A low-temperature sintered conductive silver paste containing Bi₂O₃-B₂O₃-ZnO glass frit was used for sintering thick silver film on the surface of aluminum alloy to realize aluminum alloy soft soldering. First, Bi₂O₃-B₂O₃-ZnO glass with glass transition temperature (T_g) of 360 ℃ was synthesized by using a melt-quenching method. Then, it was mixed with submicron silver powder to prepare lead-free low-temperature sintered silver paste, which was coated on the surface of 6061 aluminum alloy and sintered at temperatures of 440, 470, 500 and 530 ℃, respectively. The effects of sintering temperature on the resistivity and the solderability of silver thick film, and the bonding strength of the silver thick film on the substrate were studied. The results show that a thick silver film with glass and silver powder content ratio of 1∶9 (wt.%) sintered at 530 ℃ for 10 min has a low resistivity of 2.2 μΩ·cm and a high shear strength of 56.0 MPa at room temperature. Increasing the sintering temperature can effectively promote the flow, wetting and spreading of the glass, the growth of necking between Ag particles, and the growth of Ag particles, thereby improving the solderability of silver thick film significantly. In addition, the nano-scale elemental bismuth produced by the oxidation-reduction reaction of Al, Mg and Bi₂O₃ was detected at the interface of silver thick film and aluminum substrate. It shows that an excellent metallurgical bond was formed between the silver thick film and the aluminum substrate.

Wire and arc additive layer manufacturing (WAALM) is a novel manufacturing technique in which metal components can be fabricated layer by layer. In this study, microstructural characteristics of TC4 components after CMT-WAALM deposition were investigated. During arc additive manufacturing process, epitaxial growth of prior columnar β-grain boundaries that were from the high temperature, horizontal stripes, martensite and basket weave microstructures formed due to the heat input, multi heat cycles and cooling rates. The microhardness values at the middle and bottom regions (about 336 HV0.1) were higher, while those at the top regions were significantly decreased (about 323.3 HV0.1).

The influence of arc stability on different process parameters during Laser-arc hybrid welding which used self-shielded flux-cored wire (414N-O) with the help of Hannover Analysator and high speed photography were studied. The results indicated that the probability of arc point drift and short circuiting transfer of self-shielded flux-cored wire are reduced with the addition of laser. Oppositely, arc length is elongated and the arc stability is improved. In the parameters, the distance between laser and arc(D_LA) and wire feed speed have appreciable impact on the mean actual output current, and the stability of current coefficient of variation.is significantly affected by welding voltage and wire feed speed. The influence range of laser power to mean actual output current is related to D_LA and wire feed rate, and the influence declines with D_LA and wire feed rate increase. The influence range of welding voltage to mean actual output current is related to D_LA and it has the greatest impact when D_LA is 0 mm. Laser leading is more beneficial than laser trailing to the stability of current coefficient of variation.

The selective laser melting technology shows great advantages in the field of manufacturing of complex parts, but the organization and the comprehensive performance of the specimens have yet to be further optimized. Specimens of 316L stainless steel were fabricated by selective laser melting technology, the microstructure characteristics of different regions were analyzed, the tensile mechanical properties were tested. The results showed that the micro-structure were mainly cell crystal. However, the grain growth direction were different in some "micro-melting pools", and almost perpendicular to each other, which showed a small typical columnar crystal in the same field of view (subgrain) and "hexagonal cellular crystal" coexistence of micro-structure characteristics. Compared with the traditional specimens, the tensile strength of had greatly improved, but the elongation decreased. This was mainly due to the fact that SLM was a process of rapid melting and solidification which maked the difference of laser incident angle, scanning strategy and heat dissipation conditions resulting in complex crystals at different regions and different microstructure. The fine columnar crystal formed by rapid cooling that was submicron order and densely distribute was the main reason of the increases in tensile strength. However, the obvious anisotropy of grain, which resulted in the uneven deformation of grain in different directions and restrained mutually during the tensile test, and the inevitable remarkable internal stress at the interface of fusion lines leaded to a decrease in elongation.

