Weld Center Research Articles

多次补焊对30CrMnSi钢焊接接头组织与性能的影响

以焊缝中心连续气孔为代表，研究了多次补焊对30CrMnSi钢TIG焊接头组织与性能的影响。结果表明，由于多次补焊对焊接接头的重复热作用，导致完全淬火区晶粒粗化、不完全淬火区回火软化，使焊接接头力学性能下降，一、二、三次补焊接头的抗拉强度相比焊接接头分别降低了8.5%、15%和19.8%。 In this paper, the influence of multiple repair welding on the microstructure and properties of 30CrMnSi steel welded joints was studied, and the continuous porosity in the weld center was taken as the representative. The results indicate that the grain coarsening in the complete quenching zone and tempering softening in the incomplete quenching zone occur, due to the repeated thermal effect of the multiple repair welding on the welded joints. As a result, the mechanical properties decrease, and the tensile strength of the welded joints for once, twice and three times repair welding decreases by 8.5%, 15% and 19.8% respectively, comparing with the non- repair welding.

Microstructure and Porosity of Laser-welded Dissimilar Material Joints of HR-2 and J75

Dissimilar laser welding of HR-2 and J75 has a wide range of applications in high-and low-temperature hydrogen storage. The porosity distributions of the welded joints were investigated at different line energies, penetration status, and welding positions (1G, 2G, and 3G). The effect of the welding position on the welding appearance was evident only at high line energies because of the essential effect of gravity of the larger and longer dwelling molten pool. The porosity of the welded joints between the solutionised and aged J75 and HR-2 at the 3G position and partial penetration was located at the weld centre line, while the porosity at the 2G position with full penetration was distributed at the weld edges, which is consistent with the distribution of floating slag. Full keyhole penetration resulted in minimum porosity, partial penetration resulted in moderate porosity, and periodic molten pool penetration resulted in maximum porosity.

Local microstructure evolution in Al 6061-T6 friction stir weld nugget enhanced by ultrasonic vibration

Ultrasonic vibration enhanced friction stir welding (UVeFSW) experiments were conducted to examine the effect and role of ultrasonic assistance on weld by comparing local microstructure evolution and microtexture of Al 6061-T6 weld nuggets in UVeFSW with those in conventional friction stir welding. Results showed that ultrasonic enhanced joints have higher deformation characteristics in the nugget zone due to ultrasonic softening effect prior to welding. Electron back scattered diffraction studies showed that application of ultrasonic vibration improves recrystallization process, causes better grain refinement and brings about variations in grain orientation along weld center axis. At the weld nugget extremities, ultrasonic energy contributes only towards changes in grain orientation. Ultrasonic assistance, however, did not induce any significant change to the local microtexture; rather the feature observed is a small angular shift in the shear plane which tilted the texture by an equivalent angle. The resulted microtextures are C {001}〈110〉 or B/B- {112}〈110〉 components of simple shear texture along the weld center axis and a mixture of shear fiber components at the weld nugget extremities. It is found that ultrasonic energy has maximum effect at the center of weld center axis and the effect is reduced towards the weld extremities.

An Experimental Study of Mechanical Properties and Effect of Welding Speed of Friction Stir Welding on Alluminium Alloy 6061

Friction Stir Welding is a versatile metal joining process, which has been adopted to join composite materials. Many research activities have been conducted on this metal joining processes which lead to the process being used in diverse field of applications. AA6061 plates of 6mm thick each were joined through butt welding configuration by Friction Stir Welding process using a CNC milling machine and a non consumable tool with square pin profile. Six joints were made using the combination of three tool rotation speed 350 rpm, 550 rpm and 900 rpm and three weld traverse speed 55 mm/min, 100 mm/min, 110 mm/min. The prepared joints were tested in order to analyze its microhardness, tensile strength, temperature distribution, force and microstructure along the joint. It was identified that for a given tool rotation speed, the microhardness increased proportionally with respect to the weld speed and depth along the joint. However it was noticed that for different tool rotation the maximum of the microhardness was obtained for 350 rpm. Measurement of tensile strength revealed that the strength was maximum when the weld speed and tool rotation speed was maximum. The tensile strength measurement indicated that the strength was directly proportional to the weld speed and tool rotation speed. Temperature measured during welding revealed that the temperature was maximum along the weld center, while same decreased away from the weld center. This was because of the dissipative effect of AA6061. Microstructure of the prepared joint revealed that the due to the influence of the tool, the grain structure reformed. There were finer grains at place traversed by the tool and coarse grains at place away from the tool. The joints thus fabricated can be used for applications which require reliable and defect free joints such as automobile frames and aeronautical structures.

