The thermal stability of mechanical properties of Al–B4C composites alloyed with Sc and Zr at elevated temperatures

Two experimental Al-15 vol.% B4C composites, S40 with 0.4 wt.% Sc and SZ40 with 0.4 wt.% Sc plus 0.24 wt.% Zr, were prepared to examine the mechanical properties during long holding periods and the age hardening responses at elevated temperatures. Alloying with Sc or Sc and Zr displayed a significant precipitation strengthening in Al–B4C composites. Results showed that maximum peak hardness with a long plateau was achieved at 300–350 °C for the SZ40 composite, while the peak aging with a maximum hardness was reached at 300 °C for the S40 composite. The addition of Zr in the composite containing Sc delayed the overaging by ∼100 °C. The mechanical properties of SZ40 were considerably stable after 2000 h annealing at 300 °C, while the S40 composite exhibited a good long-term thermal stability at 250 °C. At all temperatures investigated, the Zr addition enhanced the strengthening effect and the mechanical properties of the SZ40 were higher than those of the S40 composite. The reduction of the mechanical properties of composites during prolonged annealing at higher temperatures was dominated by the precipitate coarsening.