Rare Earth Lanthanum Conversion Treatment of Magnesium Alloy

Rare earth conversion coatings on magnesium alloys have been developed as an environmental-friendly surface treatment technology for magnesium alloys.The process of rare earth lanthanum conversion coating for magnesium alloy AZ91D was studied by using orthogonal test.The surface morphology and composition of lanthanum conversion coating were studied by means of scanning electron microscopy (SEM),energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS).The corrosion resistance of magnesium alloy in 5% NaCl solutions with pH 6.8~7.0 was analyzed by evolving hydrogen gas measurement.The results showed that uniform coating by the process of lanthanum conversion was obtained on Mg alloy.The lanthanum conversion coating was mainly composed of MgO,La2O3 and a little amount of Al2O3.During immersion in 5% NaCl solution for 10 h,the corrosion resistance of lanthanum conversion coating was comparable with that of chromate conversion coating.