•Ultrasound can break the grain in the ultrasonic-assisted TIG weld of pure aluminum.•The factors influencing ultrasonic grain fragmentation are investigated.•The mechanism of ultrasonic grain ...fragmentation is discussed.
Under the action of acoustic waves during an ultrasonic-assisted tungsten inert gas (TIG) welding process, a grain of a TIG weld of aluminum alloy is refined by nucleation and grain fragmentation. Herein, effects of ultrasound on grain fragmentation in the TIG weld of aluminum alloy are investigated via systematic welding experiments of pure aluminum. First, experiments involving continuous and fixed-position welding are performed, which demonstrate that ultrasound can break the grain of the TIG weld of pure aluminum. The microstructural characteristics of an ultrasonic-assisted TIG weld fabricated by fixed-position welding are analyzed. The microstructure is found to transform from plane crystal, columnar crystal, and uniform equiaxed crystal into plane crystal, deformed columnar crystal, and nonuniform equiaxed crystal after application of ultrasound. Second, factors influencing ultrasonic grain fragmentation are investigated. The ultrasonic amplitude and welding current are found to have a considerable effect on grain fragmentation. The degree of fragmentation first increases and then decreases with an increase in ultrasonic amplitude, and it increases with an increase in welding current. Measurement results of the vibration of the weld pool show that the degree of grain fragmentation is related to the intensity of acoustic nonlinearity in the weld pool. The greater the intensity of acoustic nonlinearity, the greater is the degree of grain fragmentation. Finally, the mechanism of ultrasonic grain fragmentation in the TIG weld of pure aluminum is discussed. A finite element simulation is used to simulate the acoustic pressure and flow in the weld pool. The acoustic pressure in the weld pool exceeds the cavitation threshold, and cavitation bubbles are generated. The flow velocity in the weld pool does not change noticeably after application of ultrasound. It is concluded that the high-pressure conditions induced during the occurrence of cavitation, lead to grain fragmentation in a pure aluminum TIG weld during an ultrasonic-assisted TIG welding process.
The paper presents a detailed theoretical analysis of the electromagnetic forces in the arc plasma and the weld pool metal in Tungsten Inert Gas (TIG) welding at direct current (DC) and ...high-frequency pulse current (HFPC) modulation with a frequency of 10 kHz. The electromagnetic (Lorentz) force, acting on arc plasma and metal is presented via potential (magnetic pressure) and rotational (equivalent electromagnetic force) force components. This approach allows us to substantially simplify the analysis of the Lorentz force effect on the arc plasma and weld pool metal under different arc burning modes. It was shown that in HFPC TIG welding with a given frequency, the effect of modulated current on the arc plasma is inherently non-stationary, whereas the effect on the weld pool metal is determined by the time-averaged magnitude of electromagnetic force throughout the period of current modulation. The proposed approach serves as a basis for numerical analysis of the electromagnetic forces in arc plasma and weld pool metal during DC and HFPC modes of the welding process. We established that the application of HFPC modulation promotes a greater intensity of both the gas-dynamic processes in the welding arc, thereby significantly increasing the pressure on the weld pool surface, and convective heat transfer from the most heated central region near the weld pool surface towards the weld pool bottom. Both these factors lead to an increase of the arc penetrability in the case of the HFPC mode compared with the DC mode, all other conditions being equal.
•Only rotational part of the Lorentz force initiates vortical flow.•Square-wave pulse is used as a welding current wave form.•Non-stationary magnetic field diffusion equation is solved numerically.•In-house Wolfram Language code is used for FEM-analysis.•HFPC modulation increases the effective driving force in the weld pool.
Dissimilar metals TIG welding–brazing of 5A06 aluminum alloy to SUS321 stainless steel had been conducted using 4047 Al–Si eutectic filler metal and modified non-corrosive flux. And spreading ...behavior of filler metal on the groove surface and microstructure characteristics of the butt joint were investigated. The spreading behavior of liquid filler metal consisted of two parts: one was to spread on the back face to pack the steel; the other was to uphill spread on the front face of the groove to form a sound brazed seam. The interfacial layer, unequal in thickness at different position, ranged from 5
μm to 35
μm. And it was made up of three different kinds of IMC layers: from the welded seam to stainless steel, the first was τ
5-Al
7.2Fe
2Si and α-Al phases, the second was η-Fe
2Al
5 phase, and the third was FeSi
2 and η-Fe
2Al
5 phases. Average tensile strength of the butt joint reached 120.0
MPa and fracture occurred at the interfacial layer. Cracks derived from the top part of brittle η-Fe
2Al
5 interfacial layer when its thickness exceeded 10
μm.
