Crystal-orientation-dependent corrosion behaviour of single crystals of a pure Mg and Mg-Al and Mg-Cu solid solutions

• Orientation-dependent corrosion behaviour of Mg single crystals was examined.
• Charge-transfer and film resistances exhibit strong orientation dependence.
• Variations in atomic packing density on the surface govern the behaviour.
• Adding Al predominantly affected the orientation dependence of the film resistance.
• Adding Cu decreased the orientation dependence of corrosion behaviour.

Mg alloys are promising candidates for biodegradable materials. To control their dissolution rate, the orientation-dependent corrosion behaviour of pure-Mg single crystals was examined. The corrosion rates increased in the order (0001)<(112¯0)<(101¯0)<(112¯3)<(101¯2). We found the anodic reaction governs the orientation-dependent corrosion behaviour. The charge-transfer and film resistances were strongly orientation-dependent. Effects of Al or Cu-addition to the orientation-dependent corrosion behaviour were also examined as model materials. Al-addition promoted passivation in anodic polarization, while Cu-addition activated the cathodic reaction. However, neither Al nor Cu influenced the order of orientation-dependent corrosion behaviour. Such orientation-dependence may originate from the variation in surface atomic-packing density.