Similar Welds Research Articles

Comparing bond formation mechanism between similar and dissimilar aluminium alloy friction welds

Friction welding of high strength aluminium alloys was considered in the current study. The mechanism of bond formation in dissimilar alloy welding was compared to similar alloy welding. The differences in flow properties between two different alloys of aluminium lead to uneven deformation behaviour while welding. Since flow behaviour directly affects bond formation and strength, it is important to understand its behaviour. Rods of aluminium alloys AA 2024 and AA 6061 were welded to themselves and to each other denoting similar and dissimilar weld systems. Burn-off length, which is one of the important parameters in friction welding was varied in steps to see how it affects the bond formation. The flash geometry of the welds was observed to interpret the flow differences. Reasons for variations in bond formation were discussed with the help of fracture surfaces.

Dissimilar Electron Beam Welding of Nickel Base Alloy 625 and 9% Cr Steel

To improve the thermal efficiency of fossil running power plants increasing the live steam temperature is essential. In power plant construction, 9-12% chromium martensitic steels are widely used but if steam temperatures rise above 625°C there is no way around nickel base alloys.The scope of this study was to ascertain the weldability of cast nickel base alloy 625 with cast martensitic 9% chromium steel COST CB2, using electron beam welding (EBW). Similar (A625/A625) and dissimilar joint welding experiments on 50mm thick plates were executed. Microstructure of welded joints was investigated and mechanical-technological tests were carried out.Results show that work pieces were completely welded and the microstructure of the seam shows no problems except some δ-ferrite grains near the fusion line on the CB2 side. The joints exhibit good mechanical properties in spite of the presence of a thin layer with very high hardness in the heat affected zone (HAZ) on the CB2 steel side. [1].

Studies on Welding of Maraging Steels

This work involves with investigations on Maraging steel weldments done by GTA welding technique. Similar welding of maraging steel plates of 5mm thick using ErNiCrMo-3 filler wire was done in order to evaluate the weldability and performance characteristics. Micro structural and X- Ray diffraction analysis were done to analyze the structure and phases developed post – weld. Block martensite was formed in the heat affected zones of the parent metal. Tension testing using different strain rates and hardness profile measurements were done to investigate the mechanical properties and the study concludes that the strain rate has considerable influence on the nature of ductility whereas it has very less influence on the Ultimate Strength of Maraging steel.

A Finite Element Analysis of Temperature Profiles and Cooling Rates of ERW Pipes during TIG Welding

AbstractThe present investigation deals with the determination of temperature profile and subsequent cooling rates of certain points on the external surface of an ERW pipe with the help of ANSYS Finite Element Modeling and Analysis method, under simulated TIG welding conditions. A TIG welding condition for an ERW pipe is first simulated through ANSYS Finite Element Modeling. The physical and material properties along with the dimensions and size of the ERW pipe are all included in the modeling part. The TIG welding arc is simulated as a point heat source of a given power traversing the periphery of the pipe surface during welding. In the ANSYS program, after modeling the TIG welding problem, the same is run in the post – processing analysis part to get the temperature profile along the external surface of the pipe at various time intervals from the start of the welding. The rate of cooling of a few particular nodes on the modeled pipe surface, from the start of welding to the completion of one welding pass is also studied and results are indicated in graphical form. Later, these cooling rates on the modeled pipe surface are compared with those of an exactly similar ERW pipe, physically welded by TIG welding method in the workshop under similar welding conditions and welding parameters.

Feasibility study of resistance spot welding of dissimilar Al/Mg combinations with Ni based interlayers

Microstructure and mechanical properties of the dissimilar aluminium–magnesium resistance spot welds made with gold coated and bare nickel interlayers are investigated. Welds were made with different welding currents in a range from 16 to 24 kA with a fixed welding time of five cycles. No joints were achieved with a bare nickel interlayer; after welding, specimens were separated without applying any force. Addition of gold coating on nickel surface greatly contributed to the metallurgical bonding at the interfaces and welds easily met requirements of AWS D17·2 standard. Average lap shear strength reached 90% of similar AZ-31B spot weld strength. Fusion nugget size, interfacial microstructure and fracture surface morphology of the welds were analysed.

