Weld Reinforcement Research Articles

Evaluating the fatigue property of S355J2W steel butt-welded joint: Multiple notch effects

The fatigue fracture mechanisms and the fatigue property evaluations of S355J2W steel butt-welded joints relieved welding residual stresses with and without welding reinforcement were systematically investigated by microstructure characterization and fatigue tests. Experimental results show that the complex evolution of microstructure at welded joint results in the notable degradation of mechanical properties. The fatigue performance of the as-welded specimen with welding reinforcement is significantly poorer than that of the smooth-welded specimen without welding reinforcement. Stress concentration under the fish-scale pattern at the weld toe caused by geometric dimension change is the major reason for the fatigue fracture of the as-welded specimen. By comparison, the cementite segregation at grain boundary in the partial recrystallization zone of the heat affected zone caused by the sharp change of microstructure should be responsible for the fatigue fracture of the smooth-welded specimen. The fatigue notch coefficient (Kf=1.89) calculated by the effective notch stress method is consistent with that (Kf=1.9) measured by the fatigue tests, which shows that the effective notch stress method can well evaluate the multiple notch effect under the coupling of the weld toe and the fish-scale pattern. Furthermore, the fatigue risk factor (Rf) model was employed to evaluate the fatigue performance of welded joint, and the intuitive Rf curves show that the fatigue fracture occurs at the fatigue life exceeding 2 × 106 cycles, i.e., Rfmax exceeds 0.7.

Investigating the multiscale effects of a novel post–weld composite processing treatment on minimizing weld softening in AA6061-T6 Al–alloy

The fusion welding of heat-treatable AA6061-T6 aluminum alloy results in significant joint softening which results in the ultimate tensile strength (UTS) and elongation (El) of the welded joint only reaching up to 60–70% and 40–50% of the base metal (BM), respectively. A post–weld composite processing treatment (PWCPT) that uses solution treatment (ST), artificial aging treatment (AT) and cold rolling (CR) has been proposed in this study to mitigate this issue. The effect of different composite process sequences and parameters on the microstructural characteristics and mechanical properties of the joints were investigated. The results show that the formation of the fine-grained microstructure in the fusion zone (FZ) and abnormal sandwich microstructure in the heat-affected zone (HAZ) was highly dependent on the dislocation density and fraction of the insoluble phases. By clarifying the strain characteristics of the joints, a strategy was developed to optimize the homogeneity of the microhardness distribution which improves joint ductility. The optimal PWCPT involved the ST and AT for the AA6061-T6 joint that was produced by tungsten inert gas (TIG) welding with filler wire, with subsequent cold rolling of the weld reinforcement to achieve a rolling reduction of 1.2 mm. The PWCPT could completely eliminate joint softening and improved the joint UTS and El to 100% and 88.6% of the BM, respectively. By systematically expounding the evolution law of microstructure and mechanical properties of the welded joint under the coupling of thermal and mechanical, the strengthening mechanism of the PWCPT is revealed.

Improving heat-affected zone softening of aluminum alloys by in-situ cooling and post-weld rolling

The welding of aluminum alloys (Al-alloys) is of great practical relevance in several industries, but the process can be problematic due to the prevalence of a well-known softening phenomenon in the fusion zone (FZ) and heat-affected zone (HAZ) surrounding the weld. This phenomenon has a unique gradient-like characteristic such that the HAZ near the FZ softens the most and the softening degree decreases as the distance from the FZ increases. To minimize the adverse effect of joint softening, this study proposes the use of a novel hybrid manufacturing process for joining AA5083-O and AA6061-T6 dissimilar Al-alloys, using tungsten inert gas (TIG) welding with filler wire under in-situ cooling conditions using specialized welding fixtures followed by the subsequent rolling of the weld reinforcement. The results show that welding under in-situ cooling conditions can improve the joint softening gradient, and the rolling of the weld reinforcement can introduce a strain hardening gradient, that greatly improves the integrity of the joint. By employing the proposed method, the fracture is successfully transferred from the HAZ of the AA6061-T6 side, where it normally occurs, to the base metal (BM) of the AA5083-O side. The proposed process has an extremely high impact potential as it can greatly increase the adoption of Al-alloys in the manufacturing of lighter automotive vehicles which will improve their efficiency and performance.