Features of Microstructur al Changes of an Aluminum Alloy D16T Samples Welded with Linear Friction Welding

The microstructure and microhardness of joint welds formed with linear friction welding (LFW) of an Al-Cu-Mg alloy was investigated. Welds of two samples of rectangular shape do not show any macroscopic defects and are characterized by high strength. The substantial transformation of the microstructure occurs in the weld. The lattice parameter decreases in the weld centre compared to the base material.

Effect of Reeling on Sour Service Fatigue Crack Growth Behavior of Welded API5LX65 Line Pipe

The effect of reeling on the fatigue crack growth rate (FCGR) behavior of welded pipe was investigated both in-air as well as in sour environment. The FCGR behavior of the reeled pipe in various notch locations, such as parent pipe (PP), weld center line (WCL), and heat affected zone (HAZ), did not exhibit any effect of reeling (i.e., the properties in the strained and aged conditions were similar to the as-fabricated welds). Frequency scan FCGR tests in sour environment (pH = 5/0.0031 MPa H2S) exhibited maximum FCGR in the range of 10× to 35× higher than the in-air values at frequencies in the range of 3–1 mHz and 3× to 5× at frequencies in the range of 0.3 Hz (risers). In sour service, WCL exhibited better fatigue performance than the PP and HAZ in all conditions. Fatigue performance of PP and WCL was independent of reeling. The poorest fatigue performance was observed in unstrained HAZ. Fatigue performance of HAZ extrados (side last strained in compression) and intrados (side last strained in tension) was similar and better than unstrained HAZ. It was also found that the FCGR in sour environments was controlled by the internal hydrogen due to bulk charging from the sour environment. The overall conclusion is that reeling has no detrimental effect on sour service fatigue crack growth behavior, i.e., sour service fatigue performance of reeled pipe is the same as unreeled pipe.

Optimization of Pulsed Current TIG Welding Parameters on Al-SiC Metal Matrix Composite - An Empirical Approach

Joining of aluminium alloys and aluminium composites are done using TIG welding, due to its economic and good quality welds among arc welding processes. During TIG welding of aluminium alloys&aluminium composites coarse grain structure formation and intermetallic formation in weld zone will result in poor mechanical properties such as reduced strength of the weld. These problems can be rectified by using the optimized pulsed current parameter of pulsed current TIG welding. Pulsed current TIG welding parameters have greater influence on weld zone and heat affected zone's microstructure&mechanical properties. To optimize the pulsed current TIG welding parameters such as peak current, base current, pulse on time and pulse frequency experiment is designed using Taguchi L 9 orthogonal array technique. From the experiment, effect of pulsed current parameters peak current, base current, pulse on time and pulse frequency on weld centre micro hardness was evaluated. Regression equation was developed using Design Expert ® statistical software to predict the weld centre micro hardness. Correlation co-efficient (r 2 ) showed 0.99 and error % showed less than 1% which means the regression equation developed was more consistent. Empirical model was developed to optimize the pulsed current parameters of PCTIG welding was also performed using Design Expert ® statistical software. Optimized values for pulse on time, pulse frequency, peak current and base current were 54.79%, 5.12Hz, 160A and 60A respectively. Optimized predicted value of weld centre micro hardness has been observed as 77 HV. Trial runs were performed for optimized PCTIG welding condition to check the consistency of the model, which resulted only 5% of deviation between experimental values and predicted values. This showed optimized pulsed current parameters of PCTIG welding resulted in higher micro hardness which implies that strength of the weld is increased.

