Weld Porosity Research Articles

Investigation of the Inhibition Mechanism of Process Porosity in Laser-MIG Hybrid-Welded Joints for an Aluminum Alloy

In this paper, 4 mm thick 7075 aluminum alloy was utilized for conducting laser-MIG hybrid welding tests to investigate the correlation between the dynamic behavior of keyholes and process-induced porosity. Additionally, the generation and inhibition mechanisms of process porosity were elucidated. Utilizing a high-speed camera test system of our own design, the formation position and movement characteristics of keyholes in the molten pool under different welding parameters were captured using a “sandwich” method. The dynamic behavior of keyholes during the hybrid welding process was analyzed, and the porosity of each welded joint was quantified, revealing an intrinsic relationship between keyhole dynamics and aluminum alloy laser-MIG hybrid welding porosity. The findings indicate that variations in the defocusing amount can influence both the morphology and stability of keyholes in the molten pool, consequently impacting welding porosity. The dynamic behavior of keyholes under different defocusing amounts can be categorized into five types: no keyhole formation, collapse of the keyhole root, complete instability of the keyhole, instability of the keyhole root, and stability of the keyhole. At a defocus of +12 mm, stable keyholes were observed, and no defects in the welded joints were identified.

Influence of travel speed on porosity and liquation cracking in cold wire pulsed gas metal arc welding of aa7075-t651 aluminum alloy

Influence of travel speed on porosity and liquation cracking in cold wire pulsed gas metal arc welding of aa7075-t651 aluminum alloy

Effect of Beam Oscillation on Weld Formation, Porosity, Grain Structure, and Mechanical Properties in Electron Beam Welding 5B70 Aluminum Alloy

Effect of Beam Oscillation on Weld Formation, Porosity, Grain Structure, and Mechanical Properties in Electron Beam Welding 5B70 Aluminum Alloy

Microstructures and mechanical properties of laser-arc hybrid welded high-strength aluminum alloy through beam oscillation

High-frequency beam oscillation and synchronous wire-powder feeding were adopted for the laser-arc hybrid welding of a 2219-T6 high-strength aluminum alloy. Increasing the beam oscillation frequency from 0 to 250 Hz not only reduced the weld porosity from 2.64% to 0.16% but also promoted the transformation of columnar dendrites to fine equiaxed grains. In addition, the content of precipitated Al2CuMg increased with the refined size of the weld microstructure. The length of the columnar grains and the diameter of the equiaxed grains in the weld center were reduced by 40% and 50%, respectively. Owing to these improvements, the weld microhardness increased and became more uniform, and the variance decreased by 74%. The ultimate tensile strength and elongation of the welded joint reached 238.5 MPa and 4.3%, respectively, which were 26.5% and 105% higher than those of the non-oscillating hybrid weld, respectively. The weld tensile strength and the proportion of the area of the pore were negatively correlated. The porosity and microcracks of the welded joints were the main factors affecting the tensile strength of welded joints.

Reduction in Porosity in GMAW-P Welds of CP780 Galvanized Steel with ER70S-3 Electrode Using the Taguchi Methodology

Reduction in Porosity in GMAW-P Welds of CP780 Galvanized Steel with ER70S-3 Electrode Using the Taguchi Methodology

Enhancing fusion welding in die-cast Mg alloys: A combined ultrasonic vibration and hot rolling approach for porosity reduction, microstructure refinement, and mechanical property improvement

Severe weld porosity has led the industry to believe that die-cast magnesium alloys cannot be fusion welded. To address this challenge, a new process of ultrasonic vibration coupled with hot rolling was employed to eliminate porosity, and the mechanism associated with weld porosity in die-cast magnesium alloys was analyzed in detail. Unlike conventional welding processes, ultrasonic vibration coupled with hot rolling is effective and efficient. In this study, a roller with ultrasonic vibrations is synchronized with the molten pool to apply pressure to the weld, which is in a semi-solid state on the upper surface. The results showed that hot rolling and ultrasonic vibration coupled with hot rolling could eliminate 78.12 % and 85.5 % of the porosity, respectively. Compared to hot rolling, the ultrasonic vibration coupled with the hot rolling process resulted in smaller and fewer porosities and finer β-Mg17Al12. This is attributed to the cavitation effect of ultrasonic vibration that promotes bubble overflow and breaks the β-Mg17Al12 dendrites in the melt pool, as well as the thermal effect that improves the plasticity of the weld. Furthermore, after closing the porosity under pressure, recrystallized grains will be produced around it. Tensile test results indicated that hot rolling was able to increase the ultimate tensile strength by 84.21 % and elongation by 44.03, whereas ultrasonic vibration coupled with hot rolling was able to increase the ultimate tensile strength by 244.46 % and elongation by 71.70 %. Combining the micron-scale industrial computed tomography results with theoretical calculations, it is found that the porosity of die-cast magnesium alloys is mainly caused by nitrogen, and they originate from gas entrapment during the die-casting process; further, the formation mechanism of die-cast magnesium alloys' fusion-welding porosity is revealed in detail. A physical model of the formation process of welded porosity morphology was established, and the analysis suggested that the pattern of the inner wall of the porosity was related to the Kelvin–Helmholtz instability. This research is expected to improve the weld quality of alloys manufactured by the die-casting process.

