Microstructures and mechanical properties of a high-strength Mg-3.5Sm-0.6Zn-0.5Zr alloy

Microstructures and mechanical properties of a high-strength extruded Mg-3.5Sm-0.6Zn-0.5Zr alloy were thoroughly investigated. The results indicate that the dominant intermetallic phase in both as-cast and extruded samples is not the widely reported Mg41Sm5 phase but Mg3Sm phase. After extrusion, the microstructures are composed of fine equiaxed dynamically recrystallized (DRXed) grains, coarse elongated unDRXed grains with ultrafine sub-grains, disintegrated intermetallic particles, and numerous small dynamically precipitated particles. Also, there are amounts of particularly < a + c > dislocations in the Mg matrix after extrusion. Finally, numerous nano-scale plate β′ particles and lamellae β″ particles homogeneously precipitated in the matrix during artificial aging treatments. Therefore, the studied alloy exhibits very high ultimate tensile strength and yield strength, whose maximum values at room temperature are approximately 427 MPa and 416 MPa, respectively, much greater than most conventional Mg-RE based alloys with comparative or even much higher RE additions.