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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. [ABSTRACT FROM AUTHOR]

Laser-MIG hybrid welding and MIG welding were carried out on 7B52 aluminum alloy, and the microstructure and mechanical properties of the joints were compared and analyzed. The results show that the average grain sizes of laser-MIG hybrid welding, MIG welding, and the laser weld zone are 18.38 μm, 24.16 μm, and 15.96 μm, respectively. The width of the HAZ of the laser zone is lower than that of the laser-MIG hybrid welding zone and MIG welding zone. The hardness is higher than that of the hybrid welding zone and MIG welding zone. The tensile strength of each laser-MIG hybrid welding joint zone is better than that of the MIG welding zone. The tensile strength of the laser zone is the worst. When stress ratio R = 0.1 and fatigue cycle Nf = 106, the fatigue strength of the laminated zone of the laser-MIG hybrid welding joint is better than that of the MIG welding joint, and the welding defect is the leading cause of fatigue cracks. [ABSTRACT FROM AUTHOR]

The cross section of the laser-melt inert gas welding (MIG) hybrid welding joint can be divided into two different heat source regions, the upper is the laser-MIG hybrid heat source region, and the lower is the laser heat source region. In this paper, the laser-MIG hybrid welding experiments were carried out on a new nickel-based alloy 4716MA0. The type, morphology and distribution characteristics of porosity in different heat source regions were researched by optical microscopy, scanning electron microscopy and energy-dispersive spectroscopy. In addition, the formation mechanism of different types of stomata was explained by the model diagram. It is found that the dominant region of the laser-MIG hybrid heat source is dominated by metallurgical porosity, which is attributed to the formation of CO gas, whereas the dominant area of the laser heat source is dominated by process porosity. The generation of process porosity is attributed to the instability of the keyhole. [ABSTRACT FROM AUTHOR]

In this paper, Al-Mg-Si alloys with a thickness of 4 mm are welded by using laser beam welding (LBW) and laser-MIG hybrid welding, respectively, and the microstructure and mechanical properties of the two joints are investigated. The results show that the fusion zone (FZ) of the two joints is composed of columnar crystal and equiaxed dendrite grain, and its main constituent phases are an α-Al matrix phase and a β(Mg2Si) strengthening phase. In the case of similar heat inputs, compared with those of the LBW joint, the grain size in the laser-MIG hybrid joint is smaller and there are more second phases such as the β phase in the FZ, which is related to the different action mechanisms on the base metal (BM) by the two welding processes. Under the three strengthening mechanisms of fine grain strengthening, precipitation strengthening, and solid solution strengthening, the laser-MIG hybrid welding joint shows better mechanical properties than that of the LBW joint. The maximum tensile strength of the LBW joint and the laser-MIG hybrid joint is 202 MPa and 253 MPa, respectively, and the elongation is 3.8% and 5.1%, respectively. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this paper, laser-MIG hybrid welding was applied to weld TC4 titanium alloy with a thickness of 5 mm. Scanning electron microscopy (SEM) analysis determined that the porosity of the laser-MIG hybrid welded joints was mainly process porosity. The evolution of the keyhole under different defocusing amount conditions was observed using a high-speed camera. The influence of the beam defocusing amount on the keyhole stability was analyzed in detail, and the formation mechanism of the process-type porosity was elucidated. The keyhole stability was poor with the defocusing amounts of + 2, 0, − 2, and − 4 mm. Moreover, the highest porosity in the weld was 4.21% when the defocusing amount was − 2 mm. The keyhole only collapsed at the root, and the porosity decreased by > 80% when the defocusing amounts were + 4 and − 6 mm. The keyhole was stable, and no porosity was generated in the weld when the defocusing amount was + 6 mm. By adjusting the defocusing amount, the diameter of the keyhole was increased, and the degree of keyhole opening was increased. Narrow and distorted keyhole morphology was avoided, and collapses and closures of keyholes that occurred during fluctuations were eliminated. Keyhole stability was improved, and process porosity in the weld was eliminated. [ABSTRACT FROM AUTHOR]

The work presented in this paper deals with the relationship between the laser and the electric arc during welding and chamfer filling operations using the hybrid laser welding process.This welding process requires perfect mastery, in order to increase the productivity and quality of welds, especially in nuclear facilities. Mastering the hybrid process involves a phase of understanding the phenomena involved in a welding operation. To better understand the role of each process in the combination of laser and MIG, we carried out a laser-only and MIG-only tests using the same operating parameters as those used in hybrid welding. Test results show that the laser preheats the surface, with some of the energy deposited on the side walls of the chamfer. The role of MIG is to deposit metal to fill the chamfer. We can therefore consider that its main role is to provide a volumetric energy deposit.Using the experimental design, we studied the influence of five parameters such as wire speed, distance between the laser and the MIG, welding speed, laser power, and laser defocusing on the power of the MIG.The results show that the interaction between laser power and wire speed has the greatest effect on arc power, followed by wire speed and other interactions.To verify the arc energy values given by the FRONIUS generator, we carried out additional measurements using a SEFRAM device. The results measured by FRONIUS are always higher than those of SEFRAM. Both series of measurements follow the same variations. [ABSTRACT FROM AUTHOR]