Interaction between Sodium Molybdate and FSWed Weld of 5083 Effected by Temperature

Similar welds composed of 5083 were produced by friction stir welding. In the solution of 0.2 M NaHSO3 and 0.6 M NaCl, with the addition of a given concentration sodium molybdate as the inhibitor, the electrochemical corrosion behaviors of the friction stir welds (FSW) and 5083 were comparatively investigated by potentiodynamic polarization curve tests and electrochemical impedance spectra (EIS) for different test temperatures (herein, 25°C,30°C,35°C,40°C). The results indicated that at 30°C, the anti-corrosion property of 5083 FSW weld and parent material was superior to those of the other temperatures.

Mechanical and microstructural properties of robotic Cold Metal Transfer (CMT) welded 5083-H111 and 6082-T651 aluminum alloys

5083-H111 and 6082-T651 aluminum alloys used particularly in shipbuilding industry especially for the sake of their high corrosion resistance and moderate strength, were welded using Pulsed Robotic Cold Metal Transfer (CMT)-Metal Inert Gas (MIG) technology. Joints were fabricated as both similar and dissimilar alloy welds using plates with a thickness of 6mm. Non-destructive tests such as visual and radiological examination were conducted before further destructive tests. Tensile, bend and fatigue tests were applied to specimens extracted from welded joints. Fracture surfaces of fatigue samples were examined by light optical microscopy (LOM) and scanning electron microscopy (SEM). Also macro and microstructures of weld zones were investigated and micro hardness profiles were obtained. In accordance with results, CMT-MIG provides good joint efficiency with high welding speed, and good tensile and fatigue performance.

Finite element simulation of welding residual stresses in martensitic steel pipes

Finite element (FE) simulations of the welding of two high grade steel pipes are described. The first is a P91 steel pipe welded with a similar P91 weld consumable, and the second is a P92 steel pipe welded with dissimilar nickel–chromium based weld consumables. Both welds are multipass circumferential butt welds, having 73 weld beads in the P91 pipe and 36 beads in the P92 pipe. Since the pipes and welds are symmetric around their axes, the FE simulations are axisymmetric, allowing high FE mesh refinement and residual stress prediction accuracy. The FE simulations of the welding of the P91 and P92 pipes comprise thermal and sequentially coupled structural analyses. The thermal analyses model the heat evolution produced by the welding arc, determining the temperature history throughout the FE models. Structural analyses use the computed temperature history as input data to predict the residual stress fields throughout the models. Post-weld heat treatment (PWHT) of both pipes has also been numerically simulated by assuming that the FE models obey the Norton creep law during the hold time period at 760°C. The residual stresses presented here have all been validated by corresponding experimental measurements. Before PWHT, it has been found that, at certain locations in the weld region and heat affected zone (HAZ) in the pipes, tensile hoop and axial residual stresses approach the tensile strength of the material, presenting a high risk of failure. It has also been found that PWHT substantially reduces the magnitude of residual stresses by varying degrees depending on the material.

Numerical and Experiment Study of Residual Stress and Strain in Multi-Pass GMA Welding

There must selection an optimal of welding parameter and condition that reduces the risk of mechanical failures on weld structures.The residual stress and welding deformation have the large impact on the failure of welded structures.To achieve the required precision for welded structures, it is required to predict the welding distortions at the early stages.Therefore, this study uses 2DFinite Element Method (FEM) to predict residual stress and strain on thick SS400 steel metal plate. A birth and death technique is employed to control the each weld pass welding. Gas Metal Arc (GMA) welding experiment is also performed with similar welding condition to validate the FE results.The simulated and experiment results provide good evidence that heat input is main dependent on the welding parameter and residual stress and distortions are mainly affected by amount on heat input during each weld-pass.

