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This article presents a reliable method of multi-performance characteristics optimization of TIG dissimilar welding of mild steel and stainless steel. Grey-integrated Taguchi optimization approach was adopted for the optimization of the welding process parameters such as the welding current, the welding voltage and the gas flow rate for multi-performance characteristics such as the ultimate tensile strength, yield strength, percentage elongation and Vickers microhardness of the fusion zone. L9 Taguchi orthogonal array was employed with three process parameters all at three levels. The welding current was the most significant process parameter for the multi-performance characteristics of the weld joint. The optimal setting for the multi-performance characteristics of the weld joint was obtained as welding current at level 1 (110 A), welding voltage at level 1 (11 V) and gas flow rate at level 3 (18 l min−1). The corresponding response variables at the optimal setting were ultimate tensile strength, yield strength, percentage elongation and Vickers microhardness of 493.29 MPa, 395.38 MPa, 31.35% and 390.52 HV respectively. These values are all found to be higher than the values obtained at the initial settings. This shows that grey-integrated Taguchi optimization is an effective method in multi-performance characteristics optimization of dissimilar welded material. [ABSTRACT FROM AUTHOR]

This study investigates a parametric multi-objective optimization of the Tungsten Inert Gas-Metal Inert Gas (TIG-MIG) hybrid welding of AISI 1008 mild steel joints. A combined grey relational system theory and the Taguchi method was used for process optimization towards achieving a set of process parameter that maximizes both ultimate tensile strength and 0.2% yield strength for structural applications. An L-9 orthogonal array based on the Taguchi method was adopted for the experimental design matrix. Grey relational grading system was used to establish a single grade for the responses. Mathematical models for first- and second-order regressions were developed and optimum process parameter combination that optimizes the response was obtained. From the results, the gas flow rate had the most significant influence on the responses with a percentage contribution of 39.77%. Also, the second-order regression models had a higher coefficient of determination (R2) compared to the first-order regression for the two responses and, thus, represents the best fit for the process. The grey relational grade was improved by 0.0489 through process optimization. The interactive effects of process parameters and their effects on the responses are also illustrated by response surface plots. This study shows the effectiveness of the grey relational grading system in achieving a multi-objective optimization for the TIG-MIG welding process. [ABSTRACT FROM AUTHOR]

In this work, dissimilar welded joints from AISI 1330 and AISI 4340 low-alloy carbon steels produced using rotary friction welding (RFW) are investigated. These steels are intended for the manufacture of exploration drill pipes: AISI 4340 — the tool joint and AISI 1330 — the body of the pipe. Statistical analysis based on response surface methodology (RSM), microstructural examination using scanning electron microscopy with backscattered electron diffraction (EBSD), and mechanical tests were performed to investigate the friction weld joints. Equations are derived for predicting the notch tensile strength, ultimate tensile strength, and relative elongation from RFW process parameters (heating pressure, forging pressure, rotation speed during heating, burn-off length). The results showed that the rotation speed during heating and the heating pressure to the greatest extent affect the quality of the welded joint. Parameters have been established that ensure obtaining the mechanical properties of the welded joint at the level of the base metal AISI 1330: heating pressure 60–80 MPa, forging pressure 120–140 MPa, rotation speed during heating 400 rpm, and burn-off length 4 mm. It is shown that the strength of the joint depends on the development of processes of mutual dynamic recrystallization at the steel interface and strain hardening in the thermomechanical affected zone. [ABSTRACT FROM AUTHOR]

Samples of AA5086 aluminium alloy were welded by gas tungsten arc welding (GTAW) with alternating current using three different shielding gases. The samples were welded with pure argon (Ar), a mixture of argon and helium (Ar + He) and a new mixture composed of argon, nitrous oxide and oxygen (Ar + N2O + O2). The effect of the shielding gas on the residual stresses and on the mechanical and microstructural properties of the welded joints was evaluated and compared with the base metal. The new gas mixture produced compressive residual stresses in the longitudinal and transverse directions in the weld metal. Tensile test of welded joints indicated similar values for yield strength and ultimate tensile strength; however, these values were lower compared to the base metal. The new gas mixture provided a welded joint with hardness values in the weld metal and heat-affected zone close to the base metal values and with greater magnitude compared to samples welded using pure argon and mixture of argon and helium. Microstructural characterisation performed by optical and scanning electron microscopy showed that the new mixture produced welded joints with lower porosity. [ABSTRACT FROM AUTHOR]

This investigation aims to make clear the relationships among geometric features, macrostructures, microstructures, and mechanical performances of the weld bead in the gas metal arc welding (GMAW) process for ASTM A606 type IV weathering steel. The results indicate that with the increase of welding heat input, the geometry of the top reinforcement and penetration increases proportionally until reaching the peak value, and then declines with the further increase of welding heat input; while the values of bottom reinforcement increase continuously with the increase of welding heat input. The average ultimate tensile strength (F), maximum displacement (L), and failure energy (E) of the welded joint produced by the moderate welding heat input are 10.27 kN, 1.88 mm, and 13.55 J, respectively, which are obviously larger than those obtained by the insufficient welding heat input (F: 8.33 kN, L: 1.20 mm, and E: 7.10 J). Although the mechanical properties of the welds achieved by the overlarge welding heat inputs present comparable levels (F: 9.73 kN, L: 1.86 mm, and E: 13.51 J), their standard deviation is much higher. Acicular ferrite, grain boundary ferrite, side plate ferrite, Widmanstätten ferrite, and pearlite are noticed in the fusion zone (FZ), while the coarse grain heat-affected zone (CGHAZ) is composed of upper and lower bainite, grain boundary ferrite, Widmanstӓtten ferrite, polygonal ferrite, and pearlite. As the welding heat input increases, the pre-austenite grain width in the FZ and CGHAZ decreases. The descending order of the microhardness distributed in the welded joints is fusion line, CGHAZ, FZ, fine grain heat-affected zone (FGHAZ), and base metal. In addition, the microhardness values of FZ and CGHAZ decline with the rise of the welding heat input. Nonetheless, no apparent links are found between the microhardness levels of the FGHAZ and welding heat input. [ABSTRACT FROM AUTHOR]

Friction stir welding (FSW) is a solid-state joining process, which has prominent advantages over common fusion welding methods like MIG welding. However, equipment costs and royalties act as the main barriers to the widespread use of this technique in today’s industry. Thus, developing low-cost FSW techniques could pave the way for potential industrial users. In this research, we are going to characterize and optimize a recently developed FSW technique at right angle (RAFSW) using low-cost three-axis CNC machine tools. To this end, a full study was done to gain a deep insight through the effect of RAFSW process parameters on generated axial forces and tensile properties of AA6061-T6 butt-welded flat bars of 6.35 mm thick. Experiment planning and modeling of the results used Taguchi design of experiments method and artificial neural network modeling respectively. From these models, an efficient working window of process parameters has been established so that CNC machines with minimized capacity and stiffness can produce high-quality welds repeatedly. After natural aging, the ultimate tensile strength reached a maximum of 253 MPa and stays above 247 MPa within the working window. Moreover, the robustness of the technique and the effect of artificial aging on the strongest samples have been evaluated. We found that the ultimate tensile strength of artificially aged samples attained 300 MPa. Finally, microstructure images and micro-hardness measurements of the strongest welded samples complete the analysis. The outcomes of this research have a great impact on making the recently proposed RAFSW technique reliable for industrial users. [ABSTRACT FROM AUTHOR]