This study delves into the impact toughness of medium-thick (12 mm thick) titanium alloy joints crafted through a multi-layer, multi-pass welding technique that blends laser-arc (MIG) hybrid welding technology. Microstructural scrutiny, employing optical microscopy, SEM and TEM, unveils a consistent composition across weld passes, with prevailing α/α′ phases interspersed with some β phase, resulting in basket-weave structures primarily dominated by acicular α′ martensite. However, upper regions exhibit Widmanstatten microstructures, potentially undermining joint toughness. Hardness testing indicates higher values in cosmetic layers (~420 HV) compared to backing layers and bending tests manifest superior toughness in lower joint regions, attributed to smaller grain sizes induced by repetitive welding thermal cycles. Impact toughness assessment unveils diminished values in the weld metal (WM) compared to the heat-affected zone (HAZ) and base material (BM), amounting to 91.3% of the base metal's absorption energy. This decrement is ascribed to heightened porosity in upper regions and variations in grain size and phase composition due to multi-layer, multi-pass welding. Microstructural analysis proximal to failure sites suggests one mechanism wherein crack propagation is impeded by the β phase at acute crack angles. In essence, this study not only underscores the practicality of laser-MIG hybrid welding for medium-thick TC4 alloy plates but also underscores the reliability of joint mechanical properties. [ABSTRACT FROM AUTHOR]

During laser–MIG hybrid welding process of aluminum alloys, the distance between laser and arc heat source (DLA) is one of the key factors which affect the welding process stability. Weld formation exhibited various penetration depths, since the interaction between laser and arc changed. Hybrid plasma morphology fluctuated significantly at DLA of 0 mm and hybrid plasma height decreased with the increase of DLA. Violent evaporation of droplet and spatters were generated at DLA of 0 mm. Moreover, keyhole fluctuated violently and significant downward flow of liquid metal was induced at the bottom zone of molten pool due to the impact action of droplet. Keyhole fluctuation was suppressed and molten pool stability was improved at DLA of 2 mm. [ABSTRACT FROM AUTHOR]

The present study investigated the inhomogeneity of microstructure and properties of hybrid laser-MIG welded 10-mm-thick 316L/AH36 joints. The study focused on the inhomogeneity of the laser zone, hybrid zone, and transition zone. The temperature field was simulated using ABAQUS and showed a higher cooling rate in the laser zone. As a result, the microstructure in the laser zone was dominated by martensite while that in the hybrid zone was composed of 84 % austenite and 16 % ferrite. The laser zone showed poorer impact toughness and corrosion resistance than the hybrid zone. However, the corrosion resistance of the whole weld was the worst. Because the inhomogeneous microstructure formed a galvanic couple that accelerated the corrosion process. This work indicated that the energy ratio (the ratio of laser to arc energy) should be considered in the welding of dissimilar thick steel to reduce the inhomogeneity in the two zones and obtain a desirable property balance among hardness, toughness, and corrosion resistance.

Laser-MIG hybrid welding and MIG welding were carried out on 7B52 aluminum alloy, and the microstructure and mechanical properties of the joints were compared and analyzed. The results show that the average grain sizes of laser-MIG hybrid welding, MIG welding, and the laser weld zone are 18.38 μm, 24.16 μm, and 15.96 μm, respectively. The width of the HAZ of the laser zone is lower than that of the laser-MIG hybrid welding zone and MIG welding zone. The hardness is higher than that of the hybrid welding zone and MIG welding zone. The tensile strength of each laser-MIG hybrid welding joint zone is better than that of the MIG welding zone. The tensile strength of the laser zone is the worst. When stress ratio R = 0.1 and fatigue cycle Nf = 106, the fatigue strength of the laminated zone of the laser-MIG hybrid welding joint is better than that of the MIG welding joint, and the welding defect is the leading cause of fatigue cracks.

External magnetic field has been employed to improve appearance and suppress defects in the single laser or arc welding, and its physical mechanism in magnetic-field-assisted single laser or arc welding has been clearly clarified. However, few studies on the physical processes in magnetic-field-assisted laser-arc hybrid welding (MFA-LAHW) are conducted and its influencing mechanism is unclear. In this research, a comprehensive three-dimension numerical model is established to investigate the keyhole dynamics and weld pool behaviors in MFA-LAHW under the effect of different magnetic flux density. The results suggest that the interaction between a lower magnetic flux density (≤30 mT) and welding current is induced due to the existence of arc. Compared to the magnetic-field-assisted laser beam welding (MFA-LBW), this interaction induces a stronger Lorentz force up to the order of magnitude of 105 N/m3. The weld pool width is reduced while its length and height are increased because the Lorentz force facilitates the backward flow of thermal fluid, increasing the heat transfer from the keyhole and droplet to the rear weld pool edge. Moreover, the steady magnetic field improves the keyhole stability. The deform on keyhole rear wall brought by the droplet and vortex is suppressed, and keyhole size is widened under steady magnetic field, which reduced keyhole collapse. Furthermore, the comparative analysis with the case in MFA-LBW is carried out and the MFA-LAHW is verified to be more valuable for medium-thickness aluminum alloy. This work provides the underlying physics understanding of MFA-LAHW, which will broaden the application value of LAHW.