Irradiation Strategy for Laser Transmission Welding of Thermoplastics Using High Brilliance Laser Source

This article describes the correlation between crystallinity degree and spatial seam homogeneity for laser transmission welding of polymers applying TWIST method, which is based on a superposition of slow regular feed and fast periodic circular or elliptical beam motion. Laser welding experiments and measurements of optical polymer properties (transmittance, reflectance and collimated transmittance) are reported for thermoplastic polypropylene PP and Polyamide PA66 as well as for thermoplastic elastomer PEBAX. The shape of the seam is visualized by measuring the heat affected zone (HAZ). Compared to the circular the elliptical motion leads to a homogeneous HAZ, which is advantageous for the welding process in many cases. Besides TWIST parameters, scattering of the laser radiation influences the welding result considerably. This is shown for high-crystallinity PA66, which needs more laser power to achieve similar weld seams than PP or PEBAX. The correspondence between homogeneous HAZ and good welding results is investigated by measuring the strength of welded T-shape samples with respect to the laser power. The elliptic TWIST motion leads to a broader processing window, if the ratio of the beam diameter and the major TWIST radius is smaller than a certain value (<1/2). For PEBAX, a local maximum of strength-vs.-power curve is obtained for all TWIST® radii. For welding PP, the maximum is observed only for big radii.

Investigations of dissimilar welds of the high temperature steels P91 and PM2000

Compared to present reactors, modern nuclear power plant as well as fusion power plant concepts are based on materials which can be operated at higher temperatures and up to higher fuel burn-up. Oxide dispersion strengthened (ODS) steels – produced by mechanical alloying – with chromium contents of 9 and 14wt.% (or even more) are the typical candidate materials. Preliminary studies have shown that these ODS steels have superior thermal creep strength and they are more resistant to irradiation damage than standard 9Cr ferritic/martensitic steels. Irradiation swelling, helium embrittlement, and irradiation hardening were observed on a much lower level [1].Joining of high temperature steels is an important aspect for modern power plant concepts. Therefore investigations on joining the ferritic ODS steel PM2000 and the ferritic/martensitic nuclear standard steel P91 were made [2]. After welding by electron beam (EB) several heat treatments were performed and investigated. First, the samples were annealing at 1050°C for 1h and then tempered at 770°C for 2h. To characterize the joints, creep and Charpy tests were performed. The microstructure was analyzed using optical microscopes, SEM and TEM.This paper presents and discusses the results of the mechanical tests focusing on the microstructure of the dissimilar welds. A comparison of Charpy and creep tests of dissimilar with similar welds shows that the later are much easier to produce. Therefore, further investigations of dissimilar welds are necessary for a full characterization, understanding, and possible optimization.

Interaction between Sodium Molybdate and FSWed Wled of 5083 Effected by Time

Similar welds composed of 5083 were produced by friction stir welding. In the solution of 0.2 M NaHSO3 and 0.6 M NaCl, with the addition of a given concentration sodium molybdate as the inhibitor, the electrochemical corrosion behaviors of the friction stir welds (FSW) and 5083 were comparatively investigated by potentiodynamic polarization curve tests and electrochemical impedance spectra (EIS) at the ambient temperature for different test periods. The results indicated that : with the extension of period, the inhibition efficiencies (IE) for both the weld and 5083 base materials enhanced, at the same period, the inhibition efficiency (IE) for the weld was beyond that for 5083 base materials, sodium molybdate may be thought of as an effective inhibitor for 5083 aluminum alloy, the interaction between inhibitor and weld is stronger than that between inhibitor and base materials.

STUDI LITERATUR PENGARUH PARAMETER PENGELASAN TERHADAP SIFAT FISIK DAN MEKANIK PADA LAS TITIK (RESISTANCE SPOT WELDING)