Tungsten-based alloy has excellent properties such as high melting point, high strength, and low thermal expansion coefficient. Steel is still the most widely used metal material at present. The structural parts formed by tungsten-based alloy and steel have broad application prospects in fusion reactors, die-casting molds and other fields. Due to the huge differences in the physical, chemical and mechanical properties of tungsten and steel, the high-performance joining of tungsten-based alloy and steel is a great challenge and a key issue in the field of joining. In this paper, we reviewed the development of the brazing and diffusion bonding of tungsten-based alloys and steels. Additionally, in order to provide reference for subsequent research, the possible future research directions of tungsten-based alloy/steel dissimilar materials joining were proposed combined with the application requirements.

With the development of additive manufacturing (AM) technology, a variety of AM technologies, such as arc, laser and electron beam AM technologies, have been extensively researched in their respective sectors. The characteristics of electron beam freeform fabrication (EBF³) were summarized in this paper. The research on EBF³ technology and the latest achievements on the equipment and technique of EBF³ in domestic and foreign were introduced. Research work of EBF³ which should be launched was analyzed. Finally, EBF³ technology should be developed along refractory metals and composite materials, preparation of gradient materials and complex component additive manufacturing was prospected.

Based on the global FE model of structural stress calculating for welded frame and considering the geometry of fillet welds and 1mm fictitious notch radius, the local hot spot stress and effective notch stress FE model of longitudinal fillet welded gusset, connecting the axle lever plate and box side-beam lower flange, were refined. The 9 levels equivalent fatigue load spectra were determined according to dynamic fatigue testing loads. The cumulative damage calculations based on nominal stress, hot spot stress and effective notch stress were carried out respectively by using the relative fatigue design S-N curves recommended by ⅡW. The result shows that, the resultant cumulative damage based on effective notch stress is far greater than nominal stress and hot spot stress, and the assessment result may be too conservative. In order to take advantage of the effective notch stress approach better, the more real notch geometries and notch strength data should be used.

To reduce big plate of 5A06 aluminum alloy laser welding defects, which enhances the stability of welding process, using a laser beam in a certain way of scanning new welding method, welding laser beam was studied different trajectories, amplitude, frequency of deep penetration laser welding aluminum alloy weld porosity, and the welding groove design optimization based on the application of narrow gap scanning laser wire filling welding technology for 130 mm thick 5A06 aluminum alloy welding test. The results show that when the scanning amplitude of the laser beam is greater than 1 mm and the scanning frequency is near the highest frequency, the porosity of the weld can be greatly reduced. The welding method of narrow gap laser scanning wire filling was adopted to obtain the high-quality welding joints of 130 mm 5A06 aluminum alloy with average porosity of 1%, no side wall non-fusion, interlayer non-fusion, crack and other welding defects.

Laser welding-brazing of 6061 aluminum alloy to galvanized steel with CuSi3 filler metal was investigated by full-factor experiments. The surface appearances, microstructures and mechanical properties of joints were studied in detail by optical microscope, scanning electron microscope (SEM), EDX analysis and tensile tests. The results indicated that steel-aluminum dissimilar metal lap joint was successfully realized by laser welding-brazing with CuSi3 filler wire, and the joint showed good appearance. The lap joint presented three feature areas:the interface at the side of steel, weld center and the copper solder wire/aluminum transition area at the side of aluminum. Further studies had shown that the copper solder wire/aluminum transition region composed of Cu₉Al₄ and CuAl₂.presented four different morphologies:ribbon, large skeleton-like, small skeleton-like mixed with small amounts of lamellar and dendritic. The hardness of copper solder wire/aluminum transition zone is much higher than that of the adjacent zone, which was up to 9.97 GPa at the coarse skeletal zone. The tensile fracture was in the coarse skeletal zone and the fracture appeared brittle fracture.

The explosive welded Al/Q235 joint was annealed under various heating time and temperature keeping the joint stay at solid state condition. The interfacial reaction layer feature was analyzed and the effects of heating temperature and time on the thickness of reaction layer were investigated, the growth of intermetallic compound at the joining interface was studied. The interfacial reaction layer consisting of Fe₂Al₅ adjacent to steel and Fe₄Al₁₃ adjacent to aluminum formed in the joining interface. The thickness of intermetallic compound increased with the longer of heating time. The results show that the growth of intermetallic compound satisfies the parabolic rule and that the growth active energy is 33.26 kJ/mol.

