Research On Microstructure And Properties Of Magnesium-Lithium-Scandium Alloys

Mg-Li alloys are the lightest of all practical metallic materials for structures with high specific strength, high specific stiffness and good formability. They are under intensive research worldwide currently with promising application potential in fields which have rigid requirements for weight-saving, such as aeronautical and astronautical engineering. In the present study, two kinds of alloys, Mg-3Li and Mg-3Li-1Sc, were prepared. Microstructure and tensile properties for as-cast, solid state and aging treatment and hot-rolled and subsequent annealed conditions of these alloys were investigated. Furthermore, dynamic impact deformation behavior for as-cast and solid state and aging treatment conditions were tested and analyzed. The influence of minor rare earth Sc on microstructure and properties ofαphase Mg-Li alloys were discussed in order to provide experimental basis for their further improvement and extended application.The main conclusions are as follows:The analysis of microstructure showed that minor Sc, after being added to Mg-3Li alloy, refines grains, uniformes microstructure and elevates the recrystallizing temperature. The results of tensile tests showed that the strength and plasticity of as cast Mg-3Li-1Sc alloy is better than that of Mg-3Li alloy. The combination of grain refinement strengthening and precipitation strengthening improves the strength of Mg-3Li-1Sc alloy evidently without visible decline of plasticity after solid solution treatment followed by aging treatment with proper parameters. After hot-rolling and annealing treatment, the strength and plasticity were improved evidently owing to the strong grain refinement caused by the pinning effect of MgSc phase on dislocation motion and grain boundaries migration in the process of recovery and recrystallization.The results of dynamic impact experiments showed that the dynamic yield strength of cast Mg-3Li-1Sc is higher than that of Mg-3Li alloy at same strain rate, and the increment has been increased with the increase of strain rate. The stress-strain behavior of both Mg-3Li and Mg-3Li-1Sc alloys shows positive effect followed by negative effect within tested strain rate. Because localized deformation occurs and furthermore micro-cracks form and coalesce, Mg-3Li-1Sc showed negative strain rate effect and the impact resistance declined while deformed at tested strain rates after solid solution treatment. the stress-strain behavior shows negative strain rate effect after subsequent aging treatment. Distinct deformation localization occurs and cracks initiate and propagate along deformation bands with the increase of strain rate, which lead to the decline of impact resistance.