Weld Microstructure Research Articles

Study on arc characteristics under high-frequency sine wave pulse current and effect of weld appearance and microstructure of AISI444 ferritic stainless steel

Based on the principle of LC resonance, high-frequency sine wave pulse DC TIG welding (HFSWP DC TIG) was developed, and welding experiments were conducted on AISI444 ferritic stainless steel (FSS). The arc characteristics of HFSWP DC TIG and its effect on weld appearance and microstructure were studied theoretically and experimentally. The experimental results show that under the same conditions, compared with constant-current DC conventional arc welding (CAW), the arc pressure and arc thermal efficiency of HFSWP DC TIG are improved, and the weld penetration of the weld is increased by nearly two times. The weld microstructure is single-phase ferrite, and carbonitride, Laves phase, and phase are formed in the joint. In addition, according to the theoretical calculation of the pulse current waveform, the reason why the arc pressure of the high-frequency sine wave pulse current is increased compared with the constant-current DC and high-frequency square wave (triangular wave) pulse current is explained. The mechanism of arc shape and weld appearance change is described from the microscopic point of view, and the reason for the appearance of equiaxed grain in the weld is analyzed. HFSWP DC TIG provides a new idea for the improvement of high-frequency pulse technology.

Investigating microstructural evolution and wear resistance of AISI 316L stainless steel cladding deposited over mild steel using constant current GMAW and pulsed current GMAW processes

Abstract The main objective of this study is to investigate the microstructure and wear resistance of AISI 316L austenitic stainless steel (ASS) cladding deposited over mild steel (MS) of grade IS 2062 using constant current (CC-GMAW) and pulsed current gas metal arc welding (PC-GMAW) processes. The PC-GMAW process was employed to overcome the problems of wider heat affected zone (HAZ), coarse grained deposited weld metal microstructure, lower penetration depth, higher dilution and reinforcement height encountered in CC-GMAW used for cladding of AISI 316L steel over mild steel. The microstructural features of cladded region were analyzed using optical microscopy (OM). The wear rate of cladded specimens was studied using pin-on-disc method and the morphology of wear surfaces was studied using scanning electron microscopy (SEM). The microhardness distribution of cladded region was analyzed and correlated to the wear performance of cladded specimens. The results showed that PC-GMAW cladding exhibit greater hardness and wear resistance compared to CC-GMAW cladding. It is correlated to the grain refinement offered by current pulsing in weld region of PC-GMAW cladding. The PC-GMAW cladding showed 5.22% increases in weld metal deposition compared to CC-GMAW cladding. The, PC-GMAW cladding showed 23.72% reduction in dilution of weld compared to CC-GMAW cladding. The PC-GMAW cladding disclosed 15.83 improvement in weld overlay hardness compared to CC-GAMW cladding. The PC-GMAW showed 20.18% average reduction in wear rate compared to CC-GMAW cladding.

Effect of a longitudinal magnetic field on arc motion and joint structure of a hollow stud

Given the non-uniform melting of the end face of a joint and the local non-fusion of the joint in large-diameter hollow stud welding, to research the law of arc motion, the joint-forming quality, weld microstructure and mechanical properties in the process of hollow stud welding propelled by a longitudinal magnetic field were investigated in this study. The results reveal that under the influence of a longitudinal magnetic field, the arc on the end of a stud is affected by the Lorentz force and spirals downward. In the welding process, with an increase in magnetic field intensity, the arc uniformly burns the stud end face, preventing local non-fusion and resulting in a well-shaped joint. Under the action of magnetic field stirring, eutectoid ferrite is broken, the content of eutectoid ferrite and bainite is diminished, the nucleation barrier is reduced and the grain is refined. Under the action of a longitudinal magnetic field, the shear strength of the hollow stud welded joint rises to 312 MPa, surpassing the strength of a joint welded without a magnetic field.

