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<p>This work investigates the effects of growth rate (GR), cooling rate (CR) and eutectic microstructure on the machinability of Al-12.6Si and Al-12.6Si-3.2Bi (wt.%) alloys. Directional solidification experiments were performed using a water-cooled upward solidification apparatus, enabling a range of GR and CR values along the length of the ingots. The as-solidified microstructures consisted of primary α-Al dendrites and interdendritic eutectic Si, while the Bi-containing alloy exhibited additional Bi globules dispersed within the eutectic regions. Machinability was evaluated based on maximum cutting temperature (<i>T</i><sub>max</sub>), heating rate (HR) and tool flank wear (Vb<sub>max</sub>). In the binary alloy, CR and eutectic spacing (<i>λ</i><sub>Si</sub>) had negligible influence on <i>T</i><sub>max</sub>, which remained approximately constant at 46&#xa0;°C. On the other hand, the ternary alloy exhibited <i>T</i><sub>max</sub> values ranging from 50 to 63&#xa0;°C. Higher HR values were associated with higher CR and finer <i>λ</i><sub>Si</sub> for both alloys. Although Bi addition did not significantly affect HR, it promoted the formation of built-up edge (BUE), which contributed to a higher <i>T</i><sub>max</sub>. The addition of Bi improved machinability by reducing Vb<sub>max</sub> by nearly 40% compared with the binary alloy.</p>

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Solidification-Controlled Microstructure and Its Effect on the Machinability of Directionally Solidified Al-Si and Al-Si-Bi Alloys

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年4月7日

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  • Fernando S. Rocha,
  • Adrina P. Silva,
  • Thiago A. Costa,
  • Otavio L. Rocha,
  • Antonio L. Moreira

摘要

This work investigates the effects of growth rate (GR), cooling rate (CR) and eutectic microstructure on the machinability of Al-12.6Si and Al-12.6Si-3.2Bi (wt.%) alloys. Directional solidification experiments were performed using a water-cooled upward solidification apparatus, enabling a range of GR and CR values along the length of the ingots. The as-solidified microstructures consisted of primary α-Al dendrites and interdendritic eutectic Si, while the Bi-containing alloy exhibited additional Bi globules dispersed within the eutectic regions. Machinability was evaluated based on maximum cutting temperature (Tmax), heating rate (HR) and tool flank wear (Vbmax). In the binary alloy, CR and eutectic spacing (λSi) had negligible influence on Tmax, which remained approximately constant at 46 °C. On the other hand, the ternary alloy exhibited Tmax values ranging from 50 to 63 °C. Higher HR values were associated with higher CR and finer λSi for both alloys. Although Bi addition did not significantly affect HR, it promoted the formation of built-up edge (BUE), which contributed to a higher Tmax. The addition of Bi improved machinability by reducing Vbmax by nearly 40% compared with the binary alloy.