Microstructure, corrosion and electrochemical behavior of Cd-modified Al-5Zn-0.5Mg alloys in 3.5 wt% NaCl solution: A comparative study

This experimental study quantitatively assesses the role of Cd additions (0–1.5 wt%) on phase formation, mechanical properties, and electrochemical behavior of Al-5Zn-0.5Mg casting alloys. Advanced characterization techniques, including electron microscopy (SEM), surface spectroscopy (XPS), and crystallographic analysis (XRD), were integrated with mechanical testing and electrochemical corrosion analysis in 3.5 wt% NaCl. The microstructural analysis reveals that Cd additions promote grain refinement (41.8% reduction at 1.5 wt% Cd) and the precipitation of Cd-rich phases at grain boundaries, resulting in a 38% increase in hardness through grain boundary strengthening. Immersion tests in 3.5 wt% NaCl shows corrosion rates decrease dramatically from 1.25 mmy (0 wt% Cd) to 0.04 mmy (1.5 wt% Cd). Electrochemical characterization indicates Cd enhances passivity, reducing passive current density by 100-fold and increasing pitting potential by 288 mV. XPS analysis confirms that Cd promotes the formation of a stable CdO/Cd (OH)₂-rich passive layer. Cyclic polarization tests showed neutral hysteresis, confirming excellent resistance to localized corrosion. Overall, Al-5Zn-0.5Mg alloys modified with Cd offer an attractive and effective approach to advancing alloy performance, expanding their potential in demanding industrial environments.