Perforation of welded aluminum components: Microstructure-based modeling and experimental validation

Perforation of welded aluminum structures by small-arms bullets is studied both experimentally and numerically in this paper. From the chemical composition, artificial aging history, and welding procedure, the spatial distribution of the flow stress at ambient temperature of MIG-welded AA6082-T6 aluminum extrusions was determined by using a thermal finite element model and a nano-scale material model. The resulting flow-stress curves which are functions of the distance from the weld center line were used in a mechanical 3D finite element model to investigate the effect of the heat affected zone (HAZ) on the ballistic properties of welded aluminum extrusions. For experimental validation, 10 mm, 20 mm and 30 mm thick extruded profiles were processed and welded to correspond to the numerical method. Hardness measurements and ballistic impact experiments were performed in the weld metal, HAZ, and base material. Uniaxial tension tests were conducted for the base material of the 10 mm and 30 mm profiles. These tests provided sufficient data for experimental validation of the numerical method. Temperature distribution, hardness values, equivalent stress-strain curves, and ballistic limit curves are reported from both the experiments and the numerical simulations. In general, the experimental results correspond well with the numerical predictions and the predicted ballistic limit velocities are within 10% of the experimental ones, suggesting that this method is a possible alternative to performing expensive and time consuming experimental testing in the early stages of the design of protective aluminum structures. The HAZ was found to impair the ballistic performance locally, but the difference between the ballistic limit for the base material and HAZ was never more than 10% in this study.

Correlation of microstructure and mechanical properties in friction stir welded 2198-T8 Al–Li alloy

In this study, the 1.8mm thick cold-rolled sheets of 2198-T8 Al–Li alloy were manufactured by friction stir welding (FSW) at a rotation rate of 800rpm and a travel speed of 300mm/min. The microstructure and mechanical properties of different regions of the produced joint were evaluated by means of optical microscopy (OM), transmission electron microscopy (TEM), hardness testing and tensile testing. Results show that the original “pancake” grains became coarser in the heat affected zone (HAZ), transformed into equiaxed grains in the stir shoulder zone (SsZ) and stir pin zone (SpZ), and formed mixed grains with both “pancake” and equiaxed shapes in the thermo-mechanical affected zone (TMAZ). The hardness distribution in the cross-section of the FSW joint exhibited a “basin” shape. When approaching the weld centre, the hardness gradually decreased compared to the base metal (BM). The BM exhibited the highest strength due to the presence of fine T1 phase. In the HAZ, the strength decreased as T1 phase was partially dissolved. In the SsZ and SpZ, in spite of strength contribution from grain refinement, the strength further decreased as T1 phase was fully dissolved. The minimum strength in the TMAZ was related to the reduced amount of T1 phase and the presence of transition layer with sharp gradient of grain size.

Friction-stir welding of ultrafine grained austenitic 304L stainless steel produced by martensitic thermomechanical processing

Abstract An ultrafine grained 304L austenitic stainless steel was produced by martensitic thermomechanical processing and joined by applying Friction Stir Welding (FSW). The thermomechanical processing comprised a cold roll procedure up to 80% reduction followed by annealing. After FSW, different grain structures in different regions of the weld nugget were observed due to the asymmetry in the heat generation during the welding process. Grain growth was found to be the most predominant phenomena in the region just ahead of the rotating tool during the thermal cycle of FSW. A banded structure was observed in the advancing side of the weld nugget. TEM observations revealed that nanometric sigma phase precipitates were present both in the grain boundaries and inside the grains of this region. Shear textures were clearly identified in the weld center. The lack of rotated cube texture shows that the discontinuous dynamic recrystallization (DDRX) is not active in the final microstructure. Increasing the welding speed can reduce the final grain size of the weld nugget leading to higher hardness. Hardness is found to increase in the weld and this is not just a grain refinement effect, but also due to the presence of sub-boundaries and a high density of dislocations.

