied by dynamic impact of metal vapours on pool free surface. As this process proceeds non-uniformly over pool surface, reactive vapour pressure can differ considerably in its different sections, leading to depression of melt free surface. This work proposes a mathematical model allowing investigation of penetration dynamics and shape of weld pool free surface in laser welding of sheet metals by a stationary pulsed source (spot welding). When developing the model, we assumed that heat transfer process in the metal is due to heat conductivity and convection, and heat losses from the surface are due to metal evaporation and energy loss for heat radiation. The work gives the results of numerical modeling of weld pool penetration dynamics derived with application of the developed model. 6 Ref., 7 Figures. [ABSTRACT FROM AUTHOR]

In this article, an in-process monitoring scheme for a pulsed Nd:YAG laser spot welding (LSW) is presented. Acoustic emission (AE) was selected for the feedback signal, and the AE data during LSW were sampled and analyzed for varying process conditions such as laser power and pulse duration. In the analysis, possible AE generation sources such as melting and solidification mechanism during welding were investigated using both the time- and frequency-domain signal processings. The results, which show close relationships between LSW and AE signals, were adopted in the feature (input) selection of a back-propagation artificial neural network, to predict the weldability of stainless steel sheets. Processed outputs agree well with LSW experimental data, which confirms the usefulness of the proposed scheme. [ABSTRACT FROM AUTHOR]

Residual stress relaxation is one of the reasons for parameter drift of quartz flexible accelerometer with laser spot welding structure. Residual stress of laser spot welding is simulated by thermal analysis and thermal stress analysis of the welding process with ANSYS. Dynamic vibration analysis is carried out to evaluate the effectiveness of VSR process for laser spot welding and investigate the effect of VSR process factors on the residual stress distribution. Results show that vibration can decrease the welding residual stress and VSR with resonant frequency has better residual stress relief effect than that of non-resonant frequency. The study may provide a better understanding of how residual stress relief occurs and how VSR can be used in precise instrument effectively. [ABSTRACT FROM AUTHOR]

Dissimilar materials joint has a great interest in industrial applications including automotives, aircrafts, medical, electronic industry, etc. Moreover, the combination of plastics and metals in the product would cater advantages in specific engineering application. In this study, direct joining using YAG laser spot welding for dissimilar materials joint between plastic and metallic materials has been investigated. Experimental result showed polyethylene terephthalate (PET) could be successfully joined to aluminum alloy (A5052), stainless steel (SUS 304) and copper (Cu). Shear tensile test was carried out to evaluate the joining strength. In the case of PET/Cu joint, the joining strength was almost constant regardless of heat input. However, the strength increased with increasing heat input for PET/A5052 and PET/SUS304 joints. Cross-sectional observation of the joined specimen showed no significant molten pool in the case of PET/Cu joint. On the other hand, an obvious weld pool was observed at the interface in metallic material side for PET/A5052 and PET/SUS304 joints. Differences of morphology at the interface would result from different material properties, such as reflectivity and absorptivity of laser, thermal conductivity, etc., of metallic materials used and might affect the joining strength. [ABSTRACT FROM AUTHOR]

This paper aims at investigating metallurgical and mechanical characterization of low carbon steel laser spot welds. Microstructural examinations, microhardness tests and quasi-static tensile-shear tests were preformed. Mechanical properties of the welds were described in terms of peak load and failure mode. The effects of laser spot welding parameters including pulse frequency, laser energy, welding speed, pulse width and welded circle diameter, on low carbon steel laser spot weld performance were studied using the Taguchi design of experiment method. It was found that the effective laser pulse energy is the controlling factor in the determination of mechanical strength of laser spot welds. [ABSTRACT FROM AUTHOR]

Abstract: Owing to its significant influence in heat and mass transfer, liquid metal flow during stationary laser welding has been studied for different concentrations of oxygen in the surrounding environment. Two predominant types of surface flow motion are observed: an inward flow, corresponding to a positive surface tension temperature gradient, and an outward flow, corresponding to a negative gradient. Time-dependent changes in oxygen concentration at the surface are observed to flip the surface tension temperature gradient from negative to positive under appropriate shielding conditions. The oxygen concentration affects not only the flow motion, but also the laser absorption coefficient, which increases with increasing environmental oxygen concentration. It is shown here that the evolution of dissolved oxygen in the weld pool as a function of temperature can have a profound influence on the fluid flow and hence on energy transport. [ABSTRACT FROM AUTHOR]

