Oscillation laser-arc hybrid welding (O-LAHW), which can homogenize the temperature distribution of the molten pool and the dynamic behavior of the liquid metal, is one of the most promising molten welding technologies, but there is a lack of research on the heat flow behavior of the molten pool and the homogenization mechanism. In this study, a numerical model coupling a high-speed rotating Gaussian laser heat source with a dual ellipsoidal arc heat source has been established, and a new Volume-of-Fluid (VOF) discrete algorithm is developed to realize the high-precision simulation of the O-LAHW of aluminum. The spatial evolution of the temperature and flow fields over one beam oscillation cycle was explored by means of slicing the transverse/longitudinal cross section of the molten pool. It is found that beam oscillation enhances temperature field uniformity, especially along the welding direction, improving by 30% compared to non-oscillating welding. Flow field of laser-arc hybrid welding (LAHW) analysis reveals significant velocity differences in different regions, with the laser-arc coupling zone experiencing continuous impacts, exacerbating keyhole fluctuations. O-LAHW reduces maximum velocity differences by 2.4 times, promoting stability. The high-speed circulation induced by beam oscillation alters the liquid metal flow direction in the coupling zone, preemptively redirecting shock waves caused by droplet transitions away from the laser keyhole. Additionally, backward-propagating liquid metal transports heat from droplets to the pool’s tail, disrupting micro-vortex circulation and enhancing flow stability and temperature uniformity throughout the molten pool. These findings are important for deepening the degree of understanding of the O-LAHW process and realizing the orderly regulation of the O-LAHW molten pool.

Directional solidification causes a columnar grain microstructure with orientation deviating from building direction to the laser scanning direction which leads to anisotropic mechanical properties of deposited parts in selective laser melting (SLM) additive manufacturing (AM). However, compared to directed energy deposition (DED), the tilt angles between the grain growth orientation and the building direction in SLM are relatively small and hard to investigate due to the high scanning velocity and small facula during processing. This paper investigates the grain growth orientation in the SLM process via finite element analysis and experiments. The maximum heat flow directions and temperature gradients at different deposition heights are studied in order to discuss the local grain growth orientation. Further investigations into the differences in the grain growth orientation under different process parameters have also been carried out. In addition, the research provides a deeper understanding of the grain structures and is expected to help control the solidification texture, which is of vital importance to properties of components.

Selective laser melting (SLM) and laser cladding deposition (LCD) are two typical kinds of laser additive manufacturing techniques that have been developed for many years independently. Although they are based on the same principle of laser cladding, there are little comparison on the fundamental studies for metallurgical behavior (including melting and solidification behaviors) and the mechanical properties of these two techniques up to now. In this paper, the single-track formation and the deposition of block sample from 316L stainless steel powders have been carried out by both SLM and LCD techniques. A comparison on pool shape, cooling rate, columnar grain size and mechanical properties under different processing conditions by LCD and SLM respectively has been studied. It is found that, due to the increase of energy input and the decrease of depth-to-width ratio of melting pool (MP) from SLM to LCD, the primary cellular arm spacing (PCAS) of the sample increases from less than 1.0µm to more than 15.0µm, and thus the cooling rate of MP decreases from about 106K/s in SLM to about 102K/s in LCD. Furthermore, due to the decrease of cooling rate from SLM to LCD, the columnar grains of the as forming alloy are getting coarser. Especially, the relationship between gain size (λ) and the reciprocal of square root of cooling rate (Ṫ) in LCD significantly meets the classical linear function of λ=a+b/Ṫ (a and b are constants), while a new relationship of a cubic function is found in SLM, showing the different solidification characteristics between LCD and SLM. Lastly, the samples of 316L stainless steel by SLM have much stronger tensile strength but lower elongation than those by LCD, and the main reason is due to that the solidification behavior of the MPs by SLM can form much finer columnar grains than those by LCD.

In this study IN718 samples were deposited by direct laser fabrication (DLF) technology in argon atmosphere from pre-alloyed powders. The microstructural evolution of the samples and the effects of energy input (Ev) on microstructural architectures, dendritic morphology, precipitated phases and thus microhardness were investigated in detail. For microstructure of the as-DLFed samples, at a lower Ev, the columnar grains were very continuous and uniform, while at a higher Ev, the columnar grains were no longer continuous and a layer banded structure was present. With increasing Ev, there was a dendrite to cell transition (DCT) in dendritic morphology evolution of the as-DLFed IN718 samples. Also, two critical points of Ev to determine whether the dendritic morphology of the as-DLFed IN718 sample is dendrites, cells or both were found to be about 220 J/mm3 and 550 J/mm3 respectively in this study. For precipitated phases, the size and the amount of the Laves phase within interdendritic boundaries were increased with increasing Ev, while the volume fraction of precipitated γ″ and γ′ phases in matrix γ of the as-deposited IN718 samples was getting small. As a consequence, the microhardness of the sample increases by decreasing Ev for a constant overlap rate between two neighbor cladding tracks, similarly, the microhardness also increases by decreasing Ev for a constant laser scanning velocity.