Weld Porosity Research Articles

Effect of beam oscillation frequency on porosity in laser welding of aluminum alloy lap-butt joints

Many investigations into laser oscillations for mitigating severe porosity in aluminum alloys have involved trading off penetration depth, potentially disrupting the porosity suppression mechanism. In this study, an oscillation laser butt-lap welding technique was designed, and the effect of oscillation frequency on cross-section morphologies and porosity rate was investigated while maintaining the constant weld depth. The findings unveiled that heightened oscillation frequencies led to diminished porosity levels, and this pattern remained consistent, even in cases where weld depths were extended. High-frequency laser beam oscillation enhanced the stability of the keyhole, increased the duration of the molten pool existence, and reduced porosity to 0.17%. Thus, this study offered significant insights into the impact of oscillation on laser welding of aluminum alloys.

Analysing suspected linear indications in narrow-gap welding of nuclear power plants via radiographic inspection

ABSTRACT In nuclear power plants, ensuring the integrity of main coolant line welding is vital. Radiographic testing often shows linear indications in these welds, posing challenges for quality assessment and requiring expensive reworking. To investigate the mechanism of the suspected linear indications observed in radiographic inspections of narrow-gap welding at nuclear power plants, the microstructure, microhardness, and porosity of welds showing such indications were investigated in this study using scanning electron microscopy and atomic probing methods, among others. The microvoid distribution in narrow-gap welds was characterised by porosity measurement. The results showed that the microstructure of the weld consists of an austenite matrix and δ-ferrite, with the latter distributed almost uniformly during welding. The average δ-ferrite content and microhardness were approximately 6.6% and 186 HV0.49N, respectively. The porosity of the welding zone with a suspected linear indication was approximately 0.06%, higher than the 0.03% observed in the zones without such indications. This difference is likely responsible for the linear indications detected in radiographic inspections. However, the results demonstrated that this difference does not affect the welding microhardness. The novelty of this study lies in explaining the role of porosity in causing suspected linear indications in narrow-gap welding in nuclear power plants.

A comparative study on welding characteristics and mechanical properties of Ti–6Al–4V laser welded joints under the sub-atmospheric pressure and beam oscillation

Sub-atmospheric pressure environment and oscillation laser are both excellent ways to improve welded joint quality. However, the differences in their effects and mechanisms are unclear. Therefore, the differences between sub-atmospheric pressure and oscillating laser in weld formation, porosity suppression and grain size refinement were analyzed in this study. The results revealed that penetration depth of welded joint was increased to 6.09 mm under sub-atmospheric pressure environment while it was decreased to 3.3 mm under oscillation laser. Furthermore, reducing fluctuating vapor pressure and suppressing vortex formation were the main means to improve the keyhole stability and promote the escape of bubbles in a sub-atmospheric pressure environment. The improvement of the oscillating laser in these two aspects was attributed to enlarging keyhole area, shortening escape path and oscillation keyhole absorption. Additionally, the average grain size in the upper weld was reduced from 134.6 μm to 118.6 μm and 114.1 μm under the sub-atmospheric pressure environment and laser oscillation, respectively. The reduction of the temperature gradient led to former grain refinement while the increase of heterogeneous nucleation rate was responsible for latter grain refinement. Correspondingly, the mechanical properties of welded joints were improved. The study offered valuable insights for the application of laser welding with oscillation laser and sub-atmospheric pressure in industrial production.

Optimization of process parameters of cold metal transfer welding-based wire arc additive manufacturing of super Duplex stainless steel using response surface methodology

