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Showing papers in "Science and Technology of Welding and Joining in 2013"


Journal ArticleDOI
TL;DR: In this article, the fundamental understanding of structure-properties relationship in automotive steels resistance spot welds is discussed. And a brief review of friction stir spot welding, as an alternative to RSW, is also included.
Abstract: Spot welding, particularly resistance spot welding (RSW), is a critical joining process in automotive industry. The development of advanced high strength steels for applications in automotive industry is accompanied with a challenge to better understand the physical and mechanical metallurgy of these materials during RSW. The present paper critically reviews the fundamental understanding of structure–properties relationship in automotive steels resistance spot welds. The focus is on the metallurgical characteristics, hardness–microstructure correlation, interfacial to pullout failure mode transition and mechanical performance of steel resistance spot welds under quasi-static, fatigue and impact loading conditions. A brief review of friction stir spot welding, as an alternative to RSW, is also included.

369 citations


Journal Article
TL;DR: In this article, it was shown that the nugget pullout failure is caused by plastic collapse and the interfacial failure is governed by crack or fracture mechanics, and the failure of a spot weld occurs when the fracture criterion for one of the mechanisms is satisfied first.
Abstract: Spot welds produced via resistance welding have been widely used in the joining of sheet metal for autobodies since the 1950s. Every modern car contains over 2000 spot welds. Failure of the spot weld is therefore an important concern in relation to autobody durability and safety design. Spot welds can fail in two completely distinct modes, namely, nugget pullout failure and interfacial failure. In the present paper, it is first shown that the nugget pullout failure is caused by plastic collapse and the interfacial failure is governed by crack or fracture mechanics. These two failure mechanisms compete with each other and failure of a spot weld occurs when the fracture criterion for one of the mechanisms is satisfied first. Test data from available literature are used to validate the theoretical predictions. Recommendations are made for minimum weld nugget size for a given sheet metal thickness so that nugget pullout failure, the acceptable mode of failure in industry, is ensured.

167 citations


Journal ArticleDOI
TL;DR: In this article, the effect of weld parameters on mechanical properties, such as lap shear fracture load, of friction stir spot welded dissimilar lap joints was studied, and the effects of the plate positioning, the plunge depth and the dwell time as well as the tool tilt angle on the joint strength were investigated.
Abstract: In this study, the effect of weld parameters on mechanical properties, such as lap shear fracture load, of friction stir spot welded dissimilar lap joints was studied. The effects of the plate positioning, the plunge depth and the dwell time as well as the tool tilt angle on the joint strength were investigated. The experimental results showed that the positioning of the sheets played an important role on the strength of the joints. The joint strength was higher when AA 5754 sheet is placed on the top, whereas lower strength values were displayed by dissimilar joints produced by placing AA 2024 as the upper sheet. It was also observed that the plunge depth, dwell time and tool tilt angle had a strong effect on the failure mode of the friction stir spot welded lap joints produced. The joints exhibited two different fracture modes, namely cross and pullout nugget under lap shear tensile testing conditions.

119 citations


Journal ArticleDOI
TL;DR: In this article, the effect of welding energy on joint strength, failure behavior and microstructure of Al-Cu ultrasonic welding was investigated in the joining of dissimilar materials.
Abstract: Ultrasonic welding is attracting increasing attentions in joining of dissimilar materials. The effect of welding energy on joint strength, failure behaviour and microstructure of Al–Cu ultrasonic w...

