Influences of aggressive ions in human plasma on the corrosion behavior of AZ80 magnesium alloy

Highlights: • Corrosion behavior of aggressive ions in human plasma on AZ80 alloy was investigated. • Hydrogen evolution rate (HER) decreased with the presence of bicarbonate and hydrophosphate ions. • HER increased with the addition of sulphate ions. • The pH changed with the increase of ions. • Low pH solutions corresponded to low corrosion rates. Magnesium alloys can work as biomedical materials due to their Young's modules similar to that of bone. Nevertheless, in a human plasma, one of the major drawbacks of these materials is the low corrosion resistance. Here, AZ80 corrosion in the solutions containing chloride, bicarbonate, sulphate and hydrogen phosphate ions were investigated by a short-term immersion test and electrochemical techniques. The results showed that bicarbonate and hydrogen phosphate could retard corrosion rate, while chloride and sulphate accelerated corrosion rate. During the early immersion stage, the corrosion rate increased with the presence of bicarbonate. It was caused by the reaction of bicarbonate and hydroxide promoting the dissolution of magnesium and accelerating corrosion. In the later stage, the reduced corrosion rate was due to the formation of various protective films. The sample formed a new sparse porous MgSO₄·5H₂O compounds in the sulphate ion solution, which could not effectively prevent chloride ions from entering the matrix and thus accelerated the dissolution of magnesium. With the presence of hydrogen phosphate, magnesium phosphate with a much lower solubility was formed, preferentially precipitated on the surface and was not influenced by the chloride ions. The corrosion mechanisms of magnesium alloys in above ions were proposed.