Abstract: Experimental and numerical studies were conducted to characterize laser and resistance spot welds to gain an understanding of load carrying capacity, temperature distributions and residual stress states of different joint geometries used in the automotive industry. Different laser spot weld path geometries are compared with conventional resistance spot welds to find the residual stress distributions in each. It was found out that the weld region in laser spot welding is surrounded by a compressive region which has higher compressive stress values and larger size than that of resistance spot welds. Simulations showed good agreement with experimental temperature distributions, and were able to qualitatively predict the residual stress distributions in each of the weld geometries. The thermal history at known failure locations within the welds and the influence of the weld geometries on cooling rate are also discussed. [Copyright &y& Elsevier]

Abstract: Numerically computed results of weld pool dimensions in conduction mode laser welding are sensitive to the estimated value of the actual beam energy absorbed by the substrate. In a conduction based heat transfer analysis, the incorporation of the laser beam induced energy as a surface only heat flux fails to realize enhanced heat transfer in weld pool as molten material attains higher temperature and convective transport of heat becomes predominant. An alternate is to include fluid flow analysis considering phenomenological laws of conservation of mass and momentum that greatly increases the complexity in modeling. Uncertainty of material properties such as effective thermal conductivity and viscosity in the weld pool also impedes such extensive fluid flow analysis. A simpler and tractable approach can be to consider a volumetric heat source within weld pool in a conduction based heat transfer analysis. Earlier efforts to accommodate volumetric heat source such as double-ellipsoidal form remained unpopular since the size of the final weld pool shapes is required to be known to begin with the calculation. The present work describes an improved approach where a volumetric heat source is defined adaptively as the size of the weld pool grows in size within the framework of a conduction based heat transfer analysis. The numerically computed results of weld pool dimensions following this approach have shown fair agreement with the corresponding measured values for laser spot weld samples. [Copyright &y& Elsevier]

A study was carried out on laser and resistance spot welds in overlapped sheets of dual phase advanced high strength steel (DP780) and deep drawing steel (DC04) of 20 mm in thickness. The aim of the study was to investigate the fatigue performance of these joints under tensile shear loading as well as the monotonic performance for applications in the automotive industry. The mechanical properties, failure behaviour and fatigue life analyses of spot welds in similar and dissimilar joints were investigated by experimental and numerical methods. The structural stress concept was used to describe the fatigue lives of spot welded specimens. The results revealed different failure types with different fatigue behaviours for laser and resistance spot welds under the application of cyclic loads at 'high load' and 'low load' levels. [ABSTRACT FROM AUTHOR]

• A laser ultrasonic technology(LUT) was proposed to inspect the quality of micro solder joints in laser spot welding. • Different dispersion curves were obtained for 1.2 mm/0.4 mm welding spot of standard/false welded components. • The standard and false welding can be visually distinguished. • Industrial CT results demonstrated the reliability of experimental results. • LUT has the potential to integrate with the current laser welding technology to realize real-time online monitoring. The quality inspection of micro solder joints in laser spot welding (LSW) is a problem of great concern in industrial application. In this paper, a laser ultrasonic technology (LUT) was proposed to inspect the quality of micro solder joints in LSW. Firstly, based on the thermoelastic model of acoustic wave propagation in solid, a theoretical model was built and used to analyze the propagation properties of the Lamb wave in the whole field by finite element method (FEM), the transmitting properties of the excited Lamb wave via solder joint were affected by the effective contacted area of solder joint. Secondly, LUT was used to inspect the 1.2 mm/0.4 mm welding spot of standard/false 304 stainless steel welded components. By comparing the propagating properties of excited ultrasonic wave in different samples with different weld quality, the standard and false welding can be visually distinguished. Finally, a industrial CT was used to check the quality of the samples used in our experiment. Inclusions and pores have been found in the false solder joints, which will reduce the effective contacted area of solder joint, and then affected the propagation of ultrasonic wave. By combining the CT results and the experimental analysis, the experimental results detected by LUT are in good agreement with the simulation results. So, the LUT is a potential method in field of the quality inspection of micro solder joints in LSW. [ABSTRACT FROM AUTHOR]