Resistance spot welding (RSW) is the most widely used for joining thin sheet metals in automotive industry. Various applications of dissimilar materials and thicknesses were commonly found in many spot welding processes especially in the manufacture of car body. The resistance spot welding of dissimilar materials are generally more challenge than similar materials due to differences in the physical, chemical, and mechanical properties of the base metals. Differences of materials have an impact on heat input generated at the spot welding. Diameter of the weld nugget size is influenced by several parameters such as electric current, welding time, different types of material, and the thickness of the plate. Nugget diameter will influence on physical and mechanical properties weld such as microstructure, shear strength and hardness. For practical use, various industrial standards have recommended a minimum weld size for a given sheet thickness, mostly in the form of tables. For example the American Welding Society (AWS), Society of Automotive Engineering (SAE) and the American National Standards Institute (ANSI). They were only suitable to be apllied on the similar metal and thickness joint because in this joint, symetrical nugget will be formed. Meanwhile a type of dissimilar metal that joined by spot welding method will result in the asymetrical nugget. This paper aims to review the results of researchs on the similar and dissimilar resistance spot welded joint to evaluate the use of similar metals weld parameters and standards on the dissimilar metals weld. It was determined that parameters welding such as electric current, welding time, and the standard for similar metals weld can not be applied on the dissimilar metals weld. The asymetrical nugget shape decreased shear strength on the weld nugget. The most important factor that was considered on the dissimilar metals weld to make high quality weld joint was nugget diameter. If the nugget diameter weld increased the strength of welding will increase.

Cross-Weld Creep Comparison of Power Plant Steels CrMoV, P91 and P92

Results obtained from high temperature creep tests of ferritic steel CrMoV, P91 and P92 cross-weld specimens are compared. Data are presented normalized with the results of the corresponding parent metals in order to compare the materials tested at different temperatures and stresses, and to identify characteristic cross-weld material trends. All cross-weld failures occurred in the heat-affected zone (HAZ) adjacent to the parent metal, known as type IV, at earlier test durations than for the parent material specimens. The relative performance of the cross-welds was found to decrease with decreasing stress. The CrMoV cross-weld specimens showed by far the lowest weld strength reduction factors and greatest notch strengthening, determined by testing uniaxially loaded bars with semicircular circumferential notches located in the heat-affected zone. The P91 and P92 cross-weld specimens were found to have similar (high) weld strength reduction factors and showed little or no notch strengthening. The failure time of a P92 cross-weld specimen relative to the P92 parent material could be estimated using data from P91 cross-weld and relative parent material tests.

Estimation of current path area during small scale resistance spot welding of bulk metallic glass to stainless steel

The current path area is a significant factor in estimating the temperature distribution via numerical modelling for resistance spot welding. This paper presents a method for the estimation of the current path area at the faying surface during small scale resistance spot welding between bulk metallic glass and stainless steel. Observation of cross-sections and fracture surfaces reveals the welding process at the faying surface for both dissimilar and similar welding. The equipotential surface that depends on the difference between the contact area of the electrode-to-sheet and sheet-to-sheet interfaces is estimated by numerical modelling. The current path area at the faying surface is estimated by measuring the electric potential between the sheets, taking into account the current distribution.

Torque, temperature and hardening precipitation evolution in dissimilar friction stir welds between 6061-T6 and 2014-T6 aluminum alloys

Dissimilar friction stir butt welds between the 2014-T6 and the 6061-T6 Al alloys were performed with various sets of welding parameters including a lateral shift of the tool from the initial separation between the plates to be welded and by placing the alloys, either on the advancing, or on the retreating side of the weld. Torque and temperature measurements during welding as well as macrographies and hardness profiles measurements were performed after welding. It was found that the welding torque, the temperature, the metal flow and the welds’ hardness profile depend on the proportion of each alloy included in the stirred zone. Those results are attributed to the difference between the softening temperatures of both alloys. The 6061 alloy's HAZ is the weak link in all dissimilar welds. The evolution of the hardening precipitation, the hardness and the local yield strength in the 6061 alloy are therefore modeled. The model reasonably well predicts the experimentally measured hardness of both similar and dissimilar welds. It also explains the influence of the alloys placement or tool lateral shift on the welds hardness by their influence on the precipitate radius and volume fraction.

Influence of Weld Bead Geometry on Thermal Deformation in Laser Micro-Welding

In this study, the thermal deformation of thin stainless steel sheet was investigated in the bead-on-plate welding by using a single- mode fiber laser with a Galvano scanning system. The numerical simulation was developed to calculate the temperature and stress fields, and its deformation characteristics were discussed. It was suggested that the specimen firstly deformed downward in the same direction of laser irradiation, and then deformed in the reversed direction after laser scanning. The final deformation angle in the negative direction, which is concave shape from the view direction of laser irradiation, was generated under the welding mode of conduction and quasi-penetration for 50 m thickness sheet. On the other hand, the positive angle of final deformation angle was obtained under full-penetration welding mode, and the extreme small distortion could be achieved by the proper weld bead geometry in micro-welding of thin sheet. It was also confirmed that the similar weld bead geometry was resulted in both quasi- penetration and full-penetration welding mode for 20 m thickness sheet, but the final deformation angle tendency was different in 50 m and 20 m specimen thickness. It was clarified that the welding deformation was influenced not only by weld bead geometry but also by specimen thickness.

