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2015  Vol. 36  No. 10

Abstract:
To meet the demand of improving welding productivity through increasing welding current for high efficiency welding, the method based on parallel connecting of inverter power for pulsed MIG welding is presented. A DSP based digital control system for high-power pulsed MIG welding is introduced, which is based on digital signal processor TMS320LF2407A. By taking advantage of rich peripherals and excellent control performance of DSP, the goal that a single DSP control two inverters was realized, which ensured the high-power output of welding power. The results show that the developed parallel high-power inverter power for pulsed MIG welding has the ability to accomplish the high efficiency welding process with high current output, and the welding performance is stable, the appearance of weld is good.
Abstract:
The 7075 aluminum alloy sheet with thickness of 10 mm was welded by VPPA vertical welding process using ER5183 welding wire. The microstructure and mechanical properties of the welded joint were comparatively investigated by means of optical microscope (OM),scanning electron microscope (SEM), X-ray diffraction (XRD),universal tensile testing machine and micro-hardness testing machine. Experimental results indicate that the finally welded products exhibit an excellent welding appearance, and have no obvious fusion zone, the microstructure of heat-affected zone is coarse, the hardness value of welded joint and heat-affected zone are 120.9 and 125.9, respectively. The tensile strength of the welded joint reaches 367.6 MPa, which is nearly 62.4% of the parent metal and corresponds to the weakest segment of the welded joint.
Abstract:
The oxide dispersion strengthened (ODS) steel was joined by friction stir welding (FSW) technique and the optimum friction welding parameter was determined. High quality of welded joints can be obtained when the traverse speed and rotation speed are 150 rpm and 30 mm/min, respectively. Microstructure observation results show that remarkable onion structure appeared in thermo-mechanically affected zone of the advanced side (AS-TMAZ). Equiaxed grain structure was achieved in stir zone. The grains in heat affected zone are quite different from that of the base material. High temperature tensile properties of FSW ODS steel were compared to those of as-received ODS steel and the results indicate that FSW process resulted in a large degradation of the joint strength, while the strength of the joint increases followed by post weld heat treatment at 1 150 ℃ for 1 hour.
Abstract:
In this paper, the influence of heat input on welding temperature field and microstructure of maraging steel C300 TIG (Tungsten Inter Gas Welding, TIG) welded joints were carried out preliminarily. The results indicate that, under these experimental conditions, as the heat input increased, the weld penetration and weld width both increased. The dark band zone (HAZ 2, Heat affected zone 2) widened and was further away from the weld center line, as well as that the difference between the top and bottom of dark band zones was also increased. The distance between 760 ℃ isotherm and the heat source basically satisfies the relationship of r=0.465E+0.987 (mm). The cellular grain size also increased with the increase of the heat input and basically satisfies the relationship λ2=3.324×E2/3 (μm), and with high applicability in the case of small heat input. Under best welding heat input, not only a good weld shape can be obtained but also a higher degree of agreement between the calculated value and the measured one.
Abstract:
In ultrasonic TOFD (time of flight diffraction) D-scan image, the lateral wave overlaps with the near surface defect wave, which makes it difficult in the testing of shallowly buried defect. In order to solve this problem, a defect testing method based on background clutter suppression is presented. The energy distribution in the image is calculated to determine the clutter wave component. Then the clutter wave is removed to separate the defect signal from the background image. The mathematical model for TOFD signal is established. The principle of clutter wave suppression method is described in details. Artificial defects contained block and the weld test pieces were made and tested. The collected D-scan images with clutter wave suppression were processed. The results show that using the proposed method, the background clutter wave can be removed from the D-scan image and the defect signal can be extracted from the overlapped waves effectively. The defect detection range for TOFD can be improved using the proposed method.
Abstract:
In this paper, a finite element model of fiber laser welding-brazing process for steel/Al dissimilar metals was established by ANSYS. The accuracy of the finite element model was verified by fusion zone boundary criteria. The stress field and welding deformation were simulated based on this mode. The results showed that the peak tensile stress along welding direction appeared on the lower surface of the steel and near the welds behind the heat source. This peak tensile stress increased continually with the welding process continued and it reached a maximum of 203 MPa when welding finished (13s). The stress distribution was asymmetric and there was high stress gradient close to the heat source. The maximum deformation of the specimen was 0.882 mm.
