Journal of Welding Science

In multi-pass welding, the heat-affected zone formed in each pass is subjected to another thermal cycle by the next pass. This problem locally changes the microstructure of the heat-affected zone depending on the position of each area relative to the melting line of the next pass, and the overlapping of the heat-affected areas will lead to complex microstructures. In this research, based on the practical conditions of pipe production in the factory, including submerged arc welding with four electrodes in two passes from the inside and outside of the pipe, the thermal cycles of the heat-affected zone were first analyzed. Simulation of thermal cycles of heating and cooling up to the peak temperatures of 950, 1150 and 1350 °C was performed in a dilatometer and the transformation behavior and microscopic structure were studied. Simultaneous modeling of precipitation dissolution and austenite grain growth was done. It was observed that the grain growth reaches a limit in 300 seconds. The main cause of grain growth at temperatures below and above 1150 °C, is the dissolution of fine and coarse deposits of niobium carbonitride, respectively. Also, the modeling of austenite formation and decomposition was done using the classic JMAK equation. It was observed that the parameter n does not depend much on temperature; while parameter k strongly depends on temperature, transformation amount and austenite grain size.
 

In Wire and arc additive manufacturing (WAAM) based on Gas metal arc welding (GMAW) is one of the methods of manufacturing metal layer by layer. One of this method's basic steps is predicting the welding geometry created in each welding step. In the current research, an experimental study was conducted in this field considering the effective parameters of welding geometry. For this purpose, three parameters of voltage, welding speed, and wire feeding speed were considered as effective parameters on the welding geometry of the process. The width and height of the weld bead was selected as the answer according to the type and application of the research. The least squares support vector machine was used to model the welding geometry in the process. The results obtained from the regression (R2) of train, test, validation, and total were 0.945, 0.793, 0.894, and 0.881 respectively. The comparison between the experimental data and the model data shows the significance of the proposed model.

This study aimed to investigate the effect of electron beam welding parameters on the microstructural characteristics and mechanical properties of the dissimilar joint between 17-4PH stainless steel and Ti6Al4V alloy. For this purpose, the welding of these two alloys was performed with an copper interlayer with a thickness of 1 mm. Two different welding speeds of 0.7 and 0.9 m/min with four levels of beam offset  (0, 0.2, 0.4 and 0.6 mm) from the center of the interlayer towards the steel were used to accomplish the experiments. The results show that by using the copper interlayer with thickness of 1 mm, the cracks caused by the formation of intermetallic compounds are removed from the weld pool. At the interface between the titanium and the weld pool, at the beam offset  of 0 and 0.2 mm, a solid solution of copper and TiCu2 intermetallic compounds is formed, while at the beam offset  of 0.4 and 0.6 mm, a solid solution of copper and TiCu intermetallic compounds is formed. The weld pool, at the beam offset  of 0 and 0.2 mm, consists of TiCr2+TiFe2 intermetallic compounds while at the beam offset  of 0.4 and 0.6 mm, solid solution of iron (α-Fe), solid solution of copper and TiCu intermetallic compounds are formed. The highest value of hardness is observed at the interface between the weld pool and the titanium alloy, as well as at the interface between the weld pool and the steel, which is due to the presence of intermetallic compounds with high hardness in these regions. By increasing the welding speed and the beam offset, the hardness value decreases, which is due to the reduction of brittle intermetallic compounds in the joint structure. By increasing the beam offset from 0.4 mm to 0.6 mm at the speed of 0.7 m/min, the shear strength increases from 180 MPa to 210 MPa and at the speed of 0.9 m/min, the shear strength raises from 230 MPa to 250 MPa. The welded sample with the welding speed of 0.9 m/min and the beam offset of 0.6 mm has the highest shear strength equal to 250 MPa. The failure in all samples happened at the interface between the weld pool and the titanium alloy, which shows that the weakest region in the joint is this interface.

In this study, gas-tungsten arc welding was used for the cladding of two high entropy alloys of AlCoCrFeNi (Al1) and Al0.7CoCrFeNi (Al0.7) onto plain carbon steel plates. The welding process was carried out at a welding current of 180 A and a welding speed of 1.4 mm/s. The microstructures, craking behavior, phase composition, and hardness of the clads were characterized using various methods, such as optical microscopy (OM), field emission scanning electron microscopy (FESEM), X-ray diffractometry (XRD) analysis, and microhardness measurements. The results indicated that the Al1 clad had a petal-like structure of the BCC and Cr-rich phases. Both intergranular and transgranular cracks were identified in the Al1 alloy, which were recognized to be solidification cracks. Thermal stress and brittleness of the BCC phase promote cracking of the Al1. On the other hand, in the Al0.7 alloy, in addition to the BCC phase, a new FCC phase was  formed with various Widmanstatten and dendritic morphologies in the clad microstructure and the Cr-rich phase was not observed. Furthermore, in this alloy with lower Al content, a crack-free clad was obtained. The crack prevention in the Al0.7 alloy was attributed to a combination of factors, including a decrease in the solidification range, formation of the FCC phase, and reduction in hardness.

