Width Of Fusion Zone Research Articles

Keyhole critical failure criteria and variation rule under different thicknesses and multiple materials in K-TIG welding

The stability of keyhole was important to determine both the process and welding quality in keyhole tungsten inert gas (K-TIG) welding. In this study, the welding experiments were conducted on three kinds of materials (TC4 alloy, 304 stainless steel, Q235 carbon steel) with four kinds of thicknesses (2 mm, 4 mm, 6 mm and 8 mm). The keyhole critical failure criteria of K-TIG welding for different materials and thicknesses was established based on Gibbsian surface thermodynamics and regression analysis. Critical stability coefficient Kc was calculated by the values of upper width (Wf) of fusion zone and lower width (Wr) of fusion zone. When Kc>G/WfWr, the keyhole collapse failure would occur. Otherwise, a stable penetration could be obtained. On the other hand, the values of Kc increase with the increase of plate thickness, which meant the keyhole stable range would be smaller. The Kc values of TC4 alloy were smallest and the corresponding stable penetration range was largest. While the values and range of Q235 carbon steel were the largest. This was consistent with the rule reflected by the fitting curves of critical heat input. Furthermore, the difference in criteria variation rule of different materials and different thicknesses were discussed.

Scale analysis of undercut and bulge driven by thermocapillary convection due to surface-active solute on a solidified surface

This study scales the shape of the undercut, a depression region near the triple-phase line parallel to the scanning direction, and the bulge in the central region within the fusion zone, considering thermocapillary convection affected by a surface-active solute in the molten pool for the first time. Undercuts, commonly encountered in welding, additive manufacturing, and re-solidification processes, reduce fatigue and fracture strength while enhancing stress concentration. Utilizing the interfacial Young–Laplace equation and Bernoulli equations in the shear layer driven by thermocapillary force influenced by the surface-active solute-affected critical temperature, and introducing the concept of mass conservation, the scale analysis finds that the undercut depth and bulge height increase as Marangoni and Prandtl numbers increase, and the loss coefficient decreases. Furthermore, the widths of the undercut and bulge exhibit increases with dimensionless beam power, fusion zone width, and the ratio of solid-to-liquid thermal conductivity. The COMSOL Multiphase code is also used for simulation and successful comparison, aligning with experimental data from laser polishing. This analysis aids in understanding and controlling microstructures in various processes beyond laser polishing.

Mechanical response and microstructural evolution of a composite joint fabricated by green laser dissimilar welding of VCoNi medium entropy alloy and 17-4PH stainless steel

In engineering structures, the application of advanced alloys, such as the VCoNi medium-entropy alloy (VCoNi-MEA), with remarkable tensile strength (> 1 GPa) and superior ductility necessitates the employment of dissimilar joints. This study pioneers the dissimilar joining of VCoNi-MEA and 17–4 precipitation hardening stainless steel (17–4PH STS) using state-of-the-art green laser beam welding (LBW). To evaluate and optimize the experimental parameters, two welding speeds (200 and 300 mm/s) along with post-weld heat treatment (PWHT) were incorporated. High-quality welded joints with a single-phase face-centered cubic (FCC) structure in the fusion zone (FZ), minimal precipitates (< 1.6 %), and no visible cracks were successfully created. The LBW process demonstrated effective low-heat input characteristics, evident from a considerably narrow heat-affected zone (HAZ). Control over FZ width and grain size was achieved, measuring 600 and 112 μm at low welding speed and 250 and 49 μm at high welding speed, respectively, significantly lower than previous studies. A remarkably high yield strength (YS) of ∼620 MPa and ultimate tensile strength (UTS) up to 845 MPa were observed in the as-welded conditions, improving to ∼645 and 875 MPa, respectively, after PWHT. This enhancement in mechanical properties is primarily attributed to lattice friction induced by V addition. PWHT also improved joint ductility, increasing from 3.5 % to 8.6 % (low-speed) and from 6.3 % to 9.2 % (high-speed). The reduction in crystallographic orientation achieved using a higher welding speed and PWHT emerged as a major reason for improved mechanical properties. Slip-based deformation mechanisms dominated across all conditions, featuring crystallographically aligned slip bands. Interactions between existing and additional slip bands formed a dense dislocation network crucial for enhanced elongation after PWHT. Thermodynamic parameters elucidating phase stability in the observed FZs and contributions to superior YS were calculated and comprehensively discussed.