Effects of In-Process Ultrasonic Vibration on Weld Formation and Grain Size of Wire and Arc Additive Manufactured Parts.

Wire and arc additive manufacturing (WAAM) is a competitive technique, which enables the fabrication of medium and large metallic components. However, due to the presence of coarse columnar grains in the additively manufactured parts, the resultant mechanical properties will be reduced, which limits the application of WAAM processes in the engineering fields. Grain refinement and improved mechanical properties can be achieved by introducing ultrasonic vibration. Herein, we applied ultrasonic vibration to the WAAM process and investigated the effects of wire feed speed, welding speed, and ultrasonic amplitude on the weld formation and grain size during ultrasonic vibration. Finally, a regression model between the average grain size and wire feed speed, welding speed, and ultrasonic amplitude was established. The results showed that due to the difference in heat input and cladding amount, wire feed speed, welding speed, and ultrasonic amplitude have a significant influence on the weld width and reinforcement. Excessive ultrasonic amplitude could cause the weld to crack during spreading. The average grain size increased with increasing wire feed speed and decreasing welding speed. With increasing ultrasonic amplitude, the average grain size exhibited a trend of decreasing first and then increasing. This would be helpful to manufacture parts of the required grain size in ultrasonic vibration-assisted WAAM fields.

Multimodal-based weld reinforcement monitoring system for wire arc additive manufacturing

With the rise of big data and artificial intelligence, intelligent welding systems (IWS) are attracting more and more attention in machinery manufacturing. The work focused on weld reinforcement monitoring in wire arc additive manufacturing (WAAM). To track deposition status, a weld reinforcement monitoring or prediction system based on multi-modality was proposed. It is expected to be used as a functional component in the IWS in the future, helping to monitor deposition quality and detect anomalies. The reasons for adopting multi-modality can be summarized as follows. Firstly, the complex deposition process is hard to characterize with a single sensor. Secondly, equipped with a multi-sensor can reduce the impact of strong arc light or splash on the monitoring system. To fuse the welding information from different sensors, an implicit fusion method based on parameter sharing was adopted. The core of the proposed monitoring system is the neural network model. The input of the model includes two parts: molten pool images and infrared temperature field. Experimental results demonstrated that the model's weld reinforcement prediction error is around 0.05 mm. The study proved the effectiveness of multi-modal information for weld reinforcement monitoring systems.

Fatigue properties and fracture behavior of Al/steel butt joints fabricated by laser‐MIG welding‐brazing

AbstractRobust 2‐mm 6061‐T6/SUS304 butt plates were obtained using laser‐MIG hybrid welding‐brazing technology. The fatigue properties and fracture behavior of Al/steel welding‐brazing joints were first discussed. Due to the change in the fracture mechanism, the weld reinforcement improved the fatigue strength, which was higher than that of the Al/steel joints using the solid‐state welding method. This strengthening effect was very different from traditional fusion welding joints with reinforcement. The fatigue test results showed that the fatigue strength of the Al/steel joints with reinforcement reached about 105 MPa at 106 cycles. After removing the weld reinforcement, the fatigue strength of the Al/steel joints reduced significantly to 55 MPa. The existence of reinforcement also led to different fatigue fracture behaviors. In the Al/steel joints with reinforcement, the fatigue fracture mode changed with increasing cyclic stress load, and the fatigue crack initiation zone was inclined to begin at the weld toe and then propagated along the weld at a lower stress load. Fatigue crack initiation sites moved to the aluminum weld near the interface and spread along with the IMC layer and the aluminum weld at higher stress loads. After removing the weld reinforcement, only the interface fracture mode was found.