Machine learning-based weld porosity detection using frequency analysis of arc sound in the pulsed gas tungsten arc welding process

Automatic welding equipment has replaced human welders in the nuclear industry for safety issues and uniform and high welding quality. However, automatic welding equipment cannot predict porosity defects. So, the weldment must be inspected by non-destructive testing. This inspection was a costly and time-consuming process, and it applies to each weldment even if it welded same material. To improve the welding efficiency, a weld porosity detection system of the same weld material with different material thicknesses was needed. This paper proposed a machine-learned porosity detection system for 3.0 mm plates with welding arc sound data from the pulsed gas tungsten arc welding (P-GTAW) process of 1.6 mm plates. Ensemble-Empirical Mode Decomposition (EEMD) was used to divide the arc sound signal according to the pulse period of P-GTAW. Fast Fourier transform (FFT) was used to convert the arc sound into frequencies for features extraction according to porosity. The validity of these weld frequency features was confirmed through k-fold cross-validation across various machine learning techniques, with evaluation of F-1 scores against experimental weld sounds.

Detection of electrode misalignment and its effect on joint quality in resistance spot welding: a low-cost computer vision-based approach

Electrode misalignment in resistance spot welding can be caused by poor fitting or deformation of electrode with continuous usage. This leads to asymmetric weld nugget formation, porosity and expulsion. This paper presents a novel low-cost real-time inspection system for angular misalignment using an image processing approach. The proposed solution can effectively segment the electrode tips even from the image captured at noisy industrial background such as automotive assembly line, by using a regional convolutional neural network based object identification method. The trained model has a mean average precision and recall of 99.01% and 96.6%, respectively. A series of image processing tools and mathematical operations were used to identify the edge line contours of electrode tips accurately from the detection mask, and determine the angular misalignment with a maximum deviation of less than 0.06°. Experimental results showed that the weld nuggets exhibited porosity, shrinkage voids, and cracks when performed under angular misalignment conditions.

Optimization of Welding Parameters for Minimizing Defects and Porosity in Electric Arc Welding of Mild Steel Grade Fe 500 Using of Taguchi Method

Abstract: Electric arc welding is a widely used technique in industrial applications for joining metals, including mild steel grade Fe 500. However, the process is susceptible to defects such as porosity, which can compromise the integrity and quality of welds. In this study, we investigate the optimization of welding parameters to minimize defects and porosity in electric arc welding of mild steel grade Fe 500, utilizing the Taguchi method. The Taguchi method, known for its efficiency in optimization studies, is employed to systematically identify the most influential welding parameters and their optimal levels. Through a series of experiments based on the Taguchi orthogonal array design, we vary parameters such as current amperage, voltage, and electrode size to explore their effects on weld quality. The experimental results reveal significant insights into the relationship between welding parameters and defect formation. By analyzing signal-to-noise ratios and ultimate tensile strength, we quantify the effects of parameter variations on weld quality. The Taguchi analysis enables us to identify the optimal combination of welding parameters that minimizes defects and porosity while maximizing weld strength.

Porosity suppression of nickel-based superalloy by modulated base temperature in laser welding and mechanism analysis

