最新刊期
期 7 ， 2023
- 摘要：Molten salt reactors (MSR) use molten salt as the heat transfer medium. Their structural materials are exposed to extreme environments such as high temperatures, molten salt corrosion and neutron irradiation. Therefore, the requirement of performance of the structural material is strict. The GH3539 alloy is a new generation of structural materials with significant mechanical properties at high temperatures and in extreme environments. This study on the GH3539 alloy was conducted utilizing laser welding technology to promote the application of this alloy. The microstructure, solidification mode, and mechanical properties of the GH3539 alloy laser-welded joints were investigated. The results indicate that GH3539 laser-welded joints have a high depth-to-width ratio, and that the welded joint is composed of three zones: the base material, the heat-affected zone, and the fusion zone. Typically, the base material zone is austenitic, with a high proportion of W-rich carbide and a minor amount of Ti-rich precipitation phase in the matrix. In the welded joint, there was no significant weld heat affected zone found. The fusion zone near the fusion line is planar crystal. Planar crystal rapidly transformed into columnar crystal. Columnar crystal direction of growth has obvious directional which perpendicular to the fusion line. The front of columnar crystal contacts at the weld center line, resulting in part of the organization at the weld center line disordered. It is also found there are some fine equiaxed crystals at the center of the weld. The average hardness of the weld zone is 273 HV.The microhardness significantly higher than the rest of the joint, and no significant soften area was found. At a high temperature of 800°C, the fracture of the welded tensile specimens occurs in the base material area, and the fracture mode is intergranular fracture, with yield and maximum tensile strengths of 212.6 MPa and 295.2 MPa, respectively. GH3539 alloy still exhibits good mechanical properties at high temperatures.关键词：GH3539 alloy;laser welding;microstructure;hardness;elevated temperature tensile strength
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发布时间：2023-08-02 - 摘要：To solve the problem of brittle fracture in welded joint of medium manganese steel, this article studied the effect of post-weld heat treatment process on the microstructure, static mechanical properties, and distribution of manganese element of laser self-melting welded joint of 1.6 mm thick medium manganese TRIP steel. The heat treatment temperature was selected between Ac1 (austenite start transformation temperature) and Ac3 (austenite transformation termination temperature), which is the same as the rolling temperature of medium manganese steel, to ensure higher strength and toughness. The results showed that the weld zone of the as-welded sample was mainly composed of martensitic structure, while the weld zone after heat treatment was mainly composed of tempered martensite with carbide precipitation. After being heated at 620 ℃ for 3 minutes, the tensile strength of the welded joint did not increase significantly, but the elongation of the welded joint increased by 1959.2% relative to that of the as-welded joint. The main reason was that the heat treatment relieved the segregation of manganese element at grain boundaries. The failed fracture of the as-welded joint was a typical brittle fracture, with more secondary intergranular cracks. The failed fracture of the heat-treated joint showed more pits and toughness dimples and presented good toughness fracture characteristics. A secondary yield was found in the stress-strain curve of the heat-treated sample, and through the VIC-3D digital image correlation (DIC) technology, it was found that this was caused by the Lüders band encountering the martensitic structure with higher hardness across the weld zone, leading to a sudden increase in stress and ultimately causing necking and fracture at the base metal.关键词：medium manganese TRIP steel;laser welding;post-weld heat treatment;mechanical property;Mn element segregation
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发布时间：2023-08-02 - 摘要：This paper predicts the temperature field and post-weld deformation of semi-truck structures with Q235-steel fillet welds fabricated by laser-GMAW hybrid welding via thermo-mechanical FEM analysis. A combined volumetric heat source consisting of planar gaussian heat source and conical volumetric heat source. was applied in the thermal analysis. The numerical results showed that the computed cross-sectional shape and weld size coincides well with the experimental ones. This consistency proves the validity of the combined planar and conical gaussian heat source in the temperature-field simulation of laser-GMAW hybrid welding. The welding sequence has been planned step by step, including the overall sequence of double-side structures, the starting position, and the selection of welding paths between sequential welding, backstep welding, and jump welding. Four key paths have been selected and the average value of z-direction displacement of points at each path has been calculated as the deformation coefficient of the entire structure so that a quantitative evaluation method for complicated-structure deformation was established. The optimum method in each step has been combined and the final strategy is to weld A side first and to adopt jump welding path and No.3 starting position when welding B side. The optimized welding deformation coefficient of the post-welding structure is 0.2 mm, which is 28.6% lower than the worst welding sequence's coefficient of 0.28 mm.关键词：laser-GMAW hybrid welding;combined volumetric heat source;thermo-mechanical analysis;welding sequence optimization