Field testing and performance optimization of a weld reinforcement device in heavy haul railways

The Bowed plates weld device (BPWD) is a new type of rail weld reinforcement device, which has been widely applied in heavy haul railway lines in China. It changes the service state and vibration characteristics of a weld. In order to explore the BPWD vibration influence on the track, static, and dynamic on-site tests were carried out on a heavy haul line. The vibration influence and spectrum characteristics of the track between BPWD and unplated weld (UW) was compared. At the same time, a 3D coupling model of heavy haul train-rail weld was established and optimization of service performance of the BPWD was carried out. The results showed that the average acceleration of rail, sleeper and ballast at the BPWDwere 52.7%, 43.5%, and 50.2% lower than that of UW. In comparison with UW, peak value of the periodic frequency spectrum and dominant frequency distribution in the BPWD track structure could be effectively reduced from rails to ballast. Length of 0.8 m for plate was found to be optimum in order to reduce the rail stress effectively. The material of the insulating interlayer should preferably be nylon.

Finite element simulation of tensile behavior of laser welded 5083 aluminum alloy joint with different filler wires

5083 aluminum alloy (AA5083) is prone to produce pores and undercut defects during laser welding because of violent fluctuations and Mg alloy elements burning in a molten pool, which seriously affected the tensile properties of the welds. In this paper, the process of laser welding with filler wire was used to improve weld properties, and through experiments and finite element simulation (FES), the effects of welding wires (ER4047, 5356, and 5087) on joint properties and failure behavior were studied. The FES simulation results are very consistent with the digital image correlation (DIC) experiment measurements, which verifies the accuracy and reliability of the finite element model proposed in this work. With the FES, it was further found that the filler wire produced the weld reinforcement, which changed the stress and strain distribution around the weld. The location of the maximum strain of the weld is changed from the undercut of the no-filler wire weldment to the weld toe of the filler wire weldments. The stress concentration at the undercut of the weld is greatly reduced, and the load-carrying capacity of the filler wire welded joint is improved. Analysis shows that the high Mg content of ER5087 effectively suppressed the formation of porosity to obtain the highest tensile strength (285 MPa), reaching 85% of the base metal (BM) strength. The filling of the welding wire changed the fracture mode from ductile-brittle mixed fracture of no-filler wire to ductile fracture with filler wires.

Sequentially combined thermo-mechanical and mechanical simulation of double-pulse MIG welding of 6061-T6 aluminum alloy sheets

Double-pulse MIG (DP-MIG) welding is an efficient aluminum alloy jointing technique, which can form heterogeneous aluminum alloy welded sheets with different microstructure and mechanical properties. In order to accurately analyze and predict mechanical properties of welded structures, the geometrical features, local material properties and residual stresses of different welded zones should be synthetically considered in the numerical simulation. This work proposes a sequentially combined thermal-mechanical and mechanical simulation to accurately characterize the mechanical properties of the welded joint through the finite element analysis (FEA) method. The thermo-mechanical simulation was carried out to analyze the transient temperature field and residual stress distribution, which are conductive to build mechanical simulation model with detailed geometric features, the corresponding local material properties as well as attached residual stress. Subsequently, the mechanical simulation was performed to investigate the stress distribution of the welded joint. The deformation behavior and load-carrying capacity of the welded joint from numerical simulation are all in good agreement with corresponding experimental study, which indicates the feasibility and superiority of the developed sequentially combined thermal-mechanical and mechanical simulation method. Also, the stress distribution of the welded joints analyzed by numerical simulation reveals that the fracture evolution mechanism depends on whether the reinforcement has been removed from the welded specimen. The existence of the weld reinforcement leads to the increase of shear stress under tensile condition; hence, the fracture morphology includes equiaxed dimples and elongated dimples. When the reinforcement is removed, the mechanism is trans-granular and inter-granular mixed fracture in the welded zone; otherwise, trans-granular fracture occurs in the heat-affected zone.

Study of weld formation characteristics in laser-arc hybrid welding

The laser-arc hybrid welding was carried out on the marine-use steel, and the effects of primary parameters on weld behavior were investigated. The results show that the weld penetration increased gradually with the increase of laser power. Meanwhile, superior weld formation, penetration and reinforcement were achieved when laser and wire distance was 2 mm. The weld width, penetration and reinforcement were increased with the increase of current, while they were decreased with the increase of welding speed. The influence of laser power on the generated microstructure was analyzed by the observation in junction of weld and heat affected zone (HAZ). The microstructure of HAZ coarsened with the increase of laser power, which is consistent with the hardness distribution trend in HAZ.