This study is carried out to investigate the laser spot welds (LSWs) of advanced high strength steel sheets of 1·0 mm thickness for application to the automotive industry. Mechanical properties and failure behaviour of LSWs for transformation induced plasticity steel sheets (TRIP800) subjected to monotonic coach–peel loading are investigated by experimental and finite element (FE) simulation methods. Microstucture of LSW and fracture surfaces of the welded specimens were examined by scanning electron microscopy (SEM) to describe the microstructural features and to clarify the crack initiation mechanism respectively. Based on simulation solutions equivalent plastic strain was obtained to describe local deformation of LSW joints. Experimental results revealed a 'plug type' of failure mode of the circular LSW joints under 'peel–coach' loading condition. This type of ductile failure is the most common failure mode for spot welds used in the automotive industry. Numerical simulation of damage process was compared with experimental results and this revealed that fracture path was successfully predicted. [ABSTRACT FROM AUTHOR]

Numerical modelling of laser spot welding process as an aid to design for welding has gained significant attention in the recent past, because experimental measurements of peak temperature and weld thermal cycle are expensive and often intractable. Accurate knowledge of the temperature history in the weld pool and the surrounding solid substrate are a prerequisite for the estimation of weld joint strength. The present work proposes a three-dimensional (3D) transient conduction heat transfer based coupled thermomechanical analysis of laser spot welding process. To accommodate enhanced heat transfer in weld pool at higher temperature owing to convective flow and greater amount of absorption of the laser energy, an expression for a volumetric heat source that is dimensionally similar to the transient weld pool is considered. The calculated weld pool dimensions have shown fair agreement with similar measured values reported in previous literatures. The calculated weld thermal cycles are subsequently used to calculate distortion and thermal stresses considering a typical butt joint geometry. [ABSTRACT FROM AUTHOR]

Laser spot welding is beneficial when welding small and/or electrical components where a small heat-affected zone is required. The modeling of heat transfer analysis carried out until now omits thermal efficiency analysis of the process involved. This may become important when optimization and cost effectiveness of the welding process is concerned. Consequently, the present study was conducted to develop expressions relevant to the welding efficiencies based on the first and second laws of thermodynamics. The study is extended to include an experimental investigation into the welding process to relate the first-and second-law efficiencies with mechanical properties of the resulting welds. [ABSTRACT FROM AUTHOR]

Laser spot welding method was employed to fabricate Al Si coated press-hardened steel (PHS) joints in overlapped configuration. Al and Si segregate at the notch root of a laser spot weld of Al Si coated PHS resulting in pre-mature cracking and weakening of the joint strength. The thickness-oriented δ-ferrite strips induced by the Al and Si segregation was mainly responsible for the mechanical deterioration though the dispersive δ-ferrite in the fusion zone also contributes. A supplemental annular stirring with beam oscillation is proposed to break up the segregation. With the annular stirring, the lap-shear peak load and energy absorption increased 57% and 80% respectively, which is attributed to the removal of δ-ferrite strips and the reduction in the fraction of dispersive δ-ferrite. Thermo-fluid numerical simulations suggest that the annular stirring promoted the melt flow and extended the duration of the melt pool, which accelerated and prolonged the diffusion of Al and Si atoms into the fusion zone, thus preventing the segregation of Al and Si and formation of δ-ferrite strips. Meanwhile, the prolonged melt flow pulled additional dissolved Al onto the molten pool surface forming the Al oxide film, resulting in further reduction of Al content and fraction of dispersive δ-ferrite. Unlabelled Image • Forming thickness-oriented δ-ferrite strips and dispersive δ-ferrite deteriorated mechanical properties of laser spot welds of press hardened steels • An annular welding with beam oscillation was proposed to break up the δ-ferrite strips and reduce the dispersive δ-ferrite. • By the developed annular welding, the lap-shear peak load and energy absorption increased 57% and 80%, respectively. • Mechanisms of the annular welding in terms of flow and thermal behaviors were revealed by numerical simulations. [ABSTRACT FROM AUTHOR]

A pulsed Nd:YAG laser welding of 1 mm thick Ti (grade 2) to 0.5 mm thick AA3105-O was performed by a ring-like spot joining. A 0.15 mm thick Al-12Si-2.5 Mg alloy was used as a filler metal. Intermetallic compounds of Ti 3 Al, Ti 2 Al, TiAl, Ti(Al,Si) 3 and Mg 2 Si were observed respectively from Ti towards Al sides at the fusion zone. Si and Mg increased the strength of the Al re-solidified zone near the Ti-Al interface because of their easy dissolution in the Al. Exothermic effect of the Mg addition resulted in porosity in the welding zone. Joint strength of up to 98% of the Al base metal was obtained, which was much 14% higher than that achieved by autogenous welding. [ABSTRACT FROM AUTHOR]