The effects of heat treatment on the microstructures and mechanical properties of tungsten inert gas-welded AZ31 magnesium alloy joints with CrO flux coating were investigated by microstructural observations, microhardness, and tensile tests. The results showed that the activating flux of CrO improved the weld penetration and the depth/width ratio of the tungsten inert gas-welded AZ31 magnesium alloy joints markedly. Heat treatment (1) eliminated the coarsened network-like β-Mg(Al, Zn) particles which formed in activating tungsten inert gas and (2) resulted in more uniform grain size distribution of partially melted zone. Apart from that, either the microhardness of the seams, the ultimate tensile strength, or the elongation of the welded joints was improved by aging treatment, while too high aging temperature would give rise to a sharply decreased ultimate tensile strength. [ABSTRACT FROM AUTHOR]

In paper, weld joints between VT1-0 titanium and AISI 321 austenitic stainless steel using laser welding were obtained. To improve the quality and strength properties of joints, two types (SS-Cu-Nb/Ta-Ti) of explosively welded four-layered composite inserts were used. Barrier layers were different from each other by refractory metal. The effect of intermediate material inserts, in particular tantalum and niobium, on microstructure, chemical composition, strength properties, and fracture behaviour of weld joints was studied. Microstructural studies have revealed two bonding types as results of welding method combination. At copper-stainless steel interface, severely deformed zone characterized by low etch ability was observed. Technological parameter's optimization provided high joint quality and absence of defects in the weld joints. According to results of strength tests, it was found that the composite insert material affects the strength of the joints. The highest ultimate tensile strength and yield strength were detected for joints containing niobium foil. [ABSTRACT FROM AUTHOR]

In this study, the effects of tool rotational and traverse speeds on the mechanical properties and the microstructure of the friction stir welded joints from Al 5086-H34 were studied. Insufficient heat generation and inadequate metal transportation at very low rotational speed and high turbulence in the plasticized metal at very high rotational speed emerged tunnel and worm hole defects into the weldment. It was discovered that as rotational and traverse speed increased, the average grain size of the weldment decreased due to more dynamic recrystallization and amplified stirring effect. An increase in the rotational speed increased the ultimate tensile strength and microhardness of the specimens. At the best welding condition, by employing the rotational and traverse speeds of 1250 rpm and 80 mm/min, respectively, 51 % enhancement in the elongation and 8 % increase in the microhardness of the welded samples were obtained. Moreover, the ultimate tensile strength of this welded joint reached to 85 % of the base metal. [ABSTRACT FROM AUTHOR]

This paper reports on the time dependency of mechanical properties and component behavior during the first hours after friction stir welding (FSW). Three different aluminum alloys, two age-hardened alloys AA 6014-T4 and 6016-T4 and as a reference 5182-O/H111, are welded and samples are taken from the steady-state region immediately. Those samples are examined at various time intervals by means of tensile and hardness testing to quantify local properties and their recovery over time. Initially, the FSW process leads to a significant reduction in mechanical properties of the age-hardened alloys and to an altered, time-dependent component behavior as opposed to the base material. For AA 6014 and 6016, all mechanical properties recover significantly within a few hours after welding, whereby the gradient is initially very steep and levels out after 1–2 days. Gradients of up to 6 MPa/h and relative increases of more than 25% are observed for ultimate tensile strength within the first 2 days. As such, the increase in strength within the heat-affected zone and with it the entire welded component can be compared to natural aging after solution annealing. The results show the importance of considering the time dependency for weld qualification and also for comparing studies of age-hardenable alloys. [ABSTRACT FROM AUTHOR]

A complex experimental study of laser welding of the V-1469 Al-Cu-Li alloy is performed for obtaining a high-strength welded joint. The phase composition, microhardness, and strength characteristics of the alloy and welded joint in various regimes of heat treatment are studied. It is found that heat treatment of the welded joint increases its ultimate tensile strength. After complete heat treatment, microhardness values of the alloy and the welded joint become close to each other. Standard heat treatment of samples after welding allows recovery of the structure and phase composition of the entire sample at the micrometer size level. The use of heat treatment allows one to obtain the welded joint strength equal to 0.85 of the base alloy strength in the as-received T1 state. [ABSTRACT FROM AUTHOR]

Thick plates of 5083 aluminum alloy are welded with GMAW and GMAW-TW processes; the influence of weld pool convection on porosity formation, microstructure, and mechanical property of the welding joints is investigated. The results showed that due to the appearance of outward flow and 'push-pull' patterns, and intense mixing and stirring effects in GMAW-TW process, a sound weld seam with less porosity can be obtained. The less probability of bubble formation, the shorter escaping distance of the bubble, the easy splitting of bubble, the higher bubble escape velocity, and lower solidification rate are responsible for porosity suppression. Even though the grain size in GMAW-TW process is larger than that in GMAW process, the ultimate tensile strength of the joints is larger, which is caused by less porosity formation, larger number, and uniform distribution of second-phase particles in the welds. Compared with GMAW process, the GMAW-TW process possesses the advantages of higher efficiency, less weld defects, and higher mechanical property in the welding of 5083 aluminum alloy thick plates. [ABSTRACT FROM AUTHOR]

A series of experiments of high-power fiber laser-arc hybrid welding of pure copper was carried out. It could be seen that the microstructure of weld metal was obviously coarsened, and the columnar grain spacing at fusion zone and the massive grain size at heat-affected zone were both linearly increased with the increase of heat input. The weld conductivity decreased with the increase of heat input because the widening weld increased the microstructure nonuniformity of test samples. The heat input as well as welding parameter has no obvious effect on the ultimate tensile strength (UTS) of cross-weld but has obvious effect on the elongation. The UTS of all the welds was 200 MPa or so. The elongation was bigger than 20% when the heat input was in the optimization range from 250 to 380 J/cm. The decrease of the elongation was attributed to either high porosity at insufficient heat input or coarser grain at excessive heat input. [ABSTRACT FROM AUTHOR]

