Influence of welding parameters on temperature field characteristics during laser welding of TA15 by infrared thermography

Using an infrared thermographic technique,the temperature field during laser welding of TA15 is quantitatively measured and investigated. The influence of two welding parameters on the weld temperature distribution is analyzed and the mechanism is discussed. New conclusions are drawn that are different from conventional weld temperature distributions. For the face of the weld,changes in welding speed induce changes in the temperature distribution because of different heat inputs and the cooling effect. Similar temperature features in the welds are observed for all speeds,which exhibit a relatively low temperature area below 1 500 ℃ between the high temperature area in the position of laser incidence and the sub-high temperature area at the end of the molten pool. For the influence of laser power on the face of the weld,the temperature on the weld is higher for P = 2. 8 k W compared to P = 2. 0 k W,especially the temperature in the sub-high temperature area. However,for the temperature field of the back of the weld,the influence of welding speeds is quite different compared to the results for the face of the weld. The highest temperature does not locate in the keyhole area,but instead in the middle of the molten pool. And there are different temperature features at different speeds. When v =6 m/min,the temperature field is like a uniform color belt and the temperature along the center of the weld fluctuates between 300 and450 ℃. When v = 4 m/min,the transient temperature distribution is not uniform and is unstable at different times. However,for v =2. 4 m/min and lower speeds,the temperature field becomes stable. The influence of laser power on the back of the weld temperature field is more complex. The measured temperature does not increase with increasing laser power,which seems to conflict with the conventional thermal conduction theory. This may be related with the characteristics of the keyhole area.     

Study on laser welding of the tin-plate can body

Laser beam welding is a new technique for the food can making.Thisresearch studied the welding technology and parameters for the tin-plate can andtheir influences on welding speed and quality,investigated the microstructureand properties of the weld,analysed distribution of tin in the weld metal andcarried out the flanging test of the can body.The results show that laser weld-ing of the can body is characterized by high welding speed,fine appearance,good quality and stable and reliable process.This technology can fulfill the re-quirements of can making.     

YAG laser welding with surface activating flux

YAG laser welding with surface activating flux has been investigated, and the influencing factors and mechanism are discussed. The results show that both surface activating flux and surface active element S have fantastic effects on the YAG laser weld shape, that is to obviously increase the weld penetration and D/W ratio in various welding conditions. The mechanism is thought to be the change of weld pool surface tension temperature coeffwient, thus, the change of fluid flow pattern in weld pool due to the flux.     

Effect of laser characteristics on the weld shape and properties of penetration laser weld of BT20 titanium alloy

The laser beam welding of BT20 titanium alloy was conducted to investigate the weld shape, microstructures and properties. The full penetration weld characteristics produced by CO2 laser and by YAG laser were compared. The results show that the full penetration weld of YAG laser welding closes to “X” shape, and weld of CO2 laser welding is “nail-head” shape.Those result from special heating mode of laser deep penetration welding. The tension strength of CO2 laser and YAG laser joints equal to that of the base metal, but the former has better ductility. All welds consist mainly of the acicular a phase and a few β phase in microstructure. The dendritic crystal of CO2 laser weld is a littlefiner than YAG laser weld. According theresearch CO2 laser is better than YAG laser for welding of BT20 titanium alloy.     

CO2 laser welding of 5A06 aluminum alloy plates with different thicknesses

CO2 laser beam welding of aluminum alloys with different thicknesses was carded out. The influences of laser power and travel speed on the weld width were analyzed. The mechanical characteristics of tailor-welded blanks （TWB） with unequal thickness were evaluated using tensile tests, and the fracture appearance was inspected after tensile tests. The microstructure of welded joints was analyzed by SEM. The results indicate that this alloy can be laser welded with full penetration. All the tensile specimens fracture on the base metal, far from the weld in the transverse direction. The tensile strength and yield strength of TWB are 89% and 91.2% compared with the base metal. The percentage of the thinner plate in the specimen has an important effect on the transverse elongation. The transverse elongation of TWB approaches that of the base metal when the thinner plate has a large percentage in TWB specimen. The weld microstructure shows extra-fine grains. Dendrite exists around weld fusion line and the equiaxed grains in the weld.     

