MGH956, a kind of oxide dispersion strengthened (ODS) alloy, which is considered as candidate structural material for advanced nuclear systems because of its excellent radiation resistance and ...high-temperature capability. However, pores in fusion welding joints seriously reduced the quality and performance of the joint and structure. Arc-ultrasonic technology was applied in this research in order to prevent pores and improve tensile strength. The results showed that the excitation current of arc-ultrasonic has great effect on the pores distribution and tensile property. When it is increased to 20A or 30A, few pores are in the joint and the tensile strength (about 550MPa) is also improved. When the arc-ultrasonic frequency decreased from 60kHz to 30kHz, bubbles floated outside more easily, the tensile strength is increased to about 543MPa. But arc-ultrasonic has little influence on weld joints microhardness change.
A tungsten inert gas (TIG) welding process was utilized successfully to produce a dense and hard iron aluminide coating on an aluminized plain carbon steel substrate. The aluminized surface of the ...steel sheets was melted using different currents in the range of 30 to 50 A. The surface and cross section of the alloyed layers were studied using optical microscopy, scanning electron microscopy, X-ray diffraction and a nano-hardness test. The results showed that the volume of the pool formed during the surface melting had a critical influence on the phases formed during the process. Forty amperes was found to be the optimum TIG current, at which a Fe-rich aluminide consisting mainly of Fe
3
Al formed on the steel substrate.
A tungsten inert gas (TIG) welding is one of the most popular kinds of welding used to join metals mainly for aluminum alloys. However, many challenges may be met with this kind of joining process; ...these challenges arise from decay of mechanical properties of welded materials. In the present study, an attempt was made to enhancing the mechanical properties of TIG weld joint of 6061-T6 aluminum alloy by hardening the surfaces using shoot peening technique. To optimize the shoot peening process three times of exposure (5, 10, and 15) min. was used. All peened and unpeened, and welded and unwelded samples were characterized by metallographic test to indicate the phase transformation and modification in microstructure occurring during welding process. Tensile test and Vickers micro-hardness measurements were performed for all samples to investigate the effect of shoot peening on mechanical properties of welded aluminum.The results indicated a significant improvement in properties for peened welded and unwelded samples compared with those unpeened one. Also, the results showed that the tensile and microhardness properties were increased with increasing the time of exposure to 15 min. due to generation of compressive residual stresses at surface.
Inconel 718 alloy is widely used in applications that require advanced strength properties especially at high temperature conditions. Combust room walls, exhaust parts, jet tribune blades and gas ...tribune equipment are the most known using areas. This alloy can be welded with various fusion welding methods, but TIG (Tungsten Inert Gas) welding is preferred since, it provides simply application, mobility and low cost. This study was aimed to clarify that how adjusting the welding parameters and welding automatically can help to achieve promising mechanical properties before heat treatments. The welding experiments were conducted on three different welding current values and attention was paid to provide full penetration for each condition. The results showed that the highest welding current value which did not cause welding defects lead to decrease heat input due to the high transverse speed usage. Moreover, by automatically welding, the heat input was decreased to a minimum level that provided excellent tensile strength and elongation properties. Dendrites turned to cellular from colon. Hazardous zones, such as HAZ and PMZ, narrowed down. The Laves phase ratio and grain size also decreased. Microhardness results confirmed these microstructure observations. The crack observations after tensile tests showed that failures were near HAZ in high-heat input conditions. However, failures were observed in FZ for low-heat input conditions. Additionally, ductile fracture and fracture similar to cleavage mechanisms were observed together due to adjusting the parameters and automatization.
The droplet ejection from an electrode during an alternative current tungsten inert gas (AC TIG) welding process was observed using a visualization system composed by a high-speed camera with a ...band-pass filter to clarify dominant factors of the droplet ejection. Different welding currents, electrode diameters and electrode positive (EP) ratios were set. The numbers of droplets ejected from the electrode tip were measured for the different conditions. The timings of droplet ejections from the electrode were also determined in one AC cycle. The results indicated that droplets were likely to be ejected when the welding current was high, when the electrode diameter was small, when the EP ratio was large, and in the latter half of the EP term. Because the electrode temperature under these welding conditions was higher, the high electrode temperature was considered to be a dominant factor for the droplet ejection. However, immediately after the start of the electrode negative (EN) term, the number of droplets decreased even though the electrode temperature was the highest in one AC cycle. Therefore, it was suggested that other factors affected the electrode ejection. Moreover, raised portions were formed on the surface of the molten electrode right before droplet ejections. It was considered that the formation of the raised part might be suppressed by the collision of positive ions in the arc plasma with the electrode at EN term. Estimated pressure due to the ion collision acting on the ridge was larger than that due to the surface tension and the electromagnetic force, respectively. Therefore, it was suggested that the collision of positive ions at EN term suppressed the droplet ejection.