Four tools with taper (TA), triangular (TB), three-grooves (TC), and square (TD) pin-tip profiles were designed to friction stir weld (FSW) thick AA7075-T6 alloy plates aiming at improving the local and overall mechanical properties of the joints. The microstructure evolution, hardness, and mechanical properties of the FSW joints were studied by scanning election microscope (SEM), X-ray diffractometer (XRD), and transmission electron microscope (TEM). The results show that equiaxed grains in the bottom nugget zone (BNZ) obtained by using TC are noticeably refined compared to in the case of other tools. Also, finer and more dispersive precipitates are distributed in this BNZ, and higher contents of η phase and dislocations are observed. A similar trend is found in the middle of weld. The bottom slices welded by employing TC show superior strength and ductility with a highest ultimate tensile strength of 388 MPa, yield strength of 315 MPa, and elongation of 7.9 %, which are in agreement with the hardness profiles. This is owing to ultrafine grains, more high-angle grain boundaries, more dispersive and higher contents of precipitates, and optimum hardness distribution. Accordingly, the global mechanical properties of the overall joints prepared by using TC significantly improve. [ABSTRACT FROM AUTHOR]

In the present study, a number of joints were fabricated successfully on DH36 marine steel sheet in underwater wet based on friction taper plug welding (FTPW). The influences of the plug and hole geometry parameters combination on the quality of welded joint forming were first investigated. It was found that tapered holes and plugs were the preferred choice and a suitable cone angle range was obtained. Using the preferred hole and plug designed further expand the range of welding parameters to explore process parameters influence on the welding quality. Bonding mechanism and microstructural evolution to FTP welds were investigated with multiple observations. Mechanical properties of the obtained joints were also evaluated with tensile and Charpy impact tests by reference to AWS D3.6 Underwater Welding Code. The best result is found as the joint welded with 7500 rpm and 40 kN which has 535.6 MPa ultimate tensile strength, 22.5 % elongation, and 42.5 J impact energy at bonding line. [ABSTRACT FROM AUTHOR]

In this paper, effect of pin position (relative to tool shoulder position) on welded joint in friction stir welding (FSW) of aluminum 5083-O was investigated. FSW is a new solid-state welding process used to join metals and alloys (especially unweldable aluminums). To do this study, a FSW process was prepared by designing and fabricating tool and workpiece fixture and installing them on a milling machine. Then, some experiments were performed using the tool with a pin coaxial with the axis of tool shoulder. Hence, the tool enters edges of joint location and moves along joint line. Achieved results showed heat generation, severe plastic deformation, and material displacement in joint location which led to completeness of joint's edges. It was also found that the tool temperature for tools with half pin and arched pin had a significant increase with the increase of rotational speed. Tools with more ability of mixing materials and forging of transferred material from the front of the pin to its back showed more ultimate tensile strength. [ABSTRACT FROM AUTHOR]

In this paper, a disk laser welding was developed to join 3-mm thin-Sect. 30Cr3 ultra-high-strength steel which was widely used in aerospace. The microstructure and mechanical properties of welded joint were investigated in detail. The results indicated that the recommended laser linear energy range were between 150 and 165 J/mm to guarantee that the melting width was up to 1 mm as well as less oxidation, spatter, and depression on the weld. Meanwhile, for the as-welded (AW) condition, the base metal (BM) consisted of ferrite matrix with distributing small spherical carbides, also known as spherical pearlite. While, the fine grained region, coarse grained region, and weld metal were all composed of martensite. However, the partially transformed region mainly consisted martensite with a little of spherical pearlite. Meanwhile, the average grain sizes of weld metal, HAZ, and base metal were 1.3 μm, 1.5 μm, and 1.8 μm, respectively. However, for the post-weld heat treatment (PWHT) condition, the whole welded joint was all composed of tempered martensite, and the average grain size of welded joint was about 1.7 μm. The tensile strength of the welded joint was higher than that of the base metal both in the AW and PWHT condition as all the fracture with shrinkage occurred in the BM of the specimens. Additionally, the average yield strength of the AW and PWHT are about 600 MPa and 1700 MPa, respectively. [ABSTRACT FROM AUTHOR]

In this study, a number of models for estimating the mechanical attributes of dissimilar joints produced by resistance spot welding (RSW) of bake-hardening (BH) 220 steel and high-strength low-alloy (HSLA) 420 steel were developed based on regression analysis. Welding conditions were achieved via design of experiment (DOE), and the Box-Behnken design (BBD) method was selected. Welding time, welding current and electrode pressure were recorded as input parameters, while maximum displacement, peak load and failure energy of the welded samples accomplished from tensile shear tests were outputs. The influence of the welding current is superior to the influence of the welding time on the increase of the weld strength as stated by the analysis of variations (ANOVA). Relatively high welding heat input conditions enhance the mechanical attributes of the welds by increasing the nugget size. The largest mechanical properties obtained under the optimum welding conditions are welding time of 14 cycles, welding current of 10.8 kA and electrode force of 0.4 MPa. By verifying the regression models of the optimal welding conditions, the experimental results of the welded specimens with the maximum mechanical properties are about maximum displacement of 2.69 mm, peak load of 11.10 kN and failure energy of 23.90 J. The results show that the proposed spot weld strength models have an estimated accuracy of 5.32%. Due to the complete growth of austenite grains, the martensite in the coarse grain heat-affected zone (CGHAZ) is much larger than that of other zones, while in the HAZ at the side of BH steel, other phases besides martensite are also spotted, such as bainite, Widmanstätten ferrite and grain boundary ferrite. This is because BH steel has a lower carbon content. All welded specimens display hardening in the fine grain heat-affected zone (FGHAZ). [ABSTRACT FROM AUTHOR]

The welding characteristics of 7075 aluminum alloy and DP980 dual-phase steel sheet were systematically studied by the friction plug-riveting spot welding technology. The effects of different welding parameters on the weld formation, tensile strength, and microstructure of welded joints were analyzed. The complete metallurgical joining interface was formed between the rivet and steel plate. A partial metallurgical joining interface was formed between the circumferential surface of the rivet shaft and the aluminum alloy close to the steel sheet. However, the position of the rivet head did not form a metallurgical joining with the aluminum alloy. During the welding process, the area of the rivet interface underwent severe plastic deformation by frictional heat and down pressure; thus, there was a violent interaction between the plastically deformed metal and the surrounding aluminum alloy. The molten aluminum infiltrated into the rivet at the most of sample joints. The penetration of aluminum had a negative effect on the shear load. The maximum shear load of the joint was 14.374 kN. There were two types of fractures: the internal fracture of the rivet and the fracture of the steel/steel friction interface. When the fracture mode was an internal fracture of the rivet, the shear load was generally greater than the steel/steel friction interface. [ABSTRACT FROM AUTHOR]

