Synergistic Effects of Sc and Ca on the Performance of Modified AZ61 Mg Alloy in Defense Application

This study investigates the synergistic effect of scandium and calcium on the microstructure and mechanical performance of modified AZ61 alloy. The additions of Sc and Ca enable a major refinement of the grain structure and improve the formation of thermally stable phases like Al3Sc and Mg2Ca and promote the distribution Mg17Al12 precipitate. The enhanced phase stability and precipitation behavior were also confirmed by microstructural and XRD analyses, which resulted in improved mechanical properties. Induced by a homogeneous precipitating phase and grain refinement, the modified AZ61 alloy displayed the maximum tensile strength for the aged at 200 °C and elongation found for 280 MPa and 15%, respectively. Sc and Ca retarded over-ageing effects at elevated temperatures (300°C and 400°C), resulting in much more stable tensile strength above 260 MPa and elongation 10% related to the stability of Al-Sc and Ca intermetallic phases. Fractography analysis showed a switch from brittle cleavage in the cast alloy to ductile dimple fracture the modified alloy at condition of high thermal.