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Additive manufacturing (AM) of ceramic particle reinforced aluminum alloy has drawn increasing attention due to the refined microstructure and improved mechanical properties in as-deposited condition. However, it is still challenging to make defect-free ceramic particle reinforced aluminum alloy deposit with desirable surface finish using wire-based AM technique because of the special thermophysical properties of the incorporated ceramic particles. In this work, a novel oscillating laser-arc hybrid additive manufacturing (OLHAM) technique was developed to fabricate TiC nanoparticles reinforced 2219 aluminum alloy deposit. The surface finish and porosity were evaluated using optical microscope and 3D XCT, respectively. Compared with wire-arc additively manufactured (WAAMed) deposit, the surface roughness and volume porosity of OLHAMed deposit decreased by 46.0 % and 88.3 %, respectively. In-situ high-speed photography was used to observe the arc and molten pool behaviors to understand the mechanism of enhanced surface finish and reduced porosity. The enhanced surface finish was attributed to smaller layer width fluctuation and higher arc stability, which resulted from the action of the hybrid heat source. The elimination of large droplet transfer, which caused pores in the WAAMed deposit, and the promotion of molten pool fluidity resulted in much lower porosity of the OLHAMed deposit.

This study is intended to examine the droplet transition in the welding process. Tests were performed using a high-speed camera to assess the effect of the vertical distance between the laser–wire intersection and workpiece (H) on droplet transition. Meanwhile, forces on the droplet were analyzed to evaluate the transition model during laser welding with filler wire. The results showed that the droplet transition model, transition frequency, droplet size and forces of the model all changed with Hlevel changing. Droplet transition and the welding process showed stability at an Hlevel of 1 mm. Based on the liquid bridge transition model, the droplet was transferred to the molten pool in the state of balance, while the droplet entered into the molten pool under non-equilibrium state during globular transition.

In this work, TiC nanoparticles (TiCps) reinforced 7075 aluminium alloy was fabricated via an oscillating laser-arc hybrid additive manufacturing process. To show the beneficial effect of TiCpsaddition on microstructure and mechanical properties, a conventional 7075 aluminium alloy was also manufactured for comparison. Upon the addition of TiCps, remarkable grain refinement was achieved with a decrease in average grain size from 111.8 to 12.5 µm, and grain boundary segregation was alleviated. It was also found that many secondary phases precipitated at the grain interior in the deposit with TiCps. Owing to the refined microstructure and favourable precipitation, as-deposited 7075 aluminium alloy with TiCpsshowed enhanced tensile properties of ultimate tensile strengths of 346 and 355 MPa along scanning and build directions.

In this work, TiC nanoparticles (TiCps) reinforced 7075 aluminium alloy was fabricated via an oscillating laser-arc hybrid additive manufacturing process. To show the beneficial effect of TiCpsaddition on microstructure and mechanical properties, a conventional 7075 aluminium alloy was also manufactured for comparison. Upon the addition of TiCps, remarkable grain refinement was achieved with a decrease in average grain size from 111.8 to 12.5 µm, and grain boundary segregation was alleviated. It was also found that many secondary phases precipitated at the grain interior in the deposit with TiCps. Owing to the refined microstructure and favourable precipitation, as-deposited 7075 aluminium alloy with TiCpsshowed enhanced tensile properties of ultimate tensile strengths of 346 and 355 MPa along scanning and build directions.

In this work, the asymmetric weld fusion geometry in oscillating laser beam welding (OLBW) of aluminium alloy was reported and investigated using a numerical approach. A multi-physics heat transfer and fluid flow model of OLBW was developed and validated with the corresponding experimental results. The weld fusion geometry, temperature fields, and fluid flow behaviours for four commonly used oscillation modes, line, circle, eight, and infinity, were calculated to analyse the origin of the asymmetric weld fusion geometry. The results show the asymmetry of local heat input along beam travelling path and the fluid flow pattern in the molten pool are the main factors that result in the asymmetric weld fusion geometry in OLBW.

In this work, the asymmetric weld fusion geometry in oscillating laser beam welding (OLBW) of aluminium alloy was reported and investigated using a numerical approach. A multi-physics heat transfer and fluid flow model of OLBW was developed and validated with the corresponding experimental results. The weld fusion geometry, temperature fields, and fluid flow behaviours for four commonly used oscillation modes, line, circle, eight, and infinity, were calculated to analyse the origin of the asymmetric weld fusion geometry. The results show the asymmetry of local heat input along beam travelling path and the fluid flow pattern in the molten pool are the main factors that result in the asymmetric weld fusion geometry in OLBW.

Wire-based additive manufacturing (AM) shows a promising prospect in fabricating large-scale titanium aerospace components at a high deposition rate and low cost. The currently used wire-based AM processes commonly utilize a lateral feeding method with an acute angle to form a deposit, which reduces the flexibility and increases the difficulty of control in making complex components. In this work, a novel coaxial laser metal wire deposition (LMWD) process was used to fabricate the most widely used titanium alloy, Ti6Al4V. The coaxial wire feeding was achieved by a coaxial laser head through a vertically fed wire surrounded by an annular shape beam at focal plane. The surface quality, microstructure and mechanical properties of the deposited Ti6Al4V were examined. To show the characteristic of the coaxial LMWD process, conventional lateral LMWD was also conducted for comparison. The deposited Ti6Al4V wall showed a high surface quality and a microstructure with a mix of equiaxed β grains and columnar prior-β grains rather than coarse prior-β grains. The refined microstructure resulted in a low anisotropy in mechanical properties. The mechanism of the equiaxed β grains formation was also discussed. The combined effect of the reduced thermal gradient and the heterogeneous nucleation from the coaxial wire feeding played an important role in determining the refined microstructures in coaxial LMWD.

The currently available high-power laser presents significant opportunities for welding of thick section components in single-pass. However, weld defects frequently occur and depth of penetration is usually lower than expected in this situation. In this work, a process of laser welding under reduced ambient pressure was investigated to achieve a single-pass complete-joint-penetration weld of 20 mm-thick high-strength steel. An experimental and theoretical program of investigation was undertaken to evaluate the characteristic of this welding process. The weld appearance, porosity inside the weld metal, microstructure and mechanical properties of weld joint were examined experimentally. The temperature field was calculated numerically using a 3D heat transfer and fluid flow model. A defect-free sound weld joint of 20 mm-thick plate was obtained just using an 8-kW laser power. The weld joint showed a very high aspect ratio characteristic of electron beam welding. From base metal (BM) to fusion zone (FZ) through heat-affected zone (HAZ), the microhardness varied significantly duo to their different microstructures resulted from the various peak temperatures and cooling rates for varying distances from weld center. All the tensile test samples fractured at the BM away from HAZ and FZ, which suggested that the welded metal was stronger than BM. The calculated weld geometry agreed with the corresponding experimental results through considering the role of ambient pressure. Their good agreement indicated the validity of the potential causative variables considered in the simulations. The modelling results also showed that the weld pool had a lower peak temperature and thinner liquid weld metal around keyhole under reduced ambient pressure.