Insights into core-shell multi-structure and strengthening by multi-microalloying (Sc, Zr, Er and Ti) of a T6 treated Al–Li–Mg alloy

The core-shell multi-structure and strengthening of a multi-microalloyed (Sc, Zr, Er and Ti) T6 treated Al–Li–Mg alloy were studied using transmission electron microscopy (TEM) and microhardness. The T6 treated microstructure contained core-shell multi-structured particles. The (Sc, Zr, Ti)-rich core was generated at the earlier stage at higher temperature rather than at the final aging stage at 160 °C and still remained during aging. The core edge was Al3Er. The shell layer was δ′-Al3Li. These were generated during aging. The coarsening kinetics and precipitate size distributions of Al3(Sc, Zr, Er, Ti, Li) particles aged at 160 °C indicated that the volume diffusion and surface reaction at the particle/matrix interfaces occurred simultaneously. The particle growth was controlled by a combination of these two mechanisms. Multi-microalloying (Sc, Zr, Er and Ti) into the Al–Li–Mg alloy did not accelerate the peak aging time but increased the strength during aging. The peak hardness of the new Al–Li–Mg-Sc-Zr-Er-Ti alloy was increased by ∼22 % compared to that of the contrasting Al–Li–Mg alloy. Orowan bypass strengthening was the operative mechanism for the core-shell multi-structure particles.