Study on the Molten Pool Fluid Behavior of PAW-Cable-Type Seven-Wire GMAW Hybrid Welding

Plasma arc welding (PAW)-cable-type seven-wire GMAW (gas metal arc welding) hybrid welding is known as a high-efficiency welding combining plasma arc, GMAW arc and cable-type welding wire. In this study, numerical simulation via Fluent of the molten pool temperature field and flow field and experimental verification were conducted on Q235 thin plate hybrid welding with cable-type wire to explore molten pool fluid behavior. The simulation results show that keyholes form in the molten pool due to the strong penetration ability of a plasma arc and then the evolved pores by the surface tension float out of the molten pool. When the GMAW welding current increases, both the length and width of the weld pool enlarge, the weld reinforcement increases and the flow rate of molten metal in the weld pool also speeds up. While the PAW current increases, the weld pool length also increases and the molten metal in the weld pool significantly flows faster, but the weld reinforcement decreases. When the welding speed increases, the weld pool length and fusion depth decrease, but the reinforcement will first increase and then decrease. The experimental results are in strong agreement with the simulation results. It shows that the numerical analysis model established in this paper is accurate, laying a certain theoretical foundation for the popularization of PAW-cable-type seven-wire GMAW hybrid welding.

Experimental investigation and optimization of weld bead shape factor and form factor using recycled steel slag as a flux in submerged arc welding process

The quality and productivity of welds produced depend upon the weld bead profile which is represented by weld penetration shape factor (WPSF) and weld reinforcement form factor (WRFF). The weld profile is further dependent upon welding parameters used hence optimization of welding parameters is essential. In this research work, the steel slag has been recycled to act as a flux in submerged arc welding. The effect of process parameters on WPSF and WRFF using recycled slag has been evaluated. The mathematical models have been developed from the data created. It was found that the weld deposited with recycled steel slag performs well as the WPSF and WRFF are comparable with that deposited with fresh flux. The welding parameters have been optimized using the desirability approach and genetic algorithm. The genetic algorithm yielded more accurate results as compared to the desirability approach.

Study of the solidified thin layer on molten pool surface in laser deep penetration welding

Morphology and temperature are two important features of molten pools in laser deep penetration welding. An experimental platform equipped with a high-speed camera and a two-color pyrometer was built to observe the variations in the morphology and temperature, and a floating layer on the surface of a molten pool was discovered. The floating layer’s morphology, temperature, and thickness were described, and there was a correlation between the morphology of the floating layer and the temperature distribution of the molten pool. The results revealed that the variation range of floating layer thickness is primarily related to three factors: the floating layer area, the molten pool’s temperature, and the inclination angle of the floating layer immersed in the molten pool. Surface tension is an important factor in allowing the solidified thin layer to float on the surface of the molten pool. During laser deep penetration welding, the floating layer area goes through three stages during laser welding: growth, reduction, and dynamic stabilization. Finally, the floating layer abbreviated as “STL”, is defined as the solidified thin layer. As the laser power increases, the STL area decreases and the weld reinforcement is lower. Weld reinforcement is linearly related to the STL area. In summary, this study’s results provide a theoretical foundation for predicting the welding quality in laser deep penetration welding in the future.

Effect of high-frequency phase shift on metal transfer and weld formation in aluminum alloy double-wire DP-GMAW

This paper presents a double-wire gas metal arc welding (GMAW) system for investigating the effects of high-frequency phase shift of the double pulse on metal transfer and bead formation. First, a theoretical analysis of the double-wire metal transfer process was carried out and a mathematical model of droplet impact was established. The metal transfer processes of different phase shifts were then photographed using a high-speed camera, the droplet velocity and impact on the weld pool at different phase shifts were calculated, and geometries of the weld beads were analyzed. Penetration of the longitudinal section fluctuated due to the modulated double pulse and the penetration depth increased with increasing phase shift; however, the weld reinforcement was irregular. The weld width increased with decreasing phase shift due to the temperature gradient. Moreover, since a reduction in double arc interference reduced the size and number of pores, porosity of the weld decreased with higher phase shifts. Stirring induced by the double pulse promoted floating and precipitation of pores. The experimental results show that a 180° phase shift leads to the most stable welding process resulting in a sound weld and an obvious fish-scale appearance. No undercut, hump, or spatter defects were observed. In addition, the deepest penetration with a uniform and smooth penetration fluctuation curve and the lowest porosity were also achieved with a phase shift of 180°.

