Welding Temperature Field Research Articles

Residual stress and simulation of 304–430 stainless steel dissimilar laser-welded joints incorporating materials heterogeneity

AbstractAn Nd:YAG laser device is used to conduct laser welding for a 1 mm austenitic stainless steel plate and a ferritic stainless steel plate. A finite element model of the shear punching test is constructed to generate the maximum shear strength in the weld, and the finite element model of laser welding is created using the welding temperature field. The hole drilling test result and the residual stress generated by two algorithms (Nonuniform-material and uniform-material) are compared. Results show that a drop-off of residual stress in the central area of the welded joint is observed when materials heterogeneity is disregarded. When materials heterogeneity is considered, the residual stress curve indicates smooth transition. The value of the latter appears reasonably similar to the experimental value. Therefore, this solution is advantageous in terms of residual stress simulation in dissimilar welded joints and does not critically affect residual deformation.

Laser welding of 6082 aluminum alloy to TC4 titanium alloy via pure niobium as a transition layer

A Ti/Al joint with an Nb transition layer was obtained, where aluminum alloy and Nb sheet partially melted to form the weld and diffusion bonding was formed at Ti/Nb interface. The remaining transition layer Nb acted as a diffusion barrier between TC4 titanium alloy and 6082 aluminum alloy thus successfully prevented the formation of brittle TiAl, TiAl2 and TIAl3 phases. A flat Ti–Nb diffusion zone composed of (Ti, Nb) solid solution was formed at Ti/Nb interface, while a narrow Al–Nb reaction zone was formed at the Nb/Al–FZ (aluminum alloy fusion zone) interface with the main microstructures of NbAl3, Nb2Al and Al-based solid solution. The simulation of welding temperature field and thermal cycle curve by finite element software was conducted to provide theoretical data support for clarifying the formation of the joint and interface reaction mechanism. The mechanical property of the joint was determined by the Al–Nb reaction zone which could be witnessed by observing the fracture location and hardness distribution of the joint. The joint fractured at the Al–Nb reaction zone and adjacent Al–FZ with the maximum tensile strength of 288.97 MPa.

Improved Recrystallization Resistance and Welding Properties of Cold-Rolled Al-Mg Alloy Sheets by Microalloying with Sc and Zr

The effects of Sc and Zr element on the recrystallization behavior and microstructure evolution of Al-Mg alloy had been researched in this paper, and meanwhile, the microstructure and mechanical properties of the friction stir welding joints were also analyzed. The results show that the recrystallization and grain growth behavior of Al-Mg-Sc-Zr alloy can be inhibited effectively by microalloying with Sc and Zr. Compared with Al-Mg and Al-Mg-Zr alloys, the recrystallization start temperature and finish temperature of Al-Mg-Sc-Zr alloy increase significantly, and the strength of alloy sheet which subjected to stabilizing annealing is increased by more than 50MPa. Moreover, the recrystallization softening effect of the welded joints microstructure, which caused by the welding temperature field and welding heat input, can be weaken by microalloying with Sc and Zr, the width of recrystallization zone is reduced, the microstructure and properties of the welded joints are improved. The friction stir welding coefficients of Al-Mg-Sc-Zr alloy increases to 86.9%.

Experimental investigation of the effect of laser parameters on the weld bead shape and temperature distribution during dissimilar laser welding of stainless steel 308 and carbon steel St 37

Fiber laser fusion welding of two applicable alloys including 308 stainless steel and low carbon steel (St 37) was performed to assess the formation mechanism of the weld bead and temperature field near the fusion zone. In this research, some parameters including welding speed, laser power, nozzle distance, and beam deviation of the laser beam were determined as the main parameters. The results showed that the effect of the nozzle distance on the temperature field was higher than that of the welding speed and laser power. It was also observed that increasing the nozzle distance caused more absorption of the beam in the parts and there was an almost two-fold increase in the dimensions and volume of the weld bead. The measured temperature near melt pool was decreased about 120 °C for st37 while a reduction about 30 °C for stainless steel according to increasing nozzle distance from 3 to 7 mm. Unlike carbon steel, the temperature of the stainless steel was clearly decreased at the nozzle distance to the highest point. By increasing the welding speed, the temperature around the molten area was decreased. The beam deflection parameter showed the effect of the temperature gradient index on changes and a temperature decrease was observed by creating a distance from the location of thermocouples. Increasing laser power from 300 to 400 W created wider weld bead about 40% and higher temperature about 40 °C for stainless steel in comparison to st37.