High nitrogen steel offers unique benefits including high strength, toughness, abrasion resistance, and corrosion resistance. The connectors have been widespread application in military equipment, medical instruments, and mining devices. The major domestic and foreign research reports in recent years on gas tungsten arc welding, gas metal arc welding, laser welding and laser-arc hybrid welding, friction stir welding and brazing of high nitrogen steel are summarized in detail.According to the three main classifications of fusion welding, solid-state welding and brazing, the paper systematically reviews the existing various types of high-nitrogen steel welding methods and process control from the aspects of shielding gas, heat input,process parameters and others, introducing the current status of the application of high-nitrogen steel materials in the field of medical devices, oil drilling collars, and armor protection. Finally, the review points out the shortcomings and aspects of the existing research on high nitrogen steel joining systems, expecting to provide information and theoretical basis for the research and application in the fields of high nitrogen steel welding, functional joining of high-strength materials and other related fields.

Based on SYSWELD finite element analysis software, the transient temperature distribution, residual stress and deformation of Q345/316L dissimilar steels were numerically simulated, and the simulation results were validated by the experimental method. The experimental results show a good agreement with the numerical simulation results, which proved the reliability of the dissimilar steel welding of SYSWELD simulation. The results show that the welding temperature field of dissimilar steel was asymmetric, and the Q345 side had a wider range of high temperature regions. Both the transverse and longitudinal residual stresses were in the shape of cap in the direction of the weld and there was a maximum residual stress in the middle of the weld. In the middle of perpendicular welding cross section, the longitudinal residual stress and transverse residual stress were not continuous weld and weld near the central section of the weld. There was a large stress gradient and the stress state was complex. The maximum residual stress appeared in Q345 side of the fusion line. The simulation results under different heat input show that, under the premise of ensuring the quality of welded joints, it was best to use a small heat in welding process.

The hot-rolled annealed hypoeutectoid steel plates with a thickness of 3 mm was processed by friction stir processing using K40 cobalt tungsten carbide tool. The microstructures and mechanical properties of the processed zone were investigated. The results show that the microstructure of stir zone and thermo-mechanically affected zone were proeutectoid blocky ferrite, "acicular ferrite" and pearlite. Its transformation characteristic was dynamic recrystallization and phase transformation. However, heat-affected zone was characterized as equiaxed ferrite and lamellar pearlite, which was mainly controlled by recrystallization. Friction stir processing had significant effect on the morphologies of pearlite and the precipitation cementite in above different zones. Microhardness in the processed zone of hypoeutectoid steel sample obviously increased after friction stir processing and its ultimate tensile strength increased by 8.2% compared to that of the base material. As a result, the fracture location of tensile specimens appeared at the base material. The fracture mechanism of samples before and after friction stir processing treatment was dimple ductile fracture. Solid solution strengthening and phase transformation strengthening were the two factors for improving the hardness and the ultimate tensile strength of hypoeuectoid steel sample.

Solid-state diffusion bonding of TZM alloy to WRe alloy was performed using spark plasma sintering (SPS). The microstructure, mechanical properties and thermal fatigue of the TZM/WRe joint were investigated in detail. The results showed that successful solid-state diffusion bonding was achieved between TZM alloy and WRe alloy using SPS at temperature of 1 500℃ for 30 min. The TZM/WRe interface is free from discontinuities or microcracks. Recrystallization occurs in both the TZM alloy and WRe alloy during diffusion bonding. comparison with W and Re, the diffuse depth of Mo is greater than that of W and Re in the TZM alloy, due to its lower self-diffusion activation energy. The TZM/WRe joint shows excellent resistant ability to thermal shock and part of Mo grains grow through the TZM/WRe interface after enduring 100-cycles thermal shock. The bending strength and shearing strength of the TZM/WRe joint are 910 MPa±65 MPa, 497 MPa±50 MPa, respectively. Fracture occurs in the TZM alloy, and the fracture mode is dominated by transgranular cleavage fracture.

Ce was introduced into BAg17CuZnSn filler metals, and the effect of Ce content on microstructure and brazing properties of low silver filler metals were studied. The results show that the spreading area on brass and stainless steel increase 12.1% and 37.4%, respectively with 0.15% Ce addition. The maximum shear strength of brazing joint could reach 340.2 MPa using BAg17CuZnSn-0.15Ce filler metal. The anticorrosion ability of BAg17CuZnSn-xCe filler metals is improved with increasing Ce content. The BAg17CuZnSn-xCe filler metals show finer and more uniform microstructure when the content of Ce is 0.15%. However, some Ce-Sn intermetallics phases occurred in the filler metals when the Ce content reaches 0.5%.

