Mechanism of AlP modifying the morphology of Si in Al-20Si alloys based on experimental studies and first-principles calculations

ABSTRACT The modifying influence of aluminium phosphide to the morphology of primary Si and eutectic Si was investigated in hypereutectic Al-20Si alloys via adding Al-Cu-P master alloy (0.5, 1, 20 wt.%). Microstructural results showed when Al-Cu-P addition from 0 to 0.5%, primary Si phase decreases and eutectic Si phase size remains invariable; when addition higher than 0.5%, primary Si phase keeps invariable, eutectic Si phase size increases. To prove the nucleation effect of AlP on Si phase, interfacial properties of Si/AlP interface were investigated using first-principles calculations. Results showed the AlP(100)/Si(100) interface energy is between −1.45 J/m2 and −1.38 J/m2 for Al-terminated and P-terminated AlP model, both is much smaller than liquid Si/crystalline Si interface (0.34 J/m2), consolidates that AlP particles possess strong nucleation potency for Si phases. Therefore, the modifying influence of AlP to the morphology Si phase is well clarified as a function of AlP content in Al-20Si alloys.