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<p>Al-Cu-Mg alloys are highly vulnerable to hot tearing during the solidification process, a phenomenon that severely compromises their mechanical properties and workability, thereby imposing significant limitations on their industrial applications. Therefore, the hot tearing sensitivity of Al-4.4Cu-1.5Mg-0.15Zr-<i>x</i>Sm (<i>x </i>= 0.1, 0.3, 0.5 and 0.7) alloys was systematically investigated using a “cross” hot tearing test system. This study delves into the effects of Sm addition on the alloy’s microstructure, second-phase distribution, solidification behavior, hot tearing sensitivity, and the underlying hot tearing mechanism. A comprehensive analysis was conducted to clarify the role of Sm in regulating hot tearing susceptibility during solidification, combining microstructural characterization with thermodynamic solidification behavior analysis. The results indicate that the <i>d-</i>value, <i>HTS</i><sub>1</sub> and <i>CSC</i> values decrease initially and then increase with the Sm content increase. When the Sm content is 0.5 wt.%, the α-Al grain is the finest, with the <i>d</i>-value of 84&#xa0;μm. Meanwhile, the <i>HTS</i><sub>1</sub> and <i>CSC</i> values are the lowest, with values of 68 and 0.288, respectively. Moreover, it is found that <i>HTS</i><sub>1</sub> and <i>CSC</i> curve and the ∆<i>F</i>/<i>F</i><sub>i</sub> ratio curve exhibit similar trends. Therefore, it is possible to predict the severity of hot tearing by comparing the ∆<i>F</i>/<i>F</i><sub>i</sub> ratio. The hot tearing mechanism can be summarized as: When hot tearing occurs, intergranular bonding can be improved by adding the appropriate rare earth Sm. The fusion mechanism has evolved from exclusive dependence on liquid films to a synergistic effect of intergranular bridging and liquid film, which substantially enhances intergranular bonding strength. Additionally, optimal Sm addition efficiently refines the grain structure and narrows the solidification temperature range, thereby reducing shrinkage strain and remarkably decreasing the hot tearing susceptibility. This dual-effect mechanism—grain refinement and solidification interval optimization—establishes a critical microstructural foundation for mitigating hot tearing tendency during solidification.</p>

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Exploring Microstructure Evolution Rule and Hot Tearing Mechanism of Al-Cu-Mg-xSm Alloys During Solidification Process

  • 期刊论文

  • 发表日期：

    2026年2月5日

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  • Chunyu Yue,
  • Yurong Shi,
  • Bowen Zheng,
  • Ming Su,
  • Lei Jin,
  • Xiaojiao Zuo,
  • Xiaoguang Yuan

摘要

Al-Cu-Mg alloys are highly vulnerable to hot tearing during the solidification process, a phenomenon that severely compromises their mechanical properties and workability, thereby imposing significant limitations on their industrial applications. Therefore, the hot tearing sensitivity of Al-4.4Cu-1.5Mg-0.15Zr-xSm (x = 0.1, 0.3, 0.5 and 0.7) alloys was systematically investigated using a “cross” hot tearing test system. This study delves into the effects of Sm addition on the alloy’s microstructure, second-phase distribution, solidification behavior, hot tearing sensitivity, and the underlying hot tearing mechanism. A comprehensive analysis was conducted to clarify the role of Sm in regulating hot tearing susceptibility during solidification, combining microstructural characterization with thermodynamic solidification behavior analysis. The results indicate that the d-value, HTS1 and CSC values decrease initially and then increase with the Sm content increase. When the Sm content is 0.5 wt.%, the α-Al grain is the finest, with the d-value of 84 μm. Meanwhile, the HTS1 and CSC values are the lowest, with values of 68 and 0.288, respectively. Moreover, it is found that HTS1 and CSC curve and the ∆F/Fi ratio curve exhibit similar trends. Therefore, it is possible to predict the severity of hot tearing by comparing the ∆F/Fi ratio. The hot tearing mechanism can be summarized as: When hot tearing occurs, intergranular bonding can be improved by adding the appropriate rare earth Sm. The fusion mechanism has evolved from exclusive dependence on liquid films to a synergistic effect of intergranular bridging and liquid film, which substantially enhances intergranular bonding strength. Additionally, optimal Sm addition efficiently refines the grain structure and narrows the solidification temperature range, thereby reducing shrinkage strain and remarkably decreasing the hot tearing susceptibility. This dual-effect mechanism—grain refinement and solidification interval optimization—establishes a critical microstructural foundation for mitigating hot tearing tendency during solidification.