The microstructure and properties of 5 356 aluminum alloy sample manufactured by TIG wire arc additive manufacturing in the different regions were studied. The results showed that interlayer of sample alternated with the deposition layer horizontally, the width of deposition layer at the bottom was the largest (~2.4 mm), and the middle stable region was the smallest (~1.6 mm). The deposition layer consisted of equiaxial grains, and the black second phase β-Al₃Mg₂ and a small amount of intermetallic compounds Mg₂Si and (FeMn)Al₆ diffused on the gray matrix. A large number of pores and shrinkage holes appeared at the interlayer. The deposition layer at the bottom had the smallest grain size, but the interlayer had the most defects. The strength and plasticity were approximately equal in the horizontal direction at the different regions (${R_{\rm{m}}} = 274\;{\rm{MPa}}, \;A = 32.3\%$). The strength in vertical direction was approximately equal to that in horizontal direction, but the elongation dropped to 26%. The tensile fracture was mainly composed of equiaxial dimples in both directions. The hardness of the deposition layer at the three regions was stable, and the hardness at the bottom was slightly higher than that of the rest regions, while the hardness of the interlayer fluctuated significantly.

According to the requirements of robot welding motion simulation and multi-layer and multi-channel path planning, an open robot welding off-line programming system based on WebGL is developed. Firstly, a robot MAG welding system based on laser vision sensing is built, and then a simulation platform is built by using JavaScript, WebGL and other technologies. The three-dimensional point cloud data of weld bead is obtained through the sensor, and the point cloud processing technology is used to extract the weld bead feature information. On this basis, a multi-layer and multi pass path planning strategy for 20 mm thick V-groove steel plate is further proposed, Finally, the welding experiment of 4 layers and 10 passes of V-groove was completed. The results show that the system provides a reliable way to realize the key technologies of robot welding automation and intelligence.

Kovar alloy and DM308 glass were bonded with YLS-6000 fiber laser. The effect of interlayer on the strength, interface structure and interface bonding mechanism was investigated. The diffusion behavior of interface elements is analyzed. The results showed that the Mo-Mn-Ni interlayer can reduce the cracks at the edge of the joint,and Ni₂O₃-MnO₂-B₂O₃ interlayer can reduce the number of micro cracks and the number of bubbles on the glass side. The weakest part of the 4J29/DM308 laser welding joint is near the glass side, which breaks through the bubble. The biggest shear strength of Mo-Mn-Ni interlayer joints is 10.96 MPa. The biggest shear strength of Ni₂O₃-MnO₂-B₂O₃interlayer joints is 13.46 MPa. The thickness of Ni₂O₃-MnO₂-B₂O₃ interlayer transition layer is about 30-40 μm. There is obvious dendrite growth in the transition layer. The results of joint interface XRD phase analysis show that the interface transition layer is FeSiO₃ and Fe₇SiO₁₀. It is belong to Fe and Si cubic complex oxides. The results of EDS analysis showed that Fe, Co, Ni, Al, Na and Si elements had diffused in the whole interface region. The interfacial bonding mainly depends on chemical reaction and element diffusion.

In order to investigate the process parameters and properties of CuNiCrSi copper alloy jointed by friction stir welding, the orthogonal experimental method was used to optimize the process parameters, and the properties and material flow were studied. The results show that the welding speed is the most significant factor affecting the welding process. The experiment has got the best combination of process parameters, and the tensile strength of the weld was 491.4 MPa, which was 84.7% of the tensile strength of the base metal under these optimum welding parameters.When the welding speed is too large, there will be tunnel defects on the advancing side of the weld, and the flow of the forward material is more complicated than that of the retreating side. When the welding speed is too small, the surface will have fin.The coarse particles in the parent material area are segnagations of chromium and silicon, and the nickel is uniformly distributed in the material. The grains in the nuggest zone become smaller as the welding speed increases. Under the optimal parameters, the grain size of the nuggest zone is small and uniform, but the hardness is lower than that of the base metal. The fracture method is ductile fracture, which indicates that the material has good toughness.

