Enhancing the corrosion resistance of dilute Mg–Zn–Ca–Mn alloys by alleviating micro-galvanic corrosion via tailoring the secondary phases

The dilute Mg-Zn-Ca based alloys with excellent room-temperature plasticity and formability show potential in the industrial fields with high forming requirements. Therefore, their corrosion resistance in the natural environment is thereby an important subject affecting their widespread application. In this paper, three Mg- x Zn-0.5Ca-0.4Mn ( x =0.45,1.1,1.6wt.%, termed Z0.45, Z1.1, Z1.6 for simplicity) alloys as high-plasticity Mg alloys, with different types of secondary phases were designed via thermodynamic phase diagrams, and were subjected to solid solution treatment and corrosion resistance examination involving immersion tests and electrochemical measurements in a 3.5wt.% NaCl solution. The solution-treated Z0.45 and Z1.1 alloys show the best corrosion resistance among all specimens, with a corrosion rate of 0.91 mm/y measured by weight loss testing, which is only one fifth of commercial AZ31 alloys. The results show that the decreased Zn addition and solution treatment contribute to the improvement of corrosion resistance. The difference in the corrosion resistance is discussed in terms of variation in the composing phase and oxide film, as well as associated the characteristics of corrosion morphology, corrosion products et al., by using Scanning electron microscope (SEM) equiped with Energy dispersive spectrometer (EDS), Laser scanning confocal microscopy (LSCM), Low angle X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning Kelvin probe force microscope (SKPFM) analysis. The results indicate that the difference in the corrosion resistance between the studied samples is mainly attributed to the different micro-galvanic corrosion responses arising from the secondary phases with distinct potentials as compared to the α-Mg matrix.