Influence of extrusion preheating temperature and aging strategy on precipitation and performance of Al–Sc–Zr conductor alloys

This study investigates how the preheating temperature of hot extrusion (420 °C vs. 480 °C) and subsequent aging strategy (one-step and two-step aging) govern precipitation behavior, microstructure evolution, and the resulting mechanical and electrical performance of an extruded Al–0.1Sc–0.1Zr (wt.%) conductor alloy. Results indicate that lower preheat extrusion at 420 °C suppresses early coarsening and produces a higher density of fine, coherent Al 3 Sc/Al 3 (Sc,Zr) particles with the L1 2 structure after aging, leading to enhanced strength. Aging conditions included one-step aging at 300, 350, and 400 °C, as well as a two-step schedule (300 °C/24 h + 400 °C/8 h). Two-step aging applied to the 420 °C-extruded alloy generated the finest precipitate distribution (4.41×10²¹ m -3 ) by promoting Sc-rich core formation at 300 °C followed by controlled Zr diffusion at 400 °C, yielding a core–shell structure with superior coarsening resistance. This optimized precipitation state delivered the highest strengthening contribution through Orowan bypass, along with controlled subgrain growth resulting from increased Zener drag pressure. Consequently, coupling a low extrusion preheat temperature (420 °C) with a tailored two-step aging treatment achieved the best property balance, delivering a UTS of 172 MPa and an electrical conductivity of 57.5% IACS—an effective pathway to producing high-strength, high-conductivity aluminum conductor alloys. In contrast, alloys extruded at 480 °C experienced significant precipitate coarsening across all aging treatments, resulting in lower strengthening and reduced thermal stability.