The effect of cooling rate and calcium content on mechanical properties and the solidification characteristics of ZX magnesium alloys using cooling curve thermal analysis

Thermal analysis was employed to investigate how cooling rate and calcium content influence the solidification behavior, microstructure, and mechanical properties of Mg–3Zn–xCa (x = 0–0.6 wt.%) alloys. Understanding these relationships is essential for optimizing Mg–Zn–Ca (ZX) alloys for structural and biomedical applications, where controlled solidification directly affects performance. Cooling rates ranging from 0.65 to 5 °C/s were applied using different mold materials, and solidification parameters were extracted using computer-aided cooling curve thermal analysis (CA-CCTA). Increasing the cooling rate from 0.65 to 5 °C/s raised the α-Mg nucleation temperature by ∼6.0% in Mg–3Zn and ∼4.6% in Mg–3Zn–0.6Ca, while reducing the eutectic nucleation temperature by up to ∼1.5% across all compositions. The solidification range increased by approximately 30–40%, while solidification time decreased by up to ∼25%, indicating accelerated transformation kinetics under rapid cooling. At a constant cooling rate, increasing Ca content decreased the α-Mg nucleation temperature but increased the eutectic nucleation temperature, with a pronounced shift at 0.6 wt.% Ca due to enhanced intermetallic formation. Mechanically, Mg–3Zn–0.3Ca exhibited the best overall performance, achieving a compressive strength of 287 MPa at 0.65 °C/s (≈22% higher than Mg–3Zn) and 308 MPa at 5 °C/s, along with the highest hardness (55.1 HB). In contrast, Mg–3Zn–0.6Ca showed comparable strength but reduced ductility due to coarse Ca-rich intermetallics. These results establish clear quantitative relationships between cooling conditions, alloy composition, and solidification behavior, providing guidance for tailoring ZX alloys with optimized mechanical performance.