This manuscript presents the microstructure and mechanical analysis of friction stir welded joints of Al 6101 (aluminum alloy) and C11000 (copper alloy) plates of 3 mm thickness with and without incorporation of silver (Ag) and zinc (Zn) interlayers. Four joints ( J 1 : Al-Cu), ( J 2 : Al-Ag–Cu), ( J 3 : Al-Zn-Cu), and ( J 4 : Al-Ag-Zn-Cu) have been made between Al-Cu plates by the FSW process. The quality of welded joints has been inspected using tensile testing, scanning electron microscopy, and energy-dispersive X-ray analysis (EDX). The Al-Cu joint made with hybrid interlayers (silver and zinc) has the highest tensile strength with a value of 121.78 ± 6.34 MPa, which is 36.44% greater than joint J 1 without interlayer, 7.32% greater than joint J 2 with Ag interlayer, and 21.97% greater than joint J 3 with Zn interlayer. Improvement in tensile strength is due to the formation and uniform distribution of Zn-generated thin intermetallic and the distribution of Ag-generated ductile Ag 2 Al intermetallic in the weld zone. Fractographic analysis on tensile sample supports the reason for achieving high tensile strength for joints with hybrid interlayer, where the combination of small and large dimples was noted, which confirm the ductile mode of fracture compared with other joints. Microstructural studies revealed the flow variation of constituents with and without interlayers. EDX analysis confirmed the formation of binary and ternary intermetallic phases. The diffusion of interlayers with Al/Cu parent metal has reduced the formation of detrimental brittle intermetallic between the parent metals. Line scan and elemental mapping show that the joints with Zn and Ag interlayer have thin, continuous, and uniform intermetallics with improved metallurgical and mechanical properties of the welds. [ABSTRACT FROM AUTHOR]

Graphene and its derivative materials have been receiving the attention of researchers worldwide, and these materials are being considered for many applications. In this sense, studies revealed significant improvements in the welding properties of the welded joint when graphene derivatives are used. In this work, graphene oxide was synthesized and deposited in shielded metal arc welding E6013 electrodes by dip coating, and bead-on-plate and joining welds were produced with and without graphene oxide addition. The synthesized graphene oxide was characterized by XRD and SEM. In weld characterization, tensile strength tests, optical microscopy, microhardness, and corrosion were performed. The results revealed that the application of graphene oxide had promoted a slight increase in the microhardness of welds and did not promote deleterious effects on tensile mechanical properties. Furthermore, despite the lack of significant effects of graphene oxide addition in microstructural development and mechanical properties, the weld metal obtained with graphene oxide addition presented corrosion rates 30 times inferior to conventional electrodes and ten times less than the base metal. [ABSTRACT FROM AUTHOR]

The aim of this paper is to investigate welded joints of high-strength steel S960 QL manufactured by using three different welding technologies, namely the electron beam, the laser beam, and the metal active gas (MAG) technologies. The experimental part included tensile strength evaluation, microstructural analysis of welded joints, and hardness measurement. Welded joints (WJ) have consisted of the identical steels and the identical thickness (10 mm). Destructive tests confirmed that welded joints are characterized by the tensile strength similar to the base material. Upon further observation, we can conclude that microhardness was characterized by the lowest value in the softening zone (SZ) and the highest value in the hardening zone (HZ). The degree of softening was 11% for the electron welding, 13% for the laser welding, and up to 27% for the conventional MAG welding. This also corresponds with the size of the SZ, which was the widest in welds made with the MAG technology. The laser beam weld produced up to 50% lower heat-affected zone (HAZ) compared to the conventional MAG technology. In case of the electron beam, this number is even higher. On the contrary, highest hardness was observed for the electron beam technology, where the hardness in the hardening zone increased by up to 40% when compared with the base material. Tests show the possibility of production of reliable welded joints, which meet the complex requirements for lifetime and quality (according to the standard EN 6520–1 focusing on defects categorization and EN 5817 dealing with defects tolerance). [ABSTRACT FROM AUTHOR]

This research investigation focuses on copper (Cu) donor material assisted friction stir welding (FSW) of AA2024-T4 and AA6061-T6 plates of 6.35 mm thickness. FSW joints were prepared at optimized process parameters of 1400 rpm and welding speeds of 1, 2, or 3 mm/s. The Cu donor material of 25% and 50% thickness with respect to the workpiece thickness were selected to assist the FSW joining during the plunge stage. The downward force generated in the FSW process was gradually decreased after introducing the Cu donor material because more heat was produced in the donor material and conducted to the base plate. The temperature profiles that the inclusion of the Cu donor material increased the temperature at the beginning of the welding process. The welded joints were characterized in terms of the micro-hardness and tensile properties. Defect-free joints could be obtained when placing high strength AA2024 alloy at the advancing side of the weld with 25% thick donor material. From the hardness profiles, it is observed that the hardness decreases from the base metal of AA 2024 to the center of the weld followed by thermomechanical affected zone (TMAZ) and the heat affected zone (HAZ). The hardness measurements are lower in the TMAZ and HAZ where tensile failure occurs. The maximum tensile strength improved by 130% with 25% Cu donor material as compared to the as welded samples. SEM Fractography images confirmed mixed modes of brittle and ductile fracture surfaces with tearing ridges and finer dimples after the inclusion of donor material in FSW. [ABSTRACT FROM AUTHOR]

The induction welding has been recognized as one of potential and high-efficiency joining methods for thermoplastic composite materials. In this study, a numerical simulation model with containing both induction wielding heat transfer and joint tensile failure process for CF/PPS-Al alloy interlocking induction welding was established based on software COMSOL Multiphysics and Abaqus/Explicit. The CF/PPS-Al7075 interlocking welding joints with special designed macro-scale interlocking were tested under tensile loads, and the corresponding single-lap shear strength, energy absorption, and failure mechanisms were investigated by combining the experimental and numerical approaches. Finally, the influence of macro-scale interlocking geometric parameters on joint tensile strength was also discussed. The results indicate that the proposed model can effectively predict the temperature distribution in the welding process and the tensile failure process of the joint. It is also presented that the addition of macro-scale interlocking features can effectively improve the ultimate load (47%) of the CF/PPS-Al alloy induction welded joints. Meanwhile, the number of addition PPS films in the welding zone and the inclination angle have greater contribution on the tensile strength of the welded joints. [ABSTRACT FROM AUTHOR]

The influence of the scale effect on the strength of mechanically inhomogeneous welded structures with a soft zone was studied. The investigated welded samples were made of two 12Kh18N10T austenitic steel plates and a low-carbon ferritic insert connected between them by two dissimilar welded joints performed by electron beam welding. Tensile strength as a function of soft zone relative thickness for tensile specimens was plotted. It was shown that with a relative thickness of the soft zone in the range from 0.2 to 0.5, the scale effect did not manifest during tension. This can be explained by low plastic compressive deformations in the soft zone after heat treatment, which typically lead to a decrease in the constraint effect due to the Bauschinger effect. [ABSTRACT FROM AUTHOR]

