Effect of laser process parameters on thermal behavior and residual stress of high-strength aluminum alloy processed by laser powder bed fusion

Laser powder bed fusion (LPBF) additive manufactured high-strength aluminum alloys modified with Sc and Zr rare earth elements have wide prospects for lightweight and high-performance applications in aerospace industries. Nevertheless, driven by the target of achieving even higher performance, significant requirements are put forward for laser parameter optimization and resultant residual stress control for the laser additive manufactured parts. In this work, the thermal behavior, solidification behavior, and microstructure evolution of Al-Mg-Si-Mn-Sc-Zr aluminum alloy under various LPBF process parameters were carefully studied through simulations and experiments, and the evolution mechanisms of residual stress during LPBF were also revealed. The finite element simulation analysis showed distinct characteristics of temperature gradient (G) and solidification rate (R) within the molten pool. The top of the molten pool exhibited a higher G center dot R value (5.8-8.5 x 106 K/s) and a lower G/R value (0.9-2.1 x 107 K center dot s/m2), contributing to the formation of fine equiaxed grains. The bottom displayed a lower G center dot R value (4.1-4.6 x 106 K/s) and a higher G/R value (1.5-5.1 x 107 K center dot s/m2), facilitating the development of coarse columnar grains. As a higher laser power was applied, the simulation results indicated an increased temperature gradient in the molten pool, and the XRD analysis confirmed that the average residual stress increased from 85.9 to 169.7 MPa. The relationship between laser process parameters, molten pool morphology, grain distribution, and residual stress was established, demonstrating that the residual stress of Al-Mg-Si-Mn-Sc-Zr alloy could be tailored by optimizing laser process parameters.