Microstructure and Mechanical properties of Dissimilar Welds of Duplex and API Steel for Offshore Applications

Microstructure and Mechanical properties of Dissimilar Welds of Duplex and API Steel for Offshore Applications

Effects of Heat Input on Weld Microstructure and Properties in Keyhole TIG Welding of Invar 36 Alloy.

The Invar alloy is widely used for aircraft wing mould manufacturing. In this work, keyhole-tungsten inert gas (K-TIG) butt welding was used to join 10 mm thick Invar 36 alloy plates. The effect of heat input on the microstructure, morphology and mechanical properties was studied by using scanning electron microscopy, high energy synchrotron X-ray diffraction, microhardness mapping, tensile and impact testing. It was shown that regardless of the selected heat input, the material was solely composed of austenite, although the grain size changed significantly. The change in heat input also led to texture changes in the fusion zone, as qualitatively determined with synchrotron radiation. With increases in heat input, the impact properties of the welded joints decreased. The coefficient of thermal expansion of the joints was measured, which demonstrated that the current process is suitable for aerospace applications.

Metallurgical characterization and high-temperature tensile failure of Inconel 617 alloy welded by GTAW and SMAW—a comparative study

Two types of the weld joint of Inconel 617 alloy were produced using gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW) processes with ERNiCrCoMo-1 filler metal and ENiCrCoMo-1 electrode, respectively. The weld metal showed the segregation of the principle alloying elements like Mo and Cr along the inter-dendritic spaces, triggering the formation of secondary phases. The microstructure characterization of the interface ensured the high dilution, which could be attributed to the closeness in melting point and chemistry of base and filler metal. Microhardness variation, tensile testing at room and high temperature, and Charpy impact test were conducted to investigate the effect of the Mo segregation in the weld zone and heterogeneity in the microstructure of weldments on the mechanical behavior of both the welded joints. The cross-weld tensile tests were conducted at room temperature and 550°C. The tensile test samples failed from the weld zone for each condition with a tensile strength value close to the base metal, which ensured the applicability of the joint for end service. The tensile strength of GTAW-RT, GTAW-HT, SMAW-RT, and SMAW-HT were measured as 766 ± 22 MPa, 570 ± 5 MPa, 760 ± 7 MPa, and 600 ± 8 MPa, respectively. A non-uniform hardness plot was witnessed with the hardness of the GTAW-weld and SMAW-weld zone of 257 ± 8 HV and 285 ± 5 HV, respectively, in the transverse direction. The impact toughness of the weld zone was 84 ± 2 J and 48 ± 4 J for GTAW and SMAW weld zone. The average impact toughness of the GTAW-weld zone was approximately 42% higher than the value of the SMAW-weld zone. In a nutshell, it can be concluded that the welded joint of Inconel 617 produced using the GTAW process with ERNiCrCoMo-1 filler had the best metallurgical and mechanical properties.

Friction welding of tungsten composite core with AA5754 ballistic cup

This paper is a study of mechanical properties and microstructure of rotary friction welded tungsten heavy alloy with aluminum alloy (AA). A plastic deformation is visible on AA side. Effects of friction time (FT) and friction pressure (FP) on the ultimate tensile strength (UTS) were studied by plotting graphs. The UTS of joints increases with increasing FP and FT and then decreases after reaching the maximum value. The fracture proceeds through the cleavage planes at the interface. Scanning electron microscopy for investigation of the fracture morphology and phase transformations taking place during friction welding process was used. Chemical compositions of the interfaces of the welded joints were determined by using energy-dispersive X-ray spectroscopy (EDS). EDS analyses across the interface of tungsten and nickel have not confirmed the diffusion to AA side. Microstructure of friction welds consisted of equiaxed grains formed due to dynamic recrystallization and coarse grains in the periphery region on AA side.

