Fabrication and Performance of Ni-Co-P/Si3N4 Electroplated Composite Coatings on Al-Si Alloys

In order to improve the wear resistance of Al-Si alloys, the electro deposition of Ni-Co-P/Si3N4 coating on a hypereutectic Al-Si casting alloy was studied in this paper. The thickness, hardness, surface morphology, composition, adhesive force and wear resistance of Ni-Co-P/Si3N4 coating were measured by optical microscope, micro-hardness tester, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), adhesive attraction scratcher and abrasion tester. It was shown that Si3N4 particulates were uniformly distributed in the composite coating. And the effect of process parameters, such as electric current density, temperature, PH, plating time and component of electroplating bath,were obtained. The wear resistance of the coating was improved with the increase of hardness and the content of Si3N4 in the coating. It was also improved by decreasing electric current density. The adhesion of the coating was poor for increasing the content of P and Co in the coating. At the same time, the coating was hard, friable, and easy to be broken with the decrease of temperature.