Fusion Line Research Articles

Investigation on underwater wire-feed laser deposition of 5052 aluminum alloy

The underwater laser deposition layer with uniform forming on the 5052 aluminum alloy was successfully manufacturing by the underwater wire-feed laser deposition (UWLD) technology with a laser deposition (LD) gas-shielding nozzle. Process parameters including deposition speed and wire feed speed were optimized and laser propagation attenuation mechanism, the geometrical characteristics, microstructure and microhardness of deposited track in the in-air and underwater environment were investigated. Increasing deposition speed or reducing wire feed speed, the wetting between the base material and deposited metal improved and a high-quality UWLD layer without defects was obtained at 15 mm/s deposition speed and 1.2 m/min wire feed speed. For UWLD, the laser beam energy decreased owing to absorption and scattering of aerosol particles, causing differences in the geometric features to in-air wire-feed laser deposition (IWLD) and reducing the wettability and fluidity of the deposited metal on the substrate. In both IWLD and UWLD layers, the microstructure of the deposition region (DR) was equiaxial dendrites while the fusion region (FR) was composed of columnar dendrites. The columnar dendrites nucleated at the fusion line and grew along the reverse direction of the temperature gradient to the centerline of the melt pool while the underwater grains were more refined attributed to the greater cooling rate under water, indicating the increase of microhardness.

Microstructure analysis and hardness prediction based on microstructure evolution theory in multi-pass welded joint

During multi-pass butt welding of high-strength steel (HSS) thick plate, it is difficult to estimate the hardness performance of thick weld since multithermal cycles can drive complex microstructure evolution. In this study, butt-welded joint of 75 mm-thick Q690 HSS was prepared by multi-pass shielded metal arc welding (SMAW) in advance; meanwhile, experiments were carried out to characterize microstructure and measure hardness distribution in butt-welded joint. Then, the welding temperature history of butt-welded joint was numerically examined. Based on the irreversibility of Martensite and Bainite, the microstructure evolution model was modified to predict the complicated microstructure evolution in multi-pass welded joint. Compared with experimental data, the validity of modified microstructure evolution model was verified. With the application of simulated thermal cycles and material chemical compositions as input parameters, volume fraction distribution of each phase was obtained by modified microstructure evolution model and hardness value was calculated by hardenability algorithm. Both experimental and predicted results exhibited that microstructure in weld metal (WM) is mainly composed of granular Bainite with a small amount of Ferrite and Martensite, and heat-affected zone (HAZ) consists of predominantly lath Martensite. Hardness distribution in butt-welded joint obtained by the prediction method is in accordance with the measurement. Average hardness value in WM and BM is 290 VPN and 250 VPN. A sharp decrease in HAZ hardness can be found from the fusion line to base metal (BM). The maximal value in the HAZ close to fusion line and the corresponding prediction deviation is 6%.

A Novel Reticular Retained Austenite on the Weld Fusion Line of Low Carbon Martensitic Stainless Steel 06Cr13Ni4Mo and the Influence on the Mechanical Properties

When performing fluorescent magnetic particle testing in steel welding-repaired zones, as traditional viewpoint usually ascribes magnetic particle indications to discontinuous welding defects such as cracks, incomplete fusion, etc., welding-repaired zones showing indications of these defects are always judged to be unqualified. In this study, a novel reticular phase was identified on the weld fusion line of 06Cr13Ni4Mo. By selected area electron diffraction, it was proved to be an austenite. By roasting test, it was proved to be induced by the thermal effect of welding. Non-ferromagnetic reticular austenite reduces the overall magnetic permeability, leading to the presence of fluorescent magnetic particle indication. Though the mechanical properties of the welding repaired zone are changed by the reticular austenite with the yield strength, tensile strength, and microhardness decreasing to 571 MPa, 752 MPa, and 279, respectively, they still exceed the required values of standard specifications. 06Cr13Ni4Mo welding-repaired zones showing magnetic particle indications induced by reticular austenite are qualified and should be accepted.