Study on the Microstructure and Property for T-Joints of Al-Li Alloy Welded by Double Sided Synchronization Fiber Laser

In the experiment, the T-joints of 2060-T8/2099-T83 Aluminum-Lithium by double sided synchronization Fiber laser welding with thickness of 2 mm was studied aimed to know the microstructure, the distributions of micro-hardness, and the tensile strength of the T-joints. The results show that the microstructure is columnar fine grain zone, dendrite zone, and equiaxed crystal zone in turn from the weld fusion line to weld centre; the micro-hardness of the weld is lower than the micro-hardness of base metal, and softening phenomenon appears in the weld; The average circumferential tensile strength of T-joints is 423 MPa at room temperature, which reaches the strength of the base metal 82%, the average longitudinal tensile strength of T-joints is 449 MPa, which reaches the strength of the base metal 87%; The fracture of circumferential tensile samples initiates at the weld toe, and breaks in the weld centre or heat affected zone. The fracture of longitudinal tensile samples initiates at varying cross-section, there are dimples in the fracture surfaces of both circumferential tensile samples and longitudinal tensile samples, and the fracture is ductile.

Numerical Simulation to Study the Effect of Arc Travelling Speed and Welding Sequences on Residual Stresses in Welded Sections of New Ferritic P92 Pipes

AbstractNew ferritic P92 steel is widely used in modern power plants due to its good combination of mechanical and physical properties. However, cracks are often formed in the welded sections during the fabrication or service. In order to ensure the structure integrity, the effects of residual stresses need to be considered. The objective of this paper is to investigate the influence of arc travelling speed and welding sequences on the residual stresses distribution in the welded sections of P92 pipes by finite element method (FEM). Results show that arc travelling speed and welding sequences have great effects on residual stresses distribution. With the arc travelling speed increasing, the residual stresses increase. Meanwhile, welding sequences of case B present smaller residual stresses and more symmetrical distribution of residual stresses at the weld centre line. Therefore, using slower arc travelling speed and case B welding sequences can be useful to decrease the residual stresses, which provides a reference for optimizing the welding technology and improving the fabrication process of new ferritic P92 welded pipes with small diameter and thick wall.

Effects of filler wire on residual stress in electron beam welded QCr0.8 copper alloy to 304 stainless steel joints

Abstract The electron beam welding (EBW) of 304 stainless steel to QCr0.8 copper alloy with or without copper filler wire was studied in detail. The temperature fields and magnitude and distribution of stress fields in the joints during the welding process were numerically simulated using finite element method. The temperature cycles and residual stresses were also experimentally measured by thermometric and hole-drilling methods, respectively. The accuracy of the modeling procedure was verified by the good agreement between the calculated results and experimental data. The temperature distribution in the joint was found to be asymmetric along the center of weld. In particular, the temperature in the copper alloy plate is much higher than that in the 304 SS plate owing to the great difference in thermal conductivity between the two materials. The peak three-dimensional residual stresses all appeared at the interface between the copper and steel in the two different joints. Furthermore, the weld was subjected to tensile stress. The longitudinal residual stress, generally the most harmful to the integrity of the structure among the stress components in EBW with filler wire (EBFW), was 53 MPa lower than that of autogenous EBW (AEBW), and the through-thickness residual stress was 12 MPa lower. The transverse residual stress of EBFW was 44 MPa higher than that of AEBW. However, analysis of the von Mises stress showed that the EBFW process effectively reduced the extent of the high residual stress region in the weld location and the magnitude of the residual stresses in the copper side compared with those of the AEBW joint.