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发布时间：2023-08-02 - 摘要：The effects of welding speed, oscillating frequency and oscillating amplitude on the macro-morphology and microstructure of the weld were studied by high power oscillating laser self-fusion welding of 12mm thick 304L stainless steel. The results show that when the laser power is 9.5 kW and the laser does not oscillate, as the welding speed increases from 0.9 m/min to 1.5 m/min, the weld changes from penetrated to unpenetrated, and the spattering of the unpenetrated specimen is obvious. When the oscillating frequency is in the range of 50~400 Hz, with the increase of the oscillating frequency, the penetration width of the weld decreases from 6.67 mm monotonic to 4.94 mm, and the penetration depth fluctuates up and down around 7.5 mm. When the welding speed is 0.9 m/min and the oscillating amplitude is in the range of 0.2~1.0 mm, with the increase of the oscillating amplitude, the penetration width of the weld increases monotonically from 5.36 mm to 7.14 mm, and the penetration depth first increases and then decreases. When the welding speed is 0.72 m/min and the oscillating amplitude is in the range of 0.5~1.0 mm, with the increase of the oscillating amplitude, the penetration width of the weld increases from 2.99 mm monotonic to 7.73 mm, and the penetration depth decreases from 12 mm monotonic to 8.42 mm. The influence of the oscillating parameters of the laser on the penetration width is more obvious than that of the penetration depth. The microstructure of the weld joint is different in the direction of weld depth, the columnar crystals are mainly distributed in the upper and middle parts of the weld, and the bottom of the weld is mainly equiaxed crystals. Laser beam oscillating changes the distribution of columnar and equiaxed crystals in the upper and middle weld.关键词：austenitic stainless steel;mid-thick plates;oscillating laser welding;microstructure
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发布时间：2023-08-02 - 摘要：The effect of different power ratios of the central laser beam and the annular laser beam on the macroscopic morphology, microstructure and mechanical properties of the weld was investigated using an adjustable annular spot fiber laser welding process for laser sputtering of aluminum-silicon coated 22MnB5 steel. The results show that the ratio of the central laser beam and the annular laser beam has a small effect on the weld melt width, and the collapse of the weld surface is minimized when the ratio is 1∶1. The hardness value in the central region of the weld increases and then decreases as the power of the annular laser beam increases, achieving a maximum value of 448.5 HV when the laser power of both the central and annular laser beams is 1 500 W. The minimum hardness value is 310.2 HV when the power of the central laser beam is 2 000 W and the power of the annular laser beam is 0 W. In the area of the annular spot laser action, the fusion line edge will Strip ferrite, tensile deformation process cracks sprouted at the ferrite expansion, is the main cause of failure of welded joints. When the center laser beam and ring laser beam power is 1 500 W, the joint tensile strength and elongation is the highest, the joint fracture in the vicinity of the weld fusion line. When the center laser beam power is less than the annular laser beam power, the weld crack starts from the upper edge of the weld fusion line, and when the center laser beam power is greater than or equal to the annular laser beam power, the crack starts from the lower edge of the fusion line.关键词：Al-Si coating;laser welding;ring beam;different power ratio;mechanical property
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发布时间：2023-08-02 - 摘要：Problems affecting the forming properties and mechanical properties of welded joints such as softening of the heat-affected zone of welded joints, embrittlement and collapse of welded joints are often prone to occur When advanced high-strength steel is used for traditional laser welding vehicles. To solve this problem, The super larger-defocus laser welding process was used to laser 1.6 mm thick TRIP800 high-strength steel to obtain a new type of welded joint with a wide weld size, and the microstructure, hardness and mechanical properties of the welded joint were analyzed. The results showed that when the laser power is 3 500 W, the welding speed is 3m/min, and the defocusing distance is 50 mm, a new laser welding joint with good morphology and no obvious defects can be obtained. The microstructure of the heat-affected zone of the welded joint was mainly composed of residual austenitic and martensitic structure, while the weld area was mainly composed of martensitic structure. The distribution curve of the hardness of the welded joint showed a gradual decrease trend from the weld area to the base metal area, the tensile strength of the super larger-defocus welded joint was comparable to the strength of the base metal, the elongation after breaking is about 1.25 times that of the traditional welded joint, and the fracture presents a large number of tenacity sockets, mainly ductile fracture. The improvement of the mechanical properties of the new welded joints of TRIP800 high-strength steel is mainly due to the wide weld area organization, which enhances the ability to resist cracks, disperses the energy concentration during laser welding, and was not easy to produce large internal stress in the welded joints, and the row performance was better.关键词：TRIP800 high strength steel;laser welding;super larger-defocus;microstructure;mechanical properties
