Microstructure and mechanical properties of thin-wall structure by hybrid laser metal deposition and laser remelting process

摘要

Laser remelting (LR) is generally applied to the coating or selective laser melting process to improve the surface quality and density of the formed structure. However, the effect of LR treatment on each cladding layer during laser metal deposition (LMD) process is still lacking. Therefore, this paper adopted hybrid LR and LMD process to form the thin-wall structure by 316L steel powder, and investigated the interaction mechanism of the hybrid process on microstructure and mechanical properties. A numerical model was carried out to simulate the temperature distributions for LMD + LR process in COMSOL in order to investigate the microstructure of single-pass remelting layers. Porosity, microstructure, hardness, and tensile property were analyzed by the remelting experiments of single-pass layer and thin-wall structure. The simulation model is verified by the geometrical analysis of molten pool and thermocouple measurements of the substrate. As a result, the porosity of the single-pass remelting layer was significantly decreased as the optimized laser remelting power is equal to the cladding power. The average hardness was improved by the LR treatment. Besides, the length of columnar dendrite increased evidently and the growth direction tended to be consistent with the increase of remelting power. For the remelted thin-wall structure, the microstructure is more regular and uniform, which is reflected on the grain's direction and size. Stronger solidification structure formed in LR process contributes to superior metallurgical bonding properties between the neighboring layers. Moreover, the hybrid process can significantly improve the ultimate tensile strength and yield strength. The elongation exceeds 37% than the un-remelted thin-wall structure.