Study into the effect of different energy sources on the structure and mechanical properties of EP693 nickel alloy weld joint

The paper provides the results of a study on the influence of welding types (laser, electron beam, and TIG welding) on the properties of a permanent connection made of an EP693 alloy of the Ni–Cr–W–Co–Mo system used in the production of gas turbine engine components and parts. EP367 filler wire of the Ni–Mo–Cr–Mn system was used to obtain a weld during laser and TIG welding. A comparative analysis of heating areas and power densities was performed for the welding types studied. It was established that TIG welding features by greater values of the heating area and power density in comparison with laser and electron beam welding. It was found that the type of welding affects the features of weld formation. For example, a weld is formed with the transition to knife fusion penetration in the weld root for electron beam welding, and in the form of an «hourglass» for laser welding. The analysis of the heat affected zone microstructure showed that the smallest grain size is formed during laser welding. The distribution of elements in the weld joint was analyzed. It was found that when welding with the use of filler wire, the Mo content increases and the W, Co, Al, and Ti content decreases in the weld and heat affected zone relative to the base metal. This determines the peculiarities of failure for samples obtained using the welding types studied. Samples obtained by TIG and laser welding broke along the heat affected zone on the weld reinforcement side. Samples obtained by electron beam welding broke along the weld. Mechanical tests of samples at room and elevated temperatures showed that samples obtained by laser and electron beam welding have the highest tensile strength.

Experimental investigation on cladding with metal cored wire using GMAW process and parametric optimization

Cladding is widely used in manufacturing industries for the production of pressure vessel by depositing thick layer of filler material for providing corrosion resistant-surface. The use of metal cored wire in gas metal arc welding (GMAW) process is popular due to its higher deposition rate and productivity. This work investigates the effect of process parameters on the deposition of cladding layer with ER 309L metal core wire (as filler material) on a corrosion resistant material (IS 2062). The welding parameters viz., wire feed rate (WFR), voltage (V), welding speed (S) and nozzle to plate distance (NTD) are employed as process parameters while penetration (P), bead width (W), reinforcement (R), weld penetration shape factor (WPSF) and weld reinforcement form factor (WRFF) as welding responses. The predictive model developed for P, W, R, WPSF, and WRFF using the response surface methodology (RSM) approach is found adequate at 95% confidence interval. The validation results for the developed model results in a model accuracy (MA) of 92.82%, 96.34%, 91.47% 88.98% and 87.75% for model P, W, R, WPSF, and WRFF respectively and it shows higher predictability and accuracy. The process parameters are optimized simultaneously with integrated optimization approach using RSM with Jaya algorithm and obtain optimal solution in less than 20 number of iterations. The minimum fitness value obtained as 1.3008 at an optimal parameter setting of WFR = 12 m min−1, V = 26 V, S = 280 mm min−1, NTD = 10 mm. The validation result at the optimal parameter setting results in an improvement of 6.45%, 11.29%, 13.58%, 16.07%, 15.38% is noted for P, W, R, WPSF, and WRFF respectively.

Coordinated monitoring and control method of deposited layer width and reinforcement in WAAM process

Wire arc additive manufacturing (WAAM) has been used extensively in metal manufacturing and other fields because of its low cost and high efficiency. In the manufacturing process, WAAM technology is often unable to be further applied due to issues such as component dimensional accuracy, layered morphology, and metallurgical defects. To overcome these problems, online monitoring and process control of the welding are necessary. Based on the monitoring of weld width and reinforcement, a regression network for extracting the global information of molten pool is proposed, and an active disturbance rejection control (ADRC) is designed to adjust the welding current. To the best of our knowledge, this is the first time to realize the coordinated monitoring and control of the width and reinforcement of the deposited layer in the WAAM process. Experiments show that the method can obtain satisfactory molten pool width and reinforcement control accuracy, which provides a feasible way for monitoring and control the weld shape in the WAAM welding process.