Influence of the metal flow in the keyhole molten pool on the molten pool stability in continuous variable polarity plasma arc keyhole vertical-up welding

The metal flow of the keyhole molten pool affects weld pool stability and weld formation vitally during continuous variable polarity plasma arc welding (VPPAW). A novel “keyhole inside alternating oscillation” (KIAO) thermal-mechanical coupling model was developed to study the influence of keyhole molten pool metal flow on molten pool stability. This model can achieve the oscillation effect of heat-force on the molten pool during the electrode negative (EN) and electrode positive (EP) phase. A heat source, with keyhole channel backward bending, was used to create a keyhole backward deviation along the workpiece thickness. An asymmetric arc pressure source was adopted to ensure asymmetric distribution of the arc pressure. The metal flow of the stable and cut molten pool are calculated in continuous VPPAW process, and the conditions needed for the stable existence of the molten pool are obtained. The molten pool must have sufficient liquid metal which needs to flow as follows: in the front of the upper molten pool, a part of the metal flows in the form of “two-way rotating confluence” along the keyhole side wall to the rear of the lower molten pool, and part of the metal flows backwards to the rear of the upper molten pool. The metal at the rear of the lower molten pool flows upwards along the keyhole side wall. Under the combined action of these flow behaviors, the expansion speed of the leading edge of the keyhole is approximately equal to the shrinkage speed of the keyhole trailing edge, and the keyhole molten pool is stable. The stability of the bottom molten pool has a significant impact on the overall molten pool stability. The calculated fusion line and the offset distance between the central axis of the keyhole exit and the welding torch corresponded with the measured results.

Study of microstructure & mechanical properties of TIG welded aluminized 9Cr-1Mo steel

Aluminide coating on 9Cr steel is candidate coating for blanket module applications of fusion reactors. The welding fabrication processes associated with coated steels are still an issue as the presence of Al in weld metal has several detrimental outcomes. To address this, the authors have attempted a study on conventional TIG welding with V-groove to mitigate the effect of coating on weld metallurgy. This work emphasizes the comparison of mechanical properties and microstructures of aluminide coated and uncoated/bare 9Cr-1Mo steel. Microstructural observations indicated presence of un-dissolved alumina inclusions at the weld fusion line. Despite such inclusions, the observed tensile strength of the weld joint for coated steel is 648 MPa±16 MPa which is in line with the weld joint of un-coated steel (667±14 MPa) and substrate (643 MPa±18 MPa). Impact toughness tests carried out at 0 °C,-25 °C and room temperature also indicate that there is no drastic effect of coating on weld joint and the observed toughness values are acceptable as per the reported data (45 J).

Numerical Simulation and Experimental Verification of Residual Stress in the Welded Joints of Weldolet-Branch Pipe Dissimilar Steels.

It is well known that welding dissimilar metals can play the advantages and characteristics of those different metals, but it is easy to encounter some problems. In this paper, the thermomechanical behavior of the weldolet–branch dissimilar steel joints in different welding cases is analyzed by establishing a three-dimensional finite element model, and the predicted thermal cycling and residual stresses are verified using experimental tools. The results show that the high temperature area and the heat affected zone on the side of the branch pipe are larger, and there is a large stress gradient at the fusion line on both sides of the weld. Too high or too low temperature between welding layers will cause large residual stress, thus, 200 °C is more suitable for the welding of weldolet–branch joints. The residual stresses of path-1, path-2 and path-3 have similar distributions at 0° and 180° sections, and the circumferential and axial residual stresses on the inner surface are larger than those on the outer surface. The residual stress on the inner and outer surfaces of path-3 is smaller than that of path-1 and path-2 at the 90° and 270° sections as a whole, and the residual stress at the 90° section reaches the minimum.

Effect of heat input on microstructure and tensile properties of laser welded Ti–3Al–6Mo–2Fe–2Zr alloy joint

The heat input during laser welding process has significant influence on microstructure and properties of the joints, whereas there is currently limited research concerning the influence of heat input during laser welding process of β titanium alloys. The microstructure and tensile properties of laser welded Ti–3Al–6Mo–2Fe–2Zr (wt.%) joints under different heat inputs were investigated in this paper. Numerical simulation process was used to explain the microstructure evolution in HAZ and fusion zone. The microstructure of HAZ is divided into three different regions from fusion line to base metal. In near-HAZ, mid-HAZ, and far-HAZ, the microstructures are composed of single β phase, β + αp, and β + αp + retained αs, respectively. In fusion zone, the microstructure consists of single β phase because of the fast cooling rate and high content of β stabilizing elements. The ultimate tensile strength (UTS) of laser welded specimens is lower than that of base metal due to the lack of strengthening phase and the coarsening of β grains. Higher heat input further exacerbates the coarsening of β grains in the fusion zone and HAZ, which consequently results in the decrement of UTS of the joints.

