Fabrication of hypoeutectic Al-4Si alloy with high electrical conductivity, high plasticity and medium strength by the dual treatment of Al matrix and eutectic Si microstructure

Highlights: • A kind of Al-4Si alloy conductor material with high electrical conductivity, high plasticity and medium strength was fabricated successfully. • Eutectic Si particles were changed from needle/plate-like along grain boundary to fine granular (uniform distribution), and have good orientation consistent with Al, significantly decreasing the electron scattering. • The formation of unique extrusion texture promotes the improvement of the electrical and mechanical properties of Al-4Si alloy. -- Abstract: Hypoeutectic Al-Si alloys exhibit excellent mechanical properties and relatively good electrical conductivity (EC), and they are often used as overhead transmission conductors. But, due to the contradiction between EC and mechanical properties (especially EC and strength), high EC and good mechanical properties are hard to be obtained simultaneously, which limits their applications in the field of electrical engineering. Thus, it is necessary to improve the matching between EC and mechanical properties. In this study, composite boron treatment, Sr modification, homogenization heat treatment and hot extrusion deformation process were done to fabricate a kind of hypoeutectic Al-4Si alloy with high EC, high plasticity and medium strength. Through the process mentioned above, not only Al matrix was purified, but also eutectic Si exhibited good orientation consistent with α-Al. In addition, eutectic Si morphology was modified from large needle/plate-like to fine particles, and its distribution was changed from segregation along grain boundary to uniform distribution. The scattering probability of solid solution TM elements to electrons was significantly reduced, and the number of channels for electron migration in the eutectic Si region was also increased obviously. Meanwhile, the optimization of the microstructure enhanced the mechanical strength and elongation of Al-4Si alloy at the same time. The special extrusion texture also promoted improvement of the electrical and mechanical properties of Al-4Si alloy. Finally, the EC of Al-4Si alloy was improved from 41.8 %IACS to 59.2 %IACS, and the corresponding ultimate tensile strength (UTS) and elongation can reach 206 MPa and 26.7%, respectively. Compared with that as-cast condition, EC, UTS and elongation improved by 41.6%, 60.9% and 136.3%, respectively, which has a certain application prospect in the field of electrical engineering.