Abstract:
A new seam-tracking method based on dynamic trajectory planning for mobile welding robot is proposed in order to improve the response lag of the mobile robot and the high frequency oscillation in seam tracking. By using front-placed laser-based vision sensor to extract dynamically the location of weld seam in front of torch, the trend and direction of the weld line is roughly obtained. Than the robot system autonomously performs trajectory planning dynamically based on the isometric approximation model. Arc sensor technology is applied to detect the offset during welding process in real time. And the dynamic compensation of weld path is done in combination with the control of mobile robot and the executive body installed on it. Simulation and experiment results demonstrate that the method can effectively increase the stability of welding speed and smoothness of weld track and hence the weld forming in the curve and corner is improved.
Abstract:
The effect of annealed Cu substrate on the microstructure of solder joints was investigated. Experimental results showed that only scallop-shaped Cu6Sn5 was observed at the interface of Cu/Sn58Bi/Cu after reflowing and aging for 24h. A bi-layer structure consisted of Cu6Sn5 and Cu3Sn was formed at interface and the thickness of IMC layers increased with the increase of aging time. With the long aging process, Bi particle segregation was producedat the interface of solder joint of un-annealed Cu substrates. However, Bi particle segregation was hardly observed at the interface of solder joint of annealed Cu substrates. Compared with the growth rate constants of IMC layer of interface of annealing and un-annealing Cu and solder, it was demonstrated that annealing treatment on Cu substrate could effectively retard the growth of interfacial IMC layers, it mainly attributed to that the annealing treatment on Cu substrate could effectively eliminate inner-stress and defects, reducing the diffusion of Cu atoms and retarding the growth of IMC.
Abstract:
The 3D finite element analysis model of plastic ball grid array(PBGA) stacked lead-free solder joints with underfills was developed. By using ANSYS the finite element analysis was performed based on the model with random vibration. The influences of PBGA assembly structure, solder joint material, underfill elastic modulus and underfill density on PBGA stacked lead-free solder joint stress and strain under random vibration load were respectively studied. The results show that comparing to the no-underfill stacked solder joints the stress and strain in the stacked solder joint can be effectively reduced under random vibration load. When other conditions being equal, for Sn95.5Ag3.8Cu0.7, Sn96.5Ag3Cu0.5, Sn-3.5Ag and Sn63Pb37, the lead free Sn-3.5Ag stack solder joint has the minimum stress and strain while the lead-free SAC305 stack solder joint has the maximum stress and strain in the solder ball. The stress and strain in the lead-free stacked solder was reduced with the increase of underfill elasticity modulus. With the increase of the underfill density, the stress and strain in the stacked lead-free solder joint increased correspondingly.
Abstract:
The pitting, intergranular and general corrosion test in the nuclear power simulation water on laser welded joint at different welding speeds, as well as stress corrosion cracking (SCC) test in high temperature and high pressure water were carried out. The results indicated that with the increase of welding speed, the passive current and pitting corrosion potential increased. At the same weld joint, the heat affected zone exhibited the best pitting and intergranular corrosion resistance, followed by weld joint, and the weld zone showed the worst performance. SCC at the lowest welding speed easily took place, and the SCC crack generally initiated and propagated from weld root of the HAZ zone.
Abstract:
Local heat treatment was performed on the clinched joints by building an experiment apparatus for local heat treatment. The metallographic specimens were prepared to observe the microstructure of the specimen with heat treatment. The microhardness was measured on the specimens with heat treatment or without. The influence of heat treatment on the static tensile strength of clinched joints was analyzed by comparing two groups of specimen with heat treatment or the one without heat treatment. The results showed that the material of the clinched joints had martensitic structure after heat treatment. The static strength of the clinched joints was promoted largely owing to the martensitic structure compared to the ferrite and pearlite structure of clinched joints had not been treated.