In the present study, by using the process of laser-MIG hybrid welding (LMHW) and raw material of invar steel wire, the effect of process parameters of LMHW on the surface macroscopic morphology and the distribution of internal defects of the weld was analyzed and a set of highly fault-tolerant, insensitive to assembly accuracy and stable optimal process parameters were determined. In addition, the microstructural characteristics and mechanical properties of welded joints under optimal parameters were analyzed. The results show that the laser power and arc power are positively and linearly related to the line energy density (LED). As the LED increased, the width and penetration of the weld increased gradually, but the effect on reinforcement was less. With the double-layer welding method, the defocusing distance, laser-arc distance, laser power and arc power were adopted to significantly inhibit the generation of porosity defects in the weld seam. The grains in the weld overheated zone grew in the cooling direction toward the weld zone to form columnar crystals, and the internal austenite organization took the lead. The average tensile strength and elongation of the weld were 422.3 MPa and 44.4%, reaching more than 96.1% and 71.2% of the base material, respectively, making the mechanical properties of the weld close to those of the base material. [ABSTRACT FROM AUTHOR]

In this study, an alternating magnetic field is applied in the narrow-gap laser-MIG hybrid welding of 2205 duplex stainless steel with a thickness of 25 mm to achieve the purpose of balancing the ration of the two phases, refining the grains and improving the corrosion resistance. With the help of OM, EBSD, TEM, and other microstructural analysis methods, the organization evolution of a 2205 duplex stainless steel narrow-gap laser arc hybrid weld under the effect of alternating magnetic field is revealed. The corrosion resistance of the welded joints is investigated by electrochemical tests. The results show that the use of a 40 mT applied alternating magnetic field can not only effectively inhibit the generation of porosity and unfused defects in the weld, but also that the addition of an alternating magnetic field improves the ratio of austenite to ferrite in the weld, and the ratio of the two phases is increased from 0.657 without a magnetic field to 0.850. The weld grain preferential orientation is affected by the magnetic field, and the weld austenite grains are shifted from the Goss texture to the Copper texture. Under the electromagnetic stirring effect of the applied magnetic field, the average austenite grain size decreased from 4.15 μm to 3.82 μm, and the average ferrite grain size decreased from 4.99 μm to 4.08 μm. In addition, the effect of the alternating magnetic field increases the density of twins in the organization. Electrochemical test results show that the addition of an alternating magnetic field increases the corrosion potential by 75.2 mV and the pitting potential by 134.5 mV, which indicates that the corrosion resistance of the cover-welded specimens is improved by the effect of an alternating magnetic field. The improvement in corrosion resistance mainly depends on the austenite grain refinement and the increase in the austenite content. [ABSTRACT FROM AUTHOR]

Ultrasonic-assisted laser-MIG hybrid welding (LMHW), the ultrasonic vibration applying respectively on the filler wire (LMHW-UF) and workpiece (LMHW-UW), was carried out on the 6 mm thick 6082-T6 aluminum alloy plates. The influences of the ultrasonic vibration modes on the weld formation, porosity defects, microstructure, microhardness, and tensile properties were investigated, and compared with those of the traditional laser-Mig hybrid-welded joints. The results indicated that the arc zone depths increased as the ultrasonic amplitudes increased, and which of the LMHW-UF and LMHW-UW joints were deeper than that of the LMHW joint. The porosity defect contents of the LMHW-UF and LMHW-UW weld seams were both smaller than that of the LMHW weld seams, especially of the LMHW-UF weld seams. The cellular dendrite size in the LMHW weld center was smaller than that in the LMHW-UF and LMHW-UW welds, and the parallel dendrite zone width of the LMHW weld was wider than that of the LMHW-UF and LMHW-UW welds, especially of the LMHW-UF weld. The lowest microhardness existed in the partially melted zone of the LMHW and LMHW-UW joints; however, the lowest microhardness existed in a certain distance from the fusion line of the LMHW-UF joints. The average tensile strengths of the LMHW, LMHW-UF, and LMHW-UW joints were 212.6 MPa, 237.5 MPa, and 228.2 MPa, the fractures occurred in the weld seam, near the fusion line and at the heat-affected zone, respectively. The LMHW and LMHW-UW joints both showed typical mixed ductile and brittle fracture feature, and the LMHW-UF joints showed representative ductile fracture feature. [ABSTRACT FROM AUTHOR]

Three-mm-thick 6106-T6 aluminum alloy extrusions were laser-MIG hybrid–welded with different assembling clearances. The effects of the assembling clearance on the weld formation, microstructure, and mechanical properties were investigated. When the assembling clearance was not larger than 0.7 mm, the optimum welding parameters were universal; the microstructure, microhardness distributions, tensile and fatigue properties were basically similar. To obtain well-formed weld formation, reducing the welding speed was more advantageous than increasing arc current when the assembling clearance enlarged. When the assembling clearances enlarged, the size of cellular dendrites increased and the width of columnar zone reduced; meanwhile, some cracks appeared near the fusion line. The lowest microhardness appeared closest to the fusion line in the heat-affected zone or existed away from the fusion line in the heat-affected zone when the assembling clearance was smaller or larger than 0.7 mm, and the lowest microhardness was reduced and the width of heat-affected zone increased as the assembling clearance enlarged. The average tensile strengths decreased when the assembling clearances enlarged. The tensile specimens fractured closest to the fusion line in the heat-affected zone or away from the fusion line in the heat-affected zone when the assembling clearances were smaller or larger than 0.7 mm, and the fracture features were changed from ductile to ductile-brittle–mixed failure mode. The median fatigue limit and safe fatigue limit were significantly decreased when the assembling clearance was larger than 0.7 mm, the fracture locations of fatigue specimens changed from in the weld zone to closest to the fusion line in the heat-affected zone, and the hot cracks that existed near the fusion line were the main reason. [ABSTRACT FROM AUTHOR]

In this paper, Al-Mg-Si alloys with a thickness of 4 mm are welded by using laser beam welding (LBW) and laser-MIG hybrid welding, respectively, and the microstructure and mechanical properties of the two joints are investigated. The results show that the fusion zone (FZ) of the two joints is composed of columnar crystal and equiaxed dendrite grain, and its main constituent phases are an α-Al matrix phase and a β(Mg2Si) strengthening phase. In the case of similar heat inputs, compared with those of the LBW joint, the grain size in the laser-MIG hybrid joint is smaller and there are more second phases such as the β phase in the FZ, which is related to the different action mechanisms on the base metal (BM) by the two welding processes. Under the three strengthening mechanisms of fine grain strengthening, precipitation strengthening, and solid solution strengthening, the laser-MIG hybrid welding joint shows better mechanical properties than that of the LBW joint. The maximum tensile strength of the LBW joint and the laser-MIG hybrid joint is 202 MPa and 253 MPa, respectively, and the elongation is 3.8% and 5.1%, respectively.

