The production of large-scale and high-strength Mg-RE alloy billets by semi-continuous casting is highly prone to destructive cold cracking, which makes the manufacturing of high-quality Mg-RE billets a challenge. In this work, the effects of casting temperature, casting speed, and cooling intensity on the temperature and stress fields were investigated using finite element (FE) casting simulation. The results show that with increasing casting speed from 20 mm/min to 45 mm/min, the temperature difference between the center and edge of the billet increases from 287 ℃ to 420 ℃, and the liquid sump depth increases from 93.5 mm to 252.7 mm. Increasing the value of the cooling intensity at the first cooling region (h1) significantly increases the temperature difference between center and edge of the billet inside the mould. When the values of h1 are 500 W/(m2·K), 1000 W/(m2·K) and 1500 W/(m2·K), the liquid sump depths are 199.1 mm, 183.5 mm and 177.1 mm, respectively. When the value of the cooling intensity at the second cooling region (h2) increases from 1000 W/(m2·K) to 4000 W/(m2·K), the temperature difference increases from 312 ℃ to 447 ℃, and the liquid sump depth decreases from 222 mm to 167 mm. The casting temperature have a small influence on the temperature gradient of the cross-section and the liquid sump depth of the billet. The results of the simulations of stress fields show that the interior of the billet is subjected to three-dimensional tensile stress, and reducing the casting speed and cooling intensity can significantly reduce the stress in the interior of the billet. The maximum principal stress at center of the billet can be adjusted to less than 150 MPa, which is lower than the tensile strength of the as-cast Mg-8.5Gd-2.5Y-1.5Zn-0.5Zr (wt%) alloy. The optimal casting process parameters are obtained as follows: casting speed of 25 mm/min, casting temperature of 700 ℃, h1 of 1000 W/(m2·K) and h2 of 2000 W/(m2·K). Finally, a semi-continuous casting Mg-8.5Gd-2.5Y-1.5Zn-0.5Zr (wt%) billet with 450 mm in diameter and 3000 mm in length was successfully produced. The microstructures of the billet were investigated using the SEM, EBSD and XRD analyses. The results show that the types of eutectic phases at different regions are consistent, that the differences in area fractions of the eutectic phases are small, and that the grain orientation is random. After homogenization heat treatment, the yield strength of the billet at different regions are relatively homogeneous, with the yield strength of edge, R/2 and center specimens being 190 MPa, 182 MPa and 184 MPa, respectively.

Semi-continuous casting of large-scale Mg-Gd-Y-Zn-Zr alloy billet guided by finite element analysis

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发表日期：

2026年6月15日

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Jiyu Li,
Jian Zeng,
Shuai Dong,
Fenghua Wang,
Fulin Wang,
Li Jin,
Jie Dong

摘要

The production of large-scale and high-strength Mg-RE alloy billets by semi-continuous casting is highly prone to destructive cold cracking, which makes the manufacturing of high-quality Mg-RE billets a challenge. In this work, the effects of casting temperature, casting speed, and cooling intensity on the temperature and stress fields were investigated using finite element (FE) casting simulation. The results show that with increasing casting speed from 20 mm/min to 45 mm/min, the temperature difference between the center and edge of the billet increases from 287 ℃ to 420 ℃, and the liquid sump depth increases from 93.5 mm to 252.7 mm. Increasing the value of the cooling intensity at the first cooling region (h₁) significantly increases the temperature difference between center and edge of the billet inside the mould. When the values of h₁ are 500 W/(m²·K), 1000 W/(m²·K) and 1500 W/(m²·K), the liquid sump depths are 199.1 mm, 183.5 mm and 177.1 mm, respectively. When the value of the cooling intensity at the second cooling region (h₂) increases from 1000 W/(m²·K) to 4000 W/(m²·K), the temperature difference increases from 312 ℃ to 447 ℃, and the liquid sump depth decreases from 222 mm to 167 mm. The casting temperature have a small influence on the temperature gradient of the cross-section and the liquid sump depth of the billet. The results of the simulations of stress fields show that the interior of the billet is subjected to three-dimensional tensile stress, and reducing the casting speed and cooling intensity can significantly reduce the stress in the interior of the billet. The maximum principal stress at center of the billet can be adjusted to less than 150 MPa, which is lower than the tensile strength of the as-cast Mg-8.5Gd-2.5Y-1.5Zn-0.5Zr (wt%) alloy. The optimal casting process parameters are obtained as follows: casting speed of 25 mm/min, casting temperature of 700 ℃, h₁ of 1000 W/(m²·K) and h₂ of 2000 W/(m²·K). Finally, a semi-continuous casting Mg-8.5Gd-2.5Y-1.5Zn-0.5Zr (wt%) billet with 450 mm in diameter and 3000 mm in length was successfully produced. The microstructures of the billet were investigated using the SEM, EBSD and XRD analyses. The results show that the types of eutectic phases at different regions are consistent, that the differences in area fractions of the eutectic phases are small, and that the grain orientation is random. After homogenization heat treatment, the yield strength of the billet at different regions are relatively homogeneous, with the yield strength of edge, R/2 and center specimens being 190 MPa, 182 MPa and 184 MPa, respectively.