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The dual laser-beam synchronous welding (DLBSW) technology is newly developed to improve productivity and weld seam quality. In this investigation, AA2060 and AA2099 Al-Li alloys were welded using ER4047 welding wire under different heat input in DLBSW process. The microstructure characteristics especially the fine equiaxed grain ribbons along the fusion lines of T-joints were investigated by observing the micro morphology both in cross section and vertical section. It was found that the non-dendritic equiaxed grain near the fusion line was spherical in three dimensional with small size compared with the equiaxed grain in the weld seam center. Besides, the action of thermal buoyancy flow and Marangoni convection was found to have great effect on the formation of fine equiaxed grain ribbons in the molten pool. Moreover, the energy dispersive spectrometer (EDS) results of non-dendritic equiaxed zone (EQZ) indicated that the strip-shaped intergranular precipitation phase in EQZ is rich in Cu, while the bulk-shaped intergranular precipitation phase is rich in Si.

Laser beam deep penetration welding (LBDPW) was performed to connect the 2219 aluminum alloy butt joint with different parameters. Then, the LBDPW process of 2219 aluminum alloy was modeled using a coupled FE-CA model, i.e., finite element couple with cellular automaton, which contained FE model that simulates temperature field and CA model that calculates microstructure evolution. Furthermore, the microstructure evolution in LBDPW of 2219 aluminum alloy was characterized under optical microscopy and a scanning electron microscopy (SEM). At the same time, the association between LBDPW processing thermal cycles and macrostructure/microstructure evolution is studied. The results show that the final microstructure of the welded joint included fine equiaxed grains in the equiaxed grains zone (EQZ), columnar in the fusion zone (FZ) and coarse equiaxed grains in the weld seam center zone. Moreover, it was indicated that the size of grains is associated with the temperature gradient of the welding process. Besides, the size of EQZ became narrow and uniform because of the undercooling increase, leading to the rise in the heat input.

The purpose of the present study is to investigate pores formation mechanism in the laser-MIG hybrid welded joint of 20 mm thick mild steel. The microstructure and energy dispersive spectroscopy (EDS) of the welding joint are analyzed to verify the pores mechanism. Experimental results show that a well-formed weld bead can be obtained in the backing welding using a wide range of the process parameters. Besides, pores in the laser-MIG hybrid welded joints can be divided into two types, metallurgical pores, and process pores. The small, regular circle shaped metallurgical pores are generally concentrated in the upper part of the weld bead, which is mainly caused by insufficient pre-weld cleaning. In contrast, large, irregular shaped process pores are generally concentrated in the bottom of the weld bead, which is caused by the instability of the keyhole because of unreasonable welding parameters.

The laser welding of 5 mm thick TA15 titanium alloy was realized by fiber laser of IPG YLS-6000. The microstructure and porosity formation mechanism of the welded joints were investigated under different welding conditions. The microstructure and porosity of welded joints were observed using optical microscope and energy dispersive spectrometer (EDS), respectively. Moreover, the influencing mechanisms of porosity formation and evolution induced by metallurgical and instability of keyhole were also discussed. The experimental results indicated that the outline of metallurgical porosity is regular, which is mainly caused by the absorption of water from the outside environment into the molten pool and the evaporation of Al element. Fast welding speed contributes to the keyhole fluctuating sharply or even collapsing, which causes the shielding gas to enter the molten pool and further form bubbles. The fundamental reason for the formation of porosity is that the laser welding speed is so fast that the molten pool cooling speed is high, which makes it difficult for dissolved gas to escape sufficiently and finally form porosities. It lays foundation for understanding the formation mechanism of porosity and optimizing the process for laser welding of TA15 titanium alloy.

With the increasing of laser power and energy density, laser welding has the potential to replace electron beam welding for aluminum alloy in many conditions. This paper present an comparison investigation between laser beam welding and electron beam welding for 5A06 aluminum alloy. The characteristics of laser beam and electron beam welded joints are compared, including the micro-structure, mechanical property, area of melting zone and depth-to-width ratio. Moreover, the component distribution in different zones of the welded joints is analyzed. It is found that the micro-structure and mechanical property of electron beam welded joint is better than that of laser beam welded joint.