The intention of this study is to explore the influences of welding settings upon the geometry, microstructure transformation, and tensile properties of the gas metal arc welded joints of weathering steel ASTM A606 type IV. The individual effect of the welding variables (welding speed, welding current, and wire feed speed) on the geometries of the weld bead and its tensile properties was explored. The characteristics of the microstructure and macrostructure with various welding technological parameters were also investigated. It is indicated that all the selected welding process parameters significantly affect the welding microstructural and macrostructural features of the welded joints as well as their tensile properties. The results imply that no major defects were observed based on the macrostructure examination. The fusion zone (FZ) changes ferrite and pearlite morphology, relying upon the cooling speed and duration time. The FZ exhibits acicular ferrite, Widmanstatten ferrite, and grain boundary ferrite, resulting in its inferior hardness to that of the coarse grain heat-affected zone (CGHAZ) and weld interface (WI). The adjustment of the welding process parameters bringing about the reduction of the welding heat input contributes to the production of acicular ferrite. The hardness of the weld metal steadily decreases from the heat-affected zone (HAZ) to the base metal (BM). The average tensile strength of the weld metal is 596 MPa, which is comparable to that of the BM. The fracture location is in BM, and the fracture behavior retains ductility. After that, models computing the correlations between welding parameters and welding quality indexes (failure energy of the welded joints, depth of the penetration and bottom reinforcement, and standard derivation of the failure energy) were established and analyzed. The optimal welding parameters were figured out using the desirability approach. [ABSTRACT FROM AUTHOR]

In the present study, dual-phase (DP590) steel sheets were joined using single-pulse and double-pulse resistance spot welding in lap joint configuration. Effects of the welding method on microstructure, texture, tensile shear properties (load carrying and energy absorption capacity), and fatigue strength of welded joints were investigated. Tensile shear test results showed that double-pulse weld exhibits an average of 15.6% and 83.1% higher peak load and failure energy, respectively than single-pulse weld. Fatigue test results showed that double-pulse welds withstand 10.8%, 22.7%, 1.8%, 158.7%, and 20.2% higher number of cycles than single-pulse welds at an applied load of 2.3, 2.76, 3.45, 4.6, and 8.1 kN, respectively. The better mechanical performance of the double pulse spot welds is attributed to the large nugget size resulting in higher bonding area, the tough microstructure of the nugget consisting of tempered martensite structure, acicular ferrite, and Widmanstätten ferrite, and the formation of randomly orientated grains with a high fraction of high angle boundaries in the fusion zone, which resulted in improved resistance to crack propagation during mechanical loading. [ABSTRACT FROM AUTHOR]

The wide application of high-strength low-alloy (HSLA) steels in the automobile industry makes the metallurgical properties and mechanical attributes of spot welds essential. The relationships among macrostructure, microstructure, mechanical properties, and failure modes of welded joints of HSLA 420 steel were studied. An optical microscope was employed to describe the microstructure, macrostructure, and geometry of the welds, while their mechanical properties and failure modes were characterized via tensile shear tests. It turns out to be that the weld nugget mainly contains lath martensite. The results of the microhardness test show that the microhardness of the fusion zone (FZ) is superior to those of the heat-affected zone (HAZ) and base metal (BM). The increase in heat input brings about a decrease in FZ martensite hardness, but the hardness distribution is more uniform. The grain size of the FZ is 38 µm, 51 µm, and 62 µm when the welding time is at the levels of 11 cycles, 15 cycles, and 19 cycles, while its values increased by about 58% as the welding current increases from 7.2 to 9.6 kA. As the welding time increases, the differences between the maximum hardness and minimum hardness decrease from 74 to 54 HV. In the tensile shear test, interfacial fracture and pullout fracture were observed, followed by BM sheet tearing. Evidently, the weld nugget with the size of 4t0.5 (t = sheet thickness) will not bring about pullout fracture. Furthermore, existing standards for determining the acceptable load capacity of welded joints cannot guarantee good welding quality. Finally, moderate welding current (from 8.4 to 9 kA) and long welding time (above 15 cycles) should be used to obtain the welded joints with sufficiently large FZs which present good mechanical properties in the tensile shear test. [ABSTRACT FROM AUTHOR]

Ti–6Al–4V sheets of 3 mm thickness were joined via friction stir welding (FSW) technique using industrial purpose I-STIR machine. Since the welding speed is a key parameter in production, it was varied from 40 to 200 mm/min in steps of 40 mm/min. Sound joints were obtained without macroscopic defects using a lanthanated tungsten tool. The microstructure, hardness, and residual stress of the joints were evaluated. Stir zone encountered phase transformation and the microstructure of the base metal transformed into a lamellar structure resembling a widmanstätten structure. There was a marginal improvement in hardness subsequent to welding. Tensile kind of residual stresses were recorded along the longitudinal direction of the weld seam. Compressive stresses were observed outside the weld region. Fatigue tests were carried in as welded and polished condition at a stress ratio of 0.1. All specimens failed at the stir zone irrespective of the surface condition and the welding speed. Shoulder formed striation marks served as crack initiation sites for as welded specimens. Slip bands within the lamellar structure or root flaws act as crack initiators in case of polished specimens. The microstructural variation influenced the fatigue strength to a certain degree. The increase in welding speed lowered the fatigue strength. [ABSTRACT FROM AUTHOR]

Under internal high pressure, the stress of the intrados of the elbow is higher than that of the extrados, so the extrados single-welded elbow can withstand greater internal pressure than the intrados single-welded elbow. In this paper, a novel cold stamping process of extrados single-welded elbow is proposed. It mainly includes blanking, U-forming, O-forming, welding, and cutting excess material, which is especially suitable for the production of large thin-walled pipeline elbows. The initial blank shape and size of the 90° elbow with extrados single welded are obtained by the one-step formability analysis of DYNAFORM. The stamping process of the elbow is simulated by ABAQUS. The die structure is designed, and the forming defects such as wrinkling and lack of material are overcome. When the compression ratio is 0.75% during O-forming, the ovality of the central plane and end face of the elbow reach 0.55% and 0.69%, respectively. The maximum thickening rate and thinning rate of the formed elbow are 8.8% and 12%, respectively. All geometric parameters of the elbow meet the API 5L standard. [ABSTRACT FROM AUTHOR]

In this work, the microstructural evolution and mechanical properties of 304 austenitic stainless steel welds produced by GTAW process were examined after post weld heat treatment (PWHT). Thermal treatment was carried out at different temperatures ranging from 450 to 1050 °C. The optical microscope and scanning electron microscope were used to study the microstructure and fracture surface of the welded joints. X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) techniques were used to investigate the possible formation of intermetallic phases as σ or chromium carbide. Based on the results, no σ phase or chromium carbide precipitation was found. Also, the mechanical behavior of the joint was evaluated by tensile and microhardness tests. The microstructure of the 304 stainless steel was found to consist of equiaxed austenite grains (γ) of various sizes limited by grain boundaries and twin crystals with small amount of delta ferrite (δ) in grain boundaries. The microstructure of the weld metal was austenite with dendritic structure containing skeletal delta-ferrite. The skeletal type delta-ferrite changed from columnar + equiaxed to cellular type by progression during heat treatment. The base metal (BM) and heat affected zone (HAZ) grain size decreased with increasing heat treatment temperature. Therefore, the mechanical testing results were appropriately correlated with the microstructure analysis. Tensile testing analysis showed that the highest tensile strength value was recorded for the as-welded specimen. On the other hand, the PWHT temperature has less effect on the tensile strengths but improves the elongation of the weldments. The micro-hardness for all the weld zones WZs exhibited lower values than that of the base metal BM and the heat affected zone HAZ. The latter presents similar micro-hardness values for all samples and slightly higher than that of the BM except for the weld heat treated at 850 °C, which attained high micro-hardness values. The weldment solution heat treated at 1050 °C shows the best and stable micro-hardness profile similar to that of the as-weld specimen but with higher values in the weld zone. [ABSTRACT FROM AUTHOR]

