Search

The Z-axis lifting height is significant in layer-by-layer fabrication using laser directed energy deposition (L-DED). In this paper, we have deeply examined the porosity and grain morphologies in the double layers of AlSi10Mg by blue laser directed energy deposition (BL-DED). After the deposition of a single track, the depositional head was raised by a certain Z-axis lifting height and then a second layer was deposited. As the Z-axis lifting height increases, the quantity density of pores in the second layer increases, leading to higher porosity. Especially, the boundary of the overlapping area exhibits the highest porosity, measuring 0.84%. The Z-axis lifting height can be set lower than the height of a single track, while maintaining high dimensional accuracy and surface quality. [ABSTRACT FROM AUTHOR]

[Display omitted] • Infrared laser beam circular oscillation was used in the I-BLH cladding process of pure Cu on the rolled AlSi7Mg substrate. • Circular oscillation reduces the defects, decreases the surface roughness, and promotes the formation of equiaxed grains. • The main influence factors for eliminating defects and improving microstructures are the cooling rate, temperature gradient, and oscillating effect. Infrared-blue laser hybrid (I-BLH) has been proven to have high power conversion efficiency and stability in the cladding process of some high-reflectivity alloys for the infrared laser, e.g., Cu-alloys and Al-alloys. The highly concentrated energy input in the overlap zone between the infrared laser and blue laser beam may lead to the formation of severe micro-pores and coarser columnar grains. To solve this difficulty, a new way, infrared laser beam circular oscillation, was successfully used in the cladding process of pure Cu on the rolled AlSi7Mg substrate. The circular oscillation of the infrared laser beam reduces the defects in the hybrid cladded samples and increases the relative density to ∼ 100 %. Besides, the circular oscillating scanning decreases the surface roughness of the cladded samples to ∼ 40 μm. Finally, the circular oscillating scanning is conducive to forming equiaxed grains in the cladded samples, with a minor coarsening of the Al-dendrite and Al 2 Cu phases. The main influencing factors for eliminating defects and improving microstructures of the I-BLH cladded samples are the cooling rate, temperature gradient, and oscillating effect. Thus, infrared laser circular oscillation scanning shows a great potential to improve the quality of the I-BLH cladding technology and contribute to applications in the further industry. [ABSTRACT FROM AUTHOR]

• A new method for manufacturing high-performance motors with blue laser spot welding of electrical steel sheet. • The effects of defocus on the molten pool evolution, surface characteristics and microstructure of weld spot were studied. • −2 mm is the recommended defocus parameter for blue laser spot welding electrical steel sheet. We first developed a spot welding method that utilizes a flat-topped blue laser to join electrical steel laminations, specifically designed for high-performance motor applications, which boasts a high laser absorption rate and low heat input. This paper focuses on the impact of defocus distance on the welding quality. The results show that under negative defocus, the laser beam irradiates on the substrate in a convergent state, which improves the efficiency of laser penetration, intensifies the evaporation of silicon steel coating and melting metal, forming a "single hump" molten pool with a plume above it. As the defocus decreases from 0 mm, the penetration depth first increases (maximum value at −2 mm) and then decreases. Positive defocus leads to a wider and shallower molten pool without generating a plume. The welding melting mode can be changed by the defocus distance, but it can't be quantified by conventional laser power density due to the characteristics of beam convergence or divergence. Furthermore, the grain size decreases as the focus position moves up, and the shape of columnar grains changes from slender to coarse. The grain type at the molten pool boundary is quantified by the G/R value calculated via the mathematical model of the thermal profile. Finally, it is recommended to select the −2 mm defocus distance to obtain a large weld area and high surface quality. [ABSTRACT FROM AUTHOR]

