•The motion characteristics of droplets in hybrid arc space are described.•The action of metal vapor ejected from laser keyhole on droplet is analyzed.•The laser plasma compresses the arc and leads ...to the increase of the electromagnetic resistance of the droplet transfer.
The droplet transfer, plasma morphology and droplet morphology of laser arc hybrid welding process are collected and analyzed using high speed camera. The force magnitude and acceleration of motion droplets in the arc space are calculated by the image processing and mathematical calculations. The value and distribution of the recoil force from the metal vapor on droplets are calculated. The results show that the globular transfer mode corresponds to the welding current is approximate 180 A; the streaming transfer mode corresponds to the welding current is approximate 200 A. The laser has a compress effect on the arc, and the compression on the surface of the weld pool is stronger. The acceleration of the droplet detachment from wire is 70 m/s2 and 50 m/s2 for arc welding and laser arc hybrid welding separately. In the actual welding process, the reaction force of metal vapor on molten droplets is very small, when the distance between droplet and keyhole in the surface of the weld pool is 3 mm. The pressure difference on the surface between upper and lower of the droplet is great, which results the droplet coalescence and the transfer frequency slows down.
Based on the first principle method of density functional theory, the effects of alloying elements Cr, Mn and Ni on the electronic structure and mechanical properties of high nitrogen austenite were ...calculated. The alloying effects of alloying elements Cr, Mn and Ni in high nitrogen austenite were analysed from the aspects of cohesive energy, formation heat, electronic population and elastic constant. The results show that the alloy atoms Cr, Mn and Ni all preferentially occupy the top corner of the high nitrogen austenitic cell. The cohesive energy between Cr and the cell is the largest, the cell is the most stable, Mn is the second, and Ni is the lowest. The solid solution of Cr, Mn and Ni increases the strength of covalent bond and ionic bond in the system, which is the main reason for the performance improvement. Mn has the strongest interaction of ionic bond in high nitrogen austenite cell, and is an excellent austenite stable element. All alloy systems meet the mechanical stability criterion. After Cr and Ni are solid dissolved in high nitrogen austenitic cell, the strength and stiffness of the system decrease, and the plasticity and ductility increase. After Cr is solid dissolved, the corrosion resistance of the system can be significantly increased, and the strength, stiffness and brittleness of the system increased after Mn solid solution.
To study the corrosion mechanism of high-nitrogen steel welds, this study investigated the effects of laser outputs on the corrosion behavior of high-nitrogen steel hybrid welded joints in hybrid ...laser-arc welding. The relationship between the ferrite content and laser output was characterized. The ferrite content increased with the increase in the laser power. The corrosion phenomenon first occurred at the two-phase interface, thereby forming corrosion pits. Ferritic dendrites were first corroded to form dendritic corrosion channels. Furthermore, first-principles calculations were performed to investigate the properties of the austenite and ferrite content. The work function and surface energy indicated that solid-solution nitrogen austenite exhibits a higher surface structural stability than austenite and ferrite. This study provides useful information for high-nitrogen steel weld corrosion.
The plasticity of welded 441 ferritic stainless steel joints was controlled by varying the laser beam spot diameter during laser welding. A stainless steel plate thickness of 1.2 mm was used. The ...microstructures of the welded joints were analyzed for various spot diameters. The elongation of breaks and the reduced area of tensile specimens were analyzed to study the effects of spot diameter on plasticity of the welded joints. The results showed that the weld melt width and weld column crystal size increased with the spot diameter, but isometric crystals in the center of the weld were gradually reduced. Increasing spot diameter resulted in decreased tensile strength, elongation after breaks, and area reduction. So the parameter must be controlled during the laser welding.
12-mm thick high strength steel was welded by a hybrid Laser-MAG welding. The microstructure, the micro-hardness, and the mechanical properties of the welded joints were studied by optical ...microscopy, scanning electron microscopy (SEM), electron backscattering diffraction (EBSD), and tensile and impact tests. The formation of the weld crack can be eliminated by a heat preservation treatment after welding. The microstructure of the weld and the heat-affected zone (HAZ) is mainly made of martensite. The highest hardness of the welded joint was measured in the HAZ and the tensile fracture is located in the center of the weld. The impact tests show that the impact fracture in the weld is brittle and the impact fracture in the HAZ is ductile. The heat preservation step added after the welding improves the impact toughness of the welded joints.
