Corrosion resistance of ultrafine-grained Mg-1Zn and Mg-1Zn-0.2Ca magnesium alloys subjected to high pressure torsion

Abstract

The paper considers the structure and corrosion properties of ultrafine-grained magnesium alloys Mg-1Zn and Mg-1Zn-0.2Ca processed by high pressure torsion (HPT). The average grain size and phase composition of particles were determined by electron microscopy and X-ray diffraction. The corrosion rate in the studied samples in the homogenized state and after nanostructuring by HPT was calculated by the gravimetric method. It is shown that the presence of Ca in the Mg-1Zn-0.2Ca alloy leads to the formation of cathode-type Ca2Mg6Zn3 particles, which have a positive effect on corrosion resistance in the homogenized samples compared to the Mg-1Zn alloy. The HPT samples of the Mg-1Zn-0.2Ca alloy subjected to additional heat treatment at a temperature of 300 °C also showed better corrosion resistance compared to the Mg-1Zn alloy subjected to similar treatment. The difference in corrosion properties is discussed from the point of view of the formation of galvanic pairs between the matrix and cathode particles, which are observed in the ternary Mg-1Zn-0.2Ca alloy and are absent in the binary Mg-1Zn alloy due to the complete solubility of zinc in magnesium at a Zn content of less than 1 wt%.