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

The Ni-SiO2 nano-composite coatings were fabricated by electrodeposition on AZ91HP magnesium alloy, which the Ni was used as the metal matrix and nano-SiO2 was chosen as the second-phase particulates. Moreover, 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 the combine between nano-composite coatings and magnesium alloy base body was fine. The maximum value of microhardness reaches HV367 when content of nanoparticles is 10 g/l, however, the microhardness of pure nickel coatings are HV274 and the hardness of magnesium alloy only are HV82.7. The frication and wear experiments reveal that the wear resistance of nano-composite coatings are improved obviously compared to magnesium alloys base body and pure nickel coatings, which are induced by dispersive strengthening effect and grain refining effect. The main of wear mechanism of nano-composite coating is abrasive wear, the wear mechanism of magnesium alloys base body is adhesion wear and pure nickel coating is exfoliation wear.