Studies the Influence of Pulsed Current and Activated Flux with TIG Welding on the Microstructure and Mechanical Properties of Stircasted Al-SiC Composite

In the present study, an attempt has been made to study the effect of weld parameters on as-cast Al-SiC metal matrix composite plates using a newly developed active flux composition. Stir cast Al - 8% SiC plates were welded using different variants of TIG welding such as Constant Current TIG (CCTIG) welding, Pulsed Current TIG (PCTIG) welding, activated TIG (ATIG) welding and Pulsed Current Activated TIG (PCATIG) welding. Microstructure, macro structure, thermal profile, micro hardness and tensile properties were evaluated for different variants of TIG welding conditions and compared with each other. The combined effect of the active flux composition and pulsed current in PCATIG welding was compared with other variants such as TIG welding technique such as CCTIG welding, ATIG welding and PCTIG welding. Thermal profile revealed the increase in the peak temperature and the cooling rates for the PC-A-TIG weldments. Due to increased cooling rate, fine grain microstructure was observed in weld zone and heat affected zone. Fine grain microstructure of the PCATIG weldment is responsible for improved mechanical properties such as micro hardness, ultimate tensile strength, yield strength and elongation (%) compared to other welding variants. Maximum micro hardness value was found in weld zone in all the variants of TIG welding. PCATIG welding showed maximum weld zone hardness as 75HV, heat affected zone hardness values of the all TIG welding variants have more or less same value after 4mm away from weld centre. Due to active flux coating on PCATIG welding lead to increase in weld depth as 4.5mm. This increase in the weld depth directly increase the depth-towidth ratio (D/W = 0.82). Tensile strength of PCATIG welded sample showed (Ultimate Tensile Strength = 153MPa; Yield Strength = 137 MPa; elongation (%) = 16%). It confirms that the Al-SiC composite welded using PCATIG welding were improved mechanical behaviour than other TIG welding variants such as CCTIG welding, ATIG welding and PCTIG welding.

The Influence of Multiple Welding Repairs of Pipelines in Residual Stress Assessment Related to Stress Corrosion Cracking

The effect of residual stress of multiple welding repairs in seamless API 5L X52 on the stress corrosion cracking (SCC) susceptibility was evaluated. Four repairs of the girth weld were evaluated through X-ray diffraction (XRD) on the internal face of the pipe to measure residual stresses in longitudinal and circumferential direction. Residual stresses in the circumferential and longitudinal direction reach values of about 77% and 58% of the UTS (460 MPa) respectively, approaching to the YS of the steel (360 MPa). It was observed that its magnitude increases as move away from weld center line. SCC susceptibility of X52 steel welded joints with the residual Original Research Article Contreras et al.; BJAST, 6(6): 621-634, 2015; Article no.BJAST.2015.117 622 stresses generated was evaluated through slow strain rate tests (SSRT) in a soil solution at low and high pH. Relation between mechanical properties and residual stresses on the SCC susceptibility was analyzed. SCC index obtained from the mechanical properties of SSRT indicate good SCC resistance of X52 steel exposed to soil solution at low and high pH. From these results, it is suggested that the region with high residual stresses before to generate cracks in the steel surface due to the combination of soil solution and the strain applied, should favor pitting formation and not cracking. Initiation of micro-cracks from these pits will depend on the geometrical form of the pit and the stresses state can be established at given pitting. It is suggested that initiation of micro-cracks from these pits may depend on the dissolution rate and morphology of the pitting and stresses on the bottom of the pitting. This favorable condition could appear increasing the soil exposition time of the steel and reducing the strain rate applied on the SSRT.

Evaluation of Metal-Active Gas Double-Sided Double-Power Arc Welded Joints of High-Strength Low-Alloy Steel

High-strength low-alloy steel 50 mm thick is well joined by metal-active gas double-sided double-power arc welding, which does not require preheating, postheating, and back chipping. Mechanical properties of the weld seam and base metal were investigated. Results of the tensile test indicate that the strength of the weld seam is about 862.73 MPa and its average elongation is 20.74%. The hardness of the base metal and weld zone is 299 and 361 HV, respectively. The maximum hardness (395 HV) is observed in the heat-affected zone. The average toughness of the face and root sides of the weld center is 75 and 71 J, respectively.

