Investigation on microstructure heterogeneity of the HPDC AlSiMgMnCu alloy through 3D electron microscopy

Abstract

The microstructural characteristics of the high pressure die casting (HPDC) AlSiMgMnCu alloys in the skin layer, segregation band and the central zone were investigated in three dimensions by serial block-face scanning electron microscopy (SBFSEM). The results present that the volume fractions of α-Al15(Fe, Mn)3Si (α-Fe phase), β-Mg2Si (β phase) and Q-Al5Cu2Mg8Si6 (Q phase) in the skin layer and the central zone are higher than those in the segregation band zone. The volume fractions and sizes of the θ-Al2Cu phase (θ phase) in the skin layer and the central zone are lower than those in the segregation band zone. In the skin layer, the preferential growth orientation of the α-Fe phase with plate-like morphology is parallel to the heat transfer direction, while the other phases exhibit a complex seaweed-like morphology. In the central zone and the segregation band zone, the shearing stress and turbulent flow during the filling process lead to the morphology of α-Fe and β-Mg2Si relatively regular. However, the morphology of Q-Al5Cu2Mg8Si6 and θ-Al2Cu phases are irregular owing to their lower solidification temperatures. The distribution and morphology of β-Mg2Si, Q-Al5Cu2Mg8Si6 and θ-Al2Cu in the segregation band zone mainly determined the distribution and morphology of the α-Fe phase.