The parameter selection is essential to achieving the desired bead geometry and minimizing the various defects such as discontinuous weld beads, cracks, porosity, and waviness during the fabrication of wire arc additive manufacturing (WAAM) samples. The purpose of this study is to examine the effect of three input process parameters (current, welding speed, and gas flow rate) at three distinct levels on the properties (weld bead width, bead height, and dilution) of samples fabricated using super Duplex 2507 stainless steel through the cold metal transfer (CMT)–WAAM process using response surface methodology (RSM). To create a design of experiment involving three process parameters, a central composite design (CCD) matrix was utilized, and adequacy was checked by ANOVA analysis. The maximum values for weld bead width and bead height were 6.57 mm and 3.43 mm, respectively; the minimum dilution observed was 31.30%. The predicted optimal input parameters were 190.46 A current, 8.94 mm/s welding speed, and 15 l/min shielding gas flow rate. The results indicated that current was the most influential factor in determining the multiple responses, followed by welding speed and gas flow rate. The microstructures were characterized by optical microscopy, and results indicated that the microstructure of weld bead region consisted of ferrite and austenite. The microhardness of the CMT-based WAAM fabricated samples was also evaluated. This study holds significant potential for the fabrication of stainless-steel additive manufacturing products using a CMT-based arc welding process.

Effect of welding speed on microstructure, nano-mechanical and nano-tribological characteristics of dissimilar friction stir welded AA6061-T6 and AZ31 alloy

The microstructural, tribological, and mechanical performance of friction-stir welded AA6061-T6 and AZ31 alloys were investigated using electron back scattered diffraction, scanning electron microscope, X-ray diffraction, and electron dispersed spectroscopy methods. The non-destructive X-ray microcomputed tomography test was used to analyse weld porosity. The distribution of volumetric and surface flaws (pores) was found to be confined across the weldment. Using a novel atomic force microscopy method, the nano-tribological characteristics of the base metal and localized regions of welded sample were studied for the first time. The significant difference in wear and friction behaviour was observed in all weld zones and base metal of magnesium side, which was correlated with the hardness of these regions. AFM results showed strong variation in tribological properties in correlation with the hardness trends of different weld zones, i.e. higher hardness leads to low wear. In weldments, intermetallic compounds such as Al12Mg17 and Al3Mg2 were produced, resulting in nanohardness differences as measured by the nanoindentation test. The joint efficiency of 65%, 84%, and 91% were obtained at welding speeds of 16 mm/min, 20 mm/min, and 25 mm/min, respectively.

High-frequency oscillating laser-arc hybrid welding of 8-mm-thick high-strength aluminum alloy through synchronous wire-powder feeding

Laser-arc hybrid welding of high-strength aluminum alloy faces the problems of serious evaporation and burning loss of alloying elements, which cause instability on the plasma and melt flow, and reduce weld mechanical properties. In the current study, both high-frequency beam oscillation and synchronous wire-powder feeding were adopted to solve the above problems during the hybrid welding of 8-mm-thick AA2219 aluminum alloy. The results showed that compared with none-oscillating hybrid welding, wire-powder synchronous oscillating hybrid welding reduced weld porosity from 10.7% to 0.7%, and increased the ultimate tensile strength and elongation by 12% and 72% respectively. The feeding of Mg powder promoted the formation of fine Al2CuMg strengthening phase by substituting the block Al2Cu eutectic. Besides, the oscillating laser at frequency of 250 Hz induced the strengthened stirring of molten pool, which benefited to break and inhibit the growth of dendrite grains, capture bubbles and solidified pores, and reduce the probability of bubble formation due to the instability and collapse of laser keyhole.

Ultrasonic fatigue testing of welds made of structural steels S355JR and S275JR

There is a limited data on VHCF for structural steels welds for over 10 million cycles. The purpose of this research is a fatigue performance comparison of the welds made of steels S355JR+AR and S275JR+AR. The goal of reaching gigacycle fatigue domain is achieved using the ultrasonic fatigue testing at 20kHz. Fatigue samples are prepared to investigate the influence of two surface conditions – polished and pre-corroded. Fatigue failures are driven primarily by the welding porosity with the fatigue life duration dependent on the size and location of pores. Visual comparison of fatigue data for steels poses a challenge, because of the massive scatter of experimental data points. Therefore, a statistical approach is used with a Fatigue Performance Parameter applied to the fatigue data for welded samples to quantify the quality of the material.