3D Ultrasonic Non-destructive Evaluation of Spot Welds Using an Enhanced Total Focusing Method

Spot welds are used to join sheets of metals in the automotive industry. When spot weld quality is evaluated using conventional ultrasonic manual pulse-echo method, the reliability of the inspection is affected by selection of the probe diameter and the positioning of the probe in the weld center. The application of a 2D matrix array is a potential solution to the aforementioned problems. The objective of this work was to develop a signal processing algorithm to reconstruct the 3D spot weld volume showing the size of the nugget and the defects in it. In order to achieve this, the conventional total focusing method was enhanced by taking into account the directivities of the single elements of the array and the divergence of the ultrasonic beam due to the propagation distance. Enhancements enabled a reduction in the background noise and uniform sensitivity at different depths to be obtained. The proposed algorithm was verified using a finite element model of ultrasonic wave propagation simulating three common spot weld conditions: a good weld, an undersized weld, and a weld containing a pore. The investigations have demonstrated that proposed method enables the determination of the size of the nugget and detection of discontinuities.

Effect of welding polarity on bead geometry, microstructure, microhardness, and residual stresses of 1020 steel

This work examines the effect of welding polarity as a measure of heat input on thebead geometry, microstructure, microhardness and residual stresses of AISI 1020carbon steel that was processed by shielded metal arc welding (SMAW). Single weldbeads were deposited on the steel plate using a constant current but with differentwelding polarities of AC, DC- and DC+. Optical microscopy indicates that weldingby DC- provides the widest weld bead and largest heat affected zone (HAZ) due tothe large heat input subjected to the plate. Nevertheless, similar microstructures in theHAZ and fusion zone (FZ) of the weld were found for all welding polarities. Vickersmicrohardness tests also show that the large heat input by DC- polarity provided theminimum microhardness for all microstructures of the weld. In addition, across-weldmeasurements of the residual stresses by neutron diffraction indicate that the threewelding polarities produced similar profile. High tensile longitudinal residual stresseswere found to extend horizontally from the weld center to the HAZ, which becomecompressive further away from the bead. The highest tensile residual stress in theHAZ occurred for DC- polarity, while it has the lowest value for AC polarity. Throughthicknessmeasurements also indicate that the residual stresses within the HAZ areapproximately constant for AC polarity. This suggests that equal distribution of heatinput by AC polarity to the electrode and plate is not only important for reducingresidual stresses but also on minimizing the differences in residual stresses throughthe weld thickness.

Influence of Activating Flux and Surface Oxidation on Micro Structure and Mechanical Properties of TIG Welded Stainless Steel Weldments

The present study deals with the effect of activating flux and surface oxidation on micro structure, micro hardness and tensile strength of Tungsten Inert Gas welded 304 austenitic stainless steel plates. The thickness of the plate of 6.5 mm is considered for the investigation. The Tungsten Inert Gas welding is performed with 2.4mm diameter conical electrode tip profile with the surface condition of the plate as natural, oxidized and coated with an activating flux. Results have shown that the microstructure and mechanical properties are greatly influenced by activating flux and surface condition of plate. A-TIG welded plates give highest tensile strength when compared to TIG welded plates. Vickers micro hardness value is maximum nearer to the weld center on the cross section of the A-TIG butt weld joint.

Stress state and strength of an inclined soft interlayer in mechanically heterogeneous welded joints with a lack of fusion defect in the weld centre

The static strength of mechanically heterogeneous welded joints with a lack of fusion defect in the centre of the welded joint is calculated. The stress state of mechanically heterogeneous inclined butt-welded joints with a lack of fusion defect is investigated. A method is proposed for evaluating the static strength and ductility of the welded joints with a mechanical heterogeneity which can be used to determine the load-carrying capacity by adding the mechanical heterogeneity coefficient, the size of the lack of fusion defects and the angle of inclination to the calculation equations.