For the basic ant colony algorithm in the robot welding path planning, some problems such as too long searching time, low efficiency and falling into local optimum in the process of searching were found. For the basic ant colony algorithm, Adadelta algorithm was introduced in this paper. By updating the parameters of Adadelta algorithm, the update of ant pheromones was improved and the volatility coefficient of pheromones was improved. The adaptive method was adopted to update pheromones. The improved algorithm was simulated with MATLAB and the result analysis show that the improved ant colony algorithm in this paper had better search capability than the basic ant colony algorithm and higher algorithm efficiency, which was about 20 generations ahead of the basic ant colony algorithm. The method in this paper effectively solved the local optimization and slow convergence speed of the basic ant colony algorithm and made the search results better.

In this paper, the mechanical clinching, self-piercing riveting(SPR) and resistance spot welding were applied to connect the aluminum alloy sheets. The fatigue experiments were conducted to the joints. Then the statics performance and fatigue properties were compared between the three types of joints. The results showed that the static strength of the resistance spot welding joint is the best and far higher than the others. The fatigue property of the clinched joint and the SPR joint are favorable. When the amplified applied load is high, the fatigue property of SPR joint is better. When the amplified applied load is low, the fatigue property of clinched joint is better. In the case of two million times of fatigue limit, the fatigue property of the cliched joint is the best, the fatigue property of the SPR joint is second and that of the resistance spot welding is the last. That was because the poor performance, the residual stress superposition, and the fatigue crack expansion with continuity of the thermal influence zone of the spot welding joint. However, the slight slips for mechanical joining and self-piercing riveting have effect on relaxing the concertation of stress. In this way, the fatigue property of the cliched joint and the SPR joint can be improved.

In order to accurately predict the fatigue life of materials and improve the accuracy of structural fatigue life prediction, the method of ABAQUS finite element numerical simulation to predict the fatigue life of specimens was studied. Based on Tanaka-Mura dislocation theory, ABAQUS was redeveloped by using Python language. The fatigue crack initiation life of S960QL martensitic steel and Ti₂AlNb titanium alloy joint was simulated and predicted. The representative volume element is generated by Tyson polygon method, and the micro sub-model is established. Two perpendicular slip bands of bcc structure are considered as potential crack initiation locations, and several parallel slip bands with the same orientation are simulated. The crack initiation life at the critical point from the crack initiation stage to the crack growth stage is given by the calculated crack growth rate change. The simulation results show that the crack initiation life is in good agreement with the experimental data except the columnar crystal structure.

The visual monitoring of welding process and welding defect identification are vital to the intelligent control of welding processes. In this paper, a mid-wave infrared CCD was used to acquire the infrared images of the welding pool on-line during the welding process. The images captured are preprocessed by the improved filtering algorithm and image enhancement algorithm. To obtain the temperature distribution information of the welding pool, the relationship between the gray value in infrared image and the temperature is established based on temperature calibration of the used thermocouple. The improved edge extraction algorithm is used to extract the characteristic parameters of the welding pool. Then the identification algorithm of welding defect is developed. The results of verified experiments show that the proposed algorithm has good practicability and accuracy in the on-line identification of welding shape, burn-through and unmelted defects.

Polymethyl methacrylate (PMMA) and 304 stainless steel were welded by laser heat conduction joining technique, and welding quality between transparent PMMA and 304 stainless steel was investigated by orthogonal test method. Tensile test and section test were carried out, and welding results were quantitatively determined by energy density. The effects of various welding factors on tensile strength and weld width were analyzed. Experimental data were processed by the difference analysis method of orthogonal test, and optimal welding parameters of laser heat conduction welding between PMMA and 304 stainless steel were achieved. The results showed that the welding speed was the most dominant factor in determining the joint strength, and the pulse width, gas protection volume, peak power, spot diameter and pulse frequency were the 2nd to 6th effective factors.

The influence of nano-particles addition on the microstructure and mechanical properties of soldering joint of low silver SAC0307 soldering paste was studied. The results show that the island-like Cu₆Sn₅ phase exists in a larger size and is difficult to keep dispersion in solder eutectic regions with the addition of nano-Cu. When the additive amount of nano-Cu exceeded 0.3%, the Cu₆Sn₅ phase was easy to accumulate, merge and grow up in the liquid/gas interface. This behavior leaded the deterioration of the flowability of solder, and produced large amount of pores because the flux gas in the solder paste is difficult to escape during the soldering process. While there is no pores in solder joints with 0.1%~5.0% nano-Ag addition. The Ag₃Sn phase exists in a tiny size and diffuses distribution in these solder eutectic regions, and the β-Sn primary crystals are refined significantly in solder joints. With the increase of nano-Ag addition, the shear strength increases firstly and then decreases. when the addition is 0.5% the shear strength is the largest, meaning the shear strength in this addition is 30.8% higher than the shear strength of solder joint the SAC0307 solder paste under the same conditions.