The microstructure and mechanical properties of Mg–Al–Zn alloy joints by using autogenous laser beam welding (LBW) and laser-MIG hybrid welding, respectively, are investigated. The results show that the weld formation of the hybrid welding joint is relatively good, and there are mainly α-Mg matrix phases and β-Mg17Al12 strengthening phases in the weld metal. The microstructure in the fusion zone (FZ) of the two joints is different. The LBW joint is composed of columnar crystal and equiaxed dendrite. The hybrid welding joint consists of fine equiaxed grains, and the grain size in the laser zone is larger than that in the arc zone. The microhardness in FZ is higher due to the precipitation of the β-Mg17Al12 phase in this region. Under the optimized welding procedure, the strength coefficient of the two joints is >90%. There are many dimples on the tensile fracture surface of the hybrid welding joint, which is characterized by the pattern of the ductile fracture.

6A01-T5 aluminum alloy extrusions with a thickness of 4.5 mm were welded by laser-MIG hybrid welding, and the effects of gap width on the microstructure and properties were studied in details. The results indicated that the priorities of the welding parameters on the tensile strength of joints were laser power, defocusing amount and arc current when the welding speed was constant. The gap tolerance of the optimal welding parameters could reach up to 1.1 mm. The morphology and size of the microstructures were similar when the gap width was no larger than 1.1 mm. The grain boundaries became obvious and even cracks appeared near the fusion line when the gap width increased to 1.5 mm. The microhardness distributions almost the same with the different gap widths: highest in the base materials zone, secondly in the heat-affected zone, then in the weld zone, and lowest near the fusion line. The microhardness values reduced in each zone except base materials when the gap width increased to 1.5 mm. The tensile strength reduced as the gap width increased, the specimens all fractured near the fusion line due to where had the lowest microhardness and the fracture showed ductile failure mode. [ABSTRACT FROM AUTHOR]

In the present study, 20 mm EH36 steel was welded by multi-layer and multi-pass laser-MIG hybrid welding, and the influence of different laser-arc heat input ratios (LHI/AHI) on weld formation was studied. Tensile, hardness, and residual stress tests were performed on hybrid welded joints to evaluate their microstructure and mechanical characteristics. The experimental results showed that when the LHI/AHI of the first layer hybrid welding was 0.23 and the LHI/AHI of the second layer hybrid welding was 0.27, the weld quality was the best. The weld width and depth decreased with the increase in LHI/AHI. With the decrease in LHI/AHI, the porosity near the fusion line decreased, and the martensite content in the fusion zone and heat-affected zone increased. EH36 steel welding specimens under different LHI/AHI satisfied the ASTM standard for mechanical properties. There are tearing edges and dimples on the tensile fracture, which is a typical quasi-cleavage fracture. The maximum hardness of the welded joint is located in the heat-affected zone due to the coarser martensite structure created during the cooling process. The maximum residual tensile stress of the test plate is 275 MPa at the depth of 2 mm on the top surface of the weld center. As the distance from the weld center increases, the tensile stress reduces dramatically and transforms into compressive stress. [ABSTRACT FROM AUTHOR]

Purpose – This study aims to solve the problem of weld quality inspection, for the aluminum alloy profile welding structure of high-speed train body has complex internal shape and thin plate thickness (2–4 mm), the conventional nondestructive testing method of weld quality is difficult to implement. Design/methodology/approach – In order to solve this problem, the ultrasonic creeping wave detection technology was proposed. The impact of the profile structure on the creeping wave detection was studied by designing profile structural test blocks and artificial simulation defect test blocks. The detection technology was used to test the actual welded test blocks, and compared with the results of X-ray test and destructive test (tensile test) to verify the accuracy of the ultrasonic creeping wave test results. Findings – It is indicated that that X-ray has better effect on the inspection of porosities and incomplete penetration defects. However, due to special detection method and protection, the detection speed is slow, which cannot meet the requirements of field inspection of the welding structure of aluminum alloy thin-walled profile for high-speed train body. It can be used as an auxiliary detection method for a small number of sampling inspection. The ultrasonic creeping wave can be used to detect the incomplete penetration welds with the equivalent of 0.25 mm or more, the results of creeping wave detection correspond well with the actual incomplete penetration defects. Originality/value – The results show that creeping wave detection results correspond well with the actual non-penetration defects and can be used for welding quality inspection of aluminum alloy thin-wall profile composite welding joints. It is recommended to use the echo amplitude of the 10 mm × 0.2 mm × 0.5 mm notch as the criterion for weld qualification.

