Structure formation and multistep nucleation in CASTING Al-Mg-Si alloys

ABSTRACT

The process of multistep nucleation during solidification in hypoeutectic Al-Mg-Si casting alloys was investigated. The morphology of the nucleating particles, Mg₂Si primary crystals and Al-Mg₂Si eutectic, was investigated with scanning electron microscopy (SEM) on polished and deep etched microsections. The mechanism of formation of the Mg₂Si crystal was attributed to heterogeneous nucleation on the nucleating particles. It was observed that the majority of the alloys particles found in the studied are oxides. It was established that eutectic Al–Mg₂Si in hypoeutectic alloys has the morphology of ‘eutectic crystal’, where one face of the crystal has triangular-spiral morphology. The mechanism of formation of Al-Mg₂Si eutectic cells is attributed to epitaxial growth on Mg₂Si crystals. The microhardness of the structural components (Mg₂Si crystals, α-Al dendrites, Al-Mg₂Si eutectic, and Al₃Ti crystals) was measured using Vickers hardness tester.

KEYWORDS:

• Al-alloys
• heterogeneous nucleation
• multistep nucleation
• nucleating particles
• primary crystals
• spiral eutectic

Acknowledgements

Authors gratefully thank the center “ICDAM” and especially to M.Puchnin, with the assistance to obtain SEM-images for Figures 3, 5 and 6 (for the project “Features of structure formation and changes in the mechanical properties of cast Al-Mg-Si-Mn alloy with the addition of (Ti+Zr)” [9]). The authors also gratefully thank the Visegrad Fund for the support provided for the mentioned research project. The authors are also thanking J.Hornik (ICDAM) and K.Mykhalenkov (NTUU “KPI”) for supervising the mentioned project.

Disclosure statement

No potential conflict of interest was reported by the authors.