Study on electroless Ni–P–ZrO₂ composite coatings on AZ91D magnesium alloys

Abstract

Electroless Ni–P–ZrO 2 composite coatings on AZ91D magnesium alloys was developed and their characteristics were investigated. The experimental results showed that the composite coatings were uniform and compact. The hardness of Ni–P–ZrO 2 composite coatings reached the maximum value at 350°C heat treatment, and then decreased at 400°C. The nickel phosphor alloys provided solution strengthening and precipitation strengthening, while the ZrO 2 nanoparticles provided dispersion hardening, making the composite coatings harder than that of Ni–P coatings. The wear resistance of Ni–P–ZrO 2 composite coatings was obviously superior to Ni–P coatings, especially with longer wear time, which can be attributed to the dispersion strengthening and load support effect of ZrO 2 in the coatings. The Ni–P–ZrO 2 coatings exhibited better corrosion resistance than that of Ni–P coatings owing to codeposition of ZrO 2 together with NiP leading to a more compact composite coating.