Mechanical behavior investigation for quenching and partitioning steel dissimilar resistance spot welds

Resistance spot welding is still the most common joining process for autobody structure assembly. It has many advantages and is simple to use, but the main challenge is controlling the process parameters that affect mechanical properties and weld quality. Advanced high-strength steels were developed to meet the demands of automakers such as lighter and stronger autobody. Quenching and partitioning (Q&P 980) steel is a third-generation advanced high strength steel with a combination of high strength and high ductility. In this study, effect of resistance spot welding parameters on the mechanical performance of dissimilar combination of Q&P980 steel and SPFC780Y high strength steel was investigated. Welding current, welding time, electrode pressure and holding time were chosen as the most important process parameters influencing the weld quality. A comprehensive investigation was conducted on geometrical attributes such as nugget size, fusion zone width, fusion zone area, electrode indentation and heat affected zone area and their correlations with peak load (Pmax), failure energy, fracture energy, and elongation at peak load (Lmax). In contrast the failure modes and fracture behavior were studied using scanning electron microscopy. It was observed that using high levels of welding current and welding time while maintaining low levels of electrode pressure and holding time result in a maximum peak load, energy absorption and maximum (Lmax) with pullout failure mode (PF) and this was demonstrated for large nugget size to a critical limit. The methods and findings of this research can be used as a basis for further research and development in the field of dissimilar resistance spot welding.

A Comparative Analysis of the Influence of Welding Current on Microstructure and Mechanical Properties in TIG Welded Ti5Al2.5Sn Alloy

Tungsten inert gas (TIG) welding was performed on a 1.6 mm thick Ti5Al2.5Sn alloy sheet to analyze the influence of welding current on the resultant microstructure and mechanical properties in the weldments. Fusion zone (FZ) width was observed to increase with increasing the welding current. The heat-affected zone (HAZ) showed acicular α, primary α and α' martensite phases depending upon the cooling rate. FZ was comprised of α´ martensite at the high cooling rate, acicular α at a low cooling rate and some retained β. The ultimate tensile strength (UTS), notch tensile strength (NTS) and impact toughness in all the weldments increased from 754 MPa to 810 MPa, 703 MPa to 785 MPa, and 2.3 J to 3.3 J, respectively, by increasing the welding current. However, percentage elongation decreased from 10% to 6.5% by increasing the welding current from 12 A to 18 A. Moreover, the impact toughness value was observed to increase by increasing welding current owing to the formation of a higher proportion in acicular α, α' martensite phases within the FZ. Furthermore, higher microhardness was achieved at higher currents.

Contrasting the mechanical and metallurgical properties of laser welded and gas tungsten arc welded S500MC steel

S500MC steel is a grade of high-strength low-alloy steel (HSLA) which is widely used in the automotive industry and for agricultural machinery and equipment. Considering properties of this alloy, selection of the welding process and parameters becomes essential to ensure that HSLA assemblies meet specific service requirements. In this work, mechanical and metallurgical properties of S500MC steel produced by autogenous laser beam welding (LBW) and automatic gas tungsten arc welding (GTAW) were compared. Tensile testing, metallography, hardness testing, and fractographic analysis were performed on the welded specimens, revealing that the heat input by these welding processes caused significant microstructural changes within the joints. In LBW samples, the heat input about 10 times lower than that in GTAW produced a finer microstructure, narrower fusion zone width, and smaller heat-affected zone. All fractures of the GTAW specimens occurred in the base metal, while all fractures of the LBW specimens occurred in the weld zone, both regardless of the heat input. GTAW joints exhibited higher mechanical properties (even higher than those obtained in the base metal) as compared to LBW joints.

Experimental and Numerical Analysis on TIG Arc Welding of Stainless Steel Using RSM Approach

This study involves the validating of thermal analysis during TIG Arc welding of 1.4418 steel using finite element analyses (FEA) with experimental approaches. 3D heat transfer simulation of 1.4418 stainless steel TIG arc welding is implemented using ABAQUS software (6.14, ABAQUS Inc., Johnston, RI, USA), based on non-uniform Goldak’s Gaussian heat flux distribution, using additional DFLUX subroutine written in the FORTRAN (Formula Translation). The influences of the arc current and welding speed on the heat flux density, weld bead geometry, and temperature distribution at the transverse direction are analyzed by response surface methodology (RSM). Validating numerical simulation with experimental dimensions of weld bead geometry consists of width and depth of penetration with an average of 10% deviation has been performed. Results reveal that the suggested numerical model would be appropriate for the TIG arc welding process. According to the results, as the welding speed increases, the residence time of arc shortens correspondingly, bead width and depth of penetration decrease subsequently, whilst simultaneously, the current has the reverse effect. Finally, multi-objective optimization of the process is applied by Derringer’s desirability technique to achieve the proper weld. The optimum condition is obtained with 2.7 mm/s scanning speed and 120 A current to achieve full penetration weld with minimum fusion zone (FZ) and heat-affected zone (HAZ) width.