Laser welding seam of titanium alloy is a non-ideal acicular structure. The research on its superplastic deformation mechanism can promote the application of titanium alloy LBW/SPF technology, and also have benefits of significance to the development of material forming mechanism. The results show that the laser welding of TC4 titanium alloy after welding have good superplastic deformation ability. During the deformation process, two important microstructure changes are taken placed in the weld, that is, the microstructure transformation of the acicular structure lamellae and the lamellar tissue equiaxed. Under the action of stress, the lamellar structure is transformed into equiaxed grains through the process of fracture, disintegration and equiaxed. The dynamic recrystallization and compression is the main mechanism of the lamellar fracture; the mechanism of the lamellar disintegration is grain boundary sliding and rotation, the plastic flow mechanism of the weld joint is grain boundary sliding and rolling mechanism.

Real time dynamic measurements on the vibration amplitude of the sonotrode, the upper and lower copper sheet were performed using laser displacement sensor during ultrasonic welding of copper sheets. The welding process was analyzed on the basis of the relative motion among three parts and the microcosmic evolution of fracture surface. The results showed that during the welding process the amplitude of sonotrode changed little and that of the lower sheet increase gradually. Meanwhile, the amplitude variations of the upper sheet progess is increased at first then decreased and increased again. In the amplitude increase stage, a quantity of friction heat were generated owing to the relative motion between the two welded sheets. Besides, the microjoining appeared at the welding interface, In the amplitude decrease stage, the relative motion between the upper sheet and the sonotrode increased rapidly. It prompted the occurrence of the severe plastic deformation and the effective bonding area increased rapidly. Finally, the upper and lower sheets vibrated at the same amplitude. A large number of dimples were observed on the fracture surface.

In order to obtain high-strength dissimilar metals joints of T2 copper and Ti-6Al-4V titanium alloy, electron beam welding was used to carry out experiments, and the interfacial microstructure and mechanical properties of the joints were analyzed. Based on the Ti/Cu welding-brazing process, the remelting temperature field of intermetallic compounds layer at the Ti/Cu bonding interface was constructed by secondary composite welding on the Ti side of high melting point, and then the remelting modification of Ti/Cu intermetallic compounds layer was realized. By temperature field simulation of FEM and detection of SEM, XRD, the results shown that a high temperature of about 1 000℃ at the interface was formed by remelting welding at titanium side, leading to local remelting of intermetallic compound layer. In the process of solidification, due to the direction of heat dissipation and the redistribution of elements, the formation sequence of the phase was changed, the diffusion distance of titanium atoms was reduced and TiCu with high hardness was transformed to Ti₂Cu. The phase structure was optimized and finally the strength of the welded joints improved.

Aimed at the weld vision detection problem of arc welding robot in CCD directly photographed image, an algorithm for the extraction of special weld seam track with large discontinuity, sharp turning point and more interference was proposed. The algorithm firstly use wavelet transform to smooth the weld edge line to get the initial weld track that is very close to the final weld, and then use Snake model and genetic algorithm to get accurate matching and extraction of special welds. Experimental results demonstrate that the algorithm can improve the precision of special weld track recognition and detection, and has strong adaptability, and can also provide some technical reference for further improving the intelligent vision detection of arc welding robot.

Fe-based and Co-based cladding coatings were prepared on the surface AISI H13 hot die steel by laser cladding technology. The microstructure, hardness and abrasion resistance of two kinds of the cladding coatings were compared and analyzed by an optical microscope, a scanning electron microscope, a rockwell hardness tester and a high temperature friction and wear tester. The cladding coatings were heated to 600℃ for 1 h and repeated 4 times by a muffle furnace. The red hardness was measured. The results showed that the hardness values of the substrate, the Fe-based and the Co-based coatings were HRC 47, HRC 52 and HRC 48, respectively. The red hardness values of the substrate and the Fe-based cladding coating decreased, while that of the Co-based coating increased. The wear loss weight and the coefficient of friction of the Co-based cladding coating were the minimum. The wear mechanisms of the substrate, the Fe-based and the Co-based coatings were mainly abrasive wear, adhesion wear and mixed modes, respectively.

