• Chinese Journal of Lasers
  • Vol. 50, Issue 4, 0402017 (2023)
Jikang Fu1、2、3, Hongjun Liu1, Jibin Zhao2、3, Yuhui Zhao2、3、*, Chen He2、3, and Zhiguo Wang2、3
Author Affiliations
  • 1School of Mechanical and Electrical Engineering, Shenyang Aerospace University, Shenyang 110135, Liaoning, China
  • 2Shenyang Institute of Automation, Chinese Academy of Sciences, Shenyang 110016, Liaoning, China
  • 3Institute of Robot Intelligent Manufacturing and Innovation, Chinese Academy of Sciences, Shenyang 110169, Liaoning, China
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    DOI: 10.3788/CJL211621 Cite this Article Set citation alerts
    Jikang Fu, Hongjun Liu, Jibin Zhao, Yuhui Zhao, Chen He, Zhiguo Wang. Characteristics and Elimination Method of Dense Porosity Defects in Laser Melting Deposition Connection Region of AlSi10Mg Formed with Selected Laser Melting[J]. Chinese Journal of Lasers, 2023, 50(4): 0402017 Copy Citation Text show less

    Abstract

    Objective

    Aiming at the dense porosity defects detected using X-ray in laser melting deposition connected AlSi10Mg alloy, which is manufactured using selective laser melting, the characteristics of the defect and its influence on the mechanical properties are analyzed, and the elimination method of the defect is also explored. Selective laser melting methods cannot prepare large-scale aerospace structural components, laser melting deposition overcomes the forming size limitations, and provides a feasible solution for the additive manufacturing of large structural components.

    Methods

    In this study, the AlSi10Mg alloy prepared using selective laser melting was used as the base, and a laser melting deposition connection experiment was performed. First, connection samples under different laser powers were prepared. The relationship between the distribution range of dense porosity defects and the laser power was analyzed by an X-ray inspection, and the effect of dense porosity on the microhardness of the connection region was measured. The dense porosity was observed and analyzed using scanning electron microscopy (SEM) to determine its type and formation mechanism. Then, a substrate preheating experiment was performed to explore the best preheating temperature, which is used to solve the dense porosity defects in the connection region. Finally, the microhardness and tensile properties of the connection region before and after preheating were tested, and the fracture morphology was analyzed.

    Results and Discussions

    The inspection of the prepared connection samples with different energy densities shows that the dense porosity primarily appeared at the position of the interface fusion line between the connection region and substrate, and the dense porosity decreases the microhardness of the bonding zone (Fig. 7). Using SEM to observe the dense porosity, it is discovered that the porosity is primarily hydrogen porosity (Fig. 9). The solubility of hydrogen in molten pool decreases fastly, causing most bubbles to escape and form bubbles. However, the bubbles rise slowly, giving numerous bubbles no time to escape. So, some dense porosity defects are formed in this position. The preheating experiment shows that the optimum preheating temperature is higher than 100 ℃, which can effectively solve the dense porosity defects. The hardness at the fusion line reaches 90.8 HV after preheating (Fig. 14); the tensile strength is 287 MPa, and the elongation is 5.0% (Fig. 15). The observation of the fracture morphology shows that the fracture types before and after preheating are all brittle fractures and numerous dimples and quasi-cleavage morphologies can be observed on the fracture surface (Fig. 17).

    Conclusions

    Dense porosity is the primary defect of the AlSi10Mg alloy, which is produced using laser melting deposition. The defect is located at the position of the interface fusion line between the connection region and substrate, which is characterized as a watermark phenomenon on the X-ray inspection film. The accumulation of dense porosity results in a much lower hardness at the fusion line than in the connection zone and substrate. Preheating can effectively change the agglomeration effect of the dense porosity, making them evenly dispersed from the fusion line to the connection region. The mechanical properties of the samples after preheating were significantly improved. The hardness at the fusion line increased by 45% compared with that without preheating. The tensile strength increased by 19%, and the elongation increased to 5.0%.

    Jikang Fu, Hongjun Liu, Jibin Zhao, Yuhui Zhao, Chen He, Zhiguo Wang. Characteristics and Elimination Method of Dense Porosity Defects in Laser Melting Deposition Connection Region of AlSi10Mg Formed with Selected Laser Melting[J]. Chinese Journal of Lasers, 2023, 50(4): 0402017
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