Inhibition Effect of Sodium Molybdate on Friction Stir Weld of 5083 in Aqueous Solution

Similar welds composed of 5083 were produced by friction stir welding. In the solution of 0.2 M NaHSO3 and 0.6 M NaCl, the electrochemical corrosion behaviors of the friction stir welds (FSW) and 5083 were comparatively investigated by static weight loss experiments and potentiodynamic polarization curve tests at the ambient temperature. The results indicated that the average corrosion rate of the weld was less than that of 5083. Then, sodium molybdate was added to the corrosive solution and its effect on the corrosion behaviors of the weld and parent metal was comparatively assessed. The inhibition efficiency (IE) for the weld was beyond that for 5083 base materials, sodium molybdate may be thought of as an effective inhibitor.

Lap shear strength and fatigue life of friction stir spot welded AZ31 magnesium and 5754 aluminum alloys

Lightweighting is today considered as one of the key strategies in reducing fuel consumption and anthropogenic greenhouse gas emissions. The structural applications of lightweight magnesium and aluminum alloys in the transportation industry inevitably involve welding and joining while guaranteeing the safety and reliability of motor vehicles. This study was aimed at evaluating lap shear strength and fatigue properties of friction stir spot welded (FSSWed) AZ31B-H24 Mg and 5754-O Al alloys in three combinations, i.e., similar Mg-to-Mg, Al-to-Al, and dissimilar Al-to-Mg joints. The Mg/Mg similar weld had a nugget-shaped stir zone (SZ) around the keyhole where fine recrytallized equiaxed grains were observed. While the hardness profile of the Mg/Mg similar weld exhibited a W-shaped appearance, the lower hardness values appeared in the TMAZ and HAZ of both Mg/Mg and Al/Al similar welds. In the Al/Mg dissimilar weld, a characteristic interfacial layer consisting of intermetallic compounds (IMC) Al12Mg17 and Al3Mg2 was observed. Both Mg/Mg and Al/Al similar welds had significantly higher lap shear strength, failure energy and fatigue life than the Al/Mg dissimilar weld. While the Al/Al weld displayed a slightly lower lap shear strength than the Mg/Mg weld, the Al/Al weld had higher failure energy and fatigue life. Three types of failure modes were observed. In the Mg/Mg and Al/Al similar welds, at higher cyclic loads nugget pullout failure occurred due to fatigue crack propagation circumferentially around the nugget, while at lower cyclic loads fatigue failure occurred perpendicular to the loading direction caused by the opening of keyhole through crack initiation in the TMAZ and HAZ. In the Al/Mg dissimilar weld nugget debonding failure mode was observed because of the presence of an interfacial IMC layer.

Comparative study of fatigue behaviour in dissimilar Al alloy/steel and Mg alloy/steel friction stir spot welds fabricated by scroll grooved tool without probe

Aluminium alloy A6061-T6 or magnesium alloy AZ31 sheet was welded to steel sheet by a friction stir spot welding technique using a scroll grooved tool without a probe. The material flow in the nugget of the Mg/steel weld was less than that in the Al/steel one. The Al/steel weld exhibited higher static tensile–shear strength than the Al/Al weld, while the strengths of Mg/steel and Mg/Mg welds were comparable. Tensile–shear fatigue tests were performed using lap shear specimens of both dissimilar and similar welds. The dissimilar welds exhibited nearly the same fatigue strengths as the similar ones. The effective nugget size in the dissimilar welds was defined as the area where Al or Mg alloy remained on the steel side after static fracture. When the fatigue strengths of dissimilar welds were evaluated based on the effective nugget size, the normalised fatigue strengths of Al/steel and Mg/steel welds were comparable.