Evaluation of liquid metal embrittlement-free weld by micro-plasma arc welding of Zn-coated interstitial free steel

The liquid metal embrittlement (LME) severity is a significant concern in the fusion welding of Zn-coated steel. The LME severity in galvannealed (GA) interstitial free (IF) steel processed through microplasma arc welding (MPAW) is investigated. The weld geometry, microstructure and mechanical properties of the 0.8 mm thin butt-welded structure are evaluated to check the welding quality. Optical microscopy and field emission scanning electron microscopy (FESEM) of the weld surface are considered to observe any LME cracks. The high-temperature tensile test is executed on GA-IF steel to simulate external stress-free MPAW conditions. The ultimate tensile strength of the welded joint is more than that of the base material, and it is LME-free, which signifies that the current MPAW system can be successfully used for joining GA-IF steel. The microstructure of the weld zone is having large grain structure and much more hardness than the base material. Even the high-temperature tension test does not show any LME cracks. Approximately, one-third of yield strength is reduced as the temperature rises from 600 °C to 700 °C. Overall, the parametric domain for MPAW of GA IF steel is successfully evaluated, which can produce any LME-free weld.

Refining microstructures and enhancing mechanical properties of Inconel 718 weldment via fast-frequency double pulsed waveforms adopting in FFP-TIG

Raising the frequency of pulsed welding current in conventional tungsten inert gas (TIG) welding would stimulate the arc to stir the molten metal and thus refine microstructures and enhance mechanical properties of Inconel 718 (IN-718) weldment. In the high-frequency pulsed welding waveform, scholars are usually focused on the high-frequency pulses distributing above the low-frequency pulses while seldom considering the large space inside the low-frequency pulses to accommodate the high-frequency pulses. A fast-frequency double pulsed (FFDP) waveform is proposed to apply in fast-frequency pulsed TIG (FFP-TIG) welding. The effect of FFDP waveform modulation on the stirring of the molten pool and grain refinement was studied. The electromagnetic effect of FFDP waveform concentrated the welding energy and caused the increasing depth and decreasing width of IN-718 weldments, which enhanced the cooling rate during the solidification and formation of the weldments. Besides, the melt IN-718 within molten pool would be stirred due to the Marangoni effect induced by FFDP waveform. The increasing cooling rate and inducing stirring effect synergistically acted and thus refined the microstructures of IN-718 weldments, with the minimum size being 35.15 and 0.59 µm for irregular polygonal equiaxed grain and strip Laves phase, respectively. The tensile strength and the corresponding elongation of IN-718 weldments at high temperature (700 ℃) achieved 91% and 209% of the base metal. Current work provides an important direction towards the fabrication and development of high-reliability IN-718 weldment with good mechanical performance in high-temperature.

Investigation of microstructure, hardness and intermetallic compound in friction stir welding of AA1050 aluminum alloy to copper

Investigation of microstructure, hardness and intermetallic compound in friction stir welding of AA1050 aluminum alloy to copper

Microstructure and mechanical properties in dissimilar friction stir welding between aluminum 1050 and 316L stainless steel

Microstructure and mechanical properties in dissimilar friction stir welding between aluminum 1050 and 316L stainless steel

Study on Microstructure and Properties of Mechanical Vibration-Assisted MIG Welded Joint of Aluminium Alloy Car Body

The aluminium alloy MIG welding of car body has problems such as joint softening and porosity in the weld, which directly affects the welding quality of the body structure. In this study, mechanical vibration was introduced into the aluminium alloy MIG welding process as an external excitation by improving the joint microstructure and performance of aluminum alloy MIG welding. In the research process, optical microscope and scanning electronic microscope were used to observe the microstructure of the joint, observe the size of grains, detect the number of pores, test hardness, take tensile test, and study the influence of frequency of external vibration excitation on weld forming, pore distribution, microstructure and mechanical properties. Studies have shown that mechanical vibration can effectively refine the weld grain, reduce the number of weld pores, increase the penetration depth, improve the strength and hardness of the joint, and improve the welding quality of aluminum alloy. And with the increase of vibration frequency, the grain size and number of pores of the weld gradually decrease, and the penetration depth and tensile strength and hardness of the joint gradually increase.