This paper investigates the distribution pattern of welding porosity defects in annular weld seams of superalloy during laser welding. The results reveal that the initial portion of the annular weld seam exhibits a higher density and larger size of porosity defects compared to the ending portion. At a laser power of P = 360 W, the numerical simulation combination showed that the A1 region's average cooling rate is 8.767 × 103 °C/s and the A2 region is 8.151 × 103 °C/s that the thermal conduction effect at the initial welding position leads to an elevation in the base metal temperature in the subsequent unwelded region, thereby reducing the solidification rate of the molten pool in the latter half of the weld seam and effectively decreasing the porosity rate at the weld seam. Furthermore, the study demonstrates that elevating the base metal temperature can effectively modify the cooling rate of the molten pool, thereby influencing the formation of porosity defects. At a laser power of P = 360 W, increasing the base metal temperature to 600 °C reduces the cooling rate of the molten pool from 8.767 × 103 °C/s at a base metal temperature of T = 20 °C to 7.451 × 103 °C/s, leading to a decrease in the porosity rate from 3.357% to 0.022%. At a laser power of P = 672 W, increasing the base metal temperature to 600 °C reduces the cooling rate of the molten pool from 6.781 × 103 °C/s at a base metal temperature of T = 20 °C to 5.056 × 103 °C/s, leading to a decrease in the porosity rate from 8.214% to 0.002%. The increase in laser power brings more heat input, so the solidification rate of the molten pool decreases, but the porosity increases significantly. However, increasing the base temperature can effectively suppress the porosity defects under different laser powers. The research further reveals the relationship between welding porosity rate and cooling conditions, providing a control strategy for achieving low porosity rate welds.

Effect of beam current on microstructure, tensile properties and corrosion behaviour of electron beam welded zircaloy-4 joints

ABSTRACT Butt joints of zircaloy-4 were made using electron beam (EB) welding. The effect of beam current (15–20 mA) on weld zone size, microstructure, porosity, mechanical and corrosion properties has been investigated. Local temperature and cooling rate were estimated, and the average cooling rate increased from 2.4 to 6.3°C ms–1 with a decrease in beam current in the said range. Joints prepared at lower beam current possessed smoother weld surface, narrow weld bead, and fine lamellar type widmanstätten structure in the fusion zone (FZ). The length of the α-Zr lamella (from 105 to 37 µm) and interlamellar space (from 0.8 to 0.3 µm) decreased with a decrease in beam current. The XCT result revealed that porosity increased with an increase in beam current, and large-size micro pores of 180 µm were present in joints prepared at high beam current. The hardness of the welded samples increased by 13–20% than the base metal. The joint prepared with a low beam current possessed higher ductility (29%) and a minimum corrosion rate (0.0085 mmpy in 3.5 wt-% of NaCl solution) than the joint made with a higher beam current.

Non-destructive detection and analysis of weld defects in dissimilar pulsed GMAW and FSW joints of aluminium castings and plates through 3D X-ray computed tomography

AbstractThis work focuses on porosity formation during the welding of dissimilar aluminium alloys (cast and sheet) by pulsed gas metal arc welding (GMAW) with different travel speeds (12–14 mm/s) and by friction stir welding (FSW). The case study concerns the assembling of a battery-pack enclosure prototype. The welded specimens were scanned by 3D X-ray computed tomography. The cast base material (BM) shows a porosity percentage of 1.45%, and it is characterized by pores with a strong hyperbolic relationship between equivalent diameter and sphericity. Considering the GMAW beads, porosity rises with the travel speed (from 1.80 to 5.12%), due to the reduction of the opening window in which pores can escape. Pores with volume higher than 0.10 mm3 rise with the travel speed, representing from 9.75 to 32.98% of the total porosity. These pores are responsible for the weaker hyperbolic connection for sphericity found for the GMAW beads. On the other hand, FSW mixes and homogenizes the pores in the cast BM. The novelty of the paper lays in proving the strong potentialities of FSW for weld porosity reduction. A re-designing of the battery-pack enclosures is necessary to limit arc welding in marginal areas, which are not crucial for sealing but necessary to create a stable platform to be subsequently sealed with FSW.

Weld formation and porosity in TC4 joint by oscillating laser beam welding with circle trajectory model

The pores problem is a challenging problem in laser beam welding titanium alloy TC4. Oscillating laser beam welding, as a new welding process, can effectively control the behavior of the molten pool, and is beneficial to the escape of pores, which holds promise for achieving high quality TC4 joint. Selecting appropriate oscillation parameters is the key to obtaining high quality TC4 joint by LBW. This project will focus on researching the effects of oscillating parameters on weld formation and porosity of TC4 joint by oscillating laser beam welding. Firstly, the oscillating laser beam welding experimental platform was set up, and experiments on oscillating LBW were designed and conducted. Subsequently, the microstructure of TC4 joint was analyzed, and the effects of oscillating frequency and oscillating amplitude on weld formation were studied, and the effects of oscillating frequency and oscillating amplitude on porosity were researched. The results indicate that oscillating laser beam welding with circle trajectory model can achieve high quality TC4 joint. The porosity of weld by oscillating LBW with oscillation amplitude as 1 mm and oscillating frequency as 80 Hz reaches 0.13% in value which is the lowest among the experiment cases under the condition as fixing the oscillation amplitude 1 mm in value and varying the oscillation frequency from 40 Hz to 240 Hz. When the oscillation amplitude exceeds the critical value 2.5 mm, the weld by oscillating LBW exhibits noticeable undercutting and asymmetry. The undercutting occurs on the advancing side in oscillating LBW with circle trajectory model. To a certain extent this study enriches the theory of oscillating LBW, and can provide fundamental data for oscillating laser beam welding on TC4.

