Delaying the Corrosion of AZ31 Magnesium by Coating with Manganese-Doped Magnesium Phosphate Using Electrochemically Assisted Deposition

Abstract

Magnesium alloy AZ31 surfaces are successfully coated with manganese-doped magnesium phosphate by means of electrochemically assisted deposition. The resulting coatings consist of the magnesium phosphates struvite and newberyite. Topography and composition of the coatings are analyzed by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. In L929 cell culture experiments, the maximum manganese concentration, which still allowed acceptable cell proliferation, is determined. An optimization of the coating quality regarding thickness and homogeneity is performed using the design of experiment software MODDE. The change in corrosion resistance is determined by measuring the release rate of hydrogen gas in simulated body fluid. The samples with manganese-doped coatings release less gas than the samples with undoped coatings, which in turn release less gas than the uncoated samples. In addition, the magnesium phosphate coating significantly reduces the relative mass loss rate of the magnesium substrates, suggesting it as a promising approach to mitigate the adverse effects of magnesium implant degradation in vivo.