As an efficient modifier, phosphorus (P) can significantly reduce the size of primary silicon (Si) crystals. However, modifier can aggregate when the P content exceeds a certain proportion, which decreases refining efficiency. In this study, the evolution of microstructures and mechanical properties of Al–50Si alloy have been studied by combining superheating and modification treatments. After modification, the mean size of the primary Si phase increased with superheating temperature, while the hardness decreased with increased superheating. Although the alloy was in an over-modified state when the modified content was 7 ​wt%, the overall alloy hardness was the highest. Nanoindentation tests were used to examine the mechanical properties of each alloy phase and the results showed that the nano-hardness of Al₂Cu phase was 5.52 ​GPa, three times that of an Al matrix, and was considered to be the reason for increased alloy hardness after over-modification. This phenomenon indicated that, except for size and distribution of the primary Si phase, intermetallic compounds, such as Al₂Cu, also played important roles in modifying alloy mechanical properties. The alloy melting process was observed in-situ using a laser confocal high-temperature scanning microscope and results indicated that the melting temperature of α-Al decreased with increased matrix Cu content. A model for calculating distortion energy was proposed and its rationality verified. Calculation results showed that, with increased matrix Cu content, the distortion energy gradually increased, which was the main reason for decreased matrix melting temperature. Moreover, the existence of distortion energy was verified using the EBSD method.

作为一种有效的改性剂，磷 (P) 可以显着减小初级硅 (Si) 晶体的尺寸。但当P含量超过一定比例时，改性剂会发生团聚，降低精炼效率。在这项研究中，通过结合过热和变质处理，研究了 Al-50Si 合金的显微组织和力学性能的演变。改性后，初生Si相的平均尺寸随过热温度升高而增大，而硬度随过热度升高而降低。虽然改性含量为7wt%时合金处于过度改性状态，但合金整体硬度最高。采用纳米压痕试验检测各合金相的力学性能，结果表明，Al ₂的纳米硬度Cu相为5.52GPa，是Al基体的三倍，被认为是过度变质后合金硬度增加的原因。这一现象表明，除了初级 Si 相的尺寸和分布外，金属间化合物，如 Al ₂铜在改变合金力学性能方面也发挥了重要作用。使用激光共聚焦高温扫描显微镜原位观察合金熔化过程，结果表明α-Al的熔化温度随着基体Cu含量的增加而降低。提出了一种计算畸变能量的模型并验证了其合理性。计算结果表明，随着基体Cu含量的增加，畸变能逐渐增大，这是基体熔化温度降低的主要原因。此外，使用EBSD方法验证了畸变能量的存在。