Mechanism of pore suppression in aluminum alloy laser-MIG hybrid welding based on alternating magnetic field

An experiment was conducted on the laser-metal inert gas hybrid welding of 7075 aluminum alloy under alternating magnetic field assistance, in order to investigate the effect of the magnetic field on weld porosity defects in aluminum alloy. The internal porosity of the weld seam under different magnetic field conditions was compared and analyzed through radiographic inspection. The impact of the alternating magnetic field on the arc shape and keyhole dynamic behavior was observed and analyzed by high-speed photography. The results showed that without a magnetic field, the arc shape underwent continuous scaling during the transition of molten droplets, the keyhole root was unstable, and there were a large number of process-induced porosities distributed in the center of the weld. When the magnetic field strength was 10 mT, the keyhole was completely unstable, and the size of the internal porosities in the weld seam significantly increased while the number of porosities decreased. At a magnetic field strength of 20 mT, the arc exhibited a rotating oscillation behavior, the keyhole was in a stable open state, and no porosity was detected in the weld seam. Upon reaching a magnetic field strength of 30 mT, the keyhole was also in a root unstable state, but the collapse and recombination speed of the keyhole were faster than that without a magnetic field, and the size and number of internal porosities in the weld seam significantly decreased.

Effects of beam oscillation on porosity and microstructure of laser welded TC11 titanium alloy

Oscillating beam was used for laser welding of TC11 titanium alloys. The porosity, microstructure, and mechanical properties of welds with different parameters were studied. It was found that increasing the oscillation frequency could effectively suppress porosity. When the oscillation amplitude was less than or equal to 1 mm, the laser power was about 3 kW, and the welding speed was less than 15 mm/s, porosity could be effectively suppressed. Both oscillation frequency and amplitude could increase the number of α′-phase. The oscillation frequency promoted the cross distribution of α′-phase and α″-phase in the columnar crystal. The oscillation amplitude promotes the uniform distribution of α′-phase in the columnar crystal. Increasing the oscillation frequency and the oscillation amplitude was beneficial to increase the tensile strength. In the case of low defect rates, the tensile strength of the weld could reach more than 90% of the base metal, and the maximum elongation was 7.5%.

Arc and keyhole behavior in narrow-gap oscillating laser-MIG hybrid welding of thick aluminum alloys

Narrow-gap oscillating laser-MIG hybrid welding was developed to weld thick aluminum alloys. Weld formation and porosity defect with various oscillating laser parameters were systematically analyzed. Furthermore, the corresponding influencing factors, i.e., arc and keyhole dynamic behaviors were discussed. The difference between both sidewall penetrations was small while wire feeding speed was high and oscillating laser diameter was lower than 3 mm. When laser oscillating frequency was higher than 300 Hz, porosity was less than 0.5 %. Arc burnt stably and the deflection angles were small while laser oscillating frequency was 300–450 Hz and diameter was 1–2 mm. The small fluctuation of arc resulted in small difference between both sidewall penetrations. With the action of oscillating laser, the charged particles increased and diffused to the upper part of the groove. Therefore, arc was attracted by the charged particles and struck at the center bottom of groove. While the arc burnt stably, the difference between both sidewall penetrations was small. The pore formation was significantly inhibited by oscillating laser, as the keyhole opening size increased and fluctuation degree decreased. With the action of oscillating laser, the ratio of keyhole opening width to depth increased, the probability of Rayleigh jet instability on the keyhole wall was reduced.

Effects of oscillating frequency on keyhole stability and porosity inhibition in high-power laser-arc hybrid welding of 10-mm-thick 6082 aluminum alloy

Keyhole instability and high porosity are prone to occur in laser-arc hybrid welding (LAHW) with an increase in aluminum alloy thickness. In this study, a high-power laser up to 8.0 kW at different oscillating frequencies (f) was used to achieve acceptable hybrid welding of a 10-mm-thick 6082 aluminum alloy. According to the observations of the laser keyhole from a high-speed camera, increasing f from 0 to 100 Hz increased the opening diameter from 1.3 to 1.6 mm and decreased the collapse frequency from 642 to 353 Hz. With the improved keyhole stability, the weld porosity decreased from 4.5% to 1.8%. In addition, beam oscillation refined the weld microstructure by 15% and transferred the tensile fracture from the weld center to the heat-affected zone (HAZ). Although the change in the ultimate tensile strength (UTS) was not obvious, the elongation increased by 25%. Beam oscillation promoted the formation of turbulent flow inside the molten pool, homogenized the melt flow, and reduced the necking tendency of the keyhole caused by the melt flow, thus greatly improving the keyhole stability.

