Study on the Coupling Mechanism of Si Content on the Microstructure Evolution and Strength–Conductivity Properties in Low-Magnesium Al-0.2Mg-xSi Alloys

High-silicon, low-magnesium aluminum alloys are important for lightweight electrical applications, yet they face a typical strength–conductivity trade-off. This study investigates Al-0.2Mg-xSi alloys with Si ranging from 0.4 to 1.0 wt%. The wires underwent homogenization, solution treatment, cold working, and controlled annealing. In the cold-worked (Y) state, increasing Si raised tensile strength from 190 MPa to 291 MPa but reduced conductivity from 57.6% IACS to 52.1% IACS, with limited ductility. After annealing (R state), strength dropped by half (105–137 MPa), while elongation recovered beyond 22% and conductivity exceeded 62.1% IACS. Notably, the 1.0% Si alloy showed superior overall performance: its strength (137 MPa) was 32 MPa higher than the 0.4% Si alloy, with only a 0.2% IACS conductivity loss. This reveals that under low Mg content, increasing Si enhances strength via work hardening and, more critically, promotes annealing-induced precipitation that relieves lattice distortion, enabling significant strength improvement at minimal conductivity cost. These findings offer a useful strategy for optimizing strength and conductivity in such alloys.