95 citations


Journal ArticleDOI
TL;DR: In this article, a new class of ferritic alloys, known as creep strength enhanced ferritic steels, has been developed to meet the requirements of increasing the efficiency and reducing the carbon footprint of new and existing fossil fired power plants.
Abstract: Fossil fuels continue to be the primary source of energy in the world. The worldwide demand for clean and affordable energy will continue to grow, and a strong emphasis has been placed on increasing the efficiency and reducing the carbon footprint of new and existing fossil fired power plants. Throughout Asia, Europe and the USA, this demand is being met with programmes to develop advanced materials that have enhanced high temperature creep and corrosion properties. A new class of ferritic alloys, known as creep strength enhanced ferritic steels, has been developed to meet these requirements. This article focuses on the weldability of the advanced ferritic alloys used in boilers and boiler components of ultrasupercritical coal fired power plants. This review focuses on alloy selection; welding and weldability issues, including in service weld failure such as type IV cracking; welding of dissimilar metals; and weld repair. Future articles will address the welding and weldability issues of two other...

90 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed a methodology to measure the torque and the traverse force by monitoring the current and power transients of the electrical motors that drive the rotational and linear motions of the FSW tool.
Abstract: Experimental measurements of torque, traverse force and thermal cycles in friction stir welding (FSW) are challenging due to the simultaneous rotational and linear motions of the tool and the deformation of workpiece material around the tool pin. We propose here a methodology to measure the torque and the traverse force by monitoring the current and power transients of the electrical motors that drive the rotational and linear motions of the FSW tool respectively. The measured values of torque and traverse force in FSW of AA 7075-T6 and AA 2524-T351 at different combinations of tool rotational speed and tool shoulder diameter are validated with the corresponding computed results from a well tested numerical model. The proposed method alleviates the need to use expensive torque and force dynamometers, and provides an economical and robust route for indirect measurement of real time torque and traverse force in FSW.

82 citations


Journal ArticleDOI
TL;DR: In this paper, microstructure and mechanical properties of the dissimilar aluminium-magnesium resistance spot welds made with gold coated and bare nickel interlayers are investigated; the welds were made with different welding currents in a range from 16 to 24 kA with a fixed welding time of five cycles.
Abstract: 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.

56 citations


Journal ArticleDOI
TL;DR: In this article, the cold metal transfer (CMT) welding-brazing joining of Ti6Al4V and Al A6061-T6 was carried out using AlSi5 wire.
Abstract: Cold metal transfer (CMT) welding–brazing joining of Ti6Al4V and Al A6061-T6 was carried out using AlSi5 wire. The joining mechanisms and mechanical properties of the joints were identified and characterised by scanning electron microscope, energy dispersive spectroscopy and tensile–shear tests. Desired CMT joints with satisfied weld appearances and mechanical properties were achieved by overlapping Ti on the top of Al. The joints had dual characteristics of a welding joint on the aluminium side and a brazing joint on the titanium side. Three brazing interfaces were formed for the joint, which increased the strength of the joint. An intermetallic compound layer was formed at the brazing interface, which included Ti3Al, TiAl and TiAl3. Two different fracture modes were also observed: one fractured at the welding/brazing interface and weld metal and the other at the Al heat affected zone (HAZ). Clearly, the joints fractured at the Al HAZ had higher tensile strength than those fractured at the weldin...

54 citations


Journal ArticleDOI
TL;DR: In this article, the microstructural characterisation, mechanical testing and fractography investigation were performed on twinning induced plasticity (TWIP) steels, fabricated with resistance spot welding, and failure mode during the cross-tensile test was found to follow the sequences of strain localisation of both sheets, crack initiation at notch tip, crack following along the fusion boundary and finally, ductile shear fracture along the sheet thickness direction.
Abstract: In this study, the microstructural characterisation, mechanical testing and fractography investigation were performed on twinning induced plasticity (TWIP) steels, fabricated with resistance spot welding. Failure mode during the cross-tensile test was found to follow the sequences of strain localisation of both sheets, crack initiation at notch tip, crack following along the fusion boundary and, finally, ductile shear fracture along the sheet thickness direction. On the other hand, failure in the tensile shear test was always directed along the sheet/sheet (s/s) interface; the interfacial failure and shear deformation were observed at the weld centreline. Solidification occurred as a primary austenitic solidification mode, and no martensitic transformations were detected through electron backscatter diffraction analysis. The fusion zone was mainly composed of austenite with directional solidification towards the centreline; the columnar dendritic and equiaxed structures were identified. Interdendr...

