Deposition Mechanism Study of a Novel Electroless Nickel Plating Technique on AZ91D Magnesium Alloy

A novel direct electroless nickel plating method was developed for the AZ91D magnesium alloy. The electroless nickel initial deposition morphology was analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The initial deposition characteristics of the coating and the deposition mechanism of the nickel layer are discussed. The results show that after activation, an uneven scaly-activated membrane was formed on the AZ91D magnesium alloy surface. The weakest part of the activated membrane dissolved first, where small Ni particles deposited initially. These deposited Ni particles had high catalytic activity and they were involved in the catalytic reduction reaction of hypophosphite, from which P was precipitated. As the plating proceeded, the number of the deposited Ni particles gradually increased in a three-dimensional manner and the surface was gradually covered by the growing cellular particles. A compact pore-free nickel-plated film was finally formed.