Exploration of Parametric Effect on Fiber Laser Weldments of SS-316L by Response Surface Method

Fiber laser welding experiments are conducted on SS316L austenitic stainless steel plates based on the statistical design of experiments technique. A special kind of fixture is designed and fabricated with a facility to provide argon gas and is made up for bead protection. The influence of beam power, welding speed, and defocused position on fusion zone width, fusion zone area, and tensile strength of weldments is studied and discussed briefly. The most influencing factors and their percentage contribution on output responses are identified by analysis of variance technique. Beam power directly influences the bead features, whereas welding speed inversely affects it. However, the defocused position shows an insignificant effect on the fusion zone area within the selected range. The tensile strength increases with an increase in both beam power and welding speed up to a particular optimum value, and beyond that, it starts reducing. The highest hardness value is observed in the fusion zone at ‘1’ mm defocused position below the workpiece surface due to a decrease in grain size and interdendritic spacing. Ductile mode of fracture failure is found in both base material and weldment. The optimum welding condition obtained in this study yields full penetration, narrower weld width, lesser fusion zone area, minimal weld defects, and acceptable tensile strength of weldments.

Simulation of hybrid (LASER-TIG) welding of stainless steel plates using design of experiments

A solid drive for the improvement of higher productivity welding forms lead to the advancement of Hybrid welding process. This research combines arc and laser welding processes providing more robust joints. Hybrid laser welding is a perfect combination of the advantages of laser and arc welding processes. It provides high welding depth at high welding speeds and also good gap bridging capability. This process finds potential applications in shipbuilding, pipeline and automotive industries where high productivity and quality are important. Many researches are in progress to analyze the effect of process variables. This present work is mainly carried out to study the effect of various process parameters like laser beam power, arc power, welding speed on the weld bead dimensions, i.e., bead width and depth of penetration. A three-dimensional transient thermal analysis has been performed for the hybrid welding (LASER + TIG) process using ANSYS. The computed results of width and depth of fusion zone indicates the weld pool shapes. Good agreement was achieved between computed and experimental weld bead dimensions. Mathematical equations were developed using a three factor 5-level factorial technique to predict the geometry of the weld bead. These equations were used to correlate the hybrid welding process parameters with the bead geometry. From these mathematical equations the response of weld bead dimensions with the variation of various hybrid welding parameter were predicted.

Underwater laser welding for 304 stainless steel with filler wire

Underwater laser welding for 304 stainless steel with filler wire was successfully performed with a self-designed double-side gas-shielding nozzle. The effects of the back gas flow rate, travel speed and wire feed speed on the welding appearance, geometry characteristics of cross section, defects and mechanical property of butt joints were investigated. While the bottom surface of joint touched the water directly, the surface appearance was uneven and some small pores formed. With increasing the back gas flow rate to 50 L/min, the stable local dry cavity around welding zone was generated and an underwater laser welded joint without defects was obtained. After the optimization of process parameters, the tensile strength and impact toughness of the underwater laser welded joint approached those of in-air joint basically, and the using of filler wire improved the tensile strength of butt joint significantly. Compared to the in-air joint, the water cooling effect decreased both the area and width of fusion zone of underwater joint. This accelerated cellular dendrites grew up from fusion line to the bead center, which reduced the number of equiaxial grain and thus decreased the tensile strength slightly. In addition, the high cooling rate decreased the grain size, but increased the lathy ferrite content in fusion zone of underwater joint, decreasing the toughness of weld metal.

Effect of active flux MgF2 on weld geometry and joint strength in laser beam welding of titanium

In the present study laser beam welding of commercially pure titanium is carried out at different welding speeds. Effect of the addition of active flux layer of MgF 2 on the morphology and geometry of the weld zone and surrounding regions is investigated along with its influence on the tensile strength of the welded joints. The active flux narrowed down the weld zone geometry compared to the hour-glass shape obtained in the welding without the flux, accompanied with a decrease of top fusion zone width by around 50%. The tensile strength improved by around 10–12% along with the improvement in the joint ductility with the addition of the active flux.