Mechanism of grain refinement in FSW joints of 6063-T6 aluminum alloy under different rotational speeds

Abstract The inherent properties of aluminum alloys often result in defects like deformation and porosity in joints and welds created through conventional fusion welding. Our paper investigates the impact of varying rotational speeds in the friction stir welding of 4mm thick 6063-T6 aluminum alloy, focusing on microscopic grain refinement and mechanical property alterations in T-joints. Using mechanical stretching and numerical simulation methods, we observed that the initial weld joint is robust, with minimal flying edges and a distinct fish-scale pattern on the surface. Moreover, the grain sizes in the weld’s core area are notably smaller than those in the region affected by the upper axial shoulder. The mechanical properties of the joint experienced a first increase and then a decrease in mechanical properties when the friction stir welding rotational speed, was increased from 600r/min to 1500r/min. Moreover, in 1000r/min rotational speed, the material welded tensile strength and yield strength of the best tensile strength compared to the raw material to enhance the 21MPa, yield strength of 30MPa, elongation close to the raw material of 89.86%.

Experimental analysis of the effect of ultrasonic vibration on porosity suppression in narrow gap laser welding

Abstract The welding process has a wide range of applications in aerospace, military manufacturing, machinery, and other fields, and with the continuous improvement of welding technology requirements, the inhibition of porosity in the welding process is also increasing. This study, through the narrow gap laser welding characteristics and porosity formation mechanism of the depth of analysis, for the existing narrow gap laser welding method exists in the side wall of the weld fusion is poor porosity, poor uniformity of organizational properties and other issues, proposed ultrasonic-based welding method to achieve effective inhibition of porosity. The experimental analysis of ultrasonic vibration on the formation of porosity is carried out based on narrow-gap laser welding. The peak sound pressure of narrow gap welding increases when the ultrasonic current amplitude changes from 24A to 32A. Under different ultrasonic vibration conditions, the number of welds without applied ultrasound was as high as 95, while the number of porosities gradually decreased to 48 with the increase of applied ultrasound amplitude from 12% to 37%. Furthermore, as the ultrasonic amplitude increased, the residual height decreased by 0.45 ml. In addition, at fixed ultrasonic amplitude, with the increase of laser power, the porosity increased from 0.89% to 2.21%, and the average diameter of the porosity increased from 0.29 mm to 0.43 mm. The porosity for the porosity diameter of less than 200 μm was reduced to 0.020%. The percentage of stomata with a diameter greater than or equal to 200μm increased to 2.098%. This study analyzes the inhibition effect of ultrasonic vibration on porosity to a certain extent. Moreover, the inhibition effect of ultrasonic vibration in narrow gap laser welding is significant and the smaller the laser power under the same amplitude, the better the inhibition effect, which provides a valuable reference for the research of the narrow gap laser welding process.

Effect of Ultrasonic Vibration Assistance on Microstructure Evolution and Mechanical Properties in Laser-Welded AZ31B Magnesium Alloy

Given the susceptibility to weld porosity and poor weld formability in laser beam welding (LBW), this study delves into an examination of the impact of ultrasonic vibrations on microstructural morphologies and mechanical properties in AZ31B magnesium (Mg) alloy. A comparative analysis was conducted between ultrasonic vibration-assisted LBW and conventional LBW. The results established that the effective elimination of weld porosity, an outcome attributed to the combined effects of cavitation and acoustic streaming, resulted in a weld characterized by a visually seamless and structurally robust appearance. Furthermore, the incorporation of ultrasonic vibration assistance in the welding process yielded a finer microstructure as compared to the conventional LBW. Moreover, the lamellar structures of β-Mg17Al12 were transformed into particles and evenly distributed throughout the α-Mg matrix. In addition, the incorporation of 50% ultrasonic vibration assistance yielded notable improvements in tensile strength (259.6 MPa) and elongation (11.1%). These values represented enhancements of 4.8% and 35.4% as compared to joints fabricated by using conventional LBW.

