Influence of Zr on structure development in rapidly solidified AI-Si alloys

Abstract

The method of rapid solidification from the melt enables a nano-structured zone to develop that is clearly visible in cross-section of ribbon-like specimens. The study of this zone (referred to earlier as structureless) is performed on a model Al-Si eutectic alloy with different Zr-additions. Due to the low Zrconcentration in equilibrium Al-solid solution, rapidly solidified ribbons are obtained and processed. The structure of a ribbon reveals two different zones. The first (near to the cooling surface) has shown nanosized intermetallic phases and Si-particles, which are easy to change during thermal treatment. Zr-additives to the Al-Si eutectic influence the solidification mechanism, and change the quantity, the composition and crystallography of the phase's comparing its state as-cast and after thermal treatment. There is evidence for the processes obtained by DSC analyses and by light microscopy. Thermal treatment at elevated temperature was used to detect changes, which could take place if hot-extrusion processing was used to compact chopped ribbon to bulk material. The micro-hardness tests were used to reveal new properties of compacts and oxidation experiments.