• 3500 W blue laser with 7.5 mm2 rectangular spot is applied for depositing copper. • Achieving 62.84 mm2/s when cladding copper on Inconel 718 with 3500 W blue laser. • High-power blue laser promotes smooth composition transition in Cu/Ni interface. • Compared to infrared laser, blue laser can achieve almost defect-free cladding. High efficiency deposition of highly reflective copper on a nickel-based superalloy substrate presents a significant challenge. This study first used a 3500 W high-power and 7.5 mm2 large-spot blue laser in Directed Energy Deposition, and successfully deposited copper on an Inconel 718 substrate. The process exhibited stability, with no significant cracks or pores observed. To the best of our knowledge, we have achieved the highest cladding efficiency of 62.84 mm2/s in the current cladding of copper. The interface between copper and Inconel 718 displayed a smooth composition transition at 3500 W, and the width reached 418 μm. The cladding layer displayed a columnar dendritic morphology at the bottom, gradually transitioning to equiaxed dendrites at the top. Dendrites enriched in elements found in Inconel 718 solidified, while Cu from the powder mainly solidified in the interdendritic region. The utilization of a high-power, large-spot blue laser offers a promising process for the efficient fabrication of large Cu/Ni dissimilar structural components. [ABSTRACT FROM AUTHOR]

Laser Directed Energy Deposition (DED) is an important process for additive manufacturing because of the advantage of high manufacturing speed. 450 nm blue laser has a higher absorption rate than traditional infrared laser for highly reflective materials such as Al and Cu. However, it is still unclear how the blue laser affects the particles and the molten pool flow in the DED process. In this work, we first designed two models to reveal the mechanism of the molten pool behaviors in the blue laser DED process: the transient model and the steady deposition model. The models are validated by in-situ and ex-situ experiments respectively. It is found that the three stages can be concluded for a particle impacting the molten pool: particle impacts, surface oscillates and the molten pool recovers. The particles whose diameter is less than 100 µm are necessary for steady deposition. The influence of process parameters on DED is investigated, and a suitable process parameters window is found. we also verified the superiority of the blue laser for DED of highly reflective materials through the simulation models. The current study provides new insights into the mechanism from the interaction in the molten pool scale to single-track forming in the blue laser DED, and can provide theoretical guidance on the application of blue laser DED of highly reflective materials. [Display omitted] • A 3D multi-physics field model was first developed to visualize the molten pool dynamics in the blue laser Directed Energy Deposition (DED) process. • We found that insufficient melt pool depth and unmelted powder agglomeration were the main causes of porosity in blue laser DED. • We verified the superiority of the blue laser for DED of highly reflective materials through the simulation models. [ABSTRACT FROM AUTHOR]

[Display omitted] • 2000 W blue laser welding system is developed for conduction mode welding of conventional high-reflectivity metals. • The molten pools of welding of both copper and aluminum with 1950 W blue laser are stable without spatters. • Though blue laser has a higher absorptionfor Cu than Al, high heat conductivity of Cu decreases melting efficiencies. High-reflectivity metals, e.g., copper and aluminum, have been widely applied for various industrial products such as power battery, electrical machinery, et al. However, owing to the low absorption rate of copper and aluminum to the conventional infrared laser (900–1080 nm), the keyhole welding mode is required, which is extremely unstable. A blue laser (450 nm) can improve the absorption rate of copper and aluminum evidently, which has potential to weld copper and aluminum at the conduction mode. This work studies the bead-on-plate welding of copper and aluminum by the blue laser. At a blue laser power of 1950 W, the welding depths of copper and aluminum can acquire 1.20 and 1.83 mm. Then, this work exhibits the molten pool characteristics of copper and aluminum in high-power blue laser welding, and builds a relationship between the molten pool characteristics and the welding bead qualities. The unstable boundary of the middle gray-scale region in welding of copper and the ripple phenomenon in welding of aluminum indicate a small depth and rough appearance. This work validates that the 2000 W high-power blue laser can weld conventional high-reflectivity metals (e.g., copper and aluminum) at the conduction mode without spatters, while the keyhole mode is required for welding with the infrared laser. [ABSTRACT FROM AUTHOR]