• Tension-compression fatigue properties of laser-MIG hybrid welded joints were studied. • The fatigue strength of the welded joints at 2 × 106 cycles is 83 MPa. • The broken particles inhibit secondary crack propagation. • Softening behavior influences tensile properties and defects affect fatigue fracture. Light alloys represented by aluminum alloys have a wide range of applications in railway transportation, the key load-bearing parts of high-speed train bodies are welded with a large number of medium-thickness plates, so the study of the welding performance of medium-thickness aluminum alloy plates is significant. In this study, laser-MIG hybrid welding technology is used to realize the single-layer, single-pass welding of 6005A aluminum alloy plate with a thickness of 10 mm. The grains in the weld zone (WZ) are coarsened by welding heat, and the average diameter is about 1.6 times that of the base metal (BM), while the average grain diameter in the heat-affected zone (HAZ) is similar to that of the BM. A softening phenomenon is observed in the welded joint, with a minimum hardness of 72.6 HV in the HAZ. TEM analysis shows that the softening phenomenon is caused by the coarsening of precipitate phases in the HAZ. In terms of tensile properties, the ultimate tensile strength (UTS) of the welded joint is approximately 237 MPa, which is 70.1 % of the BM. The fatigue strength (N f = 2 × 106 cycles) of the welded joints is predicted to be 83 MPa, which is 64 % of the yield strength (YS), from the S-N curve obtained by fitting the tension–compression fatigue test data. Different morphologies of secondary phase particles are observed in the fatigue crack propagation zone, and their formation and effects on secondary crack are described. The fracture location indicates that softening behavior in the HAZ is the main factor influencing tensile performance, while defects in the WZ are the primary factors affecting fatigue fracture. The experimental results can enrich the tensile and compressive fatigue data of 6005A aluminum alloy. [ABSTRACT FROM AUTHOR]

To expand the application of laser-MIG hybrid welding in the arc-welded aluminum alloy profile manufacturing for high-speed trains, the laser-MIG hybrid welding characteristics of 4 mm thick A6N01S-T5 arc-welded aluminum profiles were studied in this work. The welding parameters were optimized using the orthogonal test; the microstructure and properties of the joints were analyzed. The results showed that the optimal welding parameters were: welding speed 1.0 m/min, laser power 2.7 kW, arc current 200 A, spot diameter 0.8 mm, heat source distance 3 mm, and defocusing amount 0 mm. The columnar crystals and dense dendrites were observed near the fusion line and in the weld center, respectively, and the grains in the heat-affected zone were slightly coarse. The microhardness of the softening zone in the heat-affected zone was the lowest. The average tensile strength of the joints was 212 MPa, about 86% of the base metal. The samples fractured in the heat-affected zone, and the fractures showed typical plastic fracture characteristics. The results showed that laser-MIG hybrid welding has good applicability and feasibility for the arc-welded profile welding manufacturing. [ABSTRACT FROM AUTHOR]

The present study investigated the influence of energy ratio on microstructure and mechanical properties in the transition zone of hybrid laser-MIG welded 316L/AH36 joints. The region between the laser zone and hybrid zone was defined as the transition zone. The ratio of laser to arc energy was defined as energy ratio. Similar microstructure types including ferrite, austenite, and martensite were observed in the transition zone under each energy ratio. However, obvious difference in microstructure distribution and crystallographic characteristic in transition zone was found in varying energy ratio. With the energy ratio decreasing from 2:1 to 1:2, the fraction of martensite was decreased from 83.1% to 65.6%, the fraction of high angle grain boundaries was increased from 44.8% to 61.3% and the average grain size was increased from 3.62 to 17.20 μm. The phenomenon was attributed to the improvement of cooling rate and reduction of filler metal. Therefore, the highest average microhardness value of 445 HV in the fusion zone was obtained under the highest energy ratio compared to that of 223 HV under the lowest energy ratio. Besides, the low-temperature impact absorption energy was increased from 41 to 90 J and the tensile fracture mode was changed from cleavage fracture mode to ductile fracture mode as the energy ratio decreased from 2:1 to 1:2.

The purification of laser keyhole is an important means to remove the oxide layer of laser-MIG hybrid welding of aluminum alloy. Four common auxiliary gases (argon, nitrogen, air and oxygen) were used to prepare kerf with different characteristics, which were defined as argon-weld, nitrogen-weld, air-weld and oxygen-weld. The results show that the remelted layer has little effect on the weld morphology. Microstructures characteristics of Argon-welds and nitrogen-welds were the same as machined welds, while the narrow columnar grain zone and coarsen grains exist in air-welds and oxygen-welds. When the thickness of kerf remelted layer increases, the width of columnar grain zone is reducing and the diameter of equiaxed grain is increasing. The argon-weld is with the best tensile property. When the thickness of remelted layer (d) is less than 70 μm, the tensile strength and elongation of argon-weld can reach 278 MPa and 3.1% respectively, which equivalent to that of machined weld. The tensile property of nitrogen-weld is slightly lower than that of argon-weld because of aluminum nitride impurities. The tensile properties of air-weld and oxygen-weld are low because of a large number of oxide impurities and grain coarsening. Regardless of the types of kerf, when the d is less than 136 μm, the tensile strength reaches more than 250 MPa, which meets the application requirements.