Effect of carbon migration on mechanical properties of dissimilar weld joint

After welding or servicing at high temperature, carbon migration will occur in dissimilar welded joint. Correspondingly, the carburized layer with high carbon content and decarburized layer with low carbon content are formed near weld fusion line. Carbon migration has a great influence on the properties of the joint and leads to premature failure. However, due to the small size of carburized layer and decarburized layer, it is difficult to use the traditional uniaxial tensile test method to study their mechanical properties. In this work, the elastoplastic properties of base metal (BM), carburized zone (CZ), decarburized zone (DZ) and weld metal (WM) in A302/ Cr5Mo dissimilar weld joint were investigated by nanoindentation tests. nanoindentation tests results indicate that the decarburized zone is the weakest position in the weld joint. Metallographic and carbon content distribution analysis were also carried out and found that the width of CZ is related to the width of fusion zone (FZ) and the CZ does not exceed the boundary of FZ.

Joining of zircaloy-4 of dissimilar thickness using electron beam welding

Electron beam butt welding of zircaloy-4 plates of dissimilar thickness (with different thickness ratio, defined as the thickness of one side plate with variable thickness to that of another reference plate of fixed thickness) was performed in order to investigate the effect of plate thickness on the evolution of cooling rate, microstructure and its correlation to mechanical properties. Faster cooling rate on thicker plate results in lower peak temperature, finer grain size both in fusion zone and heat-affected zone with more but uniform porosity distribution than those in the thinner plate. The size of HAZ was higher on thinner plate compared with that of thicker plate. Although the width of fusion zone remained unaffected, the depth of penetration decreased with increase in thickness ratio at same heat input rate. Fusion zone consisted of columnar grains with lamellar widmanstatten features, while HAZ consisted of equiaxed grain with randomly oriented small acicular α-Zr phase in β-Zr phase. A small amount of fine second-phase particles of Zr(Fe,Cr)2 was identified in the fusion zone, which affected the tensile properties marginally. Weld failed in the base metal during tensile test, and YS and UTS are found to be comparable to that of base metal. However, the ductility and notch toughness of the joint was found to be inferior to those of base metal, which deteriorated with increase in thickness ratio. At constant heat input, porosity was found to be higher in dissimilar joint than its similar counterpart, which might be one of the reasons for inferior ductility and notch impact strength in addition to unfavourable microstructural features.

Experimental and Numerical Analysis of Laser Surface Melting by Using Enthalpy Method

In this study, experimental and numerical applied of heat distribution due to pulsed Nd: YAG laser surface melting. Experimental side was consists of laser parameters are, pulse duration1.3ms, wavelength 1064nm, laser energies 1.5, 2. 6 and 4.3 J, laser beam diameter is 0.6 mm and spot diameter 0.78 mm was applied a low carbon steel type St37 with a dimension 10, 10, 3 mm, length, width and thickness respectively. Numerical analysis side consist of a mathematical model and calculating a thermal cycle by using equation in the enthalpy method applied to determine the cooling rate in fusion zone. The simulation by using the enthalpy method, applied on conduction heat transfer to estimate the cooling rate model in fusion zone and heat affected zones. Cooling rates models are helping to estimate the microstructure and micro hardness distribution in fusion and heat affected zones. The complication of the heat transfer in laser surface melting process, because at in rapid solidification, therefore the enthalpy model is more appropriate for this case. The result shows that increases of laser energy lead to decrease cooling rates and increase width and penetration of fusion zone, also decrease micro hardness in fusion zone and we found an increase in the pool size of fusion and heat affected zones.

Optimization of Process Parameters Using Surface Response Methodology for Laser Welding of Titanium Alloy

Laser beam welding input conditions are greatly influence the quality of the welded joints and they have significant role on the controlling of their strength and metallurgical properties. The metallurgical properties and weld bead geometry and mechanical properties of the joints determine the quality of the joints. In this study, the fusion zone width, penetration, width of the heat affected zone and strength of the titanium alloy welds were investigated using laser welding process. The surface response methodology design is carried out for the experimental design by the development of regression equations. Analysis of variance (ANOVA) was used to check the validity of the model. In order to identify the significant parameters, student’s test is conducted. The obtained results from response surface methodology were compared with the experimental results and validated.

The Influence of Gas Tungsten Arc Welding Parameters on Mechanical and Microstructure Properties of the TC4 Titanium Alloy

In the present study, TC4 titanium alloy was gas tungsten arc welded to evaluate the mechanical and metallurgical properties of the welds. The welds were carried out at different welding conditions such as welding speed and current to identify their effect on microstructural changes and strength of the welds. The results of bead geometry measurements suggests that the fusion zone width and depth was greatly varying with the welding speed and current. It is also observed that the fusion zone microstructure and heat affected zones are greatly controlled by welding conditions. Therefore the mechanical properties of the welds were improved with the changes in welding conditions and are correlated with the metallurgical features of the welds. The optimal welding conditions were analysed using Box-Behnken design and analysis of variance technique for identifying strength of the welds and better bead geometry parameters.

