论文部分内容阅读
In this paper,magnesium fluoride and its compounds were synthesized into oxide coating on magnesium alloy for increasing the compactness of the coating and hence its anti-corrosion ability,therefor,ceramic oxide coatings with different microstructure containing fluorides (named S-KF coating,S-KF-A coating and D-KF-A coating,respectively) have been prepared on AZ91D magnesium alloy by adjusting the electrolyte constituents and power supply mode.SEM observation indicated that D-KF-A coating formed in modified KF electrolyte by using bipolar pulse mode presented a very compact,homogeneous and continuous coating microstructure,whereas the two coatings with mono-polar pulse voltage,in KF electrolyte with and without additive,respectively,both were loose and porous with some scattered granules.X-ray diffraction (XRD) analyses showed that these coatings were all composed of MgO,MgF2 and KMgF3 phases,but,the highest content of MgF2 and KMgF3 and lowest content of MgO were obtained by D-KF-A coating.The corrosion current density (icorr) of D-KF-A coating,as measured by potentiodynamic polarization,was four orders of magnitude lower than that of the uncoated one.The modulated phase component and bipolar pulse regime directly lead to improvement of the microstructure and therefore the protective ability of PEO coating.