Controlling the corrosion and cathodic activation of magnesium via microalloying additions of Ge

The evolution of corrosion morphology and kinetics for magnesium (Mg) have been demonstrated to be influenced by cathodic activation, which implies that the rate of the cathodic partial reaction is enhanced as a result of anodic dissolution. This phenomenon was recently demonstrated to be moderated by the use of arsenic (As) alloying as a poison for the cathodic reaction, leading to significantly improved corrosion resistance. The pursuit of alternatives to toxic As is important as a means to imparting a technologically safe and effective corrosion control method for Mg (and its alloys). In this work, Mg was microalloyed with germanium (Ge), with the aim of improving corrosion resistance by retarding cathodic activation. Based on a combined analysis herein, we report that Ge is potent in supressing the cathodic hydrogen evolution reaction (reduction of water) upon Mg, improving corrosion resistance. With the addition of Ge, cathodic activation of Mg subject to cyclic polarisation was also hindered, with beneficial implications for future Mg electrodes

The mechanical properties and corrosion behavior of quaternary Mg-6Zn-0.8Mn-xCa alloys

In present study, the influence of calcium content on the microstructure, mechanical properties and corrosion behavior of quaternary Mg-6Zn-0.8Mn-xCa alloys, where x = 1, 1.5, 3 or 4.5 wt.% Ca, was examined. The grain structure of this quaternary alloy system became more refined with increasing additions of Ca. In addition to a-Mg, the Ca2Mg6Zn3 phase was found to be present in Mg-6Zn-0.8Mn-1Ca and Mg-6Zn-0.8Mn-1.5Ca according to microstructural and thermal analysis (TA). In addition to the a-Mg and Ca2Mg6Zn3 phases, the Mg2Ca phase was found to be present in the Mg-6Zn-0.8Mn-3Ca and Mg-6Zn-0.8Mn-4.5Ca alloys. Alloys with 1 or 1.5 wt.% Ca led to increases in the tensile strength of Mg-6Zn-0.8Mn, although further Ca additions had a deleterious effect. The TA of Mg-6Zn-0.8Mn-xCa during its solidification indicates that the fraction of liquid phase increases with increasing Ca content at the dendrite coherency point, leading to an increase in secondary phases and increased corrosion rate of Mg-6Zn-0.8Mn-xCa alloys