Weld Quality Assessment in Fiber Laser Weldments of Ti-6Al-4V Alloy

Laser welding experiments are performed on Ti-6Al-4V alloy sheets by adopting fiber laser. A special kind of workpiece fixture is designed and fabricated for providing shielding gas. After experiments, penetration depth, fusion zone width and heat-affected zone size at different locations within weld bead are measured and discussed in detail. Influence of line energies on the formation of non-uniform microstructure within weld bead is explored by conducting microstructural analysis. Various kinds of microstructural morphology of martensitic structure such as α′ martensite, blocky α, massive α and basket-weave microstructure are found in fusion zone. Experimentally, it is found that beam power is the key parameter for controlling penetration depth. Higher hardness is noticed within fusion zone due to the existence of large volume of α′ martensite. Tensile strength and hardness of welded specimens are increased with decreasing line energy. Small amount of micropores are also found in solidified weld bead. However, its sizes are in acceptable range as per BSEN:4678 standard. Most favorable welding condition is identified as a combination of beam power of 800 W and welding speed of 1000 mm/min which yields full penetration, narrower bead width, small heat-affected zone, minimal defects and acceptable mechanical properties.

Effect of heat input in pulsed Nd:YAG laser welding of titanium alloy (Ti6Al4V) on microstructure and mechanical properties

In the present investigation, titanium alloy Ti6Al4V of 1.4 mm thickness has been laser-welded in butt joint configuration using pulsed Nd:YAG laser system. The effects of heat input on weld bead shape, fusion zone width (top, middle, and bottom), heat-affected zone (HAZ) width (top, middle, and bottom), and fusion zone area have been studied. The microstructure and mechanical properties of laser-welded specimens at various heat inputs (43.7–103.5 J/mm) have also been investigated. Microstructures of the fusion zone, HAZ, and parent material have been compared at various heat inputs using optical microscope and field emission scanning electron microscope (FESEM). The mechanical properties such as microhardness and tensile strength of the welded joints at varying heat inputs have been studied. Tensile tests of the welded specimen and base metal have been conducted for analyzing ultimate tensile strength and percentage elongation. Surface topography of the tensile fractured specimen of the welded joints and base metal has been examined to analyze the ductile and brittle behavior. EDS analyses of base metal and fusion zone of the welded specimen have been studied. XRD of the as-received base metal and welded specimen have been measured in the range of 30 to 85° to study the crystallographic structure.

Study on microstructure and composition segregation of laser welded joints of 2A14 aluminum alloy

Laser welding is an attractive welding process for aluminum alloys, because its low heat input minimizes the width of fusion zone (FZ) and heat affected zone (HAZ). The present research is mainly concerned with the effect of welding parameters on microstructure morphology, composition segregation microhardness and tensile test of laser welding of 2 mm thickness 2A14 aluminum alloy. The results show that the welded joint with good quality can be achieved when the laser power is 2.5 kW and the welding speed is 2.4 m min−1. The center of the weld seam exhibits fine equiaxed grains, while the FZ consists of coarse columnar crystals and Cu segregates at the boundary of the columnar crystals. And the tensile strength of sample 4 is 274.3 MPa and about 74.4% of that of BM, which is higher than that of 3 samples. In addition, the welding speed has greater influence than the laser power on the microhardness of the joints.

Microstructure, mechanical properties and residual stress distribution in pulsed tungsten inert gas welding of Ti–5Al–2.5Sn alloy

Pulsed tungsten inert gas welding with full penetration was performed on 1.6 mm thick Ti–5Al–2.5Sn alloy sheet. Hole-drill strain measurement method was employed to measure the distribution of residual stresses across the weld line. Tensile tests were performed on the specimens sectioned in transverse direction of the welded sample. The evolved microstructure in the welded zone was investigated by metallography and X-ray diffraction. Transverse residual stresses of tensile nature were present at different depths below the surface and decreased the yield strength and ultimate tensile strength. However, this decrease was not dependent on the maximum value of transverse residual stress. Fracture location was found to be dependent on the micro-hardness profile and fracture took place in base metal where micro-hardness was the lowest. Furthermore, the presence of tensile residual stresses in the welded sample had no influence on the fractured surface morphology. Peak current and background current had a significant influence on the fusion zone width, heat-affected zone width, and fusion zone grain size.