Cracking Mechanism of Al-Cu-Mg-Si Alloy during Laser Powder Bed Fusion by Numerical Simulation

Based on the actual conditions of laser powder bed fusion (LPBF), a three-dimensional transient thermal-structural coupling single-layer finite element model was established to simulate the LPBF of Al-Cu-Mg-Si alloys. After characterizing the thermal behavior and residual stress distribution of the molten pool under different LPBF parameters, the cracking mechanisms of the Al-Cu-Mg-Si alloy were revealed. With an increase in the number of scanning tracks, the maximum cooling rate decreased gradually, whereas the maximum heating rate first increased and then decreased. The residual stress of the printed parts after cooling was primarily tensile stress. The residual stress along the scanning direction was mainly distributed in the center of the printing layer, whereas the residual stress perpendicular to the scanning direction was mainly concentrated in the center of the track. The residual stress along the deposition direction decreased with increasing distance from the substrate, with the highest stress occurring at the contact position with the substrate. Compared with the scanning speed, the laser power had a greater effect on the temperature and residual stress. The reliability of the numerical simulation was verified based on the size of the molten pool and the direction of crack propagation.