In this study, the microstructure and mechanical properties of dissimilar resistance spot welding of AISI 430 steel and S500 MC steel were investigated. To carry out this research, Taguchi's L9 array was used to determine the number of samples and determine the range of variables of each sample, and after welding the samples and performing the shear tensile test, the sample with the highest tensile shear strength (13740 N) and the highest amount of fracture energy (102160 Joules) ), was considered as the best example; Also, the variables of this sample, i.e., welding current of 12 kW, welding time of 12 cycles, and electrode force of 3 kN, had the highest signal-to-noise values, and these values were chosen among the best range of variables among the proposed variables. Then, a microhardness test was performed on the welded sample with the above variables, and microstructural studies were performed by optical microscope and scanning electron microscope. The hardness of the weld zone was observed to be about 400 Vickers, and the microstructure of the weld metal consisted of ferrite, martensite, and Widmannstatten ferrite.
 

5xxx and 6xxx series alloys are among the most widely used aluminum alloys in various industries, including automobile, shipbuilding and aviation industries. In this research, the joint of two alloys AA6061-T6 and AA5052-H12 was investigated at 4 transmission speeds of 60, 90, 120 and 180 mm/min and 3 rotation speeds of 600, 800 and 1000 rpm. These investigations were carried out in the condition that each of the two alloys was placed in two progressive and regressive sides. The results of these studies showed that the highest tensile strength is when the AA5052 sample is placed on the advancing side and the transfer speed is 90 mm/min and the rotation speed is 600 rpm, and in this case, the final tensile strength value is equal to 197 MPa. In addition, the results showed that, generally, the tensile strength decreases with an increase in the transmission speed at a constant rotational speed, and with an increase in the rotational speed at a constant transmission speed, the tensile strength increases. In addition, microscopic and macroscopic examination of the sections of all samples was performed and various areas and defects were examined. According to the investigations carried out on the microstructure, the grain size in the weld nugget compared to the base metal, HAZ and TMAZ decreases. The grain size in HAZ is the largest in all samples, and this causes a decrease in weld strength in this zone.

In this study, non-homogenous welding of nimonic 75 superalloy to Monel 400 with 1 mm thickness was investigated with pulsed Nd:YAG laser welding. The mechanical properties of the joint were analyzed with optical and scanning electron microscope, X-ray diffraction, micro-hardness test and tensile test. In the case of non-homogeneous welding of Nimoinc 75 superalloy to Monel 400, defects such as liquation cracks and porosity in the welded samples were observed. these defects were removed with increasing the preheating temperature and decreasing the heat input. The results showed the voltage, pulse width, pulse frequency and welding speed should be selected as 500 volts, 9 milliseconds, 3 Hz and 0.9 mm/s respectively to reach the proper penetration depth. Also, the investigations show that the welding structure is composed of austenitic matrix containing columnar dendrites and some cellular areas. The mechanical properties of the weld metal were reduced after joining and segregation causes a change in the amount of elements and the appearance of intermetallic compounds in the spaces between dendrites and cells. All non-homogeneous samples broke during the tensile test from the weld metal area.

In this study, we employed the active TIG method with ultrasonic vibration (UV) for welding 316L steel. Throughout the active tungsten inert gas (A-TIG) welding process, a high-frequency ultrasonic generator produced high-intensity acoustic waves at an optimal frequency of 20.3 kHz and a vibration amplitude of 8 micrometers. These waves were directed into the molten weld pool, covered by SiO2 nanoparticles serving as an activating flux. The effect of UV and nanoparticles on weld geometry and weld microstructure was analyzed and compared with conventional TIG welding proces. The results indicated that the use of nanopowder not only increased weld penetration by approximately 17.5% but also reduced the Weld Bead Width (WBW) by 28% compared to Conventional TIG. These values increased by 25% and decreased by 35%, respectively, in the presence of ultrasonic waves. Additionally, the introduction of nanomaterials into the molten pool led to finer grains. The ultrasonic waves played a crucial role in ensuring the uniform distribution of these nanomaterials in the melt, ultimately resulting in an enhanced microstructure of the weld.