Corrosion behavior of Mg-Zn-Y-Zr alloys in NaCl solution

In recent years, Mg-Zn-Y-Zr alloys have attracted significant interest due to the high strength at room and elevated temperature. Current researches mainly focus on the microstructures and mechanical properties of Mg-Zn-Y-Zr alloys, however, the corrosion behaviors of Mg-Zn-Y-Zr alloys have been seldom studied. In the present paper, the mass loss corrosion and electrochemical corrosion behavior of three Mg-Zn-Y-Zr alloys with Zn contents of 4.3% (mass fraction), 6% and 8.6% in 5% (mass fraction) NaCl solution were studied, respectively. The morphology, microstructure and phase composition of these alloys after different immersion time were observed. The results showed that the type of second phase and the content of Zn in these alloys significantly affect their corrosion resistance performance and the Mg-Zn-Y-Zr alloy with 4.3% Zn exhibited better corrosion resistance. With the increase of Zn content, the W phase with stronger effect of galvanic corrosion formed at grain boundaries and the content of Zn in α-Mg matrix also increased, which resulted in the worse corrosion performance. Experimental results also showed that the corrosion process of Mg-4.3Zn-0.7Y-0.6Zr alloy can be divided into three stages: galvanic corrosion, Zr-rich zone-Zr-poor zone corrosion and pitting corrosion.