Oxidation Behavior of AZ91D Magnesium Alloy Containing Nd or Gd

The influence of Nd and Gd additions on the evolution of microstructure, surface hardness and oxidation behavior of the extruded AZ91D magnesium alloy exposed to air was investigated in the temperature range from 290 to 410 degrees C. The kinetics of the oxidation process was obtained from gravimetric measurements performed during 28 days. Nd and Gd formed Al-rich intermetallic compounds (Al2Gd, Al2Nd, Al-Mn-Gd and Al-Mn-Nd) and reduced the volume fraction of beta-Mg17Al12 phase. Surface degradation of the AZ91D alloy, with and without Gd or Nd, was negligible for temperatures below 370 degrees C. At 410 degrees C, the grain size and oxidation rate significantly increased, although lanthanide-containing alloys revealed lower degradation compared with the unmodified AZ91D alloy.