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<p>The mechanical properties of Al–Mg–Si–Mn alloy are severely limited by the coarse lamellar eutectic Mg<sub>2</sub>Si phase. To overcome this challenge, this study systematically investigates the effects of individual additions of Sr and Bi elements as well as the combined addition of Sr/Bi on the modification of eutectic Mg<sub>2</sub>Si in Al–6.5Mg–2.6Si–0.7Mn alloy. The results show that Sr/Bi composite addition exhibits a better modification effect than Sr or Bi addition alone: The lamellar eutectic Mg<sub>2</sub>Si transforms into a fine fibrous and granular morphology. The average length and average aspect ratio of eutectic Mg<sub>2</sub>Si phase decrease from 6.3&#xa0;μm and 7.0 to 1.9&#xa0;μm and 2.4, respectively. Compared with the base alloy, the tensile strength and elongation of the Sr/Bi composite-modified alloy increase from 248.7&#xa0;MPa and 8.0% to 305.1&#xa0;MPa and 21.7%, respectively. During the solidification process, Bi enriches at the solid–liquid interface front, increasing the constitutional undercooling degree and decreasing the eutectic nucleation temperature. Sr adsorbs on the Mg<sub>2</sub>Si surface, inhibiting the growth of the eutectic phase and reducing the eutectic growth temperature. This synergistic effect effectively improves the size, morphology and distribution of eutectic Mg<sub>2</sub>Si and significantly enhances the mechanical properties of the alloy. This study provides a novel and low-cost Sr/Bi composite modification strategy for the design of high strength and toughness Al-Mg-Si-Mn alloys.</p>

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Effect of Synergistic Modification of Sr and Bi on the Microstructure and Mechanical Properties of Hypoeutectic Al–Mg–Si–Mn Alloy

  • 期刊论文

  • 发表日期：

    2026年7月29日

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  • Zhiheng Li,
  • Weizhong Fan,
  • Zhenjiang Yang,
  • Jun Yan,
  • Shuang Hu,
  • Jun Du,
  • Songlin Mu

摘要

The mechanical properties of Al–Mg–Si–Mn alloy are severely limited by the coarse lamellar eutectic Mg2Si phase. To overcome this challenge, this study systematically investigates the effects of individual additions of Sr and Bi elements as well as the combined addition of Sr/Bi on the modification of eutectic Mg2Si in Al–6.5Mg–2.6Si–0.7Mn alloy. The results show that Sr/Bi composite addition exhibits a better modification effect than Sr or Bi addition alone: The lamellar eutectic Mg2Si transforms into a fine fibrous and granular morphology. The average length and average aspect ratio of eutectic Mg2Si phase decrease from 6.3 μm and 7.0 to 1.9 μm and 2.4, respectively. Compared with the base alloy, the tensile strength and elongation of the Sr/Bi composite-modified alloy increase from 248.7 MPa and 8.0% to 305.1 MPa and 21.7%, respectively. During the solidification process, Bi enriches at the solid–liquid interface front, increasing the constitutional undercooling degree and decreasing the eutectic nucleation temperature. Sr adsorbs on the Mg2Si surface, inhibiting the growth of the eutectic phase and reducing the eutectic growth temperature. This synergistic effect effectively improves the size, morphology and distribution of eutectic Mg2Si and significantly enhances the mechanical properties of the alloy. This study provides a novel and low-cost Sr/Bi composite modification strategy for the design of high strength and toughness Al-Mg-Si-Mn alloys.