Identification of butt welded joint penetration based on infrared thermal imaging

In the gas metal arc welding (GMAW) process, the intense arc light and high temperature conditions bring great difficulties to the online identification of welded joint penetration. At present, visual sensing method and arc sound detection method are mainly used to identify the welded joint penetration, there are few reports about using welding temperature field to identify welded joint penetration. In this paper, a method of using infrared thermal imaging to identify the welded joint penetration was proposed, a single infrared thermal imager was used to monitor the welding temperature field in real time, the solidified weld area outside the weld pool area was selected as the region of interest (ROI) for real-time temperature measurement. The temperature field distribution features of ROI were extracted, taking these features as input and welded joint penetration as output, the identification model for welded joint penetration was established based on artificial neural network (ANN). The identification accuracy and generalization ability of the identification model were verified by a variety of butt welding experiments, the experimental results show that the identification accuracy of the established model for three penetration states of welded joint is higher than 96%, which can be applied in the online identification of welded joint penetration.

Experimental analysis of temperature field and distortions in multi-pass welding of stainless cladded steel

The stainless clad steel materials (particularly A283-Gr-C hot-rolled to austenitic stainless steel plate SA240 TP 316L) have become widely used in the fabrication of heat exchangers, pressure vessels, and other components owing to their very interesting properties and low production cost. These cladded materials are mostly joined using multi-pass welding techniques. The temperature distribution that supervenes during welding affects the microstructures and the mechanical properties and may generate residual stresses in the heat-affected zone of the welded plates. Since limited experimental data are available in the literature regarding the complex cases of multi-pass welding of cladded steel materials, a thorough experimental study was performed in order to evaluate the temperature distribution on the welded plates. In fact, eight K-type thermocouples were fixed at different distances from the weld centerline in order to record the temperature evolution along longitudinal, transversal, and thickness directions during the welding process. Due to the unavoidable effects of the generated heat fluxes that always follow the welding, several dimensional changes were occurred on the welded plates. In this study, the longitudinal shrinkage and the angular distortion generated during the welding process by the effect of the heat fluxes were investigated. Then, tensile and bending tests were performed in order to check the welded plate reliability. It was found that (i) the welded joint presents a higher mechanical tensile strength than the parent metal and (ii) no separations, fractures, or tearing appear on the weld joint surface after the bending test.

Mechanism and optimization of activating fluxes for process stability and weldability of hybrid laser-arc welded HSLA steel

The effects of activating fluxes on weld bead morphology, arc behavior, electrical signals, and temperature field were investigated. Real-time weld pool dynamics, electrical signal waveforms, and temperature contours were obtained by high speed camera, real-time electric signal acquisition card, and infrared thermal camera. The additions of SiO2, TiO2, ZnO, and Fe2O3 not only improved the weld formation and penetration depth but also reduced the welding voltage and increased welding current. Decomposition and evaporation of activating fluxes produced oxygen caused arc constriction and increased the laser efficiency. The effect of MnO2 was little. CaO and B2O3 dramatically deteriorated process stability since CaO and B2O3 gave rise to droplet transfer mode changing from spray transfer to short-circuit/ large globular repelled transfer.

Micro structure and finite element analysis of fitness and unfitness square butt joint of aluminium based nano composite plates

The main objective of this paper is analyzed the welding temperature and stress field distribution in aluminum based nano composite plates by varying the different welding parameters of Tungsten Inert gas welding (TIG). The residual stresses of the welded butt joint and unfitness joints of Aluminium based Nano Composite (ABNC) plates are predicted by conducting tensile test; as the results are shown with the unfitness of the weld joint, which had a greater impact on the welding residual stresses than that of the interval. The simulated and experimental results are compared with each other samples. With the help of a mathematical model, the effect of welding parameters such as heat input of the weld, preheating of the work piece and moving velocity of heat source on weld penetration in moderately thick plates are discussed in this experimental work. Hence the steady state temperature profiles of welded ABNC plates are solved by finite difference method. The simulated values are verified with the experimental results in addition to comparison with that of previous experiment result. The predicted values from the proposed ABNC models are compared favorably with the experimental data of welded ABNC samples.

Simulation and Experimental Study on Temperature and Flow Field in Friction Stir Welding of TC4 Titanium Alloy Process

Simulation and Experimental Study on Temperature and Flow Field in Friction Stir Welding of TC4 Titanium Alloy Process

The Microstructure and Mechanical Properties of Dual-Spot Laser Welded-Brazed Ti/Al Butt Joints with Different Groove Shapes.

