Corrosion resistance and biocompatibility of the ultrafine-grained Zn-1%Li-2%Mg and Zn-1.0% Mg-1.0%Fe alloys produced by severe plastic deformation

Abstract

The corrosion resistance and biocompatibility of the ultrafine grained (UFG) Zn-1%Li-2%Mg and Zn-1%Mg-1%Fe zinc alloys, which exhibit unique mechanical properties as a result of severe plastic deformation (SPD) processing, were investigated. The corrosion rate in the UFG Zn-1%Li-2%Mg alloy was found to be 0.0891 mm/year and in the UFG Zn-1%Mg-1%Fe alloy – 0.061 mm/year. The conducted comparative tests with their coarse grained (CG) analogues showed that corrosion processes proceed most intensively at the periphery of the UFG samples, which are characterized by a larger accumulated strain, strong refinement of structural elements, intensive phase transitions and completeness of dynamic ageing. The increase of corrosion rate in the UFG Zn-1%Li-2%Mg alloy in comparison with its CG analogue is explained by the presence of the Mg2Zn11 phase of a high content, an increased weight fraction of the Zn phase alloyed with Li and Mg atoms, the precipitation of the Mg2Zn11 particles in it and a decrease of ~LiZn3 fraction. The growth of corrosion rate in the UFG Zn-1%Mg-1%Fe alloy is also explained by an increase in the alloyed Zn phase and the precipitation of precipitates in the Zn and Mg2Zn11 phases. In addition, the phase transition of FeZn13 into its FeZn10.98 modification (FeZn13 → FeZn10.98), which is uncharacteristic for the CG state, was found in the near-surface layers of the UFG sample when exposed in Ringer's solution. The results of the Alamar Blue metabolic test demonstrated the biocompatibility of the MG-63 cells for 7 days (more than 30%) when incubated with 12.5% extracts of the UFG Zn-1%Mg-1%Fe and Zn-1%Li-2%Mg alloy samples.