Effect of Neodymium Modification on the Corrosion Behavior of AZ63 Magnesium Alloy

The microstructure and electrochemical behaviors of Mg—6 wt.%Al—3 wt.%Zn (AZ63) and Mg—6 wt.%Al—3 wt.%Zn + (0.25, 0.5, 0.75 and 1.0 wt.%) Nd were investigated via immersion and electrochemical tests, materials characterization including x-ray diffraction (XRD) and scanning electron microscope (SEM) associated with energy spectrum (EDS). The results indicate that Nd alloying prefers to combine with Al and gives rise to the formation of Al2Nd phase, which distributes discretely in α-Mg grains. The corrosion rates of these magnesium alloys can be ranked as: AZN1.0 (10.43 mm·y−1) > AZ63 (4.47 mm·y−1) > AZN0.25 (4.18 mm·y−1) > AZN0.5 (3.61 mm·y−1) > AZN0.75 (2.58 mm·y−1), manifesting that the appropriate Nd alloying (less than 0.75 wt.%) can decrease the corrosion rate of AZ63, but over alloying (1.0 wt.%) would results in the rapid degradation. The decrease in corrosion rate by Nd alloying (no more than 0.75 wt.%) can be attributed to the anodic barrier effect of increasing intermetallic phases and the compact corrosion product layer generated, but over Nd alloying (1.0 wt.%) vary the predominant intermetallic phase in AZ63 from Mg17Al12 to Al2Nd, which gives rise to a fierce galvanic corrosion and porous product layer.