50 citations


Journal ArticleDOI
TL;DR: In this paper, defect free friction stir welding of pure copper plates was conducted in air condition at a rotation speed of 1600 rev min−1 and traverse speeds of 50 and 100 mm min− 1.
Abstract: Defect free friction stir welding of pure copper plates was conducted in air condition at a rotation speed of 1600 rev min−1 and traverse speeds of 50 and 100 mm min−1. The microstructural and mechanical properties of defect free joints produced in air and underwater conditions were compared. The results revealed that a finer microstructure can be achieved by underwater friction stir welding. The hardness of joints welded in both conditions was higher compared to the base metal. Moreover, in comparison with the base metal, the joints welded in air and underwater conditions exhibited lower and higher tensile properties respectively.

46 citations


Journal ArticleDOI
TL;DR: In this article, a serrated intermetallic compound (IMC) layer was found at the interface between fusion zone and stainless steel, and the morphology of IMC layer was uniform from the top to the bottom, and its average thickness was 3 μm.
Abstract: Fibre laser–cold metal transfer hybrid welding was introduced to join AA 6061 aluminium alloy with AISI 304 stainless steel using Al–12Si filler wire. Interface properties and microstructure of welded joints were observed by optical microscope, scanning electron microscope, energy dispersive spectrometry and X-ray diffraction techniques. A serrated intermetallic compound (IMC) layer was found at the interface between fusion zone and stainless steel. The morphology of IMC layer was uniform from the top to the bottom, and its average thickness was 3 μm. The IMC layer consisted of two layers: Al8(Fe,Cr)2Si layer close to fusion zone and (Al,Si)13Fe4 layer close to stainless steel. The joint fractured at the IMC layer and presented a tensile strength of 165 MPa. The formation of the IMC layer was closely related with the thermodynamic and kinetic behaviours of the interface and fast cooling rate of hybrid welding.

Journal ArticleDOI
TL;DR: In normal production of resistance spot welded galvanized structures, it is difficult to completely avoid surface breaking cracks as mentioned in this paper, and known key factors to cause cracking are zinc coating, electrode we...
Abstract: In normal production of resistance spot welded galvanised structures, it is difficult to completely avoid surface breaking cracks. Known key factors to cause cracking are zinc coating, electrode we ...

Journal ArticleDOI
TL;DR: In this paper, a micro-tensile test was performed on a friction stir welded A6061/SUS 304 lap joint and the results showed that ∼62% of the area along which the rotating tool passed the specimen was regarded as the bonded region and that the joint was fractured at the A60 61 matrix owing to the formation of very thin interfacial reaction layers.
Abstract: Microscale evaluation of the mechanical properties of a friction stir welded A6061/SUS 304 grooved lap joint was performed using a microtensile test and transmission electron microscopy. The microtensile test revealed that ∼62% of the area along which the rotating tool passed the specimen was regarded as the bonded region and that the joint was fractured at the A6061 matrix owing to the formation of very thin interfacial reaction layers. Equiaxed aluminium grains were observed at the interface of the specimen after it was fractured, indicating that the interface deformed only slightly during the microtensile test. It should be noted that although the maximum tensile strength of the joint was approximately the same as that of the base alloy, the proof stress of the joint decreased with the dissolution of the β″ phase in the A6061 aluminium alloy.