Laser welding-brazing (LWB) technique is considered to offer advantages over fusion welding in terms of dissimilar jointing since it can avoid liquid dissimilar alloys mixing in the molten pool. In this paper, LWB technique is utilized to join 1050 aluminum alloy to Ti-6Al-4V. A 3D finite element model is developed to calculate the temperature field in the LWB process with a combined Gaussian heat source model. The simulated asymmetric temperature field is in good agreement with the experimental metallography, which confirms the validity of the present combined heat source model. The peak temperature of the center of the weld seam increases with time in the welding process. The experimental and simulation results both indicate that the heat-affected zone (HAZ) width of the upper is narrower than that of the bottom. Besides, the growth orientation of coarsened dendrite near the interface at root face is substantially perpendicular to interface. The grain morphology of the molten pool appears as dendrite, cellular dendrite and equiaxed crystal from the fusion line to the center of the weld seam.

The Invar Fe-36Ni alloy plates are welded by multi-layer multi-pass MIG welding with two kinds of filler metals in this paper. The microstructure of the joints is studied using scanning electron microscopy, x ray diffraction, and energy dispersive x-ray spectroscopy. And the morphology and microstructure of the joints with two different filler metals are compared. Moreover, the element distributions at different location are discussed. The results indicate that there are no pores or crack defects on the surface of the weld seam. The sizes of the incomplete fusion, which occurred in the interior of weld seam, using stainless steel filler metal are much larger than that of using Invar M93 filler metal. The distributions of elements in the interlayer are homogeneous using two filler metals. However, the element distributions, which are perpendicular to the fusion line, are not uniform using steel filler metal. The experimental results illustrate that the M93 Invar welding filler is better than stainless steel filler metal for multi-pass welding process of Invar Fe-36Ni alloy.

Laser melting deposition with different parameters was performed on invar alloy powder and substrate by KUKA Robot with a fiber laser of YSL-6000. The deposition porosity, microstructure and component enrichment behavior were studied. It revealed that the deposition porosity could be effectively controlled with laser power of 2300 W and scanning speed of 1.5 mm s−1. The microstructure evolution suffered from elongate cellular crystal to equiaxed cellular crystal, while the constitutional supercooling increased from initial solidification to final solidification. The component enrichment behavior was observed near the surface of deposition layer measured by EDS. The ferrum content near the surface reached the highest value 64.39 wt%, but only 62.52 wt% in the center. In addition, the distribution of ferrum component and Vickers hardness along the center line of deposition layer were investigated. It was also found that the component content in the top of deposition layer is highest ~57%. The decrease tendency of microhardness (in a range of 96.1 to 110.5 HV) from the bottom to the top of DL is performed. The marangoni convection behavior, that is slower velocity at the edge, is the key factor that dominated the ferrum distribution.

A band of equiaxed grains is found near the fusion boundary of Al–Li alloy weld seam. In order to clarify the formation mechanism of this equiaxed grain zone (EQZ), experimental investigations and numerical simulation of laser butt welding for 2060 Al–Li alloy are conducted in this paper. The macrostructures and microstructures of welded joint under different welding parameters are evaluated. In addition, a 3D finite element model with the same dimension as the experimental workpiece is established and the temperature field of welded panel during laser welding process is simulated. The analysis results indicate that the formation of EQZ is related to the temperature gradient at the fusion boundary. With the increase of heat input, the undercooling rate increases accordingly, making the grains in EQZ get coarser.

A coupled thermal–metallurgical model is developed to predict the temperature fields and spatial distribution of volume fraction of phases during laser beam welding of 1020, 1045, and 1060 steels. The classical transient heat conduction model is used to calculate the temperature fields during laser beam welding. For phase transformation, the austenization, the austenite-to-pearlite/ferrite transformation, the austenite-to-bainite transformation, and the austenite-to-martensite transformation are modeled respectively. All of these transformation models are solved by the finite element method (FEM) based on the simulated temperature fields. The thermal properties of the three steels are determined by the linear interpolation base of the phase fractions, and thermal properties for each pure phase. The temperature fields and spatial distribution of phases are predicted by 3D finite element method (FEM) code which is developed by the authors to solve the thermal–metallurgical models. In addition, comparison between the coupled model and the pure conduction model without considering phase transformations is carried out to study the influence of phase transformation on temperature fields during welding. According to the comparison, the temperature of the coupled model is higher than the pure conduction model in the temperature region above 1000 °C, but the temperature profiles are very similar at the temperature region under 1000 °C. The predicted volume fractions of 1020 and 1060 steels are close to experimental results. However, there is an obvious difference between predicted and experimental results of the phase fraction of 1045 steels.