Relationship between the corrosion behavior and the thermal characteristics and microstructure of Mg–0.5Ca–xZn alloys

Effects of secondary phases on corrosion behaviour of the Mg–0.5Ca–xZn alloys were investigated by polarization, immersion and hydrogen evolution tests. The Mg2Ca phase nucleated at 520 °C while, Ca2Mg6Zn3 and Mg51Zn20 phases were formed at 420 °C and 330 °C respectively. The corrosion resistance of Mg–0.5Ca alloy was enhanced with the addition of Zn up to 1%, while further addition reversed the effect. The Mg–0.5Ca–1Zn alloys with (α-Mg + Ca2Mg6Zn3 + Mg2Ca) phase showed lower corrosion rate than the alloys with (α-Mg + Ca2Mg6Zn3) and (α-Mg + Ca2Mg6Zn3 + Mg51Ca20) phases. The amount of corrosion product, composed of Mg(OH)2 and hydroxyapatite on the surface of the alloy, increased with increasing Zn content.

► The corrosion rate of Mg–0.5Ca–xZn alloy increased after the addition of 3 wt.% Zn. ► The secondary phases are responsible for different corrosion behavior of the alloy. ► Role of Ca2Mg6Zn3 phase on the galvanic corrosion has been evaluated. ► The corrosion rates increased with increasing Zn/Ca ratio higher than 1.25.