Severe porosity and coarse columnar grain are prone to be formed in the laser-MIG welded joint of aluminum alloy, deteriorating the strength and ductility seriously. In this study, the ultrasound was designed to assist the laser-MIG hybrid welding of aluminum alloy, and the influence of ultrasonic vibration on weld formation, porosity, and microstructure was investigated. The weld depth was increased from 3.6 to 4.2 mm when external ultrasound with the pressure of amplitude transformer (PAT) of 132 N was used, indicating that the penetration ability of hybrid heat sources to the welded plate could be improved. It was attributed to the dispersion effect of ultrasound on arc plasma in the laser channel. The porosity rate was reduced from 5.66 to 1.05% under PAT of 132 N, because of the increase in escape velocity of bubbles. Moreover, the columnar to equiaxed transformation (CET) of grain in the weld was promoted and the width of columnar grain zone was gradually reduced with the increasing ultrasonic energy, owing to the breaking effect of cavitation and the stirring effect of acoustic stream. As a result, lower porosity rate and finer grain size led to improvement of the microhardness and the strength of weld by ultrasound. The study provides more guidance on employing ultrasound to improve the quality of welded joints. [ABSTRACT FROM AUTHOR]

During laser-metal inert gas (MIG) hybrid welding, a large amount of welding status information is generated in droplet transfer, keyhole and molten pool. In this paper, austenitic stainless steel was adopted as an experimental object, with a dual high-speed camera system used to obtain real-time images of droplet transfer, keyhole and molten pool in a laser-MIG hybrid welding process. The changing regulation of a keyhole in three different penetration states (i.e., non-penetration, partial penetration and normal penetration) was analyzed by extracting the morphological characteristics of a keyhole shape, and combining the droplet transition information and the shape of the weld pool. Experimental results show that the proposed method could effectively reflect the variation characteristics of the keyhole, and the correlation among the keyhole characteristics, the droplet transfer information, the weld pool shape and the welding status, and provide a new perspective for online detection of the laser-MIG welding quality. [ABSTRACT FROM AUTHOR]

In this study, an external transverse magnetic field was used to assist laser-metal inert gas (MIG) hybrid welding of Ti-6Al-4 V (TC4). The microstructure and mechanical properties, such as microhardness and tensile properties of the weld joints, under an external magnetic field (EMF) and a reference weld joint without the EMF were investigated. The results showed that the laser-arc interaction zone (LAIZ) and heat-affected zone (HAZ) expanded, and the laser fusion zone (LFZ) and fusion zone (FZ) changed with the application of the EMF, resulting in a change in the distribution of microhardness. The microstructure of the FZ was comprised of Widmanstatten α′-grains and primary boundary β-grains without the EMF. After applying the EMF, the diameter of the primary globular β-grains in the FZ decreased by 38.6%, from 78.4 to 48.1 μm, and a small amount of residual dot-like β-grains appeared in the FZ of the joint. The mechanical properties of the weld seam improved significantly under the EMF; the average microhardness in the FZ increased by 9.7%, and the failure strain and stress of the tensile specimens improved by 45.6% and 6.6%, respectively, owing to the solid solution strengthening of the residual dot-like β-grains and finer primary β-grain boundary. In addition, a mixed fracture mode was observed on the fracture surfaces. This study revealed that the elementary microstructure of laser-MIG hybrid welded TC4 was correlated with the welding heat input of the EMF. [ABSTRACT FROM AUTHOR]

An alternating magnetic field was employed to improve inhomogeneity of microstructure and mechanical properties of laser-MIG hybrid welded 316 stainless steel joints. More uniform distribution of elements and ferrite phase, and austenite crystallographic characteristics in upper arc zone and lower laser zone of weld were obtained by alternating magnetic field, due to mixing of molten metal in whole weld. Longer solidification time of molten pool and more nucleation sites of austenite grain were obtained by stirring effect of magnetic field, leading to reduction of ferrite content and refinement of austenite grain. The hardness in vertical weld was more homogeneous and difference of tensile strength in both zones was reduced from 74 MPa to 10 MPa by magnetic field, due to microstructural homogeneity. [ABSTRACT FROM AUTHOR]

High-nitrogen austenitic stainless steel (HNASS) has many excellent properties, such as high strength and toughness, high strain-hardening ability, strong corrosion resistance and low magnetization compared with the traditional widely used Ni–Cr austenitic stainless steel. The high nitrogen content in HNASS leads to the welded joint in the risk of many problems, such as nitrogen escape and loss, nitride precipitation, formation of pores and thermal cracks, resulting in the poor welding performance. The HNASS joints without obvious defects were obtained by metal inert gas (MIG) welding and laser-MIG hybrid welding, separately. The microstructures and properties of welded joints were compared. The nitrogen content in fusion zones of the two joints was tested by an oxygen, nitrogen and hydrogen analyzer. The tensile strength and the impact absorption energy of laser-MIG hybrid welded joint were about 27% and 20% higher than those of MIG welded joint, respectively. It could be attributed to the stronger solid solution strengthening effect resulted by the high nitrogen content of laser-MIG hybrid welded joint. The finer grains and the reduction of ferrite and precipitation phase in the microstructure of laser-MIG hybrid welded joint contributed to the improvement of toughness.

Bead profile and microstructure analysis are greatly influenced by heat input in any welding process. The present work provides a comprehensive comparative investigation on these aspects during Autogenous Laser welding (ALW) and Laser-MIG Hybrid welding (LHW) processes in Inconel 617 superalloy. In case of LHW, weld bead profile formed was a typical wine-cup shaped one, whereas, in case of ALW, bead profile observed was Y-type shape on account of differences in number of heat sources and intensity profiles. Weld bead width and penetration depth were found to increase with heat input in both ALW and LHW processes. The fusion zone (FZ) area of LHW was found to increase by 3 times as compared to ALW as a result of high heat input in LHW than ALW. Indeed, the addition of MIG source to laser in LHW produced wide upper bead width (trebled) as compared to ALW. Radius of curvature (ROC) at neck zone, an important bead profile characteristic for assessing liquation cracking susceptibility, was found to increase with heat input and was significantly higher in LHW than ALW due to heat stagnation at neck zone. In comparison with ALW, LHW showed a coarser columnar/cellular dendritic microstructure in FZ with segregation of inter-dendritic carbides relatively richer in Mo and Cr. Secondary dendritic arm spacing (SDAS), cooling rates and microhardness will also be discussed. [ABSTRACT FROM AUTHOR]