THE INTERFACIAL BEHAVIORS OF ALUMINUM MATRIX COMPOSITE IN DIFFERENT WELDING METHODS

Non-interlayer liquid phase diffusion welding (China Patent) and laser welding methods for aluminum matrix composite are mainly described in this paper.In the noninterlayer liquid phase diffusion welding,the key processing parameters affecting the strength of joint is welding temperature.When temperature rises beyond solidus temperature, the bonded line vanishes. The strength of joint reaches the maximum and becomes constant when welding temperature is close to liquid phase temperature. Oxide film in the interface is no longer detected by SEM in the welded joint. With this kind of technique, particle reinforced aluminum matrix composite Al2O3p/6061Al is welded successfully, and the joint strength is about 80% of the strength of composite(as-casted).In the laser welding, results indicate that because of the huge specific surface area of the reinforcement, the interracial reaction between the matrix and the reinforcement is restrained intensively at certain laser power and pulsed laser beam.The laser pulse frequency directly affects the reinforcement segregation and the reinforcement distribution in the weld, so that the weldability of the composite could be improved by increasing the laser pulse frequency. The maximum strength of the weld can reach 70% of the strength of the parent.     

Mechanism of laser beam welding for SiCp／6063Al composite

The laser beam welding technique was used to process SiC particles/6063A1 alloy matrix composite, the influence of laser power and welding speed on the properties of joint was studied. Decreasing the laser beam power with same welding speed can make the quantity and size of A14C3 decreased, and the interactive mechanism of the reinforcing particles and the matrix in the joint and the causes for joint strength reduction were analyzed.Increasing welding speed properly can improve the distribution of energy and restrain the interfacial reaction in the molten pool, and measures for improving were proposed.     

Effect of filler wire on the joint properties of AZ31 magnesium alloys using CO2 laser welding

Laser welding with filler wire of AZ31 magnesium alloys is investigated using a CO2 laser experimental system. The effect of three different filler wires on the joint properties is researched. The results show that the weld appearance can be effectively improved when using laser welding with filler wire. The microhardness and tensile strength of joints are almost the same us those of the base metal when ER AZ31 or ER AZ61 wire is adopted. However, when the filler wire of ER 5356 aluminum alloy is used, the mechanical properties of flints become worse. For ER AZ31 and ER AZ61 filler wires, the microstructure of weld zone slws small dendrite grains. In comparison, for ER 5356 filler wire, the weld shows a structure of snowy dendrites and many intermetallic compounds and eutectic phases distribute in the dendrites. These intermetallic constituents with low melting point increase the tendency of hot crack and result in fiagile joint properties. Therefore, ER AZ31 and ER AZ61 wire are more suitable filler material than ER 5356 for CO2 laser welding of AZ31 magnesium alloys.     

Temperature field simulation of laser-TIG hybrid welding

The three-dimensional transient temperature distribution of laser-TlG hybrid welding was analyzed and simulated numerically. Calculations were based on a finite element model, in which the physical process of hybrid welding was studied and the coupling effect of the laser and arc in the hybrid process was fully considered. The temperature fields and weld crosssections of the typical welding parameters are obtained using present model. The calculation results shou that the model can indicate the relationship of energy match between laser and arc to joints cross-sections objectively, and the simulation results are well agreed with the experimental results.     

Prediction of wire transfer behaviors in laser hot wire welding

With preheating wire by resistance heat, laser hot wire welding improves process stability and wire deposition efficiency, which gives broad potential applications in sugracing and narrow gap welding. It is a critical issue to control the temperature of preheated wire in this process. The temperature which is so high that the wire fuses outside molten pool or so low that the wire cannot melt timely in the molten pool, results in poor wire transfer stability and bad weld formation. This paper is purposed to calculate the wire temperature for the prediction of wire transfer behavior under various welding parameters. A heat conduction model is set up. Heat sources of the wire include resistance heat and reflected laser, and the heat source of molten pool is laser. The calculated temperature of wire part outside the molten pool is verified by infrared ratio temperature measurement. The calculated temperature of wire part in the molten pool is verified by measurement of the molten pool size. Analyzing the wire temperature and welding process observed by the high speed video imaging, the temperature criteria of wire transfer behaviors are obtained. Thus, numerical simulation of the wire temperature can be used to predict wire transfer behaviors in laser hot wire welding.     