The present study focuses on the dissimilar joining of P92 steel and 304H austenitic stainless steel plates of thickness 8 mm using A-TIG welding with aim to select a proper flux for through ...thickness penetration. The effect of four different oxide fluxes named: Cr2O3, MoO3, SiO2 and TiO2 on weld bead geometry was studied. A detailed investigation on possible mechanism for increase in depth of penetration has been carried out. Out of four oxide fluxes, TiO2 provided through thickness penetration. Further, the integrity of weld joint developed using TiO2 flux was assessed in light of microscopy, hardness test, tensile test and impact toughness test. Microstructure study of the weld joint showed the formation of untempered martensite, polygonal austenite grains and ferrite stringers in different zones of weld joint. In tensile testing, the specimens were failed from 304H austenitic stainless steel base metal. The tensile properties were found as tensile strength 688.6 MPa, yield strength 562.2 MPa and elongation 37.4%. The V-notch Charpy impact toughness of the weld joint (30 J) was quite lower than the base metals due to the formation of untempered martensitic structure.
This study aims to investigate the strengthening effect of incorporated nickel coatings with different weight percentages (wt.%) of tungsten carbide (WC) microparticles on the various properties of ...the applied coatings on plain carbon steel. Therefore, different applied coatings, including pure and reinforced nickel with various wt.% of tungsten carbide were applied to the samples using the tungsten inert gas (TIG) welding method. Then, the microstructure, wear behavior, hardness, and corrosion of the coated samples with pure and incorporated nickel with 5, 10, and 20% tungsten carbide were obtained and compared with the uncoated sample. The obtained results show that reinforcing the applied coatings with WC has improved the behavior of the coatings in different properties so that the filled coating with 20% of tungsten carbide had the best results. For example, the wear rate of coated surfaces reinforced with 5, 10 and 20% of tungsten carbide was 12.56, 7.52, and 5.28 mg/m, respectively, which was much lower than the uncoated sample with a value of 24.41 mg/m. The maximum coating hardness equal to 49.6 Rockwell C was obtained for nickel coating reinforced with 20% of tungsten carbide, which can be due to the high percentage of powder compared to other samples, and the formation of finer grains. The corrosion results of the samples using cyclic polarization diagrams showed the improvement of the corrosion behavior by adding tungsten carbide so that the nickel coating reinforced with 20% of tungsten carbide had a corrosion current density of 7.15 × 10−7 amps/cm2. Finally, the obtained results show that strengthening the applied coatings by the TIG method using different wt.% of tungsten carbide up to 20% can improve the various properties of the coating.
•Fabrication of incorporated Nickel Coatings with Different Loading of WC Nanoparticles:•Mechanical and Chemical Properties Investigation.•Reinforcing the applied coatings with WC improves the behavior of the coatings.•Strengthening the coatings by TIG method using different wt.% of tungsten carbide.
5mm thick austenitic stainless steel was welded using an A-TIG welding process with in-house developed activators. The microstructure, mechanical properties, and intergranular corrosion resistance of ...the weld joint were characterized. The microstructure of conventional TIG and A-TIG welds were all austenite with a small amount of δ-ferrite. The included angle between the fusion line and rolling direction of the conventional TIG and A-TIG welds were nearly 0° and 90°, respectively. The microstructure of the A-TIG weld had more and finer δ-ferrite under conditions of less heat input. Compared with the conventional TIG weld, the tensile strength of the A-TIG weld was enhanced approximately 10%, and the elongation was increased by 30%. The microhardness of the conventional TIG weld was found to be 280HV, and the microhardness of the A-TIG weld was 210HV. The corrosion rates of substrate, conventional TIG and A-TIG welds were measured and found to be 0.056mm/h, 0.110mm/h and 0.065mm/h respectively. The chromic carbide content in the conventional TIG weld was higher than that of the A-TIG weld.
