Fabrication of a novel Mg-RE(Nd,Ce) intermetallic compound coating by molten salt diffusion and its effect on corrosion resistance of magnesium alloys

A novel Mg-rare earth(Nd,Ce) coating containing intermetallic compound was fabricated on the surface of the AZ91D magnesium alloy by bathing the sample in a NaCl-KCl-LiCl-NdCl_3-CeCl_3 molten salt. The cross-sectional morphology, microstructure and phase composition of the coating were investigated by scanning electron microscopy(SEM), transmission electron microscopy(TEM) and energy dispersive spectroscopy(EDS). The corrosion resistance was characterized by the potentiodynamic polarization curves. The SEM observation indicated that a continuous and compact diffusion coating was obtained on the surface of SMATed AZ91D magnesium alloy and the XRD and TEM investigations revealed that the new phases were Al_2Ce and Al_2Nd intermetallic. The potentiodynamic polarization curves showed that the Mg-RE coating improved the corrosion resistance of the AZ91D magnesium alloy, and the corrosion current density of the coated sample was about 1510 mA /cm~2 lower than the uncoated sample.