Hybrid Laser-GMAW Welding of High Strength Quenched-Tempered Steels

High-strength quenched and tempered (HSQT) steels have been widely used in structural applications where light weight is of primary design interest.Gas metal arc welding is a common way to join QT steels.When GMAW is used to join the HSQT steel,multi-pass is usually required to achieve full penetration.In addition,weld crack is often observed because of HSQT steel’s high susceptibility to hydrogen embrittlement.In addition,due to the large amount of heat input from the arc,the heat affected zone is often softened.This reduces the ductility and strength of welds and makes the weld weaker than the base metal.In this study,a hybrid laser/GMAW process is proposed to produce butt joint for 6.5mm thick HSQT A514 steel plate.Hydrogen diffusion mechanism is first discusses for GMAW and hybrid laser-GMAW welding processes.Metal transfer mode during the hybrid laser/GMAW welding process is also analyzed.A high speed CCD camera with 4000 frame/second is used to monitor the welding process in real time.Welds obtained by GMAW and hybrid laser/GMAW techniques are compared and tested by static lap shear and dynamic impact.Effects of gap between two metal plates and laser beam/GMAW torch spacing on weld property are studied.By appropriately choosing these two parameters,crack-free butt joints with full penetration can be successfully obtained by the hybrid laser/GMAW welding process for HSQT A514 steel plate.     

Effect of welding speed on the material flow patterns in friction stir welding of AZ31 magnesium alloy

The clear zigzag-line pattern on transverse cross sections can be used to explain the formation mechanism of the weld nugget when friction stir welded AZ31 magnesium alloy without any other insert material is used as mark. It provides a simple and useful method to research the joining mechanism of friction stir welding. The rotation speed is kept at 1000 r/min and the welding speed changes from 120 mm/min to 600 mm/min. The macrostructure on the transverse cross section was divided into several parts by faying surface. The results show that the shape and formation procedure of the weld nugget change with the welding speed. There are two main material flows in the weld nugget： one is from the advancing side and the other is from the retreating side. A simple model on the weld nugget formation of FSW is presented in this article.     

Research on the properties of laser welded joints of aluminum killed cold rolled steel

Aluminum killed cold rolled steel used for automobiles was welded in this paper by using CO2 laser with wavelength 10.6μm.The experiment shows that high quality of welding can be realized at welding speed of 4500mm/min by optimizing the parameters.The strenth and hardness of laser welded joints for aluminum killed cold rolled steel increased compared to those of the base metal while the formability decreased.Forming limit diagram of joint material indicated that the laser weld seam should avoid the maximum deformation area of automobile parts during the designing period for the position of weld seam.     

Microstructure and mechanical properties of wrought magnesium alloy AZ31B welded by laser-TIG hybrid

The laser-TIG hybrid welding was mainly used to weld the wrought magnesium alloy AZ31B. The tech-nical characteristics of laser-TIG hybrid welding process was investigated and the interactional mechanism between laser and arc was discussed, at the same time the microstructure and mechanical properties of the wrought magnesi-um alloy AZ31B using laser-TIG hybrid welding were analyzed by optical microscope, EPMA, SEM, tensile ma-chine, hardness machine. The experimental results show that the presence of laser beam boosts up the stability of the arc during high speed welding and augments the penetration of weld； the crystal grains of magnesium alloy weld are fine without porosity and cracks in the best welding criterion and the microstructure of HAZ does not become coarse obviously. The elements profile analysis reveals that Mg content in the weld is lower than that of the base metal, but Al content is higher slightly. Under this experimental condition, the wrought magnesium alloy AZ31B joint can be achieved using laser-TIG hybrid process and the tensile strength of the joint is equivalent to that of the base metal.     

Friction stir welding of copper alloys

Copper plates ,brass plates and copper/brass plates were friction stir welded with various parameters. Experimental results show that the microstructure of the weld is characterized by its much finer grains as contrasted with the coarse grains of parent materials and the heat-affected zones are very narrow. The microhardness of the copper weld is a little higher than that of parent plate. The microhardness of brass weld is about 25% higher than that of parent material. The tensile strength of copper joints increases with increasing welding speed in the test range. The range of parameters to obtain good welds for copper is much wider than that for brass. When different materials were welded, the position of copper plate before welding affected the quality of FSW joints. If the copperplate was put on the advancing side of weld, the good quality of weld could be got under proper parameters.     