An Schweißsimulationsproben eines vergüteten Feinkornbaustahls S960QL wurde der Abbau von Eigenspannungen unter zügiger und kombiniert zügiger und zyklischer Belastung bei unterschiedlichen ...Beanspruchungshöhen untersucht. Die Untersuchungsergebnisse zeigen einen vorwiegend durch Streckgrenzenüberschreitung gekennzeichneten quasistatischen Abbau der Makroeigenspannungen, der sich weitgehend proportional zur Beanspruchungshöhe bzw. zur Oberspannung verhält. Signifikante Veränderungen der Mikroeigenspannungen treten dabei nur auf, wenn die Lastspannungen die Streckgrenze überschreiten. Ein Nachweis eines zyklischen Eigenspannungsabbau ist nur unter Rückgriff auf die aus den verschiedenen Eigenspan-nungskomponenten und den Lastspannungen berechneten Vergleichsspannungen möglich.
High-quality thick Ti-6321 titanium alloy welded joints were obtained by tungsten inert gas（TIG）welding， the microstructure changes of fusion zone， heat affected zone and base metal zone of the ...welded joints before and after annealing were compared.The impact properties， fracture toughness and tensile properties were tested， and which were compared with the base metal. The results show that the microstructure of the fusion zone before annealing is composed of coarse β columnar grains with fully grown intragranular acicular martensite α′ phase， and heat affected zone consists of equiaxed structure with β matrix and primary α phase， martensite α′ phase precipitates in β matrix.After annealing， the martensite α′ phase in β matrix of the fusion zone and heat affected zone completely transforms into secondary α phase. The impact toughness， fracture toughness， tensile strength and elongation of Ti-6321 titanium alloy welded joints are 80.3 J/cm2， 113.00 MPa·m1/2， 873 MPa and 9%， respectively， which are 104.7%， 84.1
Since the Japanese reduced activation ferritic/martensitic steel named F82H is considered as the primary candidate structural material for application in water-cooled ceramic breeder test blanket ...module, qualification on weldability of F82H based on France regulation and construction code should be identified to aim for works at ITER environment. In this study, based on the proposed welding procedure specification (WPS), two test pieces (TP) were welded by the tungsten inert gas (TIG) arc welding method and turned to post-weld heat treatment. Welded TPs were conducted by non-destructive testing (NDT) and destructive testing (DT) to investigate welded performance including defect phenomena and mechanical properties. Out of acceptance criteria of welded TPs were not observed by NDT and DT investigations. It was indicated that TIG welded F82H including the welding process performed sufficient margin to satisfy the criteria of France regulation and construction code. The qualification on weldability of F82H could be validated according to the limited WPS and dimension of TPs. Furthermore, an extended evaluation on fatigue lifetime based on the modified universal slope method was performed. Compared with the base metal of F82H, the same magnitude of fatigue lifetime was observed at 550 °C.
•MgO particles are introduced into the welding pool by welding wire.•A fully equiaxed grain structure in fusion zone of AZ31 alloy is achieved.•The mechanism of the columnar-to-equiaxed transition is ...revealed.
Due to the low content of alloying elements and the lack of effective nucleation sites, the fusion zone (FZ) of tungsten inert gas (TIG) welded AZ31 alloy typically exhibits undesirable coarse columnar grains, which can result in solidification defects and reduced mechanical properties. In this work, a novel welding wire containing MgO particles has been developed to promote columnar-to-equiaxed transition (CET) in the FZ of TIG-welded AZ31 alloy. The results show the achievement of a fully equiaxed grain structure in the FZ, with a significant 71.9% reduction in grain size to 41 μm from the original coarse columnar dendrites. Furthermore, the combination of using MgO-containing welding wire and pulse current can further refine the grain size to 25.6 μm. Microstructural analyses reveal the homogeneous distribution of MgO particles in the FZ. The application of pulse current results in an increase in the number density of MgO (1-2 μm) from 5.16 × 104 m−3 to 6.18 × 104 m−3. The good crystallographic matching relationship between MgO and α-Mg matrix, characterized by the orientation relationship of 112‾0α−Mg//01‾1MgO and (0002)α−Mg//(111)MgO, indicates that the MgO particles can act as effective nucleation sites for α-Mg to reduce nucleation undercooling. According to the Hunt criteria, the critical temperature gradient for CET is greatly enhanced due to the significantly increased number density of MgO nucleation sites. In addition, the correlation with the thermal simulation results reveals a transition in the solidification conditions within the welding pool from the columnar grain zone to the equiaxed grain zone in the CET map, leading to the realization of CET. The exceptional grain refinement has contributed to a simultaneous improvement in the strength and plasticity of welded joints. This study presents a novel strategy for controlling equiaxed microstructure and optimizing mechanical properties in fusion welding or wire and arc additive manufacturing of Mg alloy components.
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