Precipitation strengthening of Al–B4C metal matrix composites alloyed with Sc and Zr

A series of Al-15 vol.% B4C metal matrix composites containing different concentrations of Sc and Zr were isothermally aged at 300–450 °C for up to 200 h. The effects of Sc and Zr on the aging behavior, precipitation strengthening and precipitate coarsening of the composites were investigated. The addition of Sc resulted in considerable precipitation hardening of the composite matrices for all aging temperatures applied. Alloying both Sc and Zr in the Al–B4C composites produced a remarkable synergistic effect, which provided not only an increase in strength at peak aging but also improved the stability of the mechanical properties. The precipitate volume fraction, the average radius and the size distribution of nanoscale Al3Sc and Al3(Sc,Zr) precipitates formed during aging were measured. The Al3(Sc,Zr) precipitates generally exhibited better coarsening resistance than Al3Sc precipitates. It was confirmed that Orowan bypassing was the most probable control mechanism for the precipitation strengthening of both precipitates.

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► Effects of Sc, Zr on aging behavior, precipitation strengthening of Al–B4C composites.
► The combination of Sc, Zr produced a remarkable synergistic effect of strengthening.
► Nano-size precipitates Al3Sc and Al3(Sc,Zr) with different coarsening resistances.
► Orowan bypassing was the controlling mechanism for the precipitation hardening.