Ti+Nb/Mo thin films were deposited onto Al₂O₃ ceramic by magnetron sputtering with a subsequent nickel-plating to ensure the robust brazing of Al₂O₃ ceramic to Kovar alloy using the filler of AgCu28. Microstructures of the metallization layer and the brazing joints of Al₂O₃/Kovar were investigated systematically by scanning electron microscopy (SEM) and energy dispersive X-ray (EDS). The results show that the interfacial reaction layers are created between filler alloys and base materials. Interdiffusion of Ni and Cu at the interface of AgCu/Kovar resulted in the formation of the reaction layer. The metallization layer plays an important role in hindering the formation of intermetallic compounds and relieving residual thermal stress at Al₂O₃/AgCu interface. In addition, the presence of eutectic region arising from nickel-plating can improve the thickness of the brazing seam and therefore a good bonding betweenAl₂O₃ ceramic and Kovar was achieved.

Ag-Cu filler was used to braze ZTA ceramic and TC4 alloy. Scanning electron microscopy, energy disperse spectroscopy and X ray diffraction were used to identify the interfacial microstructure and the reaction mechanism of the joints was clarified. The typical interfacial microstructure was ZTA ceramic/TiO+Ti₃(Cu,Al)₃O/Ag(s,s)/Ti₂Cu₃/TiCu/Ti₂Cu/α+β-Ti/TC4 alloy. The experiments were carried at the brazing temperature from 810 ℃ to 910 ℃. The results indicated that as the brazing temperature increased, Ag-based solid solution layer thinned and Ti-Cu intermetallic compound layers thickened. When brazed at 890 ℃ for 10 min, Ti-Cu intermetallic compounds occupied almost the entire brazing area, and the shear strength of the joints reached the highest value of 43.2 MPa.

In order to alleviate the softening problem of 6N01 aluminum alloy during fusion welding, the microstructure and mechanical properties of MIG welded joints with water accelerated cooling were studied and compared with the joints under natural cooling conditions. The results of metallographic experiments showed that the partially melted zones of filling pass and cover pass were narrowed by water cooling. The columnar grain regions of the weld near the fusion line were widened and the equiaxed grains in the weld were refined. Microhardness test results showed that the softening zone of the joint was significantly narrowed and the hardness increased under water cooling conditions. The TEM morphology of the softened zone showed that the sizes of β' precipitation were also reduced. The yield strengths and tensile strengths of MIG welded joints were also improved by water cooling. The experimental results confirmed that water cooling can optimize the microstructure and improve the mechanical properties of MIG welded 6N01 aluminum alloy joints.

Crack penetrating through bridge deck in the joint of longitudinal rib and deck plate can only be repaired by re-welding, however, it will be recurred on account of high residual stress deriving from re-weld process. In this paper, the cracks through the bridge steel deck plate at the joint of longitudinal rib and deck plate are selected as research object, then the residual stress is calculated by substructure method and the influences of welding procedure are considered meanwhile. The results show that, in the same conditions, the numeric value and distribution range for RDF cracks are higher than RD cracks and symmetry welding from middle to both ends is useful to decrease the longitudinal tensile stress. The relationship between the longitudinal residual stress and the re-welding length or the groove angle at welding toes is congruous with the power function relation.

In the paper, on the basis of the theory of atomic diffusion, ZChSnSb11-6/30CrMnSi bimetal composite material was prepared by means of hot dipping tin plating as intermediate transition layer. The transition zone morphology and element distribution of ZChSnSb11-6/30CrMnSi bimetallic material were characterized by a scanning electron microscope (SEM) equipped with an energy disperse spectroscopy (EDS). Also, the hardness and interface bonding strength were tested. The research results prove the functionality and availability of the method using the hot dipping tin to attach the ZChSnSb11-6 with 30CrMnSi. There is a transition area generated by the diffusion between the steel substrate and the middle layer tin, and the thickness of the transition area increases significantly with the increasing of tin plating temperature. Besides, the hardness of transition zone is significantly higher than both sides of the substrate. Interface bonding strength increased with the increasing of tin plating temperature, and peaks arrived to 60.6 MPa at 900℃.