Laser welding-brazing was performed to join Ti and Al together. The dual-spot laser beam mode was selected as the heat source in this study. Ti-6Al-4V and 6061-T6 Al alloys were selected as the experimental materials. Al-12Si welding wire was selected as the filler material. The effect of groove shape on the weld appearance, microstructure, temperature field, and mechanical performance of Ti/Al welded-brazed butt joints was investigated. The interfacial intermetallic compound (IMC) layer at the Ti/Weld brazing interface was inhomogeneous in joints with I-shaped and Y-shaped grooves. In Ti/Al joints with V-shaped grooves, the homogeneity of temperature field and IMC layer was improved, and the maximum thickness difference of IMC layer was only 0.20 μm. Nano-sized granular Ti7Al5Si12, Ti5Si3, and Ti(Al,Si)3 constituted the IMCs. The tensile strength of Ti/Al joints with V-shaped grooves was the highest at 187 MPa. The fracture mode transformed from brittle fractures located in the IMC layer to ductile fractures located in the Al base metal, which could be attributed to the improvement of the IMC layer at the brazing interface.

Numerical simulation of laser-arc hybrid welding of high strength steel

The numerical simulation of high-strength low-alloy steel in the welding temperature field is carried out. The SYSWELD special welding analysis software is used to establish the geometry model of the butt joint of the flat Y-shaped groove. The temperature field of single-layer and multi-layers welding of 12 mm high-strength low-alloy steel provides a theoretical basis for the welding process and has engineering practical value.

Effect of welding sequence on residual stress and deformation of Mg alloy fillet welds

In order to investigate the effect of welding sequence on stress distribution and deformation of Mg alloy fillet welds, DE-GMAW modified Gaussian heat source model established by MSC. Marc software was applied to the numerical simulation analysis of welding temperature field and stress field and proved by measurement of residual stress by blind hole method. The results indicated that the deformation and residual stress were lowest according to the sequence of welding fillet welds from the head of cylinder to the end on one side first and then welding in the opposite on the other side. The trend of residual stress measurement results was consistent with numerical simulation analysis results with 10% error, which provided theoretical support for stress distribution and deformation control of Mg alloy fillet welds.

Numerical Simulation and Experimental Investigation on Electron Beam Welding of Spray-Formed 7055 Aluminum Alloy

The spray-formed 7055 aluminum alloy is welded by electron beam welding. Combined with the numerical simulation of a welding temperature field, the effect of different welding procedures on the microstructure and mechanical properties of welded joints is investigated in this study. Results show that the joints with good properties can be obtained under proper welding procedures. The microstructure analysis demonstrates that the fusion zone mainly consists of equiaxed grains, while a fine equiaxed grain zone is formed near the fusion line. There are mainly α(Al), MgZn2, Al2CuMg, and Mg32(Al,Zn)49 phases in the weld metal. The morphology of the weld can be improved by modification welding after the first bead welding, which is also advantageous to the mechanical properties of a welded joint. In the as-welded condition, compared with that of the base metal, the hardness of the weld zone decreased to a certain extent. The maximum tensile strength of a welded joint reaches 371.7 MPa. There are many dimples on the tensile fracture surface of a welded joint, and it dominantly presents the characteristic of ductile fracture. The simulated molten pool is consistent with the experimental weld morphology, and the reliability and accuracy of the simulation analysis are verified.

Influence of tool tilt angle on heat transfer and material flow in friction stir welding

The tool tilt angle is an important factor determining the microstructure and properties of friction stir weld joints. In this study, both experiments and numerical simulations are made to investigate the influence of tool tilt angle on heat generation, temperature field and material flow behavior in friction stir welding (FSW). The tool tilt angle induced non-contact area between tool shoulder and workpiece is determined under different sets of process parameters, and numerical simulations are conducted. It is found that the crescent-shaped uncontacted area gets larger when either the tool rotation rate or the welding speed increases. Compared with the case of 0° tool tilt angle, a tilted tool produces stronger forging effect at trailing side, a larger region of high temperature at the trailing advancing side, a higher peak temperature and more intensified material flow around the tool. With consideration of tool tilt angle and pin thread in the new model, the predicted peak temperature at tool/workpiece interface and the thermo-mechanically affected zone match well with the measured ones.

Underlying reasons of poor mechanical performance of thick plate aluminum-copper alloy vacuum electron beam welded joints

As a light-weight and high-strength structural material, aluminum alloy has become an irreplaceable metal material in the aerospace field. In this paper, 25 mm thick Al-Cu alloy (2A12) was welded by electron beam. The welded joints softened leading to the hardness and tensile strength of the joint decreased. In view of the decrease of mechanical properties, the microstructure in different areas of the welded joint was analyzed. At the same time, the formation mechanism of rosaceous microstructures and eutectic structures was revealed. The influence of impurity elements on the joint was analyzed. In addition, the reason of joint strengthening effect weakening was explained combining with welding temperature field and the precipitation model of competition.