Failure Analysis of an Elbow Tube Break in a Pyrolysis Furnace

The pyrolysis furnace, a critical component in a pyrolysis unit, inevitably faces operational challenges during its use. This study investigates a case of pyrolysis furnace failure, particularly focusing on an occurrence at the 90° lug elbow and furnace tube weld. The failure, characterized by a comprehensive fracture of the furnace tube in the circumferential direction along the weld vicinity, transpired within a timeframe significantly shorter than one-third of the design life. To unravel the root cause, a series of experiments was conducted on a sample extracted from the failed tube. These experiments, comprising visual inspection, chemical composition analysis, metallographic examination, microstructure analysis, fracture scanning electron microscopy, and energy spectrum analysis, collectively aimed at a comprehensive understanding of the failure mechanisms. The results disclosed that the fracture between the lug elbow and the inlet pipe stemmed from the presence of porosity and inclusions in the butt weld. The initiation of cracks was traced to the pores and inclusions in the fusion line of the inner wall of the pyrolysis tube, extending to connect with the pores in the heat-affected zone on the side of the pyrolysis tube parent material. Subsequently, under the influence of high temperature and stress, the cracks propagated, crept, and expanded along the circumference of the pyrolysis tube parent material until the final fracture occurred. In light of these findings, practical recommendations are proposed to mitigate the risk of similar failures in the future.

Study on the Physical Characteristics of Plasma and Its Relationship with Pore Formation during Laser-Metal Active Gas Arc Hybrid Welding of 42CrMo Steel

The automobile industry puts forward higher requirements for the design and manufacture of steel pistons. However, the welding of 42CrMo steel pistons still has unsolved technical problems, especially welding defects that cannot be directly detected, such as pores, which are easily generated inside the weld. A plasma experiment of laser-metal active gas arc (MAG) hybrid welding 42CrMo steel was conducted in this paper, and plasma signals inside and outside the keyhole were detected during the laser welding, leading laser laser-MAG hybrid welding, and leading arc laser-MAG hybrid welding of 42CrMo steel. The characteristic parameters such as electron temperature and electron density were calculated and analyzed to investigate the relationship between plasma behavior and the formation of weld porosity in the welding process of 42CrMo steel. Based on the fluctuations in plasma electron temperature and electron density, the prediction of pore formation in the weld of 42CrMo steel was made, aiming to provide guidance for achieving a stable and reliable laser-MAG hybrid welding process for 42CrMo steel.

Effect of laser oscillation and beam incident angle on porosity in double-sided filler welding of 2219 aluminum alloy T joint

In the current research, the double-sided laser beam oscillation filler welding (DLBOW) with beam incident angle from 20° to 40° were carried out for 2219 Al-Cu alloy T joint welding. Double-sided laser beam filler welding (DLBW) was conducted as a reference group. 3D computed tomography (CT) scanning analysis method was performed to investigate the precise three-dimensional locations of the porosity defects in the T joints. High-speed photography was conducted to evaluate the keyhole stability. The dynamic behavior of keyhole of DLBW and DLBOW was simulated by Flow-3D to study the formation process of pores. The effects of beam oscillation and beam incident angle on the macrostructure, microstructure, porosity, and mechanical property of T joints were discussed. It was found that beam oscillation and smaller beam incident angle promoted porosity suppression. The mechanical properties of T joints were improved by laser oscillation. With the beam incident angle of 20°, the porosity of T joint welded by DLBOW was lowest (0.26 %). The hoop tensile strength and T-pull tensile strength of the T joint were 403 MPa and 302 MPa, approximately 89.5 % and 71.6 %, in contrast with that of the base metal.

Effect of placement configuration on the microstructure, porosity and mechanical performance of dissimilar remote laser welding of additive manufactured AlSi10Mg alloy and conventionally manufactured 1050 aluminium sheet

