Effect of microstructure evolution on the corrosion behavior of extrusion-shearing Mg-3Zn-XCa-0.6Zr alloys

Abstract

In order to promote the application of new biomedical materials Mg-Zn-Ca-Zr alloy, the Mg-3Zn-xCa-0.6Zr (x = 0.6, 1.2, 1.8 wt.%) alloys were fabricated by an extrusion shearing (ES) process. The effect of secondary phase precipitation, grain size and texture on the corrosion resistance of Mg-3Zn-xCa-0.6Zr (wt.%) in Hank's solution were studied using electrochemical, immersion and electron back-scattering diffraction (EBSD) tests, and the corrosion mechanism of ES alloys was discussed. With increasing the addition of Ca element, the grain size of alloys first decreased and then increased, and the constitution of second phase was transformed from MgZn and Ca₂Mg₆Zn₃ phases to Mg₂Ca and Ca₂Mg₆Zn₃ phases, the texture changed from a bimodal texture intensity with stronger basal texture to a DRX texture intensity with a weaker texture. Mg-3Zn-0.6Ca-0.6Zr alloy showed the lowest corrosion rate of ~0.3140 ± 0.0642 mm/y. The excellent corrosion resistance of Mg-3Zn-0.6Ca-0.6Zr alloy could be attributed to the High-potential dispersion distribution of MgZn and Ca₂Mg₆Zn₃ phases and the strong basal texture. As well as more dense corrosion product films formed after alloying, effectively hindering local corrosion. In contrast, corrosion product films formed by the fine grain structure of Mg-3Zn-1.2Ca-0.6Zr alloy were not sufficient to resist the galvanic coupling corrosion between the Mg₂Ca phase and the Ca₂Mg₆Zn₃ phase, which caused the decreasing of its corrosion resistance.