A single track, as the basic unit of laser directed energy deposition (L-DED) process, plays a significant role in the dimensional accuracy and mechanical performances of the ultimate products. However, there is almost no systematic investigation on the formation process and three-dimensional characteristics of the internal pore defects. Here, we used a high-speed camera, laser scanning confocal microscope (LSCM), and synchrotron radiation X-ray computed tomography (SR-CT) to study single tracks of AlSi10Mg alloy fabricated by blue laser directed energy deposition (B L -DED). A comprehensive investigation is conducted on the impact of processing parameters on the sizes, shapes, and formation mechanism of pore defects. Three types of pore defects are examined in single tracks: Type I lack of fusion, Type II spherical gas pores and Type III large irregular pores. Besides, large irregular pores are the transition between other two types. In particular, the results of SR-CT show that porosity decreases gradually with the increment of laser power and scanning speed. Therefore, high laser power accompanying with fast scanning speed will reduce the porosity. The lowest porosity of 0.074% is achieved under the power at 1600 W with scanning speed at 1080 mm/min, which has an obvious improvement over the current infrared L -DED. In addition, the mapping relationship among laser power, scanning speed and pore defects is established, which will provide a fundamental understanding of the origin of the defect and strategies for controlling the defect in L -DED towards high-quality printing. [Display omitted] • The porosity decreases with the increase of laser power and scanning speed by blue laser directed energy deposition. • Three types of defects are observed: Type I lack of fusion, Type II spherical gas pores, Type III large irregular pores. • The lowest porosity is 0.074% under the power of 1600 W and scanning speed of 1080 mm/min. • The mapping relationship among laser power, scanning speed and types of pore defects is established. [ABSTRACT FROM AUTHOR]

Laminated electrical steels are the key material structure of the stator and rotator of a motor, where high-quality welding is crucial for improving the performance of the electric machine. However, it is challenging to achieve a desired balance among the magnetic properties, mechanical properties, and welding efficiency for the laminated electrical steels at present. This work first adopted a 450 nm flat-top blue laser with a maximum power of 2000 W, which has a higher primary absorption rate to Fe compared to that of the conventionally used 980–1080 nm infrared laser, to join the laminated electrical steels. The dynamic process, weld bead characteristics, mechanical properties, and magnetic properties of the blue laser welding of laminated electrical steels were investigated. The results showed that a flat-top and large-spot blue laser could make the molten pool have a self-stabilizing ability to keep the continuity when encountering the gap and unsmooth surface. Moreover, a further improved self-stabilizing ability was observed for a small welding speed. The largest depth and width of the blue laser weld bead in this work were 2.30 and 0.57 mm, respectively, with a shear strength of up to 1700 N, which were achieved at the laser power of 1500 W and welding speed of 10 mm/s. In addition, the work also validated that the blue laser could significantly reduce the splashing in welding of electrical steel laminations and improve the welding efficiency, which provides a promising solution for high-performance electrical machine manufacturing. [Display omitted] [ABSTRACT FROM AUTHOR]

A coaxial infrared-blue hybrid laser with low power infrared laser was used to clad high-reflectivity CuCrZr alloy on the AlSi7Mg substrate, and the formability and solidification behaviour in cladding with the high crack sensitivity materials under the infrared, blue and hybrid laser were compared. We demonstrated that the combination of a small power (100–200 W) infrared laser with 960 W blue laser can effectively eliminate the cracking and balling phenomenon existed in the cladded samples under the action of both infrared and blue laser. Compared with the coarser Al-dendrite (1.37–2.50 µm) and Al 2 Cu phase in the cladded tracks formed under the infrared laser (2600 W) and the hybrid laser with high infrared power (1000–2600 W), finer Cu-dendrite (0.45–0.89 µm) is the main precipitation phase in the cladded tracks under the combination of 960 W blue laser and low power infrared laser (100–200 W). The improvement of the formability and solidification behaviour should be related to the stable and high absorption rate (∼65%) of blue laser, as well as the concentrated power density of low power infrared laser. This work validated the potential of the infrared-blue hybrid laser with low power infrared laser in cladding with high-reflectivity and high crack-sensitivity alloys. [Display omitted] • Achieving crack-free CuCrZr/AlSi7Mg interface by infrared-blue hybrid laser cladding with low power infrared laser. • Finer Cu-dendrite is the main precipitation phase in the cladded tracks. • The improvement of the formability and solidification behaviour should be related to the stable and high absorption rate (~65%) of blue laser, as well as the concentrated power density of infrared laser. [ABSTRACT FROM AUTHOR]