Microstructure and wear resistance of electrodeposited Ni-SiO2 nano-composite coatings on AZ91HP magnesium alloy substrate

The Ni-SiO2 nano-composite coatings were fabricated by electrodeposition on the AZ91HP magnesium alloy surface, in which nano-SiO2 was chosen as the second-phase particulates. The microstructure was observed by SEM, the microhardness was measured by micro-density tester and the wear resistance was estimated by M-200 type block-on-wheel dry sliding frication and wear tester. The results indicate that the Ni-SiO2 nano-composite coatings with uniform crystalline, dense structure can be obtained on AZ91HP magnesium alloy. The interface morphology shows that the combination between the nano-composite coatings and magnesium alloy is fine. The maximum value of microhardness reaches HV367 when the content of nanoparticles is 10 g/L, however, the microhardness of the pure nickel coatings is HV274 and the hardness of magnesium alloy only is HV82.7. The frication and wear experiments reveal that the wear resistance of nano-composite coatings are improved obviously compared to magnesium alloys and pure nickel coatings, which are induced by dispersive strengthening effect and grain refining effect. The main wear mechanism of nano-composite coating is abrasive wear, the wear mechanism of magnesium alloys is adhesion wear, and that of pure nickel coating is exfoliation wear, respectively.