The weld penetration variation in laser-MIG hybrid welding under sensitive laser power range was investigated by welding experiments and CFD (computational fluid dynamics) simulation. During this investigation, joints of AH36 sheets were welded with varying laser powers by the laser-MIG hybrid welding process. In addition, the CFD model was established based on experimental parameters and measurement results. Moreover, surface tension, electromagnetic force, buoyancy, recoil pressure, evaporative condensation, evaporative heat exchange, melt drop transfer, and other factors were considered. The influence of various factors on molten pool depth and keyhole depth were studied, including temperature, velocity, and flow direction of liquid metal. The results show that the weld-forming effect is better at the laser power is 7.5 kW in the range of sensitive laser power. After the keyhole is formed, its depth gradually entered the stage of linear increase, oscillation increase, and oscillation balance. Increasing the laser power can effectively shorten the time of the two growth stages and allow the keyhole to enter the balance stage earlier. During the oscillation balance state of the keyhole, the molten metal under the keyhole flowed to the molten pool root in the reverse direction of welding; it can also promote weld penetration. [ABSTRACT FROM AUTHOR]

The simulation method in laser-MIG hybrid welding, which involves two heat sources and multiple welding parameters, is beneficial to reveal the complex physical phenomena and dynamic behavior of molten pool keyhole during the welding process. In this investigation, laser-MIG hybrid welding for 6-mm-thick 6061 aluminum alloy was performed under different heat input by the high-power disc laser, MIG welding system, and KUKA robot. The high-speed camera system was used to observe the droplet transition phenomenon in the welding process. Besides, a thermal-fluid coupling model was established to simulate the temperature field and flow field, which was changed by the droplet transfer during laser-MIG hybrid welding. The experimental and simulated results showed that the droplet transition behavior affected the formation of the keyhole. The keyhole was the smallest when the droplet contacted the molten pool. In addition, the droplet transition brought external momentum and energy to the molten pool, which was conducive to the increase of the flow rate of the molten pool. [ABSTRACT FROM AUTHOR]

This study explores the laser-arc hybrid welding process of high nitrogen steel (HNS) in order to circumvent the problem of welding porosity. The influence of welding heat input on welding porosity has been elucidated by analyzing the changes in the morphological characteristics of the laser keyhole and the molten pool temperature. The results show that the pore ratio increases with a rise in laser power. Meanwhile, the pore ratio first decreases and then increases as the welding current intensifies. Additionally, it decreases as the welding speed and defocus amount increase. The lowest pore ratio of the weld is considered as the desired value, and the response surface method (RSM) is used to optimize the heat input parameters. When the laser power ranges from 2.80 to 2.85 kW, the welding current becomes 260 A, welding speed ranges from 0.73 to 0.80 m/min, defocus amount ranges from 0 to 1 mm, and pore ratio of the weld exhibits its minimum value (4.29 to 4.67%). [ABSTRACT FROM AUTHOR]

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5A06 aluminum alloy plates with a thickness of 6.9 mm are welded by laser-metal inert gas (MIG) hybrid welding. To investigate the influence of laser heat input on grain size and microhardness, optical microscope observation, scanning electron microscope (SEM) and microhardness test are conducted. According to the microstructure distribution characteristics, the weld seam can be divided into arc-affected zone and laser-affected zone. The crystalline morphology from the weld boundary to the weld center is coarse columnar dendrites, finer columnar dendrites and equiaxed dendrites. In addition, the calculation and comparison of the grain size indicate that, the grain size Zl of the coarse columnar dendrites and the fine columnar dendrites in the laser-affected zone has increased, compared to both of the arc-affected zone. Due to the mechanical stirring effect on the upper molten pool, the finer equiaxed dendrites are formed at the center of arc-affected zone. It is worth noting that the grain size inhomogeneity has been significantly improved due to the decrease of laser heat input. The average microhardness of the arc-affected zone in case 1 is significantly lower than that of the other three cases due to the higher laser heat input. The laser line energy of 90 J/mm is more suitable for achieving the excellent microhardness property of laser-MIG hybrid welded joint for the 6.9 mm 5A06 aluminum alloy. [ABSTRACT FROM AUTHOR]

The work aimed to investigate the effects of alternating magnetic field on the microstructure, mechanical properties and plasma characteristics during laser-MIG hybrid welding of HG785D steel. The weld appearance was improved and the weld depth was significantly enhanced by an alternating magnetic field. The same microstructure type of lath martensite (LM) was obtained in the arc zone and laser zone of all hybrid welded joints. However, grains in the arc zone were significantly refined and the ratio of high-misorientation angles was increased under alternating magnetic field. The average grain size in the arc zone reduced from 4.60 to 3.67 μm with a magnetic flux density of 30 mT. The average microhardness of the arc part and the laser part increased from 356 and 378 to 388 and 393 HV, respectively. The grain refinement and increased ratio of high-misorientation angles led to an improvement in low-temperature impact toughness. The low-temperature impact toughness was 184 J with a magnetic flux density of 30 mT, which was 95.7% higher than that without the alternating magnetic field. Additionally, the shielding effect of the hybrid plasma was suppressed with the magnetic flux density of 10–30 mT, leading to an increase in the penetration ability of hybrid heat sources and weld depth. However, the penetration ability of the hybrid heat source was no longer enhanced with a further increase in magnetic flux density.

