At present, ultra-high speed laser melting deposition is mainly used for the surface cladding of steel, superalloy and other parts, and rarely used for the forming and preparation of Al-Mg-Sc high-strength aluminum alloy, whose defect characteristics, microstructure and mechanical properties remain to be revealed. Aiming at the problem of low deposition efficiency of existing additive manufacturing technology, this work uses ultra-high speed laser melting deposition technology to study the additive manufacturing forming of Al-Mg-Sc high-strength aluminum alloy, explore the sedimentary structure and mechanical properties, and analyze the effects of scanning rate on the structure, defects and mechanical properties. The forming process was simulated by using the thermal strong coupling Lagrangian meshless method of ESCAAS numerical simulation software. The temperature, phase and shape evolution of powder particles and matrix were described in detail with the real powder properties (size, shape, etc.) as input.
The thesis links: https://jam.biam.ac.cn/CN/10.11868/j.issn.1005-5053.2023.000098
Research content
Figure 1 (c) shows the principle of laser melting deposition. The matrix is placed under the nozzle, and the alloy powder raw material is melted under laser irradiation to form a molten pool to obtain super-strong aluminum alloy. After grinding, polishing and cutting, the standard test sample used in the experiment can be obtained, as shown in Figure 2 (a). The chemical composition of the alloy powder raw material is Al-5Mg-0.5Sc-0.9Mn-0.35Zr-Si-0.6Ti-0.5Cu-0.25Cr (mass fraction /%), and the particle size distribution of the powder is shown in Figure 1 (a).
FIG. 2 Tensile specimen (a) sample photo; (b) Sample size.
The tensile test was carried out on the prepared sample, the displacement was recorded by video extensometer, and the load of the beam was recorded synchronously to obtain the load-displacement curve, and the stress-strain curve was drawn as shown in FIG. 3.
FIG. 3 Stress-strain curves of Al-Mg-Sc alloy formed by ultra-high speed laser melting deposition at different scanning speeds.
FIG. 4 is a SEM photo of Al-Mg-Sc alloy sample manufactured by ultra-high speed laser melting deposition additive. As can be seen from Figure 4, the inside of the sample is dense with no defects such as cracks, inclusions or non-fusion, but there are a small number of pores below 200μm in size, and the number of pores decreases significantly with the increase of scanning rate.
FIG. 4 Internal pores of Al-Mg-Sc alloy formed by ultra-high speed laser melting deposition at different scanning rates (a) 0.1m /s; (b) 0.4 m/s; (c) 1 m/s.
Figure 5-7 shows the ODF diagram obtained by EBSD analysis of the shaped sample at different scanning rates. The texture cross sections in ϕ2=0°, 45°, and 90° are selected for analysis, respectively. It can be seen that the samples with a scanning rate of 0.1 m/s and 0.4 m/s have obvious peaks, indicating that the material exhibits certain but not obvious anisotropy, while the samples with a scanning rate of 1 m/s do not have obvious peaks, indicating that there is no obvious texture orientation.
FIG. 8 shows the deformation configuration and temperature distribution of particles and matrix under laser irradiation with time when the laser power is 1500 W and the scanning rate is 0.1 m/s. Based on the thermodynamic strong coupling Lagrangian meshless numerical simulation method, the temperature, phase and shape evolution of powder particles and matrix are described in detail.
FIG. 9 Ultrahigh speed laser melting deposition of Al-Mg-Sc alloy simulation cross-section of forming samples at different scanning rates (a) 0.4m /s, 0.5ms; (b) 0.4 m/s, 2 ms; (c) after solidification of 0.4 m/s; (d) 1 m/s after solidification.
Figure 10 shows that the porosity of the high-strength aluminum alloy sample decreases with the increase of the laser scanning rate. As shown in Figure 9 (c) and (d), the higher scanning rate weakens the accumulation of powder materials, thereby reducing the layer porosity.