Effect of Rare Earth La on Microstructure and Corrosion Resistance of AZ91D Magnesium Alloy

The microstructure and corrosion resisitance of AZ91D alloy with different additions of lanthanum were investigated by OM, SEM, EDS, XRD and electrochemical polarization testing. Results show that the addition of La refined the microstructure of AZ91D Mg alloy, and decreased the volume fraction of β-Mg17Al12 phase, made their distribution change from continuously netlike to discontinuously disperse. At the same time, a new phase Al11La3 formed. Certain amount of La decreased the corrosion rate and the corrosion current density obviously. Also, they had more positive corrosion potential and improved the corrosion property. Especially when the addition of La was 1.0 mass%, the corrosion rate decreased to 0.157 mg·cm-2·h-1 about 58% of the AZ91D alloy. And it had more positive corrosion potential, -1 429 mV (SCE), which was 95.4 mV higher than that of AZ91D alloy. Besides the corrosion current density (8.8×10-4 A·cm-2) decreased significantly compared with the AZ91D alloy.