THE STRUCTURE AND PROPERTIES OF CONTINUOUS DIRECTIONAL SOLIDIFICATION Al-Si EUTECTIC IN SITU COMPOSITES

In this paper,the adoptable ranges of process parameters,the coupled zone,the structure and properties of eutectic and hypereutectic Al-Si alloys (A1-12.7-16.6wt,%Si) have been investigated by a new type of continuous directional solidification (CDS) apparatus.It's shown that the long casting with shining surfaece,homogeneous composition and structure can be produced within the adoptable ranges of process,and short-fine fibrous in situ composites of Al-Si eutectic and hyper-eutectic alloys can be made in some range of freezing rate depending on the silicon content by CDS technology,The flake/fibre transition of the eutectic silicon appears with increasing freezing rates from 0.02 mm/s to 2.0 mm/s,The tensile strength and percentage clongation increase with the increase of freezing rate.Corripared with cast state Al-Si eutectic alloys,the strength of continuously directionally solidified Al-Si eutectic alloys inceases by 60%,its percentage elongation inereases by two times,from 4% to 12%.The formation mechanism of the fibre structure and the effect of eutectic silicon morphology on the cracking mechanism of Al-Si in situ composites have been analysed.