Effect of Laser Remelting on Microstructure and Wear Resistance of Zr60702 in an Underwater Environment

Surface remelting is an effective method for modifying surface microstructures and improving the mechanical properties of metallic materials. However, the influence of an underwater environment on the laser remelting behaviour of zirconium alloys remains insufficiently understood. In this study, commercially pure Zr60702 was subjected to laser surface remelting in air and underwater environments under identical processing parameters. The phase constitution, microstructure, microhardness, and wear resistance of the remelted samples were systematically investigated. The maximum remelting depth decreased from 507.08 μm in air to 191.35 μm underwater because of the enhanced heat extraction and reduced effective laser-energy input in the aqueous environment. Both remelted samples were dominated by α-Zr at room temperature, while underwater remelting produced finer acicular α'-Zr and refined Widmanstätten structures. The maximum hardness values of the underwater- and air-remelted samples reached 636.7 and 546.5 HV, respectively, compared with 198.3 HV for the base material. The wear volumes of the base material, air-remelted sample, and underwater-remelted sample were 7.04 × 10⁷, 6.77 × 10⁷, and 5.66 × 10⁷ μm³, respectively. The improved wear resistance of the underwater-remelted sample was attributed to its refined microstructure and increased hardness, which suppressed plastic deformation and ploughing during sliding. These results demonstrate that underwater laser remelting is a promising method for improving the surface properties of Zr60702.