The Microstructure and Mechanical Properties of 5083, 6005A and 7N01 Aluminum Alloy Gas Metal Arc-Welded Joints for High-Speed Train: A Comparative Study

This study aimed to conduct a comparative study on the microstructure and mechanical performance of 5083, 6005A and 7N01 Al joints used in China Railway High-speed (CRH) trains. We connected 10 mm-thick plates by three-layer and three-pass gas metal arc welding (GMAW). The results indicated that 6005A and 7N01 Al joints were more sensitive to grain boundary liquation in the partially melted zone (PMZ) than 5083 Al joins. Besides, recrystallization was obtained in heat-affected zones (HAZ). The 5083 Al joints experienced the most severe recrystallization and the grain size changed from 6.32 (BM) to 32.44 (HAZ) μm duo to intracrystalline strain induced by cold-rolled processes. The 7N01 Al alloys experienced the lowest extent of recrystallization and the grain size increased from 5.32 (BM) to 22.31 (HAZ) μm. Furthermore, significant precipitate evolution in the HAZ was observed. Original thin β” precipitates dissolved in HAZ of 6005A Al joints and transformed to the softer β phase. However, less precipitation transition was examined in 5083 and 7N01 Al joints. The precipitates’ evolution produced a softening region in HAZ of 6005A joints where the hardness was only 55 HV. The microhardness profile of the other two Al joints was less affected. The tensile strength of 5083, 6005A, and 7N01 Al alloy joints reached 323, 206 and 361 MPa, respectively. The 5083 Al and 6005A Al joints failed at HAZ near the fusion line while 7N01 Al joints failed at the fusion zone owing to the high strength of the base metal. The liquation, coarse grains by recrystallization, and precipitate evolution all decreased local strength, resulting in the fracture at HAZ.

The microstructure evolving and element transport of Ni-based laser-cladding layer in supercritical water

To improve the oxidation resistance of the low-cost materials in supercritical water (SCW), the mild steel surface was laser cladded with Ni-based alloy powder. The oxidation behavior of coated material was investigated in SCW. Consequently, because of the constrained melting and solidification, extensive microstructure changes. Crystals in different regions are transformed into equiaxed crystals, which enhances the interatomic bonding strength of the solid solution. Additionally, the Ni-based cladding layer has an observable growth direction near the fusion line and the oxidation reactions could be inhibited by the formed NiO and (Cr, Ni) solid solution.

Formation mechanism and control of welding cracks in dissimilar materials of Ni50Ti50 SMA and Ti-6Al-4V

In this paper, the crack problem of welded joint between NiTi SMA and Ti-6Al-4V was studied. The crack morphology and propagation state were analyzed, which was found that the microstructure uniformity of the fusion zone was poor. And there was a eutectic reaction layer at the fusion line of Ti-6Al-4V. A large number of brittle compounds NiTi2 phase led to severe hardening of the welded joint. By means of thermodynamic calculation and finite element simulation, the precipitation of brittle phase and stress distribution were studied, and the formation mechanism of crack defects was clarified. According to the above research, the beam offset welding process was used to melt the NiTi SMA with low melting point, which by the fusion brazing method to achieve the reliable connection. Optimizing the microstructure of the fusion zone and eliminating crack defects, the most suitable electron beam offset amount was 0.4 mm.

Narrow Gap MAG Welding and Joint Performance Analysis of 25Cr2NiMo1V Thick Plate

The narrow gap MAG welding system was used to successfully weld the 50mm thick butt joint of 25Cr2NiMo1V rotor steel. After 15-layer bead welding, heat treatment is performed on the welded joint. Compare the changes in the microstructure, tensile strength and impact energy of the welded joints and the heat-treated joints at 580°C (20h). The results show that after the heat treatment of the structure, the side lath ferrite in the coarse-grained region grows up, and the eutectoid ferrite grows up in the fine-grained region first. The strength of the welded joint is about 605MPa, and the fracture is characterized by ductile fracture. After heat treatment at 580°C (20h), the strength is about 543MPa, the fracture is characterized by ductile fracture, and there are also a large number of discontinuous small surface platforms, and the characteristic of brittle fracture appears slightly. The impact energy of the weld center of the welded joint is about 141J, the fusion line area is about 113J, and the toughness of the fusion line is slightly lower than that of the weld center. After heat treatment, the impact energy at the center of the weld is about 183J, the fusion line area is about 95J, the toughness of the weld center increases, and the toughness of the fusion line decreases.