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发布时间：2023-08-02 - 摘要：Deep penetration laser welding experiments were conducted on Ni-clad stainless steel plates with a total thickness of 20 mm using a 30 kW ultra-high power fiber laser. And the influences of laser power, welding speed and defocus on surface appearances of welds were investigated. The results showed that under the conditions of welding speed of 2.1 m/min, defocusing amount of -8 mm, with the increase of laser power, the welds of side welding both sides formation were obtained, but with spatter, undercut, surface undercut and root hump defects. At a laser power of 26 kW, the weld with uniform forming and continuous back, good root penetration was achieved in the stabilization stage of the welding process (except the arc generating and quenching positions). When the laser power was 25 kW, the defocusing amount was -8 mm and the welding speed range was from 1.8 m/min to 2.4 m/min, the defects of surface undercut and root hump appeared at the top and bottom surfaces respectively. At a speed of 2.4 m/min, the partial penetration welds were obtained. With the change of defocusing distance from -3 mm to -10 mm, the full penetration welds were obtained with spatter, undercut and surface undercut defects. The research in this paper provided an experimental basis for further optimization of deep penetration laser welding process.关键词：Ni-stainless steel clad plate;deep penetration laser welding;thick plate;weld formation
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发布时间：2023-08-02 - 摘要：It is often necessary to weld brass and copper in aerospace, automobile, refrigeration equipment and other fields, because the dissimilar metal composite structure formed by the two has the mechanical properties of brass and the thermal conductivity of copper. In this paper, the laser welding of H62 brass and T2 copper plate was studied by fiber laser. The influence of laser power, welding speed and other main process parameters on the forming properties and mechanical properties of the weld was studied, and the welded joint with good appearance was obtained. When the heat input was greater than 105 J/mm, the penetration depth increased greatly , and the welding mode changed from laser thermal conductivity welding to laser keyhole penetration welding. When the laser power was 1800 W and the welding speed was 13 mm/s, the maximum depth to width ratio was 2.51.The distribution and evolution of the composition and structure of welded joints and interfaces were analyzed, and the relationship between the microstructure and mechanical properties was explored. It is found that the flow of molten pool is mainly annular, forming the component distribution of zinc content in the weld center is higher than that in the weld edge. It was suggested that the non-uniformity of the composition caused by molten pool flow and component segregation was the main reason for the non-uniformity of the joint properties. The hardness test at the weld center showed that there was a large hardness gradient near the interface of the two materials, and higher heat input could promote the mixing of two materials and reduce the difference of mechanical properties of two materials at the interface.关键词：laser welding;brass;copper;microstructure;process parameter
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发布时间：2023-08-02 - 摘要：Focusing on the problem of large residual stress and welding deformation in laser welding with titanium alloy thin-walled structures, a laser welding method with liquid nitrogen-assisted cooling was proposed for the control of welding deformation, in which liquid nitrogen cooled argon was used as the cooling medium on the surface of the specimen. The laser welding experiment of TC4 titanium alloy lock bottom structure with liquid nitrogen cooling was carried out. The microstructure, residual stress and welding deformation of TC4 titanium alloy laser welded joint under different cooling conditions were analyzed. The results show that compared with the laser welded joint with natural cooling, the width of heat affected zone of liquid nitrogen cooled laser welded joint was narrower, the middle width of weld joint was increased by 63.7%, the down melting width was increased by 70.5%, the weld structure was more uniform, the weld deformation was significantly reduced, and the overall deformation was reduced by about 5.2%. Due to the metal at high temperature behind the molten pool cooled by liquid nitrogen cools rapidly, which compensates the compressive plastic strain to a great extent and reduces the welding deformation.关键词：TC4 titanium alloy;lock bottom structure;laser welding;liquid nitrogen-assisted cooling;residual stress;welding deformation
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发布时间：2023-08-02 - 摘要：Efficient, high-precision, green laser welding technology has become one of the mainstream ways of structural parts manufacturing. The successful introduction of laser welding technology in the manufacture of medium and thick plate members has become an important symbol of technology leadership in the construction machinery industry. Due to the characteristics of construction machinery manufacturing mass and low processing accuracy requirements, it is difficult to introduce laser welding technology into the manufacturing application of medium thick plate members. This paper summarizes the characteristics of typical construction machinery structural parts, and summarizes the key problems to be solved in the process of technology introduction from three levels: process, equipment and production line. According to the engineering development experience, the key points of laser welding technology and complete set of equipment development of medium and thick plate members are clarified, the introduction paradigm of laser welding technology to the general manufacturing of construction machinery structural parts is proposed, and based on the paradigm, the work idea of comprehensive introduction of subsequent processes is proposed, and four basic works are summarized.关键词：laser welding;construction machinery;medium thick plate member;precision;normal form
