Effects of La and Ce on the microstructure, thermal conductivity and strength synergy of the as-extruded Mg-Mn-RE alloys

High thermal conductivity and high strength Mg-1.5Mn-2.5Ce alloy with a tensile yield strength of 387.0 MPa, ultimate tensile strength of 395.8 MPa, and thermal conductivity of 142.1 W/(m·K) was successfully fabricated via hot extrusion. The effects of La and Ce additions on the microstructure, thermal conductivity, and mechanical properties of the Mg-1.5Mn alloy were investigated. The results indicated that both the as-extruded Mg-1.5Mn-2.5La and Mg-1.5Mn-2.5Ce alloys exhibited a bimodal grain structure, with dynamically precipitated nano-scale α-Mn phases. In comparison with La, the addition of Ce enhanced the dynamic precipitation more effectively during hot extrusion, while its influence on promoting the dynamic recrystallization was relatively weaker. The high tensile strength obtained in the as-extruded Mg-1.5Mn-2.5RE alloys can be attributed to the combined influence of the bimodal grain structure (with fine dynamic recrystallized (DRXed) grain size and high proportion of un-dynamic recrystallized (unDRXed) grains), dense nano-scale precipitates, and broken Mg₁₂RE phases, while the remarkable thermal conductivity was due to the precipitation of Mn-rich phases from the Mg matrix.