Investigation of Corrosion Behaviour at Weld Metal, Fusion Line and Region Nearby Fusion Line of Ebw Aisi 316 Ss

Investigation of Corrosion Behaviour at Weld Metal, Fusion Line and Region Nearby Fusion Line of Ebw Aisi 316 Ss

Three Dimensional Morphological Grading of the Ankylosed TMJ for Surgical Planning: A Retrospective Observational Study

Introduction: Temporomandibular Joint (TMJ) ankylosis remains an enigma in craniofacial surgery due to the challenges encountered while restoring mouth opening, facial form and airway to normalcy. Though TMJ ankylosis is a relatively simple diagnosis to make, the specific surgical plan depends on the nature and extent of the fusion of the mandible with the cranial base. Aim: To classify the pattern of bone deformity found in TMJ ankylosis using three Dimensional (3D) Computed Tomography (CT) imaging and its role in determining the type of procedures required for effective gap arthroplasty. Materials and Methods: The 3D CT reconstructed images of 66 consecutive patients having 82 ankylosed joints treated from January 2007 to December 2019 with a standardised protocol was evaluated retrospectively. A grading system was used with the following criteria: coronoid hyperplasia, sigmoid notch to skullbase fusion and loss of residual joint space. The gap arthroplasty required for each grade of ankylosis was also analysed. The complete data in the present study was tabulated in Microsoft excel sheet and frequency (n) analysis was done for all variables. Results: Out of 66 patients (82 ankylotic joints) 37 males and 29 females), age range 2.5 years to 51 years, average age 18.2 years) 27% of the total joints surveyed belonged to grade 1 type of ankylosis. None of these joints had complete bony fusion (absence of the radiolucent zone between the cranium and condyle). A 10% of the joints had moderate ankylosis (grade 2). None of them revealed complete bony fusion (absence of the radiolucent zone) or fusion of the sigmoid with the cranial base. Grade 3 ankylosis was the most widely seen pattern of ankylosis (63% of the present study subjects) and 92% had a history of childhood onset. A 90% of the joints in this group had ipsilateral coronoid hyperplasia. A 48% of the joints with severe ankylosis (grade 3) showed bony fusion with the cranial base, with loss or absence of the radiolucent zone {Fusion Line (FL)} between the cranial base and the condyle. Conclusion: The extent and severity of TMJ ankylosis needs to be ascertained prior to planning TM Joint ankylosis surgery. A 3D CT assessment and subsequent radiologic grading provides a reliable guide for ankylosis release.

WELDING OF HIGH-HARDNESS ARMOR STEEL

Armor steels are difficult to weld due to the high percentage of carbon. The coarse-grained area and the fusion line in the welded joint are sensitive areas due to the high hardness and the possible presence of hydrogen produced during the welding process. Furthermore, multi-purpose armored vehicles made of armored steel are exposed to dynamic loading due to traffic on rough terrain. High hardness in the coarse- grained area of the heat-affected zone and dynamic loading can cause cracks. In the weld metal zone, a crack created during the welding process or due to pores can quickly propagate toward the sensitive fusion line, after which its accelerated growth can occur. Based on the above, achieving a welded joint without porosity or cracks for armor steel is necessary. This paper investigated the welding process of high- hardness armor steel with two regimes. The test aims to achieve an optimal hardness level and a compromise between ballistic requirements and toughness. The test results showed that a high-quality welded joint and an optimal balance between hardness and toughness are achieved with increased heat input.

Research on Residual Stress Distribution in Different Areas of Laser-MAG Arc Hybrid Welding by Numerical Simulation

In this research, through experiments and numerical simulations, the residual stress distribution of the top and bottom surfaces of the laser (TruDisk16002)-arc (MAG) hybrid welding seam and the weld cross-section are studied. The results show that when the arc power is 6.5KW and the laser power is 7.5KW, the weld is formed well. The residual stress on the bottom surface near the weld is higher than that on the top surface. The laser zone in the center of the weld has the largest residual stress, the arc zone is smaller, and the mixed zone is the smallest. The laser zone has the largest residual stress at the fusion line and the heat-affected zone, followed by the mixed zone, and the arc zone is the smallest. followed by the mixed zone, and the arc zone has the smallest.

Case Study About Resistance Projection Welding of Aluminized Steel Parts

Resistance projection welding is a non-polluting mechanized process used to obtain an assembly between similar or dissimilar metallic materials. The main advantages of this welding process are the possibility to achieve many different welded points at the same time and the long life of the electrodes compared to the spot-welding process. The paper analyses the effects of thin aluminium coating existing on mild steel parts of on the correct formation of welding points when assembling moulds for the manufacture of baking bread. From optical and electron microscopy analyses it resulted that some adjacent welded points show an interrupted fusion line, sprinkled with elongated islands of aluminium-rich compounds. The paper presents the effect of changing the values ​​of the welding parameters on the weld spot size, in correlation with the Al-rich inclusions that appear on the weld fusion zone. The best results have been obtained when the welding parameters values were the follows: electrode pressure of 2.6 bar, welding power of 19.18kVA and welding time of 7ms. The problems that occur when electric resistance welding of parts with aluminium coating have been highlighted, being useful for specialists who make products using this welding process.