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发布时间：2023-08-02 - 摘要：Aluminum/steel composite structure has the advantages of high strength, corrosion resistance and light weight, and is one of the most popular lightweight design schemes in automobile manufacturing, aerospace and other industries. However, connecting aluminum alloy and steel through traditional fusion welding is difficult because the physical and chemical properties of aluminum alloy and steel are seriously mismatched. Pulse laser welding technology has the advantages of precise heat input control, fast processing speed, high flexibility, and high energy density, and has greater advantages in welding aluminum/steel dissimilar alloys. This article reviews the research progress of pulse laser welding of aluminum/steel dissimilar metals both domestically and internationally from multiple perspectives, including pulse laser parameters, pulse laser composite welding, and pretreatment of the welding base material. It also provides the work that still needs to be carried out in the pulse laser welding technology of aluminum/steel, aiming to provide reference for subsequent related research.关键词：pulsed laser;aluminum alloy/Steel;dissimilar metal welding;composite welding;pretreatment
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发布时间：2023-08-02 - 摘要：The construction and operation of nuclear power plant is an extremely complicated system. Welding is one of the essential technic in the process of equipment manufacturing, assembly, maintenance and so on. The quality of weld directly affects the reliability and running state of nuclear power equipment. Compared with traditional process, laser welding can not only improve weld quality, reduce deformation and residual stress, but also raise efficiency and shorten the construction period. However, this technology is not widely used in nuclear power field. In order to promote the application of laser welding in nuclear field, the research status that about laser welding of nuclear grade materials in recent years is introduced. Including the research of laser welding properties of Zr alloy, stainless steel and new materials, etc. Its application and research status on nuclear power plant equipment maintenance and manufacturing are analyzed. On this basis, the reasons for the low application of laser welding in nuclear power plants are analyzed, and the future research directions are prospected.关键词：laser welding;nuclear grade materials;nuclear power equipment;welding properties
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发布时间：2023-08-02 - 摘要：Coal mining hydraulic support is exposed to the harsh service environment of moisture and corrosion for a long time, and the surface is prone to corrosion and wear. Laser cladding technology provides an efficient and high-quality surface repair method to improve the service life of coal mining hydraulic support. This paper reviews the research progress of laser cladding of hydraulic support. Firstly, the effects of laser cladding process and material system on the corrosion resistance, wear resistance, hardness and fatigue strength of the coating are introduced. Secondly, the application of laser cladding technology in the repair of hydraulic support is introduced from the practical application. The laser cladding material system suitable for different parts of hydraulic support and the performance of the coating after cladding are discussed. Finally, the future research focus of laser cladding repair hydraulic support is summarized and prospected.关键词：laser cladding;hydraulic support;corrosion resistance;wear resistance
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发布时间：2023-08-02 - 摘要：The effect of yttrium(Y) element on the microstructure and mechanical properties of ingot and the effect of laser welded joint microstructure, tensile properties and hot crack susceptibility of aluminum alloy were studied by preparing filler wires with different Y content. The results showed that when Y element was added into the ingot, the lumpy phase was formed, and the mechanical properties of the ingot decreased with the increase of Y content. Through laser welding with self-made welding material, it was found that when the content of Y in the welding material was 0.15 wt.%, the laser welded joint could obtain fine microstructure at weld zone, and the tensile strength of the joint was improved to a certain extent. However, with the further increase of Y element, the mechanical properties were gradually decreased, and the microstructure was also gradually coarsened. The columnar crystal area was narrower than the area without adding Y, and the number of equiaxed crystals increased. The hot crack experiment showed that adding 0.15 wt.% Y element could narrow the columnar crystal region compared to the region without adding Y, and increase the number of equiaxed crystals, which could reduce the welding hot cracking susceptibility.关键词：rare earth element Y;aluminum alloy;laser welding;hot cracking susceptibility
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发布时间：2023-08-02
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