In this paper, a 6082-T6 high-strength aluminum alloy with 5 mm thickness was taken as the research object. The TRUMP Trudisk 10002 disc laser and the Transpils synergic 4000 welder were used to weld it by laser-Metal-Inert-Gas composite welding. The property transition and uneven hardness of the base metal (BM), the heat affected zone (HAZ), and the partially melting zone (PMZ) were analyzed by a transmission electron microscope, a scanning electron microscope, and an energy dispersive spectrometer. The results showed that: grain coarsening was not the main reason for softening in the HAZ but the evolution of precipitates is the main reason. Precipitates annexation in HAZ was the main reason for hardness decrease in the HAZ. Solid diffusion occurred in PMZ, and the enrichment of main strengthening elements at grain boundary played a positive role in hardness recovery. A large number of spherical GP zones and the β″ phase had been found in the PMZ, which played a major role in strengthening and increased the hardness of the PMZ. The tensile results showed that the BM had the highest elongation and tensile strength. The strength and plasticity of the HAZ were lower than those of the BM. A lamellar second phase with lamellar tearing was found at the bottom of the fracture in HAZ. The softening fracture morphology was different from that of the BM. This paper mainly focuses on the softening of HAZ of welded joints and the hardness bump in PMZ. The distribution of precipitates, grain size, alloy element diffusion distribution, and mechanical properties were analyzed. The uneven hardness behavior of the joint and its influence on mechanical properties were further revealed. [ABSTRACT FROM AUTHOR]

The 5A06 aluminum alloy butt joint is fabricated by laser-metal inert gas (MIG) hybrid welding in this investigation. The macro morphology and porosity of welded joints under different heat input are observed by optical microscope. The effect of the laser, MIG, and hybrid heat input on macro morphology and porosity of welded joint is investigated. Furthermore, the force condition inside the laser-MIG hybrid welding pool is analyzed to explain the influence mechanism of heat input on macro morphology and porosity in theory. It is found that the cross-section area of weld seam (WS) is increased with the welding heat input. The porosity of the full-penetration WS is smaller than the partial-penetration WS owing to the different flow characteristic of molten pool. The higher MIG heat input is beneficial to reduce the porosity. It is illustrated that the welded joint with a lower porosity is expected to be obtained under the energy ratio coefficient of 0.5. [ABSTRACT FROM AUTHOR]

During laser-metal inert gas (MIG) hybrid welding, a large amount of welding status information is generated in droplet transfer, keyhole and molten pool. In this paper, austenitic stainless steel was adopted as an experimental object, with a dual high-speed camera system used to obtain real-time images of droplet transfer, keyhole and molten pool in a laser-MIG hybrid welding process. The changing regulation of a keyhole in three different penetration states (i.e., non-penetration, partial penetration and normal penetration) was analyzed by extracting the morphological characteristics of a keyhole shape, and combining the droplet transition information and the shape of the weld pool. Experimental results show that the proposed method could effectively reflect the variation characteristics of the keyhole, and the correlation among the keyhole characteristics, the droplet transfer information, the weld pool shape and the welding status, and provide a new perspective for online detection of the laser-MIG welding quality.

A 10 mm 316 L stainless steel plate was joined using multi-layer laser-MIG hybrid welding. Results showed that unmixed zone and “real” fusion zone (FZ) existed near the fusion line. Frequently met dendritic ferrite (δ) and newly encountered spherical nanoscale particles trapped in austenite (γ) were only observed in the latter region. Chemically, these particles turned out a SiO2 phase. From base metal to FZ, δ morphology was altered from originally linear to relatively diversely dendritic. Meantime, γ exhibited a converse manner where previously randomly oriented equiaxed was replaced by coarse, columnar and textured. Accordingly, a comparably high Schmidt factor in γ phase was obtained in FZ. Moreover, δ exhibited a relatively higher stress level than γ which presented a decrease in residual stress with grain coarsening in heat affected zone. In FZ, δ fraction displayed a dramatical increase with special BCC-FCC orientation relations established. Finally, tensile test and fracture appearance implied that FZ was exactly the weakest link of the whole welded joint in spite of a qualified strength achieved. In summary, lack in Σ3, largely increased δ fraction, high Schmidt factor in γ and especially being rich in SiO2 particles collectively led to the micro-void coalescence fracture in FZ.

The weld penetration variation in laser-MIG hybrid welding under sensitive laser power range was investigated by welding experiments and CFD (computational fluid dynamics) simulation. During this investigation, joints of AH36 sheets were welded with varying laser powers by the laser-MIG hybrid welding process. In addition, the CFD model was established based on experimental parameters and measurement results. Moreover, surface tension, electromagnetic force, buoyancy, recoil pressure, evaporative condensation, evaporative heat exchange, melt drop transfer, and other factors were considered. The influence of various factors on molten pool depth and keyhole depth were studied, including temperature, velocity, and flow direction of liquid metal. The results show that the weld-forming effect is better at the laser power is 7.5 kW in the range of sensitive laser power. After the keyhole is formed, its depth gradually entered the stage of linear increase, oscillation increase, and oscillation balance. Increasing the laser power can effectively shorten the time of the two growth stages and allow the keyhole to enter the balance stage earlier. During the oscillation balance state of the keyhole, the molten metal under the keyhole flowed to the molten pool root in the reverse direction of welding; it can also promote weld penetration.

Copyright of Laser Technology is the property of Gai Kan Bian Wei Hui and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)