Effect of Heat Input on LMHMW Joint of Carbon Steel

Laser-MIG hybrid multi-layer welding (LMHMW) technology has been employed in paraxial configuration with laser leading for the welding of 20 mm thick Q235 carbon steel plates to exploit the hybridization effect that addresses the shortcomings of the individual process as well as to compliment their merits. The bilateral effects of arc augmented laser welding have resulted in complete joint penetration, process efficiency, stability and gap bridge ability. Samples welded under varying heat inputs in multiple passes have been analyzed for their microstructure evaluation using an optical microscope followed by tensile and Vickers hardness testing in various regions of the weld zones. This process was conducted to characterize the effect of heat input on the mechanical properties of the welded joints. The experimental results illustrate that different heat inputs have significant effects on the microstructure, heat affected zone width and mechanical properties of welded joints. The microhardness near the fusion line decreases dramatically due to the influence of the phase transformation process, and the highest microhardness value is obtained in the center of the weld seam. By using reasonable process parameters, the strength of the welded joint can obtain 458.5 MPa.

Effect of low-temperature cooling on corrosion properties of laser welding Hastelloy C-276/304 stainless steel with filler wire

To suppress the weld defects and improve corrosion resistance of laser welded joints, the low-temperature cooling was applied to assist laser welding Hastelloy C-276/304 stainless steel with filler wire. And the different low-temperature cooling (-5 °C, 5 °C, 20 °C) were selected for experimental research. Results show that adding low-temperature cooling can increase the cooling rate and solidification rate of weld. And the temperature gradient grows with the increase of solidification rate near the fusion line of weld. Consequently, the content of precipitated phase decreases from 1.75% to 0.71%, reducing by nearly 59.0%. The increase of temperature gradient can reduce the unmixed zone, which decreases from 22.1 μm to 11.4 μm, reducing by nearly 48.0%. At the same time the contents of corrosion-resistant elements and the proportion of grain boundaries with small angles increase in the laser weld with low-temperature cooling. As the cooling temperature drops, the effect of microstructure optimization of weld is enhanced. Finally, the corrosion properties of welded joints are obviously improved with the temperature decrease. The corrosion potential of welded joints increases by 24.3%. The corrosion current density of welded joints reduces by 54.3%. The intergranular corrosion sensitivity of welded joints reduces by 76.5%.

Fracture Toughness Characteristics of High-Manganese Austenitic Steel Plate for Application in a Liquefied Natural Gas Carrier

High-manganese austenitic steel was developed to improve the fracture toughness and safety of steel under cryogenic temperatures, and its austenite structure was formed by increasing the Mn content. The developed high-manganese austenitic steel was alloyed with austenite-stabilizing elements (e.g., C, Mn, and Ni) to increase cryogenic toughness. It was demonstrated that 30 mm thickness high-manganese austenitic steel, as well as joints welded with this steel, had a sufficiently higher fracture toughness than the required toughness values evaluated under the postulated stress conditions. High-manganese austenitic steel can be applied to large offshore and onshore LNG storage and fuel tanks located in areas experiencing cryogenic conditions. Generally, fracture toughness decreases at lower temperatures; therefore, cryogenic steel requires high fracture toughness to prevent unstable fractures. Brittle fracture initiation and arrest tests were performed using 30 mm thickness high-manganese austenitic steel and SAW joints. The ductile fracture resistance of the weld joints (weld metal, fusion line, fusion line + 2 mm) was investigated using the R-curve because a crack in the weld joint tends to deviate into the weld metal in the case of undermatched joints. The developed high-manganese austenitic steel showed little possibility of brittle fracture and a remarkably unstable ductile fracture toughness.

Failure assessment of Mash Seam Weld breakage and development of online weld inspection system for early detection of weld failure

Mash seam welding of the tail end and head end of cold-rolled coils is performed to maintain continuity in the Continuous Galvanizing Line (CGL). Failure of the weld can lead to mill stoppage causing huge productivity loss of up to 48 h for one such breakdown and causing damage to the mechanical systems. The failure of the weld is a result of defects present along the fusion line such as lack of fusion, craters due to expulsion, shrinkage cavity and cracks. Improper welding parameters can lead to the formation of the above defects and can remain undetected during the subsequent processing. Hence a non-destructive weld inspection system was developed to detect defects. Additionally, the ultrasonic-based weld inspection system with a machine learning algorithm was developed to gather and train the scan data for accurate prediction of weld defects and prevent catastrophic failure due to weld breakage.