The underwater welding process used to repair offshore engineering structures involves a large number of processing parameters that must be selected and strictly controlled to achieve the required metallurgical and mechanical characteristics. Internal and surface porosity is a very common serious problem in underwater welding directly dependent on the process parameters. In this research work, a novel modeling and optimization study applying support vector regression (SVR) model and sequential quadratic programming (SQP) algorithm in order to predict and optimize the main process parameters of underwater flux cored arc welding (FCAW) on surface porosity in bead-on-plate welds of ASTM A36 steel is investigated. For this purpose, the experimental underwater wet FCAW process was carried out in an open tank with a 30-cm fresh water column. A composed central design was used to obtain the experimental matrix of 17 underwater welding tests with several combinations of parameters and variation levels: voltage (V, 22–26 V), welding speed (v, 3–10 mm/s), and wire feed speed (WFS, 6350–11,430 mm/min) and the surface porosity was counted to each weld bead. In general, the results showed that this new computational approach using SVR satisfactorily approximates the level of surface porosity according to the operational variables. The model was validated with experimental results obtained from optimization with sequential quadratic programming algorithm. Using both mathematical methods, it was possible to obtain adequate parameters (V = 24V, WFS = 8890 mm/min, and v = 3.4 mm/s) to experimentally produce underwater welds with minimal surface porosity (fewer than 10 pores in a bead length of 30 cm). [ABSTRACT FROM AUTHOR]

The environmental impacts of welding have attracted huge attention and it became a significant basis to evaluate sustainable manufacturing process. To achieve the environmental impact assessment of welding, the consumption/emission of inventory data should be collected for supporting inventory analysis. Meanwhile, the consumption/emission of these substances in welding is affected by process parameters (such as current, voltage, welding speed, and gas velocity). These parameters were always considered and designed for achieving satisfactory mechanical properties and satisfying the requirements of assembly. However, since the relationship between welding parameters and input/output of inventory data is not clear, the inventory data needs to be re-collected when the process parameters are changed, which is tedious and time-consuming. Thus, a model is proposed for investigating this relationship, which can predict the consumption/emission of inventory data in welding. Moreover, the welding experiment was performed for verifying the effectiveness of the model. The results show that the consumption/emission of inventory data can be predicted and the deviation is changed in the range of 0 to 15%. Meanwhile, the carbon footprint of welding a concrete column framework was calculated for validating the applicability of the method, which demonstrated that the model can help engineers select the appropriate process parameters for achieving greener welding. [ABSTRACT FROM AUTHOR]

In this study, both the "softening" behavior and the effect of the partial rolling on characteristics of welded joints of 7075-T6 aluminum (Al) alloy with a laser-tungsten inert gas (TIG) hybrid welding process were studied. Partial rolling of welded joints is a kind of non-uniform deformation that is different from conventional rolling. In addition, the microstructure and properties of different welding zones are also different. It is found in this study that the microstructure and mechanical properties of different welding zones have undergone diversified evolution during the partial rolling process. Reduction of microhardness occurs in the fusion zone (FZ) and heat-affected zone (HAZ) of welded joints. The application of partial rolling makes the microhardness of FZ and thermal "softening" zone increase by 43.5% and 17.8%, respectively. The tensile strength of partially rolled joints reaches up to 87% of the base metal (BM), which is 18% higher than that of hybrid welded joints. By partial rolling process, the elongations of joints increase from 3.3 to 6.6%, and the fracture position transforms from FZ to HAZ. The dislocation density of partially rolled joints increases by 58.1% and 32.5% in FZ and HAZ, respectively. [ABSTRACT FROM AUTHOR]

Duplex stainless steels (DSSs) are widely used in the oil and gas industry. Unfortunately, fusion welds of these alloys might exhibit inappropriate microstructures, face cracks, and even failures during service. In this context, friction hydro-pillar processing (FHPP) is a suitable friction-based welding technique for repairing cracks in offshore engineering with promising outcomes. Accordingly, the present work evaluates the effects of FHPP on one of the most widely used DSS known as SAF 2205. The welded joint features were evaluated by optical microscopy and X-ray diffraction (XRD). Furthermore, mechanical properties were evaluated by microflat tensile tests and microhardness, and pitting corrosion resistance was analyzed by the ASTM G48 Method A. Intense grain refinement in the dual-phase microstructure induced by the FHPP led to the formation of a microduplex microstructure, which resulted in enhanced microhardness and mechanical properties. The pitting corrosion mainly occurred near the weld interface, for which the formation of Cr2N nitrides and the consequent decrease in pitting resistance equivalent number (PREN) was found to be a significant factor. [ABSTRACT FROM AUTHOR]

The herein study investigated defects, microstructure, and mechanical properties of two dissimilar welded joints between a twinning induced plasticity (TWIP) steel and the austenitic stainless steel (ASS) of grade AISI 304L. Dissimilar two-pass welded joints were performed through the pulsed gas tungsten arc welding (GTAW-P) process. Weld defects were characterized through radiographic testing, light optical (LOM), and scanning electron microscopy (SEM). Discontinuities (lack of fusion) formed in autogenous and filler metal joints were associated with distortion and uneven heat input distribution. Macrographs and radiograms of weld bead cross-section revealed that discontinuities were linear (in the autogenous weld) and rounded (in filler metal weld). The linear discontinuity induced hot cracking in the fusion zone (FZ). The energy-dispersive X-ray spectroscopy (EDS) line scanning performed on both dissimilar weldments indicated that the element diffusion process was produced from the base material (BM) to the FZ. The mechanical characterization demonstrated that the dissimilar welded joint with filler metal (ER309L-Si) had higher mechanical properties than the autogenous one. The Si addition to the welded metal and the heterogeneous grain size distribution in the TWIP steel side contributed to enhancing the mechanical strength and elongation to fracture. [ABSTRACT FROM AUTHOR]

The local residual stresses (tensile) generated on the surface of a component during its manufacturing (machining, welding) cause deterioration of its service life. To eliminate the negative effect of the stresses, the surface is treated using different methods (shot peening, laser shock peening, heat treatment, water jet peening). The application of ultrasonic technology to modify the continuous jet has been intensively researched for treating advanced stages of erosion. In this work, the modifications in the mechanical properties (tensile strength, micro-hardness and residual stress measurements) of AISI 304 Tungsten inert gas welded joints were investigated after ultrasonic pulsating water jet treatment in the incubation stage of erosion. This revealed that the initial tensile residual stress in the welded joints was converted to compressive stress after the treatment. The micro-hardness of the joints after the treatment increased about 40% in the heat affected zone in the near-surface region. Also, the tensile properties increased by about 37.8% and 34.6% in yield strength and ultimate strength, respectively. The microstructural examination of the near-surface region showed the grain reformation mechanism. [ABSTRACT FROM AUTHOR]