Journal ArticleDOI
TL;DR: In this paper, the effect of welding speed on weld bead geometry, microhardness, microstructure and tensile properties was investigated, and a critical welding speed for acceptable joint was determined as 25 mm s−1.
Abstract: The increasing demand of lightweight and durability makes advanced high strength steel attractive for future automotive applications. In this study, 0·8 mm thick bare 600, 800 and 1000 MPa grade dual phase steel and 1500 MPa grade martensitic steel were laser welded, and the effect of welding speed on weld bead geometry, microhardness, microstructure and tensile properties was investigated. The steels exhibited similar weldability, and a critical welding speed for acceptable joint was determined as 25 mm s−1. A linear relationship of the hardness at fusion zone with carbon equivalent was observed, while carbon content showed a poorer linear fit. Heat affected zone (HAZ) softening increased with the steel grades due to the higher martensite volume fraction of the base metal in stronger steels. In addition, decrease of welding speed led to longer tempering time and consequently higher degree of HAZ softening. Correlations between tensile strength and hardness were also investigated.

Journal ArticleDOI
TL;DR: In this article, the authors describe the characterisation of residual stress in electron beam welded P91 ferritic-martensitic steel plates (9 mm thick) by neutron diffraction and contour measurement methods and reveal the residual stress profile at a fine length scale associated with a ∼1 mm wide fusion zone.
Abstract: This paper describes the characterisation of residual stress in electron beam welded P91 ferritic–martensitic steel plates (9 mm thick) by neutron diffraction and contour measurement methods. The novelty of the work lies in revealing the residual stress profile at a fine length scale associated with a ∼1 mm wide fusion zone. A characteristic ‘M’ shaped distribution of stresses across the weld line is observed with high tensile peaks situated just beyond the heat affected zone/parent material boundary. Measured stresses close to the weld centreline are significantly less tensile than the adjacent peaks owing to martensitic phase transformation during cool down of the weld region. The effect of applying a second smoothing weld pass is shown to be undesirable from a residual stress standpoint because it increases the tensile magnitude and spread of residual stress. The results are suitable for validating finite element predictions of residual stress in electron beam welds made from ferritic–martensit...

Journal ArticleDOI
TL;DR: In this article, a series of 4, 6 and 8 mm DH36 steel welds were produced using optimum conditions for friction stir welding (FSW) and compared with SAW comparators.
Abstract: A series of 4, 6 and 8 mm DH36 steel welds were produced using optimum conditions for friction stir welding (FSW). Comparator welds in the same thickness from the same plates were produced using a single sided single pass process submerged arc welds (SAW). This work was carried out to evaluate the mechanical properties of FSW material with a view to its possible application in a shipbuilding production process route. Overall, the performance of the FSW material was superior to the SAW comparators. Areas such as distortion and fatigue were particularly positive in the FSW material. An 8 mm thick plate was also produced using two FSW passes, one from either side, and it was found to have superior toughness and fatigue performance when compared to the single sided 8 mm FSW material. Some of these benefits are thought to have originated from the internal overlap zone between the two passes.

Journal ArticleDOI
TL;DR: In this article, the upward electromagnetic force given by adjusting the conditions of magnetic field can lift the molten metal up, resulting in the remarkably improved shape of a penetration bead, and the applicability of this method to industry is examined.
Abstract: In fusion welding, gravity makes a molten metal flow downward and it sometimes causes an irregular shaped weld bead and weld defects such as an undercut. To solve this problem, the authors propose a new electromagnetic controlled molten pool welding process method which controls the molten metal flow by using upward electromagnetic forces, and the applicability of this method to industry is examined. In flat position welding with excessive heat input, the molten metal tends to sag down and an undercut defect is likely to occur. It is found that the upward electromagnetic force given by adjusting the conditions of magnetic field can lift the molten metal up, resulting in the remarkably improved shape of a penetration bead. It is further found that, even in overhead position welding, a well shaped penetration bead without undercuts is obtained by adjusting the welding touch angle as well as magnetic field conditions.

