Coating Formation By Plasma Electrolytic Oxidation On Zc71/sic/12p-t6 Magnesium Metal Matrix Composite

摘要

Plasma electrolytic oxidation (PEO) of a ZC71/SiC/12p-T6 magnesium metal matrix composite (MMC) is investigated in relation to coating growth and corrosion behaviour. PEO treatment was undertaken at 350 mA cm~(-2) (rms) and 50 Hz with a square waveform in stirred 0.05 M Na_2SiO_3.5H_2O/0.1 M KOH electrolyte. The findings revealed thick, dense oxide coatings, with an average hardness of 3.4 GPa, formed at an average rate of ～1 μm min~(-1) for treatment times up to 100 min and ～0.2 μm min~(-1) for later times. The coatings are composed mainly of MgO and Mg_2SiO_4, with an increased silicon content in the outer regions, constituting <10% of the coating thickness. SiC particles are incorporated into the coating, with formation of a silicon-rich layer at the particle/coating interface due to exposure to high temperatures during coating formation. The distribution of the particles in the coating indicated growth of new oxide at the metal/coating interface. The corrosion rate of the MMC in 3.5% NaCl is reduced by approximately two orders of magnitude by the PEO treatment.