Welding costs associated with the laying of pipes for deepwater oil and gas extraction can be reduced using high interpass temperatures (ITs). However, a high IT can decrease the mechanical properties of the heat-affected zone (HAZ) of welded joints. With the use of high strength-toughness steels, this decrease may be an acceptable trade-off. Therefore, it is necessary to evaluate the influence of high ITs on the HAZ. The influence of the IT on the coarse-grain HAZ (CGHAZ) and intercritically reheated coarse-grain HAZ (ICCGHAZ) of an API 5L X70 pipe joint welded by gas metal arc welding was investigated. The welding was numerically simulated using finite element method software. The microstructure of the HAZ was predicted using thermodynamic simulation software. The CGHAZ and ICCGHAZ were also physically simulated and evaluated via optical microscopy and scanning electron microscopy, dilatometry, and Vickers microhardness and Charpy V-notch (CVN) impact tests. The increase in IT led to a decrease in CGHAZ microhardness but did not affect the ICCGHAZ. The CVN energies obtained for all ITs (CGHAZ and ICCGHAZ) were higher than that set by the DNVGL-ST-F101 standard (50 J). These results show that increasing the IT is an interesting and effective method to reduce welding costs. In addition, thermodynamic simulation proved to be a valid method for predicting the phases in the HAZ of API 5L X70 pipe welded joints. [ABSTRACT FROM AUTHOR]

Ferritic stainless steel has been applied frequently owing to its advantages such as good thermal conductivity, low coefficient of linear expansion, good stress corrosion resistance, and no Ni. However, the welding process will cause the grain size of the weld zone and the heat-affected zone to grow seriously, resulting in a decrease in the toughness of the welded joint. The paper discusses in detail the traditional and improved welding methods of ferritic stainless steel. These improved methods can effectively reduce the grain size or increase the penetration. The process of introducing electric and magnetic pulses can compress the arc, increase the weld penetration, stir the molten pool, refine the grains, and improve the strength and toughness of the weld. The future development direction of ferritic stainless steel welding is discussed at the end of the article. [ABSTRACT FROM AUTHOR]

In order to increase the bonding area of friction stir spot welding (FSSW) welds, AA6061-T6 aluminum alloy was successfully welded in swept friction stir spot welding (SFSSW) process. The orthogonal experiment design was used to investigate the effect of welding parameters (tool rotation speed (ω), welding traverse speed (F), and swept radius (R)) on the joint lap shear and cross-tension performances. SFSSW welds present typical defects of keyhole, flash, and hook. Multi-objective particle swarm optimization (MOPSO) was used to determine the Pareto front and compromise solutions for the maximum lap shear failure load (LSFL) and cross-tension failure load (CTFL) simultaneously. The optimum LSFL and CTFL were 6.916 and 4.11 kN obtained under the tool rotation speed of 2050.4 rpm, the welding traverse speed of 95.48 mm/min, and the swept radius of 2.96 mm. Compared to the initial solution, the LSFL and CTFL were increased by 83.76% and 34.77% respectively. Under optimal welding parameters, the lap shear and cross tension of SFSSW welds exhibit shear and nugget pull-out fracture modes, respectively. [ABSTRACT FROM AUTHOR]

The profile of the welding bead changes with the welding process parameters during the gas metal arc welding (GMAW) process, the top reinforcement disappears, and the penetration becomes sunken when the excessive welding heat input is applied. However, little research work is specially planned to cope with the studying of welding bead under these circumstances. A systematic study of the relationships among the welding process variables and welding bead geometric features as well as optimization of the welding quality is presented. The influences of the welding technological parameters (voltage, welding speed, and wire feed speed) on the welding geometry were revealed, and the models correlating them were established. The features of the weld bead geometry were composed of top reinforcement width, top reinforcement height, penetration depth, bottom reinforcement width, and bottom reinforcement height. By the desirability function approach, the recommendation of suitable welding parameters to meet the contradicting demands of multiple bead geometric features is fulfilled. The microstructure in different welding regions and mechanical performances of the welding joints produced by the verification test were also studied. [ABSTRACT FROM AUTHOR]

The high-speed welding of friction stir welding can improve the production efficiency of the equipment. The orthogonal experiment method was used to study the high-speed welding process parameters of aluminum alloy. The mechanical properties of welded joints were tested, and the influence of process parameters on welding quality was analyzed. A data collection platform was designed, and the spindle axial force of the spindle and the three-directional force of the worktable were collected during the welding process. The relationship between the process force and process parameters was studied. From the perspective of macroscopic metallography, the causes of welding defects and the influence of process parameters are studied. The research results show that the mechanical properties of the welded joint are optimal and meet the requirements of welding quality when the process parameters are the tool rotational speed of 5000 rpm, the welding speed of 3000 mm/min, and the plunge depth of 0.25 mm. [ABSTRACT FROM AUTHOR]

Determining the optimal parameters of the friction stir welding (FSW) process, which are suitable for a given joint configuration, remains a great challenge and is often achieved through extremely time-consuming and costly experimental investigations. The present paper aims to propose a strategy for the identification of the optimal parameters for a butt-welded joint of 3-mm thick quasi-pure copper plates. This strategy is based on FEM (finite element method) simulations and the optimal temperature that is supposedly known. A robust and efficient finite element model that is based on the Coupled Eulerian-Lagrangian (CEL) approach has been adopted and a temperature-dependent friction coefficient has been used. Besides, the mass scaling technique has been used to significantly reduce the simulation time. The thermo-mechanical behavior of the butt-welded joint was modeled using a Johnson-Cook plasticity model that was identified through lab tests at different temperatures. The results of the parametric study help to define the numerical surface response, and based on this latter one can find the optimal parameters, advancing (va) and rotational (vr) speeds, of the FSW process. This numerical surface response has been validated with good agreement between the numerical prediction of the model and the experimental results. Furthermore, experimental investigations involving x-ray radiography, digital image correlation method, and fracture surface analysis have helped a better understanding of the effects of FSW parameters on the welded joint quality. [ABSTRACT FROM AUTHOR]

In this study, friction stir welding of AA2014-O and AA2014-T6 aluminum alloy was performed at various welding speeds to evaluate the influence of temper conditions of base metal (BM) on the properties of the welded joints. The results showed strong influence of BM temper conditions on the microstructural morphologies and mechanical behavior of the welded joints. In the 2014-O joints, different zones of weld joint were diffused into each other and there was no clear interface between them. In 2014-T6 joints, there was a distinct demarcation between the nugget zone (NZ), thermomechanically affected zone TMAZ, heat-affected zone (HAZ), and BM. The welded joints in 2014-O temper condition showed increase in hardness in the vicinity of weld center due to grain refinement whereas, in 2014-T6, softening occurred in the same region by the dissolution of strengthening precipitates. The mechanical properties of 2014-O joints were equivalent to the base metal showing a 100% weld efficiency with fracture located in the base metal, whereas 2014-T6 welds exhibited about 70% weld efficiency with fracture located at the NZ/TMAZ interface. All the samples in mechanical testing fractured at retreating side (RS) which exhibited heterogeneity in the mechanical properties of the welded joints. Scanning electron microscopy fractographic analysis revealed a ductile fracture mode comprising of dimples in both temper conditions. The size and shape of the dimples were strongly dependent on base metal temper condition. [ABSTRACT FROM AUTHOR]

