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<p>Thermal and microstructural analyses were used to study the effects of cooling rate (0.65–5&#xa0;°C/s) and calcium addition (0–0.6 wt%) on the solidification, grain refinement, secondary phase formation, and hot cracking susceptibility of Mg-3Zn alloys. Both parameters strongly influenced dendrite coherency, solid fraction at coherency, and mushy zone development. The solid fraction at coherency showed a nonlinear response to cooling rate, with Mg-3Zn-0.6Ca reaching the highest value (26.96%) at 5&#xa0;°C/s. Grain size decreased consistently with faster cooling and higher Ca content, dropping from 175&#xa0;µm to 100 µm in Mg-3Zn and from 90&#xa0;µm to 55&#xa0;µm in Mg-3Zn-0.6Ca. The fraction of secondary phases increased from ~2.3% (0 wt% Ca) to ~7.5% (0.6 wt% Ca), influencing feeding behavior during solidification. Hot cracking susceptibility declined significantly with faster cooling. At 0.65&#xa0;°C/s, the Mg-3Zn reference shows the lowest susceptibility, whereas at 0.9&#xa0;°C/s the Mg–3Zn–0.3Ca alloy is lowest; at higher rates (1.5–5&#xa0;°C/s) the Mg–3Zn–0.6Ca alloy provides the best resistance. Analysis identified solidification time as the dominant factor controlling hot cracking, followed by mushy zone width and solid fraction at coherency, while secondary phases modulated stress accumulation and crack formation. These results demonstrate the critical interplay between cooling rate and composition in defect formation, offering quantitative guidelines for optimizing microstructure and casting performance in Mg-Zn-Ca alloys.</p> Graphical Abstract <p></p>

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The Effect of Cooling Rate and Calcium Content of the ZX Magnesium Alloys on Dendrite Coherency Point and Hot Cracking Susceptibility Investigated Through Thermal Analysis

  • 期刊论文

  • 发表日期：

    2026年2月17日

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  • Moein G. Shabestari,
  • Mojtaba Hatef,
  • Saeed G. Shabestari

摘要

Thermal and microstructural analyses were used to study the effects of cooling rate (0.65–5 °C/s) and calcium addition (0–0.6 wt%) on the solidification, grain refinement, secondary phase formation, and hot cracking susceptibility of Mg-3Zn alloys. Both parameters strongly influenced dendrite coherency, solid fraction at coherency, and mushy zone development. The solid fraction at coherency showed a nonlinear response to cooling rate, with Mg-3Zn-0.6Ca reaching the highest value (26.96%) at 5 °C/s. Grain size decreased consistently with faster cooling and higher Ca content, dropping from 175 µm to 100 µm in Mg-3Zn and from 90 µm to 55 µm in Mg-3Zn-0.6Ca. The fraction of secondary phases increased from ~2.3% (0 wt% Ca) to ~7.5% (0.6 wt% Ca), influencing feeding behavior during solidification. Hot cracking susceptibility declined significantly with faster cooling. At 0.65 °C/s, the Mg-3Zn reference shows the lowest susceptibility, whereas at 0.9 °C/s the Mg–3Zn–0.3Ca alloy is lowest; at higher rates (1.5–5 °C/s) the Mg–3Zn–0.6Ca alloy provides the best resistance. Analysis identified solidification time as the dominant factor controlling hot cracking, followed by mushy zone width and solid fraction at coherency, while secondary phases modulated stress accumulation and crack formation. These results demonstrate the critical interplay between cooling rate and composition in defect formation, offering quantitative guidelines for optimizing microstructure and casting performance in Mg-Zn-Ca alloys.

Graphical Abstract