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<p>Aluminium–silicon alloys are commonly employed in manufacturing due to their advantageous strength-to-weight ratio and castability. Nonetheless, attaining refined and globular microstructures via semi-solid processing remains a pivotal challenge. This study investigated the influence of Mg addition on microstructure evolution in Al-Si alloy produced through Semi-Solid Metal Direct Thermal Method (DTM). The magnesium content was varied to evaluate its influence on grain morphology and intermetallic phase formation during solidification. Molten alloys containing 0.5–1.5 wt.% Mg were poured into a cylindrical copper mould at temperatures between 590 and 630&#xa0;°C and held for 10–20&#xa0;s prior to solidification. Microstructural characterisation revealed that the addition of magnesium significantly reduced the grain size and promoted a more globular grain structure compared with the magnesium-free alloy. The average grain size area decreased to approximately 802 µm<sup>2</sup> at higher Mg addition, accompanied by improved circularity and lower aspect ratio. The magnesium addition also facilitated the formation of intermetallic phase such as Al<sub>2</sub>Cu, Mg<sub>2</sub>Si, Al<sub>5</sub>Cu<sub>2</sub>Mg<sub>3</sub>Si<sub>5</sub>, Cu<sub>5</sub>Zn<sub>8,</sub> and β-Al<sub>5</sub>FeSi. These findings highlight the critical role of magnesium addition and processing conditions in refining the microstructure of Al-Si alloys produced via DTM.</p>

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Microstructural Evolution of Al-Si Alloys with Varying Magnesium Content Prepared by Direct Thermal Method

  • 期刊论文

  • 发表日期：

    2026年3月11日

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  • M. F. M. Tajudin,
  • A. H. Ahmad,
  • J. Alias,
  • N. A. Alang,
  • S. Naher

摘要

Aluminium–silicon alloys are commonly employed in manufacturing due to their advantageous strength-to-weight ratio and castability. Nonetheless, attaining refined and globular microstructures via semi-solid processing remains a pivotal challenge. This study investigated the influence of Mg addition on microstructure evolution in Al-Si alloy produced through Semi-Solid Metal Direct Thermal Method (DTM). The magnesium content was varied to evaluate its influence on grain morphology and intermetallic phase formation during solidification. Molten alloys containing 0.5–1.5 wt.% Mg were poured into a cylindrical copper mould at temperatures between 590 and 630 °C and held for 10–20 s prior to solidification. Microstructural characterisation revealed that the addition of magnesium significantly reduced the grain size and promoted a more globular grain structure compared with the magnesium-free alloy. The average grain size area decreased to approximately 802 µm2 at higher Mg addition, accompanied by improved circularity and lower aspect ratio. The magnesium addition also facilitated the formation of intermetallic phase such as Al2Cu, Mg2Si, Al5Cu2Mg3Si5, Cu5Zn8, and β-Al5FeSi. These findings highlight the critical role of magnesium addition and processing conditions in refining the microstructure of Al-Si alloys produced via DTM.