Quantitative prediction for weld reinforcement in arc welding additive manufacturing based on molten pool image and deep residual network

In the process of arc welding additive manufacturing, real-time monitoring weld reinforcement of the deposited layer could provide additional information for the researcher to understand the layer by layer mechanics. In this paper, a molten pool vision sensor system is utilized to collect the welding pool image at the first 1 ms of the short circuit phase. A locating system is applied to detect the position of welding pool image on the deposited layer and a three-dimensional system is utilized to measure the actual weld reinforcement. A residual-based network is designed to quantitatively predict the weld reinforcement of the deposited layer. The prediction results indicate that the proposed prediction system has low prediction error (less than 0.05 mm) and strong generalizing performance in different inter-layer cool-down time, because the shape and temperature distribution of the molten pool are the main affecting factors in weld reinforcement quantitative prediction of arc welding additive manufacturing.

Effects of welding flux on welding quality during arc stud welding process

In this paper, a welding flux powder with the main composite of Fe3O4, FeO and aluminum was developed to improve the weld quality of stud welding. The orthogonal test was used to optimize the interaction influences of welding flux powder and welding process parameters. The mechanism of welding flux reducing arc blow phenomenon during arc stud welding were clarified. The results show that optimized joints with an average shear strength of 308 MPa were obtained by the welding current of 600 A, welding time of 400 ms and flux addition amount of 0.26 g. The arc migration driven by welding flux led to the uniform heating process, and then the uniform heating led to uniform weld reinforcement fillet around the stud and minimize welding defects, which was responsible for the high shear strength of the joints obtained with welding flux. The Al2O3 with low electronic work function produced by the self-propagating reaction of FeO, Fe3O4 and aluminum powder was the main reason to drive the arc migration.

Application of Taguchi method and ANOVA analysis for optimization of process parameters and exothermic addition (CuO-Al) introduction in the core filler during self-shielded flux-cored arc welding

The main factors affecting the mechanical properties of the deposited metal in arc hardfacing are primarily the chemical composition and the cooling rate. The latter depends on the filler materials composition, hardfacing condition (mode), and hardfacing technology, determining the geometric parameters and parameters of the welded bead shape, the amount of deposited metal dilution with the base metal, and the amount of the introduced heat. The goal of this work is to analyze the effect of exothermic addition introduction to the core filler and the effect of welding condition on weld bead morphology, thermal indicators, and mechanical properties of the deposited metal. The deposited metal of the Fe-C-Cr-Cu-Ti-V-Al alloying system was used. The Taguchi technique was adopted as the experimental plan design, as follows: the orthogonal array L9 (3 ^ 4) and signal-to-noise ratio (S/N). The analysis of variance (ANOVA) was also applied for determination of the variables contribution to the dependent parameters. Application of the Taguchi method is simpler, more efficient, and quicker. It requires fewer experiments to determine the optimal values of the studied variables. Microstructural studies using an optical microscope were additionally performed for individual samples of the weld metal with the best mechanical properties, for each of the experimental flux-cored wires. We determined that introduction of CuO-Al exothermic addition of to the core filler had a significant effect on such indicators of the weld bead morphology as the weld reinforcement height and the weld reinforcement form factor (WRFF). Introduction of exothermic addition (CuO-Al) to the core filler had a significant effect on the welding current (I), heat input rate (HIR), and microhardness. The arc voltage (Р(Ua) = 45.8 %) had the greatest influence on the microhardness value, while the percentage of exothermic addition in the core filler (P (EM) = 26.9%) and the wire feed rate (P (WFS) = 21.5%) had a smaller effect. It was shown that it is important to take into account complex parameters, such as dilution variation and weld reinforcement form factor (WRFF) for the geometric characteristics of the weld bead and heat input rate (HIR) for heat indicators in order to optimize hardfacing conditions and composition of the core filler (introduction of exothermic addition). According to the results of the article, the value is the most correlated with the average values of microhardness.