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<p>Doping metallic alloys with rare-earth elements is a novel method for grain refinement and enhancing mechanical properties in laser beam powder bed fusion (PBF-LB) additive manufacturing (AM). In this work, the grain structure of Al6061 is modified by doping scandium (Sc) into the alloy system through mechanical mixing and using optimized ball milling parameters to ensure a uniform Sc distribution. Thermodynamic calculations via Thermo-Calc showed that adding 0.3 wt% Sc increases residual eutectic liquid and decreases the solidification cracking index of Al6061. Compared with Sc-free Al6061, Sc doping produces ultrafine grains, reducing the average grain size from 52&#xa0;μm to 3.7&#xa0;μm (approximately 93%) via Al<sub>3</sub>Sc formation. X-ray microscopy (XRM) was used to analyze post-solidification cracks, while optical tomography (OT) monitored crack formation during melting and solidification. Although Sc did not eliminate defects, it reduced the defect volume from 6.73% to 3.89%. The remaining defects consist predominantly of small spherical gas pores and residual solidification cracks, which are less detrimental than the irregular lack-of-fusion pores dominant in the Sc-free Al6061. Thermal analysis further indicated that the coefficient of thermal expansion of Sc-doped Al6061 was generally lower than that of both PBF-LB and conventionally manufactured Al6061. The OT method was employed during PBF-LB to assess process stability and detect porosity and cracks.</p>

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Enhanced grain refinement and thermal expansion in scandium-modified Al6061 via laser beam powder bed fusion: from mechanical mixing to in-situ monitoring

  • 期刊论文

  • 发表日期：

    2026年7月4日

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  • Faezeh Hosseini,
  • Asad Asad,
  • Haoyang Li,
  • Mostafa Yakout

摘要

Doping metallic alloys with rare-earth elements is a novel method for grain refinement and enhancing mechanical properties in laser beam powder bed fusion (PBF-LB) additive manufacturing (AM). In this work, the grain structure of Al6061 is modified by doping scandium (Sc) into the alloy system through mechanical mixing and using optimized ball milling parameters to ensure a uniform Sc distribution. Thermodynamic calculations via Thermo-Calc showed that adding 0.3 wt% Sc increases residual eutectic liquid and decreases the solidification cracking index of Al6061. Compared with Sc-free Al6061, Sc doping produces ultrafine grains, reducing the average grain size from 52 μm to 3.7 μm (approximately 93%) via Al3Sc formation. X-ray microscopy (XRM) was used to analyze post-solidification cracks, while optical tomography (OT) monitored crack formation during melting and solidification. Although Sc did not eliminate defects, it reduced the defect volume from 6.73% to 3.89%. The remaining defects consist predominantly of small spherical gas pores and residual solidification cracks, which are less detrimental than the irregular lack-of-fusion pores dominant in the Sc-free Al6061. Thermal analysis further indicated that the coefficient of thermal expansion of Sc-doped Al6061 was generally lower than that of both PBF-LB and conventionally manufactured Al6061. The OT method was employed during PBF-LB to assess process stability and detect porosity and cracks.