Influence of various initial microstructures on microstructure and mechanical property of ECAP processed Mg-8.4Li-3.58Al-0.36Si-0.05Ti-0.01B alloys

As-cast and homogenized Mg-8.4Li-3.58Al-0.36Si-0.05Ti-0.01B alloys with and without coarse AlLi and Mg2Si constituent particles are processed by equal channel angular pressing (ECAP) at 623 K for 1–4 passes in route BC (the billet is rotated 90° clockwise between consecutive pressings) to investigate their different microstructural evolutions and mechanical responses. In particle-containing cast + ECAP alloys, coarse AlLi in β-Li phase and Mg2Si constituent particles accelerated the refinement and uniform redistribution of α-Mg dendrites during ECAP to form small blocky α-Mg grains. Simultaneous particle dissolution and significant fragmentation together with the uniform mixture of small α-Mg and β-Li grains result in the highest ductility and good strength in cast+2p alloy compared to the other ECAPed alloys. Heterogeneous re-precipitation and particle coarsening as well as α-Mg grain growth lead to a gradual decline in mechanical properties of cast+3p and cast+4p alloys. While in HT + ECAP alloys, large amounts of second-phase particles dynamically precipitated during ECAP, which pinned the dislocation movement and (sub)grain boundary migration resulting in large α-Mg blocks in HT + ECAP alloys. Nevertheless, concurrent precipitation and dynamic recrystallization (DRX) lead to high-density AlLi and Mg2Si nano-precipitates and fine α-Mg grains with weak basal plane texture, resulting in the highest strength and reasonable ductility in HT+2P alloy compared to the other ECAPed alloys. Particle coarsening and coarser DRXed α-Mg grains caused the declined mechanical properties in HT+3p and HT+4p alloys.