This paper deals with laser-arc hybrid welding of high nitrogen stainless steel (HNS) with 1.2 mm diameter of austenitic stainless steel (ASS) filler wire. The welding was carried out with different ...shielding gas mixtures like 100%Ar, 95%Ar + 5%N2, 90%Ar + 10%N2, 94%Ar + 5%N2 + 1%O2 and 89%Ar + 10%N2 + 1%O2. The effects of shielding gas composition on the welding stability, microstructure and mechanical properties were analyzed. The results show that the weld seam forming and welding stability are improved when 1%O2 is added to the mixture of Ar + N2, and the nitrogen content in the weld increases significantly. The pore ratio is the lowest in 90%Ar + 10%N2 shielded weld, when 1%O2 is added to 90%Ar + 10%N2, the pore ratio increases slightly. The ferrite percentage is the lowest in 89%Ar + 10%N2 + 1%O2 shielded weld. The 89%Ar + 10%N2 + 1%O2 shielded welded joints feature better mechanical properties.
Abstract
Defects, such as cracks, typically occur in the spinning process of ternary catalyst shells. This study investigates the optimization of spinning process parameters to prevent such defects. ...In this regard, an orthogonal simulation was performed using a finite element model of the spinning process of a ternary catalyst shell. Moreover, spinning tests using a 439 stainless steel welded pipe were conducted to verify the simulation results. Thus, the microstructure, hardness, and quality of formed parts are analyzed. The simulation and test results showed that when the spinning temperature is 1000 °C, the roller fillet radius, roller speed, and feed ratio are 5 mm, 40 r s
−1
, and 1.2 mm r
−1
, respectively. In addition, the error rates of the forming thickness, port diameter, and roundness error are 1.37%, 1.25%, and 4.8%, respectively. These results verified the accuracy of the simulation. Furthermore, no defects were generated during spinning, and the spinning quality was high. The feed ratio was the main factor affecting the roundness error, followed by the roller speed. As deformation increased, hardness increased, and the crystal size decreased. The results of this study can provide crucial theoretical guidance for practical spinning applications.
Abstract
This study uses a laser to etch biomimicking locking patterns on the surface of 304 stainless steel to strengthen the connection between metal-plastic products. Under heat and pressure from ...the device, the plastic melts into the pattern and coalesces it, while the burrs formed from the etching process lock the joint of the metal-plastic. Three biomimicking configurations, honeycomb, leaf vein, and dragonfly head-and-neck hair interlocking, are studied. As shear strength determines the connection strength, we simulate the tensile-shearing process of stainless steel and plastic connectors of the three biomimicking configurations on ABAQUS, and predict the effects of the configurations on their connection strength. Experiments show that the plastic and metal are effectively connected at a heating temperature of 400 °C and a pressure of 70 kN. When the burr rate is 7.66% and the coverage rate is 29.4 ± 0.5%, the three biomimicking connectors break at the plastic base material, and the dragonfly head-and-neck hair interlocking configuration can withstand a shear force of 942 ± 9.23 N.
In this paper, the electrochemical microcorrosion behavior of High-nitrogen steel hybrid weld joints with different wires addition were investigated. Polarization curves measurement was conducted to ...evaluate the corrosion feature in 3.5% NaCl solution. Scanning electron microscopy (SEM) and x-ray diffraction (XRD) were used to analyze the specific corrosion behavior and pitting deepening mechanism induced by precipitated ferrite-dendrites. The experimental results showed that the addition of nitrogen-containing welding wire improved the corrosion resistance of whole weld joint. As a transitional region, the HAZ exhibited relative weak pitting resistance and severe shedding behavior. The coherent dendrites and similar complex geometries led to the accumulation of continuous corrosion channels. The XPS spectra results indicated that the additional nitrogen in the welding wire optimized oxide composition of the surface passive film.
High-nitrogen steel plates with a thickness of 8 mm are welded with a laser-arc composite heat source for experiment to study the impact of different heat input parameters on the blowhole defect. The ...results show that with the increase of laser power, welding current and arc voltage, the porosity of welds decreases; with the increase of welding speed, the porosity of welds increases. Appropriately increasing the heat input helps reduce the porosity of the weld.
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