Journal ArticleDOI
TL;DR: In this paper, the material behaviour and mechanical characteristics of lap joint friction stir welding between dissimilar alloys, namely, Cu and Al, are investigated in order to produce welds of a higher quality, a layer of Cu is anodised on the aluminium alloy.
Abstract: In this paper, the material behaviour and mechanical characteristics of lap joint friction stir welding (FSW) between dissimilar alloys, namely, Cu and Al, is investigated. In order to produce welds of a higher quality, a layer of Cu is anodised on the aluminium alloy. The mechanical and the microstructural characterisations are performed on the welds, which are produced using various welding parameters. Scanning electron microscope with energy dispersive X-ray spectroscopy is used to identify the elemental compositions of phases that are formed. The results reveal that the use of the copper anodised layer prevented formation of brittle intermetallic compounds due to the direct FSW of 6061 aluminium alloy to copper and, as a result, enhanced the weld metallurgical and mechanical properties.

Journal ArticleDOI
TL;DR: In this article, the authors used a 16 kW high power disc laser together with a hot wire to produce a fully penetrated keyhole, which was used to suppress welding defects and suppress welding metal oxygen content.
Abstract: This study, which pertains to the butt welding of 590 MPa high strength steel plates with a high power laser over gaps, was conducted to investigate weld penetration characteristics, to clarify welding phenomena, and to develop procedures for obtaining high quality joints. Butt welding was performed on 12 mm thick plates with a 16 kW high power disc laser together with a hot wire. In this way, welding defects are suppressed and weld metal oxygen content is controlled, thereby producing sound, fully penetrated welds. Penetrations were stable over a range of gaps from 0 to 0·4 mm, owing to an ejection of excess melt through a keyhole outlet at the bottom of the molten weld pool by a strong plume. Here, the use of a hot wire together with a laser of sufficient power to produce a fully penetrated keyhole was effective in improving the gap tolerance and suppressing oxygen inclusion within the butt weld.

Journal ArticleDOI
TL;DR: In this article, the joint structures and mechanical properties obtained under both sets of conditions were investigated, whereupon it was found that defect free joints can be successfully fabricated under either conditions, where the resulting joint microstructures mainly consisted of grain refined ferrite with some globular cementite.
Abstract: In this study, FSW of AISI 1080 high carbon (0·85 wt-%) steel was carried out at a temperature below its AC1 under two sets of conditions, one entailing natural cooling and the other rapid cooling with liquid CO2. The joint structures and mechanical properties obtained under both sets of conditions were investigated, whereupon it was found that defect free joints can be successfully fabricated under either. The resulting joint microstructures mainly consisted of grain refined ferrite with some globular cementite. Higher (harder) joint microhardness profiles were obtained under liquid CO2 cooling below AC1 than under natural cooling below AC1. In tensile testing, all joint fractures were observed to occur in the base metal. Also, stir zone tensile strength and toughness were found to be higher in liquid CO2 cooled samples (820 MPa and 76·7 mm N respectively) than in naturally cooled samples. Note that in both cases, the joints were formed at temperatures below AC1.

Journal ArticleDOI
TL;DR: In this paper, a self-support FSW (SSFSW) with adjustable dip angle to join the aluminium hollow extrusion is presented, which consists of a big concave upper shoulder and a small convex lower shoulder.
Abstract: In the present work, we design a novel tool called self-support FSW (SSFSW) with adjustable dip angle to join the aluminium hollow extrusion. This tool consists of a big concave upper shoulder and a small convex lower shoulder. Compared with conventional FSW, it eliminates root flaws and does not need backing bars during operation. In particular, the SSFSW can adapt to variation of thickness and does not need predrilled pilot holes, resulting in simplifying the welding process compared with the bobbin tool FSW tool. Significant changes are observed at the cross-section of the SSFSW joint, which looks like a ‘waist’. The average tensile strength and elongation of 6005A aluminium alloy joint with a thickness of 5 mm is 190 MPa and 6·86% respectively. Furthermore, the failure of specimen presents a ductile fracture in the typical joint.

