Picosecond laser remelting of electrodeposited Ni P coating: Parameters optimization and electrochemical corrosion behavior

Excessive P content (≥ 10 wt%) easily leads to cracks on the surface of electrodeposited NiP coatings, causing rapid deterioration of corrosion performance. This study uses picosecond laser remelting (LR) technology to close cracks and improve corrosion performance. The influence of the laser parameters on the quality of laser-remelted (LRed) coatings in ambient air is discussed in detail, and the corrosion performance is evaluated through electrochemical corrosion tests. The results indicated that the scanning rate, laser power, and repetition frequency significantly affect the degree of crack closure and LRed defects. For cracks of similar sizes, both multiple-LR with a lower power (10.4 W, five times) and single-LR with a higher power (19.2 W, once) achieved an excellent crack closure. After single-LR, the surface roughness increased from 3.9 ± 0.3 nm to 33.4 ± 3.2 nm. In addition, the LRed layer crystallized from the initial amorphous state. Although the energy-dispersive spectroscopy results indicated that the oxidation behavior during the LR process was insignificant, X-ray photoelectron spectroscopy showed that the surface composition evolved from Ni/Ni–P compounds to Ni–POx after LR. Electrochemical corrosion tests indicated that the corrosion current density decreased approximately three times from 9.19 × 10−6 to 2.91 × 10−6 A/cm2 after LR. Moreover, the corrosion mechanism shifted from the original stress corrosion to pitting corrosion. Thus, the LR technology can effectively improve the corrosion performance and reduce the issues caused by cracks.