Insights into the Corrosion Behavior of Pure Magnesium and Magnesium–Calcium Alloy (Mg-1.8 at.% Ca) in Thin-Film and Bulk Forms

This study investigates the microstructural and corrosion properties of pure magnesium (Mg) and Mg-1.8Ca (at.%) alloy in both bulk and thin-film forms. Microstructure investigations showed that the addition of calcium (Ca) to Mg resulted in significant differences in microstructures. The bulk pure Mg exhibited coarse and elongated α-Mg grains, which were refined by Ca addition, together with the formation of a Mg2Ca intermetallic phase distributed throughout the microstructure. In contrast, thin-film Mg-1.8Ca alloys displayed a refined single-phase microstructure with uniform nm-scale grains and no intermetallic formation. The electrochemical corrosion tests revealed that the bulk and thin-film pure Mg exhibited comparable corrosion rates, while a substantial difference between the corrosion resistance of bulk and thin-film Mg-1.8Ca (at.%) alloy was observed. The thin-film Mg-1.8Ca (at.%) alloy showed an exceptionally better corrosion resistance, attributed to the formation of a more stable surface film and the absence of a less noble Mg2Ca intermetallic phase, ensuring a single-phase microstructure. This study highlights the importance of different manufacturing techniques and microstructural control in improving the performance of Mg alloys for high-tech applications.