Journal ArticleDOI
TL;DR: In this paper, a 4 mm thick nickel based super alloy Inconel 718 has been friction stir welded using different traverse speeds of 30, 50 and 80 mm min−1 at a rotation rate of 400 rev−1.
Abstract: In this study, 4 mm thick nickel based super alloy Inconel 718 has been friction stir welded using different traverse speeds of 30, 50 and 80 mm min−1 at a rotation rate of 400 rev min−1. Since the Inconel 718 alloy was friction stir welded in the annealed condition, a significant increase in mechanical properties has occurred. Microstructural evolution in the nugget (NG) zone has been investigated using electron back scattering diffraction (EBSD) at the top surface and near the base of the NG as well as across the transverse cross-section. Low resolution EBSD scan across the NG to the base material showed great reduction in grain size from the base material to the NG region. High resolution EBSD scans showed that the NG region is dominated by dynamically recrystallised grain structure with very fine grains that was varied in size from the top to the base of the NG.

Journal ArticleDOI
TL;DR: Linear and weaving laser welding were performed on a self-restraint tapered specimen of an Al 5J32 alloy as discussed by the authors, and a near linear solidification crack developed along the centreline having equiaxed grains.
Abstract: Linear and weaving laser welding were performed on a self-restraint tapered specimen of an Al 5J32 alloy. Linear welding produced columnar grains along the fusion line and equiaxed grains along the centreline. Solidification crack developed along the centreline having equiaxed grains. For laser weave weld, the solidification crack disappeared at a weaving frequency of 5 Hz. However, as the weaving frequency increased further, the length of the columnar grains inside the weaving trajectory curve became smaller than that outside the curve, and the equiaxed grains did not necessarily grow along the centreline of the weld. Therefore, the wide equiaxed grains deviated from the transverse weaving profile and a near linear solidification crack developed. The simulated morphology using solidification rate and temperature gradient correlated well with the solidification morphology obtained from the experiments. The limiting boundary condition for differentiating between the columnar and the equiaxed microstructures in the alloy was G53?5R.

Journal ArticleDOI
TL;DR: In this article, the increasing and changing requirement for weldability and mechanical properties in the heat affected zone and weld metal of pipeline welds are presented along with the reported solutions to the problems.
Abstract: Recent economic and political events have further highlighted the need for new and strategically accessible sources of oil and gas. With the continually increasing demand for oil and gas, the requirement for pipeline steels with higher strength, toughness and weldability has been one of the most important factors driving the development of high strength pipeline steels, particularly with the oil exploration proceeding into arctic and deep sea regions, enhancing the weldability and mechanical properties of the new pipeline steels and weld consumables. Developments in the welding processes for manufacture and field welding are described in terms of process principles, equipment, consumables, weld quality, process economics and further developments. The increasing and changing requirement for weldability and mechanical properties in the heat affected zone and weld metal of pipeline welds are presented along with the reported solutions to the problems.

Journal ArticleDOI
TL;DR: In this article, the dynamic vibration behaviors of a welding tip and pure aluminium sheets were analyzed using the digital image correlation method, which demonstrated that the relative motion between the weld tip and the upper specimen predominantly affected the increase in joint strength.
Abstract: Ultrasonic welding of pure aluminium sheets was observed with a high speed video camera. The dynamic vibration behaviours of a welding tip and aluminium sheets were analysed using the digital image correlation method. The welding process consisted of the following three stages. First, the upper specimen in contact with the weld tip vibrated. The formation of partially welded regions was confirmed at this stage. Second, the vibration amplitude of the upper specimen decreased, while friction between the weld tip and the upper specimen increased. Growth of the partially bonded region was confirmed in the second stage. Third, the welding part began to plastically deform owing to the clamping force. The joint strength reached its maximum value at the third stage. The analysis demonstrated that the relative motion between the weld tip and the upper specimen predominantly affected the increase in joint strength.