Additive manufacturing (AM) has gained significant attention in automotive applications, while the low weldability of AM material poses challenges when assembling AM materials with conventionally manufactured materials. This study investigated the laser welding of AM AlSi10Mg and AA1050 sheet metal in an overlap configuration, specifically focusing on the impact of placement configuration of two materials on weld properties. This aims to provide valuable insights for optimizing the localized geometry of AM components to enhance the joint performance. Results showed that positioning AM AlSi10Mg on top leads to a higher weld penetration and higher Si content within the molten pool, especially in the upper sheet. Additionally, weld zone grain structure was greatly influenced by alternating the placement configuration, where welds with AM AlSi10Mg on top exhibiting more equiaxed grains in the weld centre and refined columnar grains near the fusion boundary of upper sheet. Furthermore, significantly reduced weld porosity was determined by positioning AM AlSi10Mg at the bottom (3.2 ± 0.4 %∼7.1 ± 0.9 %) compared to placing it on top (16.9 ± 0.9 %∼20.1 ± 0.9 %) in all scenarios ranging from full penetration to partial penetration. This can be related to the fact that the hydrogen bubbles originating from AM AlSi10Mg experienced a shorter exposure in the molten pool, limiting the merging and growth of small bubbles. However, a slightly lower joint strength was determined in welds with AM AlSi10Mg at the bottom which may be due to the plastic deformation incompatibility between large columnar grains in the fusion zone and the fine grains in the as-printed material.

A Review on Effects of Weld Porosity in Laser-Arc Hybrid Welding for Aluminum Alloys

It is expected that the application of aluminum alloy, a lightweight material, will continue to increase in connection with strengthening international environmental regulations and improving fuel efficiency for reducing vehicle emissions. Accordingly, aluminum alloys are widely applied to the automobile industry, and various welding methods are used for aluminum alloys. In this paper, the laser-arc hybrid welding method that combines laser and arc welding is explained. Although laser-arc hybrid welding has better weldability than a single heat source of laser or arc, the degradation of mechanical properties due to defects occurring during hybrid welding has emerged as a problem. This paper discussed the quality of aluminum alloy welds through optimization of various process parameters of hybrid welding.

Study on the influence of Al-Si welding wire on porosity sensitivity in laser welding and process optimization

Al-Si welding wire is commonly used in the aluminum alloy welding due to the excellent heat crack-resistance and corrosion-resistance, but the presence of large-sized pores hinders its widespread application in the field of laser welding. This study focuses on the cause of pores formation in the laser welding using Al-Si wires with different Si contents and investigates the dynamic behavior of laser keyhole by a high-speed camera-based molten pool monitoring system. The results showed that with the increase of wire Si content from 5% to 12% (wt.%), the keyhole stability decreased and the weld porosity increased. According to the thermodynamic calculations, the increased Si content enhanced the Reynolds number of molten pool, resulting in increased turbulence tendency. It caused the molten pool being more susceptible to external disturbances, which decreased the stability of keyhole. Furthermore, the reduced dynamic viscosity of molten pool increased both the depth-to-width ratio of keyhole and its opening and closing frequency. These combined effects ultimately contributed to the increased susceptibility to pores formation. Based on the above results, a circular oscillating laser was introduced to guide the regular flow of molten pool. The beam oscillation improved the resistance to fluctuations of molten pool and reduced the depth-to-width ratio of keyhole. Besides, the high-frequency rotating keyhole could capture and re-melt the formed pores. An optimal laser oscillating welding was determined using response surface methodology to control the porosity within the acceptable range.

Elucidating the effect of circular and tailing laser beam shapes on keyhole necking and porosity formation during laser beam welding of aluminum 1060 using a multiphysics computational fluid dynamics approach

In the attempt to produce lighter battery packs at a lower cost, replacing common copper parts with aluminum components has been a popular approach in recent years. With regard to joining technologies, there is a growing interest in applying laser beam welding in battery pack manufacturing due to several advantages such as single-sided and noncontact access while maintaining a narrow heat-affected zone. Motivated by the need to control and reduce weld porosity in AA1060 battery busbar welding with the ultimate goal to enhance durability and reduce electrical resistance, this paper has been developed with the aim to studying the effect of laser beam shaping on porosity formation and, hence, generate knowledge about the underlying physics of the welding process itself. First, a multiphysics computational fluid dynamics model has been developed and calibrated to experimental data; then, the model has been deployed to study the effect of both circular and tailing beam shapes on melt pool dynamics and the evolution of porosity due to the instability of the keyhole. The study elucidated the importance of the keyhole’s necking on porosity formation. Findings showed that the tail beam shapes, compared to the circular spot, have a pronounced effect on the reduction of the necking effect of the keyhole—this helps to reduce number of collapsing events of the keyhole itself, thereby leading to the reduction of porosity formation.