To pursue all the benefits of additive manufacturing of metals, recent studies have been aimed at assessing a proper welding technology to obtain large products by means of joining smaller parts. Indeed, at present, two or more parts must be manufactured individually and then assembled to produce the final component, when the size is incompatible with the building chamber or severe deformations arise during building. In this paper, laser beam welding is explored to join stainless steel components made by the process of laser powder bed fusion, in order to benefit from all the known advantages of this joining technique, aiming at producing a welding bead with homogeneous mechanical features with respect to the unwelded counterpart: a factorial plan is built, and the response surfaces are presented; then, the consolidated method of the desirability function is used to find the optimum condition of welding with reference to the current international standards, taking into account the geometry, the welding imperfections, and the extent of the heat-affected zone. The suggested optimum is eventually assessed via tensile testing and compared to the unwelded sample. [ABSTRACT FROM AUTHOR]

The influence of processing parameters and several combinations of natural as well as artificial aging on the mechanical properties of friction stir welded AA7075-T6 is analyzed in the present investigation. Different sets of welding parameters were employed to obtain joints characterized by different peak temperatures and thermal cycles. The joint obtained with the highest welding speed has guaranteed the best mechanical properties. The latter were shown to be strongly correlated to heat input, which influences both densities of dislocations in nugget zone grains and growth and dissolution of strengthening precipitates in the heat-affected zone that establish the mechanical characteristics of friction stir welds. On the other hand, artificial aging has drastically reduced the strain at break due to strain localization in the heat affected zones while it has proved its effectiveness in stabilizing the mechanical properties when exposed to further natural aging at room temperature. [ABSTRACT FROM AUTHOR]

The effects of different autogenous laser beam welding process parameters on the fusion zone (FZ) geometry, microstructure, and tensile mechanical properties were investigated for 5-mm-thick AA2198 alloy sheets. Porosity formation and hot cracking are observed for low laser powers and welding velocities, while the porosity level is essentially reduced with increasing laser power. The characteristic cross-sectional geometry of the welded joints changes with increasing laser power, taking shapes from narrow V shape to rectangular I shape, and the results are discussed based on the "closed" and "open" keyhole formation during laser beam welding. A methodology is exploited in terms of quantifying the geometrical dimensions of the cross-section of the FZ in order to promote the welded joints with a narrow width as well as with a rectangular shape. The optimal process parameters, leading to FZ close to the desirable rectangular I shape and with a low number of defects, are identified. Microstructural analyses reveal a pronounced transition zone in between the FZ and the heat-affected zone, which is subdivided into two narrow zones, the partially melted zone (PMZ) and the equiaxed zone. The narrow width of the FZ and PMZ, as well as the rectangular shape of the FZ, enables the autogenous welded joint to reach good tensile deformation properties. [ABSTRACT FROM AUTHOR]

Friction stir welding (FSW) is extensively used due to its low processing temperature, cost, and fast operation. The objective of this is research is to determine the optimum rotational and welding speed for welding of Al/Cu butt joint by FSW. FSW is used to produce a butt joint of pure aluminum with pure copper under two conditions; as received, i.e., not annealed, and as annealed. FSW is examined under three different rotational speeds: 910 rpm, 1280 rpm, and 1700 rpm, and each rotational speed is examined at three different welding speeds 16 mm/min, 29 mm/min, and 44 mm/min. The axial and longitudinal welding force components are measured during the welding process. Tensile and hardness tests were done to evaluate the mechanical properties, and the microstructural properties were also examined by XRD, SEM, and an optical microscope. The results showed that the welding force increased and the axial force decreased as the rotational speed increased and the welding speed decreased. Voids, tunnels, and cavities are noticed in case of a low rotational speed and a high welding speed; however, almost defect-free structure obtained at the highest rotational speed examined, i.e., 1700 rpm and the lowest welding speed of 16 mm/min, in case of Al and annealed Cu joint, but in case of non-annealed copper, it was different. It can be concluded that there is an optimal combination between the rotational speed and the welding speed in order to obtain the optimum mechanical and microstructural properties of the Al–Cu-welded joints, and that speed is a function of the material conditions. [ABSTRACT FROM AUTHOR]

Grade AH36 ship steel plate, frequently used in offshore applications, was joined underwater by shielded metal arc welding (SMAW) using two different types of electrodes (E6013 and E7014). The ship steel plate was also joined under atmospheric conditions in order to compare both joints in terms of mechanical and metallurgical properties. The E6013 rutile electrode was isolated by wrapping before use, and the underwater welding process was carried out at a depth of 8 m under the sea. The joints were first subjected to visual inspection and then liquid penetrant, ultrasonic, and radiographic tests were performed. In order to determine the mechanical properties of the joints, tensile, bending, and impact toughness tests were also carried out. In addition to the microhardness test on the weld zones, microstructural examination was also performed on the joints. As a result of the nondestructive tests, weld defects like slag remaining between the passes, gas porosities, burn-through, and lack of penetration were seen on the joints welded underwater with the two different electrodes. The study determined that these defects had significantly influenced the mechanical properties and width of the weld zone of the joints. [ABSTRACT FROM AUTHOR]

The present study centres on the effect of post-weld heat treatment (PWHT) on microstructure and mechanical properties of the deep penetration keyhole Tungsten Inert Gas (K-TIG) welded dissimilar joint between creep strength enhanced ferritic (CSEF) steel and austenitic stainless steel (ASS). The as-received normalized and tempered CSEF steel was joined with ASS in a single pass without using any filler materials and edge preparation. Detailed characterization across the welded joint was conducted using stereomicroscope, electron microscopy, energy dispersive spectroscopy (EDS), electron backscattered diffraction (EBSD), hardness test, tensile test and Charpy impact test. Results showed that PWHT had significant effect on the microstructure and mechanical properties of both the weld metal and CSEF steel heat-affected zone (HAZ), while it had little influence on the ASS side. By using proper PWHT, the hardness gradient across the welded joint could be mitigated and toughness in both the weld metal and the CSEF steel HAZ could be restored. 760 °C was considered the most appropriate PWHT temperature for such dissimilar joint in terms of the overall mechanical properties. The tensile properties of K-TIG welded joint after PWHT were comparable to both friction stir welded joint and laser and/or electron beam welded joint, indicating that deep penetration TIG welding technology may provide a good alternative for the nuclear industry. The correlation among welding thermal cycle, various heat treatment, microstructure evolution and mechanical properties was also analysed in detail. [ABSTRACT FROM AUTHOR]