Journal ArticleDOI
TL;DR: In this paper, the laser arc hybrid welding of wrought AA 2219 aluminium alloy was studied and the results showed that the strength improvement of the joint using AlMg5 wire depended on the formation of large amount of fine S-Al2CuMg precipitates.
Abstract: Laser arc hybrid welding of wrought AA 2219 aluminium alloy was studied. The cross-weld tensile strength of the joint using AlMg5 wire was 20% higher than that using AlCu7 wire. The reasons for strength improvement were analysed by microstructure observations via scanning electron microscopy, transmission electron microscopy and electron backscattering patterns. The results showed the strength improvement of the joint using AlMg5 wire depended on two reasons. One is the formation of large amount of fine S–Al2CuMg precipitates. The other is the preformed pinning effect of the precipitates on the dislocations. Finally, the formation of the fine S–Al2CuMg precipitates of the joint using AlMg5 wire was discussed by thermodynamic calculation, and the formation of the preformed dislocation pining effect was discussed by the collision theory of adjacent dendrites during solidification.

Journal ArticleDOI
TL;DR: In this article, the temperature is measured by two thermocouples mounted at the ends of both the electrode tips, and the measured temperature profiles showed a good correlation with the weld strength.
Abstract: In this paper a novel approach for temperature measurement during resistance spot welding is presented. The temperature is measured by two thermocouples mounted at the ends of both the electrode tips. The authors chose to mount them there because it was expected that it would be possible to measure the temperature at this point using a digital camera in the near future. The research was, therefore, motivated to obtain various pieces of information about the welding process from the measured temperature profiles. The measured temperature profiles showed a good correlation with the weld strength. Other phenomena, such as expulsion and electrode wear, can also be related to a temperature profile.

Journal ArticleDOI
TL;DR: In this article, the influence of droplets on the arc and weld pool in gas metal arc welding is calculated using a three-dimensional self-consistent model of the arc, workpiece and electrode.
Abstract: A new approach for calculating the influence of droplets on the arc and weld pool in gas metal arc welding is presented. A three-dimensional self-consistent model of the arc, workpiece and electrode that includes the influence of metal vapour is used to track the temperature, velocity and diameter of a droplet as it detaches and passes through the arc. The time averaged influence of the droplet on the arc and weld pool is then calculated. The approach allows very large savings of computational time compared to the usual volume of fluid method. The approach has been applied to one-drop per pulse welding of aluminium. Weld pool depth and shape were predicted accurately. The enthalpy transferred to the weld pool was found to have a strong influence on weld pool depth, while the flow in the weld pool depends on the momentum transferred by the droplet and the magnetic pinch force.

Journal ArticleDOI
TL;DR: In this paper, the influence of tool geometry on material flow during friction stir welding of dissimilar aluminium alloys is investigated, and it is shown that three flat features on the pin impose vertical material flow which can promote intermixing.
Abstract: The influence of tool geometry on material flow during friction stir welding of dissimilar aluminium alloys is investigated. Sheets of Al 2024 and Al 6061 alloys are friction stir welded in lap and butt configurations using different welding conditions. Optical microscopy with serial sectioning is utilised to systematically study material flow when small variations are made to the tool pin. It is shown that three flat features on the pin impose vertical material flow which can promote intermixing. When a threaded tool is used, the material flow and formation of the intermixed region depends on the orientation of the base materials, since the differences in viscosity of material on the advancing versus retreating side of the tool will inhibit intermixing. Decreasing the travel speed will promote intermixing by increasing the residence time to compensate for the differences in material viscosity that otherwise limit intermixing.

Journal ArticleDOI
TL;DR: In this article, a methodology based on process simulation, simple microstructural prediction and a pressure model along columnar grains is developed in order to integrate all factors that influence hot cracking.
Abstract: Hot cracking in welding is a complex phenomenon due to coupling between process, metallurgy and mechanical loading. A methodology based on process simulation, simple microstructural prediction and a pressure model along columnar grains is developed in order to integrate all factors that influence hot cracking. The model is based on some developments of Rappaz, Drezet and Gremaud and takes into account the influences of grain morphology, mechanical and welding thermal loading, on hot cracking. The model based on the microstructure behaviour is able to predict crack onset location in columnar grains on 6061 aluminium alloy.