Anodic Role of Mg12nd in the Micro-Galvanic Corrosion of Binary Mg‒Nd Alloys

Abstract

Mg 12 Nd is one of the well-known second phases in Nd-bearing biomedical Mg alloys. However, its role in the micro-galvanic corrosion especially at the initial stage of degradation is still unclear. In this paper, Mg‒5wt.%Nd and Mg‒30wt.%Nd alloys mainly consisting of Mg 12 Nd and α-Mg phases were fabricated. The increase of Nd content leads to the increase of the fraction of Mg 12 Nd phase in alloys. The quasi- in situ immersion testing in 0.9 wt.% NaCl solution shows that Mg 12 Nd phase is corroded firstly in comparison with α-Mg, suggesting the anodic role of Mg 12 Nd phase at the initial stage. Moreover, it appears that Mg 12 Nd phase is more easily to be attacked with the increase of Mg 12 Nd phase. The reason for the preferential dissolution of Mg 12 Nd can be related to the difference of work function and Volta potential between Mg 12 Nd and α-Mg obtained from the first-principles calculation and scanning Kelvin probe force microscope, respectively. This result provides a valuable reference for designing biomedical Mg alloy with good degradation properties by adjusting the phase component.

Keywords: Magnesium alloy, galvanic corrosion, work function, Volta potential, first-principles calculation