Nucleants of Eutectic Silicon in Al-Si Hypoeutectic Alloys: β-(Al, Fe, Si) or AlP Phase

A thermodynamic description of the Al-Si-P-Fe quaternary system focused on Al-(Si)-rich alloys is developed. The solidification sequence in typical Al-7Si cast alloys is derived using thermodynamic calculations of the phase diagrams and solidification simulation under Scheil and constrained Scheil conditions. The previously claimed nucleation of eutectic silicon by β-(Al,Fe,Si) particles is not possible because under all conditions, β-(Al,Fe,Si) precipitates after (Si) in pertinent alloys. Variation of P in the ppm range is crucial because it changes the solidification sequence of AlP and (Si).