In this paper, 4 mm thick 7075 aluminum alloy was utilized for conducting laser-MIG hybrid welding tests to investigate the correlation between the dynamic behavior of keyholes and process-induced porosity. Additionally, the generation and inhibition mechanisms of process porosity were elucidated. Utilizing a high-speed camera test system of our own design, the formation position and movement characteristics of keyholes in the molten pool under different welding parameters were captured using a “sandwich” method. The dynamic behavior of keyholes during the hybrid welding process was analyzed, and the porosity of each welded joint was quantified, revealing an intrinsic relationship between keyhole dynamics and aluminum alloy laser-MIG hybrid welding porosity. The findings indicate that variations in the defocusing amount can influence both the morphology and stability of keyholes in the molten pool, consequently impacting welding porosity. The dynamic behavior of keyholes under different defocusing amounts can be categorized into five types: no keyhole formation, collapse of the keyhole root, complete instability of the keyhole, instability of the keyhole root, and stability of the keyhole. At a defocus of +12 mm, stable keyholes were observed, and no defects in the welded joints were identified.

The tailored thermal heat-treatment process for Ti-6Al-4V alloy manufactured by laser–arc hybrid additive manufacturing can achieve desired microstructures and excellent mechanical properties for components. The effects of different heat treatment regimens on the microstructure and mechanical properties of Ti-6Al-4V alloy manufactured by laser–arc hybrid additive manufacturing are investigated in this study. Utilizing optical microscopy and scanning electron microscopy, we analyze the variations in microstructure with changes in heat-treatment parameters and explore the reasons for the changes in mechanical properties under different solutions’ treatment temperatures and cooling rates. The microstructure of Ti-6Al-4V alloy fabricated via laser–arc hybrid additive manufacturing was primarily composed of Widmanstätten α plate structures and a small amount of acicular martensite α′ within columnar β grains that grew outward from the substrate along the deposition direction. Following solution treatment and aging heat treatment, the microstructure transitioned to a typical high-performance net basket structure with significantly reduced α plate thickness, leading to noticeable enhancements in sample ductility and toughness. Specifically, when the solution treatment and aging treatment regimen was set at 950 °C for 1 h, followed by air cooling, and then aging at 540 °C for 6 h with subsequent air cooling, the average grain size decreased by a factor of two compared to the as-deposited samples, while the impact toughness increased by 66.7%.

Laser-arc hybrid additive manufacturing (LAHAM) based on the synergistic interaction of laser and arc has vast potential applications due to the advantages of high precision and fast manufacturing speed. Titanium alloy is a kind of indispensable material in the aerospace and marine industries because of its superior performance. This study primarily investigates the effect of laser power on formability, microstructure evolution, and mechanical properties of Ti-6Al-4V, a titanium alloy fabricated by LAHAM. The results indicate that the material utilization of the Ti-6Al-4V wire first increases and then decreases with the increasing laser power, reaching a maximum value of 95.48% at a power of 1500 W. As laser power increases, the acicular martensite α′ content in the LAHAM samples decreases, while the α phase increases and exhibits a coarsening phenomenon. Tensile strength increases with the rise in laser power, reaching a maximum horizontal tensile strength of 1080 MPa and a maximum vertical tensile strength of 1100 MPa. However, elongation decreases with increasing laser power. Microhardness decreases with the rise in laser power. The increase in laser power enhances the bonding between deposition layers, significantly improving the tensile strength of the specimens.

6082 aluminum alloy is widely applied in marine engineering, rail transportation and other industries owing to its excellent comprehensive performance. Welding heat source characteristics exert a decisive influence on the microstructure and mechanical properties of welded joints and become a major constraint for the application of medium-thick aluminum alloy welded structures. In this work, comparative tests of TIG and MIG welding were carried out on 16 mm thick 6082 aluminum alloy plates. Combining thermal simulation, metallographic observation and mechanical property tests, the temperature field distribution, microstructure, microhardness, tensile properties and bending properties of the two kinds of joints were systematically studied. The results show that TIG welding possesses high heat input, forming a broad temperature field with steep thermal gradients. Its weld microstructure is coarse and accompanied by severe coarsening of Mg₂Si precipitates, and the joint presents a highly fluctuating M-shaped microhardness distribution. The average tensile strength of TIG welded joints is 194 MPa, and all specimens fracture in the heat-affected zone. By contrast, MIG welding with low heat input produces a uniform temperature field, as well as a fine and homogeneous weld microstructure with dispersed precipitates. Its microhardness distribution is stable, and the average tensile strength reaches 256 MPa, 32% higher than that of TIG joints. Both welding methods deliver favorable bending performance. The difference in heat input and cooling behavior changes the grain evolution and precipitate characteristics and further dominates the final mechanical performance of joints. MIG welding is more suitable for multi-layer, multi-pass welding of 16 mm thick 6082 aluminum alloy. This work clarifies the correlation between heat input, microstructure and mechanical properties, and the optimized process can effectively improve the microstructural uniformity of the weld joint and enhance its mechanical properties.