The energy density attenuation of focused laser beam could induce inconsistent thermodynamic behaviors from near field to far field, which leads to the deterioration of the welding stability. ...However, the influence of energy density attenuation on welding process remains unclear. In this work, a set of innovative characterizing methods are presented to quantitatively evaluate the features of the front keyhole wall and molten pool dynamics. The energy density attenuation and correlative phenomena are numerically studied using a multiphase model. This model incorporates an improved ray-tracing method which can describe the actual beam profile more accurately. Based on experimental and numerical results, a unique melting behavior, i.e., the alternate melting between keyhole wall and keyhole bottom due to the energy density attenuation, is discovered. This melting behavior is primarily caused by movement of protrusions along the front keyhole wall, which can change the energy absorption efficiency significantly. Besides, it is found that the fluctuation amplitude of molten pool is closely related to this melting behavior. By sustaining protrusion movement process, the melting behavior can be regulated and hence improve the molten pool stability. Finally, an optimization method by adjusting the beam defocus and inclination is proposed and testified to improve the welding stability.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A multi-physics multi-scale model is developed to study the solidification process in laser welding of aluminum.•The simulated results agree well with the corresponding experimental results.•The ...evolution of temperature, solute concentration and constitutional undercooling fields is analyzed.•The distribution of constitutional undercooling ahead of the solidification front is predicted quantitatively.•The selective growth behavior of the columnar grains and equiaxed grains is revealed.
The solidification microstructures directly determine the performance of laser welds. However, the present understanding of the dynamic solidification behavior within the melt pool during laser welding is still limited. This paper developed a multi-physics multi-scale model to investigate the complex solidification process during laser welding of 5083 aluminum alloy. The model combines the macroscale model for heat and mass transfer, the microscale model for polycrystalline alloy solidification, and the continuous Gaussian nucleation distribution model for heterogeneous nucleation. The model is validated by comparing with experimental results from three aspects, namely, the fusion profile, the grain structure and the dendritic structure, and good agreements are achieved. The whole solidification process, from the planar growth to cellular growth, columnar dendritic growth and equiaxed dendritic growth, in the laser weld pool is studied through analyzing the evolution of the temperature, solute concentration and constitutional undercooling fields. In particular, the distribution of constitutional undercooling in the liquid ahead of the solidification front is predicted quantitatively. The relationship between the constitutional undercooling distribution and the nucleation/growth of equiaxed grains is demonstrated, which reveals the selective growth behavior of the columnar grains and equiaxed grains at different locations in the laser weld.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Five adjacent zones were divided from the weld metal to the base metal.•The optical microstructure of each zone was observed.•Microhardness is determined by partitioning of alloying elements and ...precipitates.•Corrosion behavior of each zone was investigated by electrochemical tests.
The microstructure, microhardness and corrosion behavior in five zones from the weld metal to base metal of a 2205 duplex stainless steel joint, which was welded by double-pass tungsten inert gas arc welding with filler wire, were investigated systematically. Results indicated that a great deal of secondary austenite appeared in weld metal due to the reheat of second pass welding and coarse ferrite grains were formed near the fusion line, while other zones had the similar microstructures with a different austenite content. It also revealed the microhardness was determined by the partitioning of alloying elements (Cr, Mo, Ni and N) and precipitates such as chromium nitride. Austenite was harder than ferrite from weld metal to fusion line, while it reversed from fusion line to base metal. Electrochemical measurement indicated the zone containing fusion line was the easiest to suffer pitting attack, followed by weld metal zone. Moreover, the surface morphologies were in good agreement with the electrochemical measurements.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Based on two-dimensional phase-filed simulations, we demonstrated how the solidification morphologies evolved during gas–tungsten arc welding of Mg–4.0 wt% Al magnesium alloy with transverse arc ...oscillation. Results showed that reheating caused by arc oscillation can cause dendrite fragmentation by remelting/pinch-off of sidebranches. Furthermore, the effects of arc oscillation frequency on the solidification morphologies during welding were investigated. We found that the oscillation frequency can significantly alter the reheating time duration during cooling, affect the sidebranches’ pinching behavior, and influence the formation of the dendrite fragments. Results from this research are consistent with previous experimental results.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In order to overcome weld joint softening of aluminum alloy, laser melting injection (LMI) methodology with 6H-SiC particles (SiCp) and 6061 aluminum alloy was introduced. In this manufacturing, the ...molten pool morphology and temperature were gained by high speed camera and thermal imager. After LMI, a graded distribution of SiCp with 4.6%–4.8% volume fraction was obtained along the depth direction of weld. The aluminum grain under LMI (12.80 μm) was much finer than that under single laser welding (SLW) (40.94 μm). It was novel that the in-situ reactant Al4C3 platelets would mainly locate discontinuously on the SiC/Al interface whereas acicular Al4SiC4 was found primarily in the aluminum matrix. In addition, the nano-spherical simple substance carbon was precipitated around the surface of SiCp. Eventually, due to these particular in-situ reactions during laser welding with SiCp injection, the Vickers hardness of weld with SiCp was larger than that under SLW; a gradual hardness distribution in the depth direction of PRW was also observed; the tensile strength of weld with SiCp (192 MPa ~ 243 MPa) became much higher without sacrificing ductility than SLW (165 MPa); the failure mechanism of weld with SiCp would change from SiCp cracking to the SiCp decohesion with the increasing welding speed.
