Understanding the high temperature oxidation and ignition behaviour of two-phase Mg–Nd alloys and a comparison to single phase Mg–Nd

Abstract

The oxidation kinetics and the mechanism of two-phase Mg–Nd alloys were investigated via isothermal heating experiments conducted in dry air at 500 °C for 12 h. The oxidation kinetic curves reveal improved oxidation resistance on neodymium (Nd)-containing alloys compared to pure Mg. A lower mass gain was detected at 2.5-%Nd than at 6-Nd%, which was related to the lower amount of intermetallic phase on the alloy surface. The intermetallic phase has a significant effect on the oxide growth stage. Nd₂O₃ formation on the intermetallic phases creates diffusion paths for oxygen to the metal/oxide interface, affecting both the oxidation kinetics and the oxidation resistance of the alloys. The formation of a Nd-depleted region at the subsurface due to extensive Nd oxidation at the oxide/intermetallic interface lowers the protective ability of the oxide scale. As increasing the Nd content of binary Mg–Nd alloys above 0.5 wt% shifts the alloys from single-phase region to two-phase region, it adversely affects the ignition resistance.

Keywords:

• metals and alloys
• oxidation
• kinetics
• scanning electron microscopy
• photoelectron spectroscopy

Acknowledgement

The authors thank Prof. In-Ho Jung and Manas Palliwal of McGill University for valuable discussions and Prof. Philippe Bocher of École de Technologie Supérieure for providing access to his DSC laboratory. The authors also thank Pierre Vermette of McGill University and Jean-Guy Gagnon of École de Technologie Supérieure for experimental work and Jung Hwan Kim of McGill University for the Factsage calculations.

Additional information

Funding

This project was conducted under the financial support of Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant.