Solidification Of Al-Si Alloys Under High Pressure

The solidification of Al-Si is carried out in a vacuum arc melting furnace. iscarried out on a CS-1B type six-anvil high-pressure apparatus. MicrostructureAl-Si alloy solidified under high pressure is compared with that solidified undernormal pressure.The growth of the eutectic silicon is studied with the eutecticgrowth model.The Al-Si alloys were prepared with the content (at.%) of Si is 11～50 at.%respectively. High-pressure solidification are carried out on the pressure 4～6GPa. The phase constitution of the Al-Si alloy solidified under high pressure ischaracterized by X-ray diffraction (XRD). The microstructures of the samplesare observed by optical microscope, scanning electron microscope (SEM),transmission electron microscope (TEM) and atomic force microscope (AFM).By observing the microstructure of the alloy, the effects of pressure areanalysed.The result of XRD shows that there is no new phase observed under highpressure, compared with the microstructure solidified under normal pressure.The microstructures observed show that a more amount of primary αAl phase isobserved in Al-21 at%Si alloy solidified under high pressure which indicatesthat eutectic point moving to the silicon direction with an increase of pressure inAl-Si alloy phase diagram. The eutectic cells of Al-Si alloy solidified under highpressure can be seen clearly and the eutectic silicon phases are presented curvedand near parallel lamellar crystals. And there tends to exist a unique lamellarspacing. The growth model of Al-Si eutectic under high pressure is investigatedtheoretically and the growth mechanism of eutectic silicon phase becomenonfaceted growth. The eutectic silicon lamella phase is found to be refined bypressure. At 5 GPa, the eutectic silicon lamella were refined with increasing thesilicon content. And also the primary β Si phase is refined by pressure effect.