Electroless deposition of Ni–W–P–B4C nanocomposite coating on AZ91D magnesium alloy and investigation on its properties

In the present work, electroless deposition of quaternary Ni–W–P–B4C composite coatings on AZ91D magnesium alloy was investigated. The coatings were characterized to study their microstructure, crystallite size, morphology, microhardness and corrosion resistance and compared with Ni–P and Ni–P–B4C composite coatings, prepared with the same method. The hardness of the Ni–W–P–B4C composite coatings was around 1290 MPa which was more than that of the Ni–P and Ni–P–B4C coatings (about 700 and 1200 MPa, respectively). According to polarization test results, the Ni–W–P–B4C composite coating exhibits less and more corrosion rates with respect to the Ni–P–B4C and the Ni–P coatings, respectively. X-ray diffraction (XRD) analysis results for the Ni–W–P–B4C coating showed that the Ni–W–P–B4C coating has a combination of amorphous and nanocrystalline structures. Also, Williamson–Hall analysis on the X-ray patterns revealed that the Ni–W–P–B4C coating has an average crystallite size of 1.5 nm.

► The average crystallite size of Ni–W–P–B4C coating was 1.5 nm.
► The Ni–W–P–B4C composite coatings microhardness was 1290 MPa, which is higher than that of the Ni–P coatings (700 MPa).
► The corrosion resistance of the Ni–W–P–B4C composite coating is better than that of the Ni–P–B4C coating.