An Al-1.5B-3P Alloy Designed for Complex Modification of a Eutectic Al-Si Alloy Based on an Al-B-P Phase Diagram

The 700 °C isothermal section of an Al-B-P ternary system was analyzed by scanning electron microscopy coupled with an energy dispersive spectrometry and x-ray diffraction. The Al-1.5B-3P master alloy, designed based on the phase diagram, was used for the modification of a eutectic Al-Si alloy. The results revealed the presence of five three-phase regions in the 700 °C isothermal section of Al-B-P ternary system, namely, Liq. + AlB₂ + AlP, AlB₂ + AlP + BP, AlB₁₂ + AlB₂ + BP, AlB₁₂ + BP + α-B and AlP + BP + P_gas. The phase constituents of the Al-1.5B-3P alloy are the Al, AlB₂ and AlP phases. After complex modification by the Al-1.5B-3P alloy, a large number of fine α-Al dendrites and some primary Si formed in the eutectic Al-Si alloy. The morphology of eutectic Si changed from a needle-like to granular or short rod form. Compared with the unmodified eutectic Al-Si alloy, the tensile strength and elongation of the alloy modified with 0.4% Al-1.5B-3P were increased by 20 and 24%, respectively. Overall, the comprehensive mechanical properties of the modified alloy were significantly improved.