Joining aluminum die castings and wrought aluminum by resistance spot welding

Resistance spot welding (RSW) is an economic, robust welding process, which is easy to automate and widely used in automotive industry. In this work, the resistance spot weldability of die-cast aluminum alloys EN AC-AlSi7MnMg, EN AC-AlSi9Mn and EN AC-AlSi10MnMg-T6/T7 to wrought aluminum alloy EN AW-AlSi1MnMg-T6 is investigated when applying the standard welding profile as recommended in VDA 238-401 considering main challenges in welding aluminum die castings, for example, porosity and inhomogenities. Weldability is best for EN AC-AlSi10MnMg-T6/T7, but the results show limited applicability of VDA 238-401 in general, especially for high total sheet thicknesses, because of invalid electrode force favouring spatter formation and weld spot irregularites. Still, all spot welds between die castings and 2 mm wrought aluminum sheets reach the recommended shear tension forces for spot diameter dw of 5·√t (2 mm: 5.95 kN; 3 mm: 8.96 kN; according to DIN EN ISO 18595), although being afflicted with solidification porosity and liquation cracking. Gas porosity is not observed and solidification porosity is only found to be significant for weld spot failure when being located close to the joining level, which is observed at welding depths of approximately 50% into the wrought aluminum sheet. Here, a failure path across the nugget is found. Weld porosity apart from the joining level is less significant and failure path is found along the fusion line between nugget and wrought aluminum. Instead, hardness difference between nugget and HAZ is the main reason for weld spot failure. Although the applied welding current profile is not suited best for RSW of mixed joints between aluminium die castings and wrought aluminium alloys, the results confirm its potential, for example, a significantly reduced gas porosity compared to applied fusion welding processes.

A novel optimizing Pulsed Plasma Gas Variable Polarity Plasma Arc Welding (PPG-VPPAW) method for improving weld quality

To enhance the reliability of aluminum alloy welding quality, a novel Pulsed Plasma Gas Variable Polarity Plasma Arc Welding (PPG-VPPAW) system is proposed. This system enables independent control and rapid adjustment of the plasma gas, allowing for flexible modulation of arc pressure output under constant thermal conditions, thereby reducing porosity and refining grain structure. The research analyzed the impact of parameters of different plasma gas on arc characteristics, welding porosity, and welding microstructure. The results reveal that the periodic changes in pulsed plasma gas induce corresponding variations in arc temperature, arc shape, arc pressure, arc voltage, and the morphology of the weld pool keyhole. The magnitude of the difference between the base value and peak value of pulsed plasma gas determines the extent of arc pressure fluctuations and the behavior of the backside keyhole. The maximum oscillation amplitude of the backside keyhole can reach up to 4.5 mm². Additionally, the oscillation of pulsed plasma gas within the molten pool has been demonstrated to effectively reduce weld porosity and refine grain size. Under this process, the grain size of the weld metal can be reduced by up to approximately 25%. Current work provides an important direction for fabricating highly reliable aluminum alloy weldments.

Investigation of the tensile strength of the CMT and PCMT joints of AA8011 aluminum alloy

The advanced variant of gas metal arc welding (GMAW) known as cold metal transfer (CMT) developed by Fronius in Austria is used to overcome heat-input- and fusion-related issues such as porosity and cracking in welding of AA8011-H18 alloy sheets. AA8011-H18 alloy sheets 3 mm thick were welded using normal CMT-GMAW and pulsed CMT (PCMT)-GMAW processes. The microstructure of the weld metal and heat-affected zone was analyzed using an optical microscope. The tensile properties and hardness of joints were evaluated and compared. The results revealed that the PCMT-GMAW joints showed 26.45, 48.97 and 40.42% improvements in tensile strength, yield strength and elongation, respectively, compared with CMT-GMAW joints. The superior tensile performance of PCMT-GMAW joints compared with that of CMT-GMAW joints is due to the current pulsing effects along with the wire retraction mechanism, which aids in reducing the heat input and controlled droplet transfer.