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

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.