An Investigation of the Role of Calcium in the Microstructure of Mg-5Al-4Sn-Based Alloys and Pitting Corrosion Resistance

In this work, the impact of alloying calcium into Mg-5Al-4Sn-based alloys on the microstructure and pitting corrosion resistance of these alloys is characterized. Electrochemical results showed that the corrosion potential ( E corr ), pitting potential ( E pit ), film stability, and film and charge transfer resistances of the investigated specimens increased when the calcium content in the alloys was increased up to 1.0 wt.%. Surface characterizations showed that the addition of calcium fosters the formation of a passive film, which contains a mixture of oxides/hydroxides of aluminum, magnesium, and tin that are uniformly distributed on the alloy surface. Notably, calcium addition also promotes grain refinement, and a more uniform distribution of the secondary phases in the alloy structure, boosting passive film formation on the alloy surfaces. These benefits could foster greater pitting resistance in the Mg-5Al-4Sn-based alloy system. Graphical Abstract