Abstract:
Based on the home-made multiphysics field coupling device, investigation was carried on the fracture behavior and the growth of intermetallic compounds (IMC) at the interface between Sn-3.0Ag-0.5Cu lead-free solder and Cu substrate. The results show that in the multiphysics field and 30-150 ℃ thermal fatigue cycles,the more the thermal fatigue cycles, the faster the IMC grows in the same aging temperature. The morphology of IMC changes from the scallop shape into the layered shape in a shorter cycle time. The growth of IMC is slowing down after 400 cycles. When the cycles are 600, the void gathered and grow up, resulting in interface cracks and fatigure failure. With the increasing thermal cycles, the shear strength of joint drops quickly and it also has a tendency to brittle fracture.
Abstract:
Butt joining of titanium alloy to aluminum alloy Al2024 was conducted using pulsed current gas tungsten arc welding. The influence of pulsed current on Ti/Al interfacial microstructure was studied. The microstructure of Ti/Al interface with different locations were investigated along the depth direction of joint. Element distribution cross the interface was analyzed by EDS. Phase constituent near the interface were determined by XRD. The results indicated that Ti/Al dissimilar alloys were successfully joined using pulsed current gas tungsten arc welding. Titanium was partially melted during welding and a welded-brazed joint was formed. Distribution of welding heat input was improved by the addition of pulsed current. Difference of Ti/Al interface along the thickness direction was mitigated. Formation of continuous brittle intermetallic compound was restricted to a low level due to the effect of pulsed current. Cracking sensitivity of the joint was decreased and performance of the joint was increased.
Abstract:
Experiment of flat butt-welding is conducted on the 2195 Al-Li alloy with 2 mm thickness using conventional TIG and ultrasonic assisted TIG welding process. The microstructural observation and mechanicaltesting were conducted on the welding joints. The results show that there is denser microstructure in the ultrasonic assisted TIG welded zone due to the effect of ultrasonic treatment. Besides, the equiaxed fine grain zone near the fusion zone in ultrasonic assisted welded jont is wider. The mechanical testing show that the ultrasonic assisted TIG welding joints have good mechanical properties whose strength coefficient is 6.7% higher than conventional TIG welding, and the percentage elongation after fracture increased by 1.36%. The fracture of the joints is in the hard brittle grain boundary phase of the heat affected zone. The microhardness test shows that the ultrasonic assisted TIG joints have a narrow heat affected zone.
Abstract:
In order to study the influence of the element of boron and carbon on the microstructure and cracking sensitivity of the high boron content iron-based overlaying weld, the hybrid powder/wire overlaying weld technology was used to prepare the coating by adding different content of B4C. The structure and the mechanical performance of the coating were studied by the microstructure observation, micro zone element analysis, micro hardness and macro hardness. Results showed that the high boron content iron-based alloy consisted of α-Fe, Fe2B and Fe3(C,B) phase. With the increase of the content of B4C, the primary land-shape α-Fe began to disappear and the diamond-shape primary Fe2B and granular Fe3(C,B) began to precipitate. The volume fraction of the fish bone shaped and lath shaped eutectic microstructure (α-Fe+Fe2B) was gradually reduced and finally disappeared. The main microstructure was characterized with flower-shape α-Fe+Fe2B+Fe3(C,B) peritectic structure in the overlaying weld. The content of boron and carbon and their ratio are the the key factor affecting the microstructure and the cracking sensitivity. The overlaying welding consisted of about 30% alloy powder (including 35% boron iron and 5% B4C) and about 70% H08Mn2Si welding wire could effectively restrain the initiation of cracking. The hardness could reach a stable value of 66HRC.
Abstract:
Based on the sectional theory, the segmented moving temperature-controlled volume heat source model was proposed by using weld equivalent temperature as control variables, and it was verified through Q345B flat butt welding model. With calculation time and accuracy as a reference, based on different mesh sizes, the computing efficiency was compared between three kinds of heat source models including the segmented moving temperature-controlled heat source model, the double ellipsoid heat source model and the segmented moving double ellipsoid heat source model. The results showed that the trend of residual stress and deformation of the proposed model was consistent with that of the moving double ellipsoid heat resource model, and its accuracy was similar to that of the segmented moving double ellipsoid heat source model, but the calculation time is shorter. Particularly, the effect was more prominent on the large and complex structures.
