Effect of thermomechanical processing on mechanical properties and the microstructure of ternary Al-Ce-Mg alloy

Al-Ce alloys are known to retain a large fraction of their room temperature properties at elevated temperatures and after exposure to temperature for extended periods. Here we work with the ternary close-to-eutectic alloy Al-10Ce-4Mg and explore the effect of extrusion on its microstructure and mechanical properties. Extrusion produces a highly refined microstructure with texture exhibiting a twofold increase in strength (tensile strength of 390 MPa at room temperature) and fourfold increase in failure strain relative to the as cast state. After exposure to 300 °C for 100 h the alloy retains 82% and 88% of the room temperature strength in the as-cast and extruded states, respectively. The ratio of the strength at 300 °C to the strength at room temperature is 0.4, below the corresponding ratio for the Al-10Ce binary alloy (ratio 0.7) but higher than that of AA2618 (ratio 0.1). The extruded Al-10Ce-4Mg has fracture toughness of 23 kJ/m2, which is retained in proportion of 97.6% after exposure to 300 °C for 100 h. The material exhibits negative strain rate sensitivity at room temperature and in the range of strain rates $$\:{10}^{-5}\:{s}^{-1}$$ to $$\:{10}^{-2}\:{s}^{-1}$$ . We show that the high room temperature strength is due to Al11Ce3 dispersoids and Mg-rich precipitates. The Mg-rich precipitates dissolve in the temperature range 200 °C to 250 °C while the Al11Ce3 dispersoids remain stable and provide strengthening at 300 °C. Mg-rich precipitates reform upon cooling, which ensures property retention upon thermal cycling. The high toughness, strength and property retention upon exposure to elevated temperatures make this alloy an excellent candidate for applications requiring lightweight temperature resistant materials.