Growth Structures in Aluminum--Silicon Alloys. Pt. 1. The Coupled Zone

• Published in: Journal of crystal growth 1984-01, Vol.66 (1), p.137-146
• Main Authors: Atasoy, O A, Yilmaz, F, Elliott, R
• Format: Article
• Language: English
• ISSN: 0022-0248

Directional solidification studies using a constant temperature gradient of 125 deg C/cm in the liquid are described and used to define the relationship between structure, Si concentration (11-20 wt.%) and growth velocity (1-1500 mu m/sec). It is shown that the angular Si eutectic structure occurs over a wider range of growth velocities than previously suggested. Quench modification of the eutectic structure occurs over a range of growth velocities depending on the Si concentration. At lower velocities in this range, branching of the (100) angular Si side plates within the plate plane begins the transition to a fibrous structure. This is completed with the transition of the flake "undercooled" eutectic to a fibrous form. Twins are shown not to be essential for the growth of the fibrous structure and the transition is attributed to a change from a layer growth to a continuous growth mechanism. The concept of the coupled zone is discussed and the observations are used to define the coupled zone boundaries. 15 ref.--AA.