Experimental investigation of temperature field and fusion zone microstructure in dissimilar pulsed laser welding of austenitic stainless steel and copper

Laser dissimilar welding of copper/ stainless steel was experimentally conducted to investigate the process parameters influence on the temperature field and formation mechanism of melt pool microstructures. The experimental approach is to estimate the influence of the Nd:YAG pulsed laser process parameters (e.g welding speed, laser power, focal length and laser beam deviation) on the temperature gradient and the resultant metallurgical aspects of the melt pool such as Solidification cracking, copper particle diffusion and microstructure of the fusion zone. Creating the appropriate temperature gradient during welding plays a crucial role to effectively control solidification cracking at the fusion zone in order to reduce heat conduction effect of the copper. Increasing welding speed from 2 to 6 mm/s not only reduces the temperature about 50 °C but also decreased the fusion zone cracking significantly. Evidently, increasing the laser power from 240 to 260 W transmitted the fusion zone cracks toward the stainless steel base due to creating higher temperature about 230 °C and 150 °C for steel and copper respectively. Therefore, higher discrepancy of the temperature field between copper and steel clearly changed the place and pattern of cracks propagation. The EDS analysis of the fusion zone confirms diffusion of copper particles inside the weld pool. The temperature measured near the molten pool region showed that clear discrepancy at the temperature gradient of the melt pool at the copper and stainless steel side has increased the possibility of cracking the stainless steel fusion zone. Also, high temperature gradient for compensating copper high rate of cooling could lead to excessive copper ablation or even diffusion of copper elements into the stainless steel fusion zone.

Finite Difference Model of Temperature Fields in Linear Friction Welding

The finite-difference model for calculating temperature fields in linear friction welding is described. A feature of the model is the heat transfer across the friction surface accounting, which makes it possible to study the case of welding parts with different physical and mechanical properties. Modelling results, obtained for combination of VT6 and VT8-1 titanium alloys welding, are described. An assessment of the temperature field and heat transfer during the parts from VT6 and VT8-1 welding is given.

Investigating the effect of process parameters on the temperature field and mechanical properties in pulsed laser welding of Ti6Al4V alloy sheet using response surface methodology

Laser welding of Ti6Al4V alloy with 3 mm sheet thickness was studied. The effect of process parameters including laser peak power, pulse duration, and welding speed was systematically investigated on the temperature field of the fusion zone, tensile strength and elongation. The laser welding experiments were performed based on central composite design and response surface method to develop multiple regression models. The accuracy of the regression models was adequate through analysis of variance to make correlations between input parameters and responses. It was found that laser peak power and pulse duration had remarkable effects on weld tensile strength melt pool dimensions and elongation rate. Increasing the laser peak power from 1800 to 2200 W, clearly increased the tensile strength about 300 Mpa. Both the elongation rate and melt pool dimensions significantly increased with augmentation of laser peak power. Increasing welding speed from 3 to 7 mm/s decreased the temperature of the region near the fusion zone from 370 to 130 °C. Increasing welding speed significantly reduced the mechanical strength for 3 mm thickness about 20 percent. On the contrary, this reduction effect is negligible for the elongation rate about 10 percent due to creating high rates of martensitic structure and brittle properties of the weld.

Modeling three-dimensional rough surface and simulation of temperature and flow field in laser transmission welding

• A numerical model for rough surface is established by applying the anisotropic 3D surface reconstruction method. • A 3D FEM model considering rough surface is developed to simulate and analyze the temperature field, molten pool geometry and flow fields in the LTW process. • The temperature of the contact surface between the transparent and absorbent layer is discontinuous, which is consistent with the incomplete contact under real welding conditions. The traditional Laser Transmission Welding (LTW) simulation method assumes that the welding contact interface is smooth. However, the actual welding interfaces exhibit a large number of rough surfaces. The mismatch may decrease the accuracy of the traditional finite element model (FEM). Thus, this work aims to establish a three-dimensional (3D) FEM model considering the rough surface. Numerical model for 3D rough surface of welding specimen is established. The distribution of molten pool area, temperature and flow field coupling are discussed. Then, a series of experiments were set up to obtain the weld width to verify the model. The results show that the temperature of the contact surface between the transparent part and the absorbent layer is discontinuous, which is consistent with the incomplete contact of the contact surface under real welding conditions. The error of weld width values between the simulated and experiment is smaller, which also confirm that the established model is more precise.

Study and application of numerical simulation method for welding process based on Marc

The bridge and shipbuilding industry have been troubled by the issues of increased production costs and delays due to the welding residual stress and deformation. It is of great practical significance to study welding residual stress and deformation. In this paper, the FEM software Marc is used to carry out numerical simulation of plate pass welding, and the welding temperature field and residual stress distribution after welding are obtained. The simulation calculation results are qualitatively analyzed.