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•The 2-3mm depth aluminum weld with SiC particles were manufactured firstly by laser melting injection.•The process of laser melting injection could refine the aluminum grains compared with single laser welding.•It was first discovered that Al4C3 and Al4SiC4 were distributed on the interface and in the metal matrix respectively.•The in-situ reactions would result in the gradient distribution of hardness and the transformation of fracture mode.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•The grain coalescence behavior and its effects on solidification cracking susceptibility are investigated using the multiphase-field approach.•The transformation of microstructure ...morphology from cellular to dendritic reduces the solidification cracking susceptibility of grains during solidification.•The grain boundary energy in the solid–solid interface suppresses the grain coalescence and increases the solidification cracking susceptibility of alloys.•The coherency point at the last-stage solidification is achieved accurately.
Solidification cracking (SC) is highly related to the grain coalescence behavior during welding of aluminum alloys. In this study, the grain coalescence behavior and its effects on solidification cracking susceptibility (SCS) were investigated using the multiphase-field approach. Why SCS is high at a certain value of Cu concentration and why SC often occurs at high misorientation angles are revealed. Firstly, nominal compositions of Cu affect the morphology of microstructure during solidification. The crystals morphology is cellular at the low concentration, while the crystals are dendritic at the high concentration in the columnar grain region. The SCS of cellular grains is higher than dendrites due to the high volume fraction of solid when the grains/subgrains bridge. Under the action of tensile stress, the scarce residual liquid phase cannot backfill in time. Secondly, high misorientation angles make grain boundary energy in the solid–solid interface (σSS) is high. It is found that σSS suppresses the grain coalescence and increases the SCS of alloys. This leads the emergence of SC at high misorientation angles during welding. In this study, the coalescence behavior of grains during solidification is visually presented by simulation and the coherency point at the last-stage solidification is achieved accurately.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The 2000 series aluminium alloys are qualified for widespread use in lightweight structures, but solidification cracking during fusion welding has been a long-standing issue. Here, we create a ...zirconium (Zr)-core-aluminium (Al)-shell wire (ZCASW) and employ the oscillating laser-arc hybrid welding technique to control solidification during welding, and ultimately achieve reliable and crack-free welding of 2024 aluminium alloy. We select Zr wires with an ideal lattice match to Al based on crystallographic information and wind them by the Al wires with similar chemical components to the parent material. Crack-free, equiaxed (where the length, width and height of the grains are roughly equal), fine-grained microstructures are acquired, thereby considerably increasing the tensile strength over that of conventional fusion welding joints, and even comparable to that of friction stir welding joints. This work has important engineering application value in welding of high-strength aluminum alloys.
Magnesium alloys, which are the lightest structural alloys and have a density that is around one-fourth that of steel, present tremendous potential for increasing the energy efficiency of the ...automobile and aerospace industries. Research on welding magnesium alloys has also increased rapidly as can be seen from journal publications. However, during the welding process, magnesium alloys are highly susceptible to solidification cracking, which prevents their usage in safety–critical applications. The article summarizes and reviews the research progress on solidification cracking of magnesium alloys during welding. The metallurgical and mechanical factors influencing solidification cracking of magnesium alloys are the primary areas of focus in this work. Models and methods for predicting solidification cracking susceptibility of magnesium alloys during welding was developed. More interesting findings on the liquid backfilling to heal cracks and effect of weld pool on solidification cracking were pointed out. The remedies to reduce solidification cracking during welding magnesium alloys were also reviewed so as to achieve high-quality welding and widen the application of magnesium alloys.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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