Anodization of rare earth-containing Mg alloy of Mg-3Nd-0.2Zn-0.4Zr(mass fraction,%)(NZ30K) was performed in composite electrolyte containing NaOH,KOH,K_2SiO_3,Na_2SiO_3,NaF,KF etc.The anodic coating was characterized by using X-ray diffraction(XRD),field emission electron scanning mieroscope(FE-SEM) and electron probe microscopic analysis(EPMA).The corrosion resistance of the anodized alloy and the substrate was evaluated in 5%NaCl solution using electrochemical impedance spectroscopy(EIS).The results of XRD show that the anodic coating is mainly composed of MgO.EPMA indicates that magnesium and oxygen are almost uniformly distributed across the coating,and the fluorine content decreases gradually from the interface of coating-substrate to the surface,whereas the distribution of silicon is reverse to that of fluorine.The results of EIS analysis shows that the anodic coating exhibits the superior corrosion resistance for NZ30K alloy.
To improve the corrosion resistance of wrought magnesium alloys through rare earth （RE） additions, the corrosion behaviour of Mg-5Zn-0.3Zr-xNd （x=0, 1, and 2; wt%） and Mg-5Zn-0.3Zr-2Nd-yY （y=0.5 and 1; wt%） alloys in a 5wt% NaCl solution was investigated using immersion test and electrochemical measurements. The results of immersion test show that Mg-5Zn-0.3Zr-2Nd alloy exhibits the best corrosion resistance among the tested alloys. Electrochemical measurements show that secondary phases in RE-containing Mg-5Zn-0.3Zr alloys behave as less noble cathodes in micro-galvanic corrosion and suppress the cathodic process. The additions of Nd and Y into Mg-5Zn-0.3Zr alloy also improve the compactness of the corrosion product film and are beneficial to the corrosion resistance.