Study on stress and deformation of keyhole gas tungsten arc-welded joints

Keyhole gas tungsten arc welding(K-TIG)of Q345 low alloy steel plates was simulated by using SYSWELD software.The temperature field of the K-TIG welding process was simulated with three different combined heat sources and was compared with the weld profile that was obtained experimentally.The temperature field that was obtained by a combination of a double ellipsoid heat source on the upper half and a three-dimensional Gauss heat source on the lower half was similar to the real situation.The effects of plate thickness,gap and welding speed on the deformation and stress of the K-TIG welded joints were investigated by K-TIG welding numerical simulation.A reduction in the thickness of the weld plates reduced the z-direction deformation and transverse residual stress;an appropriate gap reduced the residual stress and an increase in the welding speed reduced deformation after welding,but did not help to control the residual stress after welding.     

Joint performance of CO2 laser beam welding 5083,H321 aluminum alloy

Laser beam welding of aluminum alloys is expected to offer good mechanical properties of welded joints. In this experimental work reported, CO2 laser beam autogenoas welding and wire feed welding are conducted on 4 mm thick 5083- H321 aluminum alloy sheets at different welding variables. The mechanical properties and microstructure characteristics of the welds are evaluated through tensile tests, micro-hardness tests, optical microscopy and scanning electron microscopy （SEM）. Experimental results indicate that both the tensile strength and hardness of laser beam welds are affected by the constitution of filler material, except the yield strength. The soften region of laser beam welds is not in the heat-affected zone （ HAZ ）. The tensile fracture of laser beam welded specimens takes place in the weld zone and close to the weld boundary because of different filler materials. Some pores are found on the fracture face, including hydrogen porosities and blow holes, but these pores have no influence on the tensile strength of laser beam welds. Tensile strength values of laser beam welds with filler wire are up to 345.57 MPa, 93% of base material values, and yield strengths of laser beam welds are equivalent to those of base metal （264. 50 MPa）.     

A Fully Coupled Thermomechanical Model of Friction Stir Welding(FSW) and Numerical Studies on Process Parameters of Lightweight Aluminum Alloy Joints

This paper presents a new thermomechanical model of friction stir welding which is capable of simulating the three major steps of friction stir welding(FSW) process, i.e., plunge, dwell, and travel stages. A rate-dependent Johnson–Cook constitutive model is chosen to capture elasto-plastic work deformations during FSW. Two different weld schedules(i.e., plunge rate, rotational speed, and weld speed) are validated by comparing simulated temperature profiles with experimental results. Based on this model, the influences of various welding parameters on temperatures and energy generation during the welding process are investigated. Numerical results show that maximum temperature in FSW process increases with the decrease in plunge rate, and the frictional energy increases almost linearly with respect to time for different rotational speeds. Furthermore, low rotational speeds cause inadequate temperature distribution due to low frictional and plastic dissipation energy which eventually results in weld defects. When both the weld speed and rotational speed are increased, the contribution of plastic dissipation energy increases significantly and improved weld quality can be expected.     

Predictive analysis of buckling distortion of thin-plate welded structures

The welding buckling distortions of thin-plated structures were investigated based on finite element methods.An engineering treatment method for predicating the buckling distortion was proposed.The equivalent applied thermal-load was used to simulate the welding residual stress,thus the calculation of complex welding distortion can be transformed into 3D elastic structural applied-load analyses,which can reduce the quantities of calculating work effectively.The validation of the method was verified by comparison of the numerical calculation with experimental results.The prediction of buckling distortion for side-walled structures of passenger train was performed and the calculation was in agreement with measuring results in general.It is shown that the main factors for producing the buckling are the intermittent fillet and plug weld during welding general.It is shown that the main foactors for groducing the buckling are the intermittent fillet and plug weld during welding the stiffened beams and columns to the panel.     

Study on DC welding parameters of Al-alloy shaping based on arc-welding robot

The Al-alloy arc-welding shaping system based on arc-welding robot is established, and the Al-alloy shaping manufacture is realized with the DC （direct current） gas metal arc welding （GMAW）. The research indicates that the metal transfer type of DC GMA W, heat input and the initial temperature of the workpiece greatly affect the Al-alloy shaping based on arc welding robot. On the penetration, the weld width and the reinforcement, the influence of welding parameters is analyzed by generalized regression neural network （GRNN） fitting.