In this paper, the uphill welding and downhill welding tests were carried out on workpieces with different dip angles under the same MAG welding parameters by single factor test method. The characteristic parameters such as edge and size of the molten pool were extracted by High speed camera and image processing technology and the area and rear drag angle of the molten pool was corrected. The influence of workpiece dip angle on weld pool width, length, area, rear drag angle and weld forming was analyzed. The results show that when the dip angle of the workpiece exceeds 30°, the obliquity of the workpiece has obvious influence on the morphological characteristic parameters and the size of molten pool and it is different in uphill and downhill welding. It is of great significance to reduce welding defects and improve welding process in non-horizontal position welding.

The 5A06 aluminum alloy T-joints with 10 mm thick were welded by stationary shoulder friction stir welding. Through different welding parameter selection of low rotation speed matching high welding speed and high rotation speed matching low welding speed, combined with tensile testing, macroscopic and microscopic metallographic analysis, electron backscatter diffraction analysis and fracture analysis by scanning electron microscopy, the effect of heat input on mechanical properties and microstructures of T-joints was studied. The results show that the two sets of welding parameters can both obtain full penetration T-joints without any cavity defects, the weld surfaces are smooth and flat without weld-thinning. The different heat input changes the friction mode between the stir pin and the surrounding materials and then cause kissing-bonding defects in the welding joint, consequently affect the tensile strength of the joint. Under the parameter of high rotation speed matching low welding speed, the top center of the weld overlap zone is prone to cause weak bonding defects, resulting in a lower tensile strength of 198 MPa, tensile specimen fracture in the middle plate. Under the parameter of low rotation speed matching high welding speed, the weld is free of defects and the tensile strength of the joint is 287 MPa, with the tensile specimen fractured at the bottom plate.

Weld appearance, the stabilities of penetration depth, reinforcement as well as porosity, laser keyhole characteristic and plasma characteristic were studied by using a new laser-MIG hybrid welding process with filling wire of aluminum alloy. The results were also compared with those by conventional laser-MIG hybrid welding process. It is found that with the suitable process parameters, this new welding process for aluminum alloy was stable. The extra wire deposited continuously and the keyhole had obvious periodic variations, including formation, growth and annihilation. The final weld bead had fine appearance. Compared to conventional laser-MIG hybrid welding process, during this new welding process the stabilities of penetration depth and reinforcement were similar, while the keyhole opening area had differences of 15.34%, the total area of plasma and arc had differences of 1.95%.

A novel all-position welding robot for box-type steel structure was devised in order to solve the problems of low degree of automation, high risk of work high above the ground and insufficient stability of weld joint quality in the field welding for box-type steel structure. After the structural design scheme and principle of welding robot system are introduced, the welding motion process at the right-angle corner of box-type steel structure is discussed in detail according to the structural characteristics of the box-type steel structure. Then, the kinematics modeling and analysis based on Craig D-H model were carried out for its various motion states. A new method of kinematics modeling and forward solving is proposed by means of introducing one additional intermediate coordinate system under the conditions of existing connecting rod offset and joint angle variable in the process of transition movement state of welding robot. The results of working space analysis of the welding robot system show that the structural design and parameters selection are reasonable and the forward kinematics solutions is correct.

The Al₂O₃ ceramic were metallized with the Ag-Cu-Ti powder, and then used Al-Si filler to braze Al₂O₃ ceramic and 5005 aluminum alloy. The influence of brazing temperature on the interfacial structures and shear strength has been researched. It was shown that the typical interface structure of the joints was 5005 aluminum alloy/α-Al+θ-Al₂Cu+ξ-Ag₂Al/ξ-Ag₂Al+θ-Al₂Cu+Al₃Ti/Ti₃Cu₃O/Al₂O₃ ceramic. During the brazing, Al-Si-Mg filler reacted with Ti and 5005 aluminum alloy, which made the joints of Al₂O₃ ceramic and 5005 aluminum alloy. With the increased of brazing temperature, the thickness of the Ti₃Cu₃O reaction layer adjacented to the Al₂O₃ ceramic was thinned. Besides, more Ag reacted with Cu and Al, and the amount of ξ-Ag₂Al+θ-Al₂Cu increased. And the shear strength of the joints increased firstly and then decreased with the increase of brazing temperature. The maximum shear strength of joints was 15 MPa when vacuum brazing was performed at 610℃ for 5 min.