Abstract:
An database was developed to for filling the robot welding moderate-thick plate with variable groove, based on laser sensor scanning and fitting the section area. The welding section area corresponding to different welding parameters as variables was saved and the least square method was applied to deduce the relationship between the welding area and the welding speed. The system based on thef groove cross-section variation and changes of adaptive control welding speed could fill the workpiece well and solve the problem of welding parameter adjustment on variable groove. It could also use the database language to standardize the management of the knowledge base, and constantly improve the welding database. Taking a 12 mm thick variable groove of moderate-thick plate as a test, the result showed that the welding effect is good and error of groove metal filling volume is small.
Abstract:
3003 Al alloy/Cu dissimilar metals were brazed by using Zn-Al filler metals with different Al contents. The spreadability of filler metal on 3003 Al-alloy substrate was improved with the increase of Al content. When Al content is in the range of 10%~15%, the filler metal presented excellent spreadability.However,the spreadability gradually decreased when Al content exceeds 15% in Zn-Al filler metal.In addition, the spreadability on pure copper substrate was improved with the increase of Al content. Shear strength of brazed joint was measured. The results show brazed joint strength was improved with the increase of Al content in the filler metal. When Al content is 12%, the shear strength reached highest and a sound brazed joints could be obtained. However,when Al content exceeds 12% in Zn-Al filler metal, the strength of brazed joint was gradually decreased. The optimum composition possessing best comprehensive properties is 88Zn-12Al filler metal.
Abstract:
The content of Cu, Si, Mg and Ni was changed by using orthogonal experiment in order to study how the content effected on the melting point and wettablity of Al-Cu-Si-Mg-Ni filler metal. The microstructure of the filler metal was analyzed by SEM and EDS. There were three factors affecting the melting point of filler metal, namely, the content of Mg element, the Al-Cu-Si eutectic reaction and the content of Ni element in proper order. With increasing of Mg content, the wettability was improved, but excess Mg led to the increase of porosity when the Mg content was constant, the closer the ratio of (Si/Cu) to (Si+Cu) to 0.06 was, the more Al-Cu-Si eutectic reaction occured. When the Mg content and Al-Cu-Si eutectic reaction were constant, the melting point decreased with the addition of Ni. Coarse blocky Si phase generated along grain boundaries could induce the joint brittle. Pore was built up around silicon-rich phase which was generated in a few areas as a result of Si segregation. Dispersed white needles θ(CuAl2) phase also decreased the strength of welding joint to some extent. However, α solid solution(Al-Cu、Al-Cu-Si and Al-Si)with face-centered cubic structure improved mechanical properties of the filler metal.
Abstract:
Ni-based composite coating reinforced by (Ti,Nb)C was prepared on the 16Mn steel substrate by means of argon arc cladding technique with the pre-alloyed powder of Ni60A, Nb, Ti and C alloy powders. The growth morphology of the (Ti,Nb)C particles and the microstructure as well as properties of coating were investigated by SEM, TEM, X-Ray, transmission electron microscope and microhardness tester. The results showed that the interface between the coating and substrate had excellent bonding and was free of pores and cracks. The microstructure of cladded coating consisted of (Ti, Nb)C particles, γ-Ni and eutectic structure M23C6. The in-situ synthesized (Ti,Nb)C presented octahedral shape. The connection growth was in the forms of octahedron verte-linked connection and edge-shared connection with form of petal-like shape and flocculation-like shape.
Abstract:
Using high-speed camera and Analysator Hannover, three kinds of basic flux-cored wires were tested and analyzed under different welding parameters with rich argon shield gas. The results show that the metal transfer mode was globular repelled transfer with poor arc stability and much spatter under lower welding parameters. With increasing of welding parameters, the metal transfer gradually changed to small droplet transfer and the process became stable. Large granular spatter was caused from the repulsive force acting on the molten droplet and the surface tension of the melt. The long slag column played a guiding role on the metal transfer. Refining the droplet and forming stable and long slag was important to improve the usability of basic flux-cored wire.
