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The effecT of 0.2% AddiTion of Mg, co And ce on MicrosTrucTure And MechAnicAl ProPerTies of 1xxx series AluMiniuM Alloy cAsTings designed for overheAd TrAnsMission linesThe effect of 0.2% addition of Mg, co and ce to 99.9% cast aluminium was studied by evaluation of changes in microstructure and mechanical properties. The microstructure was analyzed by scanning electron microscopy and transmission electron microscopy. The al99.9 alloy contained only al-Fe-si phase particles. similar al-Fe-si particles were observed in alloy with 0.2% Mg addition, because this amount of magnesium was fully dissolved in the solid solution. The addition of cobalt resulted in the formation of al 9.02 co 1.51 Fe 0.47 phase particles assuming the shape of eutectic plates. The electron backscattered diffraction map made for the alloy with 0.2% co addition showed numerous twin boundaries with distances between them in the range from 10 to 100 µm. The addition of cerium was located in the grain boundary area. cerium also gave rise to the formation of two types of particles, i.e. al 4 ce and al-ce-Fe-si. The al-ce-Fe-si phase is a nucleation site for the al 4 ce phase, which forms eutectic plates. The results showed that the introduction of additives increases the mechanical properties of the cast materials. The 99.9% cast aluminium has a hardness of 16.9 hB. The addition of 0.2% by weight of Mg, co, ce increases this hardness to 21.8 hB, 22.6 hB and 19.1 hB, respectively.