The solidification cracking behavior in laser welds of steel/copper dissimilar metals was systematically investigated. T2 copper and SUS304 stainless steel were used in the study. The results showed that the occurrence of solidification cracking in welds was the synergistic effect of ε phase liquation, inclusions and composition segregation. During the welding process, the liquation of grain boundaries substantially reduced the cohesion between adjacent grains, as well as the resistance for intergranular crack propagation. The composition segregation inside the grains could induce lattice distortion, thus reducing the plastic deformation capacity of the material itself and concurrently increasing the susceptibility to cracks. In addition, an effective solution for inhibiting solidification cracking was proposed by using an oscillating laser, and the inhibition mechanism was further discussed. Laser oscillating welding significantly promoted grain refinement, solute diffusion and the formation of uniformly distributed ε-Cu precipitated phases in welds. It can improve the intergranular bonding, reduce the susceptibility to solidification cracking and increase the resistance to plastic deformation. The tensile strength of joints using laser oscillating welding is 251 MPa, 35.7% more than 185 MPa using laser welding. Meanwhile, the strain of joints using laser oscillating welding is 3.69, a 96% increase compared to 1.88 using laser welding.

A 3D non-axisymmetric hybrid plasma model in fiber laser-arc welding is developed, in which the laser induced plasma is considered as ejecting vapor from keyhole with specific radius, temperature and velocity. The effects of the ejecting vapor temperature and velocity, and the distance between laser and arc are simulated and discussed. From the simulation results, the height of the laser induced plasma is higher with lower ejecting vapor temperature, bigger ejecting vapor velocity and larger distance between laser and arc. The temperature of the hybrid plasma decreases compared with the temperature of arc plasma under all the simulation parameters, which is very benefical to reduce distortion resulted from bigger heat input. The current density of the hybrid plasma has a complex dependence on the studying parameters. When the ejecting temperature is 10 000 K, or the ejecting velocity is 50 m s ⁻¹ or distance between laser and arc is 4 mm, the current density in the laser-induced-plasma affected zone is larger than that of the arc plasma at the same position, while it becomes smaller under other simulation parameters. In addition, the current becomes more concentrated with lower vapor temperature, larger vapor velocity and smaller distance between laser and arc.

As a representative type of superalloy, Inconel 718 is widely employed in aerospace, marine and nuclear industries. The significant work hardening behavior of Inconel 718 can improve the service performance of components; nevertheless, it cause extreme difficulty in machining. This paper aims to investigate the influence of chamfered edge parameters on work hardening in orthogonal cutting of Inconel 718 based on a novel hybrid method, which integrates Coupled Eulerian-Lagrangian (CEL) method and grain-size-based functions considering the influence of grain size on microhardness. Orthogonal cutting experiments and nanoindentation tests are conducted to validate the effectiveness of the proposed method. The predicted results are highly consistent with the experimental results. The depth of work hardening layer increases with increasing chamfer angle and chamfer width, also with increasing feed rate (the uncut chip thickness). However, the maximum microhardness on the machined surface does not exhibit a significant difference. The proposed method can provide theoretical guidance for the optimization of cutting parameters and improvement of the work hardening.