Discharge Characteristics, Plasma Electrolytic Oxidation Mechanism and Properties of ZrO(2) Membranes in K(2)ZrF(6) Electrolyte

ZrO(2) was coated on AZ31 magnesium alloy substrate by plasma electrolytic oxidation with K(2)ZrF(6) and NaH(2)PO(4) electrolytes. The discharge characteristics and variation in active species during the plasma electrolytic oxidation (PEO) process were studied by optical emission spectroscopy. The surface morphology and element composition of the membranes were observed by scanning electron microscope. The ion transfer of the substrate was studied by atomic absorption spectroscopy. The phase composition and corrosion characteristics of the PEO membranes were examined with XRD and an electrochemical workstation, respectively. The heat and mass transfer models during the PEO process were introduced. The contributions of ions to the membranes and active species were also analyzed. The results indicated that the ion transfer at different stages exhibits different tendencies. At the first and transition stages, the migration resistance of the ions was low and increased gradually. At the initial discharge stage, the migration resistance was the highest because the highest membrane growth rate occurred at this stage. At the later discharge stage, the migration resistance tends to be stable, which is ascribed to a dynamic equilibrium PEO membrane growth rate. The intensity of active species is related to the energy state of the working electrode’s surface. The higher the energy, the greater the probability that the active species will be excited to generate energy level transitions, and the higher the plasma concentration.