Enhanced corrosion resistance of electrochemical deposited amorphous NiP coatings with surface cracks via nanosecond laser remelting: Effect of pulse width and cycle number on remelted layer

The amorphous NiP alloy coating is prone to forming surface cracks during electrochemical deposition, which weakens its corrosion resistance. In this study, nanosecond (ns) laser remelting (LR) was used to seal these cracks for surface modification. The study focused on the effects of ns-laser pulse width and the number of LR cycles on crack sealing efficiency and surface quality, with further evaluation of the electrochemical corrosion behavior. The results demonstrate that pulse width significantly affects both the effectiveness of crack sealing and the quality of the remelted surface (including pores and spatter). The optimal overall effect was achieved at a pulse width of 200 ns. The number of LR cycles significantly influenced the surface quality of the remelted layer. Compared to the original coating, a single LR cycle resulted in a considerable increase in surface roughness, accompanied by numerous pores. However, multiple LR cycles (7 cycles) effectively reduced surface roughness (approximately 75 %) and minimized surface defects, though with the formation of minor thermal microcracks. Additionally, the number of LR cycles showed negligible effects on both the remelted layer thickness and the degree of crystallization. Electrochemical corrosion tests revealed that LR significantly enhanced the coating's corrosion resistance. After 7 cycles of LR, the corrosion rate decreased by approximately 7.9 times compared to the original coating. This improvement is primarily attributed to the effective sealing of cracks in the remelted layer, which shifts the corrosion mechanism from corrosion-induced crack propagation to pitting corrosion. This study provides valuable guidance for implementing LR to modify electrodeposited coating surfaces.