The tungsten inert gas (TIG) welding method most commonly used to weld ferrous metals, nonferrous metals, and other metals since it is simple, easily implemented, and achieves consistent high-quality ...welds. In this study, butt joints produced between aluminum alloy A6061-T6 and stainless steel SUS304L have been achieved by using TIG welding with ER4047 filler metal. The macrostructure and microstructure of the resulting specimens were analyzed by means of an optical microscope (OM), a scanning electron microscope (SEM), and an energy dispersive X-ray spectrometer (EDS). A uniform intermetallic layer was found at the interface between the stainless steel and the weld seam having a thickness of 2 µm, and the intermetallic compound (IMC) includes Fe₄Al
, Fe₂Al₅, and FeAl₃ phases. The micro-hardness and tensile strength of the weld joints were also investigated. Due to Si content in the compensating metal, there was a prevention of iron diffusion into the aluminum, thus hindering the development of the IMC layer and reducing its thickness in such a way that the weld joint strength increases. The analyzed results show that the average micro-hardness of the stainless steel, weld seam, aluminum alloys, and IMC layer were 218 HV, 88.3 HV, 63.3 HV, and 411 HV, respectively. The fracture occurred at the brazed interface, and the ultimate tensile strength value reached 225 MPa.
Visual inspection through image processing of welding and shot-peened surfaces is necessary to overcome equipment limitations, avoid measurement errors, and accelerate processing to gain certain ...surface properties such as surface roughness. Therefore, it is important to design an algorithm to quantify surface properties, which enables us to overcome the aforementioned limitations. In this study, a proposed systematic algorithm is utilized to generate and compare the surface roughness of Tungsten Inert Gas (TIG) welded aluminum 6061-T6 alloy treated by two levels of shot-peening, high-intensity and low-intensity. This project is industrial in nature, and the proposed solution was originally requested by local industry to overcome equipment capabilities and limitations. In particular, surface roughness measurements are usually only possible on flat surfaces but not on other areas treated by shot-peening after welding, as in the heat-affected zone and weld beads. Therefore, those critical areas are outside of the measurement limitations. Using the proposed technique, the surface roughness measurements were possible to obtain for weld beads, high-intensity and low-intensity shot-peened surfaces. In addition, a 3D surface topography was generated and dimple size distributions were calculated for the three tested scenarios: control sample (TIG-welded only), high-intensity shot-peened, and low-intensity shot-peened TIG-welded Al6065-T6 samples. Finally, cross-sectional hardness profiles were measured for the three scenarios; in all scenarios, lower hardness measurements were obtained compared to the base metal alloy in the heat-affected zone and in the weld beads even after shot-peening treatments.
Six different types of oxides Cr2O3, FeO, Fe2O3, MoO3, SiO2, and Al2O3 were used to investigate the effect of oxide flux on weld morphology, microstructure and mechanical properties in 304 austenitic ...stainless steel welded joints. An autogenous TIG welding was used to join 8mm thick austenitic stainless steel plate and a thin layer of oxide was applied prior to welding. The results indicated that there was a significant increase in penetration depth on using metal oxides but Al2O3 does not give satisfactory result. The microstructures were found to be different on using different oxides. The mechanical properties of the weld were almost similar to that of parent metal.
In the present study, a finite element-based 3D mesh model is used to simulate the effect of welding processes on the temperature distribution, residual stress and distortion in 11-mm-thick ...2.25Cr-1Mo steel weld joints. Tungsten inert gas (TIG) and activated-TIG (A-TIG) welding processes were employed for the fabrication of weld joints. Austenite-to-bainite phase transformation is taken into account in the numerical analysis. The heat input fitting tool has been used to calibrate the heat source by matching the simulated weld bead with that of the actual weld bead. Peak temperature was higher at the weld center for A-TIG weld joint, and the weld joint exhibited a sharp temperature gradient at the weld interface. There was good agreement between the predicted and measured thermal cycles. A-TIG and multipass-TIG (MP-TIG) weld joints exhibited similar longitudinal residual stresses in heat affected zone with a difference of 50 MPa. Moreover, A-TIG weld joint fabricated by double-side welding technique employing two passes exhibited reduced distortion than MP-TIG weld joints. A higher magnitude of distortion was in MP-TIG weld joint which was attributed to more weld metal volume caused by more number of weld passes required to fill the V-groove. There was good agreement between the predicted and measured residual stress and distortion values.
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