Corrosion behavior of as-cast binary Mg-Bi alloys in Hank's solution

Abstract

Biodegradable Mg-xBi (x = 3, 6 and 9wt.%) alloys were fabricated by ingot casting, and the change of corrosion behavior of the alloys in the Hank's solution was analyzed with respect to the microstructure using optical micrograph (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS), electrochemical and immersion tests. The results show that the microstructures of the as-cast Mg-Bi alloys mainly consisted of dendritic ?Mg grains and Mg3Bi2 phase in common, with the secondary dendrite arm spacing (SDAS) decreasing significantly from 41.2 靘 to 25.4 靘 and the fraction of Mg3Bi2 increasing from 3.1% to 10.7%. Furthermore, the corrosion rate increasing from 1.32 mm昦-1 to 8.07 mm昦-1 as the Bi content was increased from 3wt.% to 9wt.%. The reduced corrosion resistance was mainly ascribed to the increasing fraction of the second phase particles, which bring positive effects on the development of pitting.

Keywords

• magnesium
• microstructure
• electrochemical impedance spectroscopy (EIS)
• pitting corrosion