Comparison of the Effects Metal Inert Gas and Laser Beam Welding on Duplex Stainless Steel Properties

In this study, optimal characteristics for duplex stainless steels (2507DSS) are attained when austenite and ferrite are present in roughly equal amounts in the microstructure. Therefore, the purpose of this study is to compare how different metal inert gas (MIG) and laser welding (LBW) parameters affect the weld characters of joints that are butt welded joints of duplex stainless steel plate with thickness of 8mm, the speed is constant and changing beam power, with argon shielding gas. Conventional MIG welding parameters are ranges; current, voltage are constant with changing speed and using gas mixture Ar and CO2 with a filler metal, and a single V groove. Investigation of welded joints has been carried out using different methods visual inspection, optical micro structure, hardness measurements, energy dispersive X-ray (EDX) microanalysis and tensile test. The results achieved in this investigation disclosed that welding parameters obtaining satisfactory properties of welded joint; no visible welding flaws, porosity and incompetent penetration. The fusion zone's grain size is finer in LB than MIG welding. EDX microscopic analysis reveals a slightly different structure in MIG and LB welds of BM microstructure, with filler altering Fe element and C-carbone content, causing brittleness due to ferrite content. The hardness results showed that no appreciable differences between MIG and LB in the welding bool area zone were equalled (265- 289Hv) respectively. Tensile strength and ductility increased with MIG and LBW in HAZ, at the same time laser welded specimens showing the highest ductility and strength.

Unveiling arc deflection instability in narrow gap laser-arc hybrid welding of thick Ti-6Al-4V plate

Unveiling the mechanism behind arc deflection under narrow gap laser arc hybrid welding (NGLAHW) is of paramount significance in mitigating laser-arc coupling failure and welding porosity for thick Ti-6Al-4V plate structure. This paper utilizes high-speed camera technology, data statistics and model prediction to comprehensively study the influence of constrained groove space and droplet transfer mode on arc deflection. The results demonstrate that narrowing groove gap exerts a substantial compressive effect on welding arc behavior, particularly rendering it more susceptible to arc deflection when the groove gap is smaller than the arc length. The small droplet transfer mode is characterized by stable arc behavior, whereas the large droplet transfer mode tends to be susceptible to arc instability due to the droplet deviation induced by turbulent metal vapor. Particularly noteworthy is the emergence of substantial arc deflection when the droplet deviation exceeds the critical threshold of 0.51 mm, which diminishes the driving force for droplet transfer and subsequently leading to potential short-circuiting explosions and unstable welding process. Moreover, the lateral force induced by arc deflection drives a deviation in arc heat source with accelerated solidification of molten pool, consequently resulting in an elevation in welding porosity. This paper has provided a comprehensive insight into the mechanism driving arc deflection in NGLAHW, which holds paramount importance in enabling effective strategies to regulate the arc behavior.

Damage evolution of titanium alloy laser-welded joint during hot deformation: Experiment and modeling

The damage evolution of TA15 titanium alloy laser-welded joint during hot deformation was studied by tensile tests and the GTN model. Tensile tests of the welded joint at 900 °C with different strain rates were carried out, and the evolution of cracks and voids in the welded joint during the tensile deformation was characterized. The response surface method combined with genetic algorithm was used to calibrate the GTN model at high temperature. The GTN parameters of titanium alloy welded joint under different strain rates at 900 °C were obtained. Results show that the voids first germinate at the grain boundary and gradually expand along the grain boundary during the tensile deformation. The inner wall of the welding porosity is easy to become the source of crack damage during the deformation, and the shape of porosity changes from round to oval gradually with the increase of strain. The true stress-strain curves obtained by simulation agree well with the experimental results, and the error between the predicted fracture strain and the experimental result is less than 5%. The developed GTN damage model was used in the simulation of hot gas free bulging, which demonstrates that it can predict the damage evolution and fracture behavior of the weld seam accurately under different conditions.