Abstract:
The SiCP/Al6063 composites containing 55% SiCP was joined by vacuum brazing process using Al5Si28Cu2.5Ti filler at 580 ℃. The influence of holding time on the joint microstructure and mechanical property was studied. The results show that the active titanium element improved the solder wettability of composite materials. The joint microstructure used holding time of 40min was the best with a shear strength of 96 MPa.
Abstract:
The fatigue crack propagation behavior of A7N01P-T4 aluminum alloy with different loading angles was investigated. The crack tip stress intensity factor (SIF) under combined I-II loading mode was calculated using the finite element method. The relationship between the loading angle and crack direction was obtained, which agreed well with the maximum circumferential stress criteria. Then, the equivalent stress intensity factor (ESIF) was introduced to analyze the relationship between crack growth rate and loading angles. The results show that after quantization treatment, the crack growth rates under different loading angles are coincident, which also meet the Paris law.
Abstract:
Aiming at difficult features in welding stability evaluation, a kind of welding stability evaluation method based on the current entropy was proposed. The mean and the standard deviation of sample entropy and was increased when current stability decreased. The product of mean value and standard deviation of the sample entropy were selected to quantified the welding stability. The effects of embedding dimension, given threshold and sample length on the sample entropy were discussed. For the given pulse MIG welding current signal, sample entropy distributed reasonably and time consumed less when m=2, r=0.08, N=2 000. Three contrast pulse MIG welding experiments were carried out at last and the results indicated that the welding stability evaluated by product of sample entropy mean and sample entropy standard deviation was coincided with actual weld quality, high value of the product of sample entropy mean and sample entropy standard deviation reflected inferior welding stability when the current was tbe same.
Abstract:
By using group method, high frequency fatigue test was conducted on X70 steel pipeline girth welding joint with a copper backing and ceramic backing respectively when the stress ratio was 0.1(r=0.1), and the crack initiation of the two kinds of samples were compared in certain fatigue load and cycle times. The results indicated that the copper infiltration in X70 steel pipeline girth welding with copper backing had little influence on fatigue strength and that the S-N curves of the two samples were almost the same. Another finding was that, under the same fatigue load and cycle condition, the crack initiation had no significant difference with the fatigue crack starting at the back weld toe. Furthermore, the fatigue fracture was analyzed by SEM.
Abstract:
The influence of different zones of high-strength steel welded joint on the hydrogen diffusion and aggregation is different. The escaping behavior of the diffusion hydrogen in different zones of TIG welded 30CrMnSiNi2 steel joint after electrochemical hydrogen charging is studied by microscopic photographing. The size and distribution of the hydrogen bubble were observed. The tracing of diffusion hydrogen in the weld zone is studied by using hydrogen microprint technique. The distribution characteristic of the escaped diffusion hydrogen in high-strength steel welded joint is explored, which is completely opposite to that in low-carbon steel. The results show that the diffusion hydrogen in TIG welded 30CrMnSiNi2 steel joint mainly gathers in the weld zone and the heat affected zone. The grain boundary in the weld zone is the main location to hydrogen diffusion and aggregation, the stress inside the structure is the primary cause of hydrogen diffusion aggregation. The results give constructive suggestions for understanding the relationship between different structure and the diffusion hydrogen.
Abstract:
Fiber laser-MIG hybrid welding using ER316 filler metal was applied to join the 1mm thickness SUS444 ferrite stainless steel sheet by butt joint and lap joint with a gap of 0.5 mm. In this study, the process window has been successfully obtained for acquiring butt joint and lap joint with good formation. Both dye-penetrant inspection and tensile experiment have been conducted on those joints. The results show that the proper match of welding speed and welding current is a key factor for acquiring large gap joint with good appearance. When welding speed is too low or welding current is too high, the excessive heat input leads to excessive penetration of the weld resulting in bad weld formation. When welding speed is too high or welding current is too low, the heat input is not capable to penetrate the joint. In addition, the highest welding speed can reach 12 m/min and 5 m/min for butt joint and lap joint with good formation with full penetration. In dye-penetrant inspections, no surface crack was found for all the joint with good formation. Meanwhile, in tensile experiments, all the butt joint fractured at the base metal, and most of the lap joint fractured near the fusion line. The tensile strength of the lap joint reached 84.2 % of the strength of base metalunder the highest welding speed (5m/min).