Study of 1xxx aluminum extrusion alloys for brazed heat exchangers: Influences of Sc/Zr microalloying and thermomechanical processing

Commercial 1xxx aluminum alloys are widely used in brazed heat exchangers. However, their limited grain stability during high-temperature brazing promotes recrystallization and abnormal grain growth, leading to a deterioration of mechanical strength. This work focused on 1xxx extruded thin strips, through which the effects of Sc/Zr microalloying on grain structure, mechanical properties and corrosion resistance under two processing routes were systematically investigated. Three alloys were examined: a 1xxx base alloy free of Sc and Zr, a low Al-Sc-Zr alloy (0.10 wt% Sc, 0.10 wt% Zr), and a high Al-Sc-Zr alloy (0.19 wt% Sc, 0.15 wt% Zr). The base alloy exhibited a very coarse recrystallized grain structure after brazing at 605 °C under both processing routes, resulting in low mechanical strengths. With Sc and Zr microalloying, the grain structure became finer and more stable, and the mechanical strengths were significantly improved. Among the three alloys studied, the high Al-Sc-Zr alloy was the only one that maintained most of the deformed grain structure after simulated brazing at 605 °C. Those findings were further validated by extruding micro multi-port tubes and subjecting them to a simulated braze. For both routes, a post-braze aging treatment further promoted fine Al 3 (Sc, Zr) precipitation and significantly enhanced the strength of the Sc-containing alloys. Overall, while the high Al-Sc-Zr alloy provided the best combination of grain stability, mechanical strength, corrosion resistance, and extrudability under Route 1 (high-temperature homogenization), the low Al-Sc-Zr alloy still demonstrated clear improvements over the base alloy.