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<p>Al–Zn–Mg–Cu alloys are highly valued in the aerospace and automotive industries due to their exceptional specific strength and stiffness. However, their severe susceptibility to hot tearing during solidification inevitably limits their application in near-net shape processes. This study investigates the influence of the Mg content on the hot tearing susceptibility (HTS) of Al–6Zn–<i>x</i>Mg–1.5Cu (<i>x</i> = 1.5, 2.0, 2.5, and 3.0 wt%) alloys using a constrained rod casting (CRC) mold. The results indicate a progressive decrease in the HTS with increasing Mg content. A comparison of the experimental results with the predictions of Kou's criterion reveals that Kou's criterion provides a considerable degree of reliability, although it slightly overestimates the decreasing trend of the HTS for alloys with higher Mg contents. Further analysis indicates that alloys with higher Mg contents exhibit superior hot tearing resistance due to five key factors: narrower vulnerable temperature range; finer grain size; higher liquid fraction and lower liquid viscosity at a given temperature during the middle stage of solidification; higher final residual Mg(Zn,Cu,Al)<sub>2</sub> phase fraction and lower liquid surface tension during the final stage of solidification; and lower solidification stress/strain. These findings enhance the understanding of the HTS of Al–Zn–Mg–Cu alloys and are expected to offer reliable theoretical guidance for optimizing the composition of industrial Al–Zn–Mg–Cu alloys.</p>

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Effect of Mg Content on the Hot Tearing Susceptibility of Al–Zn–Mg–Cu Alloys

  • 期刊论文

  • 发表日期：

    2025年3月22日

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  • Yixiong Lin,
  • Liandeng Wang

摘要

Al–Zn–Mg–Cu alloys are highly valued in the aerospace and automotive industries due to their exceptional specific strength and stiffness. However, their severe susceptibility to hot tearing during solidification inevitably limits their application in near-net shape processes. This study investigates the influence of the Mg content on the hot tearing susceptibility (HTS) of Al–6Zn–xMg–1.5Cu (x = 1.5, 2.0, 2.5, and 3.0 wt%) alloys using a constrained rod casting (CRC) mold. The results indicate a progressive decrease in the HTS with increasing Mg content. A comparison of the experimental results with the predictions of Kou's criterion reveals that Kou's criterion provides a considerable degree of reliability, although it slightly overestimates the decreasing trend of the HTS for alloys with higher Mg contents. Further analysis indicates that alloys with higher Mg contents exhibit superior hot tearing resistance due to five key factors: narrower vulnerable temperature range; finer grain size; higher liquid fraction and lower liquid viscosity at a given temperature during the middle stage of solidification; higher final residual Mg(Zn,Cu,Al)2 phase fraction and lower liquid surface tension during the final stage of solidification; and lower solidification stress/strain. These findings enhance the understanding of the HTS of Al–Zn–Mg–Cu alloys and are expected to offer reliable theoretical guidance for optimizing the composition of industrial Al–Zn–Mg–Cu alloys.