The response of force characteristic to weld-forming process in friction stir welding assisted by machine learning

In this study, the response of welding force characteristic to weld-forming process in friction stir welding (FSW) was systematically investigated. Assisted by machine learning technique, we found that both the force value and some detailed characteristics of force waveform are very important in reflecting the characteristics of weld formation. The mapping relations between force characteristics and weld/defect characteristics were comprehensively summarized for the first time. The results show that the distortion of the force waveform signifies the formation of defect, and the distortion degree and deflection direction of the force waveform show high relevancy to the size and location of defect. Meanwhile, the force waveform is decomposed into three standard sinusoidal waves with different frequencies, and the three sinusoidal waves correspond to the formation of the periodic weld microstructures in nugget zone. The causes of force fluctuations, with associated material deformation and flow behaviors during the FSW process, were also clarified to explain the above correspondences. The main reason is that force characteristics are closely related to the tool motion, probe geometric profile and welding parameter, which are key in heat generation and control the material flow in FSW. Therefore, it is concluded that the welding force characteristic is powerful in revealing some key information of the complicated weld-forming process, which can help us to make a deep understanding of FSW and develop intelligent FSW technologies.

Electromagnetic (EM) sensor measurement for residual stress characterisation in welded steel plates

ABSTRACT Residual stresses can cause compromise in structural integrity; it is desirable to assess residual stresses using non-destructive testing so that effects on structural properties can be predicted. Electromagnetic (EM) sensors can be used to characterise residual stresses in steels accounting for, microstructure and geometry effects. Residual stress characterisation in welded EN S275 steel plates using EM sensors is reported. Low-frequency, low-magnetic field EM sensors were used to assess residual stresses in the plates. A finite element model for the sensor and sample was generated in COMSOL software so the influence of weld bead geometry and microstructure could be predicted and accounted for. This allowed residual stresses to be determined from EM sensor measurements, excluding the geometry and microstructure effects, XRD was used to verify EM sensor measurements. The highest residual stresses were found adjacent to the weld fusion zone, with magnitudes of, 170±5MPa, 120±20MPa and 42±10MPa for X-ray diffraction (XRD), a small EM sensor (U-12.7) and a big EM sensor (U-31) types, respectively. The differences are due to the volume of the material measured by each measurement type. It was shown that EM sensors are capable of measuring residual stress in welded plates to a good level of accuracy.

Effects of laser oscillation on metal mixing, microstructure, and mechanical property of Aluminum–Copper welds

Laser welding of dissimilar metals is important in many industrial applications. However, as dissimilar metals get mixed during the melting process, intermetallic compounds are often formed in the welds which can significantly undermine the electrical and mechanical properties of the welds. This poses a critical challenge to the widespread utilization of this welding technique. Compared with conventional line-scan laser welding, oscillating laser welding offers additional processing parameters to control the welding process. Although some work has been reported on oscillating laser welding of dissimilar metals, a mechanistic understanding of this process was still missing. The research objective of this work was to reveal the physical mechanisms and evaluate their relative significance to the fluid flow, metal mixing, and microstructure evolution in the molten pool in oscillating laser welding of dissimilar metals. A combination of experiments and simulations was leveraged to achieve the objective. Four fluid flows have been found to determine the metal mixing in the molten pool, and their dependences on the laser oscillating parameters were discussed. In addition, the thermo-solutal conditions of the molten pool solidification were quantified as functions of the laser oscillating parameters, and the effects of the thermo-solutal conditions on the final weld microstructures were analyzed.

Welding investigations on mechanical property and microstructure of TIG and A-TIG Weld of Hastelloy C-276

Hastelloy C-276 is a nickel-based alloy with high strength and corrosion resistance at cryogenic to high temperatures. The issue of Hastelloy C-276 shallow penetration by Tungsten Inert Gas (TIG) welding was addressed in the current investigation by applying A-TIG welding with variable oxide flux. In the current investigation, constant welding conditions were used to perform TIG and A-TIG welding using SiO2, TiO2, and a 50% mixture of SiO2 + TiO2 flux. The weld bead width and depth of penetration of the weld bead profile were measured, and the mechanical and metallurgical properties of the weld metal was investigated. SiO2 flux attained the highest D/W ratio and depth of penetration during A-TIG welding when compared to other fluxes used. A-TIG welding using SiO2 flux improved the depth of penetration and the D/W ratio by 118% and 263%, respectively, in comparison with conventional TIG welding. Additionally, the A-TIG welded sample with SiO2 flux had an ultimate tensile strength of 738.295 MPa and a percentage of elongation of 52.75%.

Effect of incident angle on weld microstructure and mechanical properties of laser beam welded nitronic −50 austenitic stainless steel joints

3 mm thick nitronic-50 stainless steel sheets were successfully butt-joined using a 2 kW fiber laser beam welding. Three weld joints were fabricated for different incident angles, namely, 70°, 80° and 90° for the other constant welding process parameters. The effect of incident angle on the weld bead geometry, microstructure evolution, and strength of the laser beam welded joints was studied in detail. The incident angle significantly affected the bead geometry and its orientation. Lowering the incident angle beyond a limit caused the beam shift near the weld root of the joint, where the bead was formed away from the joint line resulting in improper fusion and a defective weld occurred. The microstructure transformed from columnar to an equiaxed dendritic structure at the center of the weld nugget for lower incident angles. Skeletal and lathy ferrite was observed in the joints' weld zone. However, the fraction of lathy ferrite was higher at lower incident angles due to a faster cooling rate. A higher weld joint strength of 1010 MPa (97% of the base metal UTS) was achieved at an 80° incident angle, owing to the formation of more equiaxed dendritic grains and the absence of the secondary phases. All of the tensile test samples showed evidence of ductile failure, and overall, an acceptable level of elongation was achieved.

Review Paper on Optimization of Metal Inert Gas Welding on Stainless Steel AISI 410by Taguchi Method

Abstract: Austenitic stainless steel is widely used materials in the current industrial area including higher and lower temperature applications such as storage tanks, pressure cups, furnace equipment etc. Using ratio of those materials are increasing constantly due to having superior corrosion resistance and mechanical properties, GTAW process are widely used for stainless steel welding, especially for full penetration welds in thin gage materials. Selection of shielding gas and filler material is crucial parameter for the quality, the micro structure and properties of weldments. The weldment properties strongly depended on the shielding gas, since it dominates the mode of metal transfer. Shielding gas not only affects the properties of weld but also determines weldability, the appearance, the shape and penetration of bead as well. Pure argon is mainly used for GTAW as shielding gas at present. The most common shielding gases are argon riches mixtures, such as argon with a few percent helium, carbon dioxide, hydrogen, oxygen, nitrogen for GTAW process. In this project we will be made many attempts for made test pieces(SS410) to predict the process parameter of MIG for getting maximum weldment, best mechanical properties and min HAZ. The planned experiments are conducted in the MIG are welding machine; the test piece examination is carried out by following process

A Technique for the Quantitative Characterization of Weld Microstructure and Application to Mo Welds

A Technique for the Quantitative Characterization of Weld Microstructure and Application to Mo Welds

Investigation of the Effects of Welding Force, Vibration and Temperature on Mechanical Properties and Microstructure in FSW Welding

Defects such as porosity and cracking are serious problems in the joining of aluminium and its alloys by melt welding methods. In this case, it is important that the aluminum pairs are welded by friction stir welding (FSW), which is depend on joining at a temperature below the melting temperature by means of a stirrer pin. In this study, AA5182 pairs were joined in the different welding parameters by FSW. The effects of tool pin profily, feed rate and rotation speed on the temperature, force and vibration formed during welding were experimentally investigated. As the rotation speed rised, the temperature increased and the welding force decreased. But, with increasing feed rate, the temperature decreased and welding force and vibration have increased. Mechanical properties of the joints were adversely affected by low temperature, high welding force and high vibration.