Research On Microstructure And Properties Of MG-3LI-1RE Alloys After Rolled And Annealed

Mg-Li alloy is representative light alloy with high specific strength and high specific stiffness. They are under intensive research currently with promising application potential in fields of aeronautical and astronautical engineering. In the present study, the microstructure and properties of rolled and subsequent anealed of Mg-3Li-1Ce, Mg-3Li-1Nd and Mg-3Li-1Sc alloys were investigated. The influence of rare earth and annealing processing on microstructure, static and dynamic mechanical properties of the alloys were discussed. The main conclusions are as follows:The analysis of microstructure showed that the grains of rolled Mg-3Li-1Ce and Mg-3Li-1Nd alloys deformed significantly. After full annealing, the grains of the alloys refined obviously. The rare earth, added to Mg-3Li alloy, elevates the recrystallizing temperature. The result of SEM and EDS showed that there are Mg12Ce in the Mg-3Li-1Ce alloy, and Mg41Nd5 in the Mg-3Li-1Nd alloy.The results of tensile tests showed that strength of rolled Mg-3Li-1Ce alloy and Mg-3Li-1Nd alloy is better than that of subsequent annealed alloys, but plasticity is worse. And the fracture mechanism of rolled Mg-3Li-1Ce alloy is quasi-cleavage crack. But the fracture mechanism of rolled Mg-3Li-1Nd alloy is cleavage fracture. The plasticity of Mg-3Li-1Ce alloy and Mg-3Li-1Nd alloy were improved by 76% and 89% after recrystallization annealing. The SEM of the nicks of annealed alloys showed that the number of dimple increased, the brittleness of the alloys reduced.The results of dynamic impact experiments showed that the strain-strengthening is observed when these tested alloys deformed under high strain rate. At strain rate from 1350s^-1 to 1500s^-1, the flow stress of rolled Mg-3Li-1Ce shows insensitivity to the increasing of strain rate. The stress-strain behavior of rolled Mg-3Li-1Sc alloys shows positive effect within tested strain rate, 1350s^-1～1750s^-1, while that of rolled Mg-3Li-1Nd alloy shows negative effect at strain rate from 1350s^-1 to 1500s^-1. After full annealing, the stress-strain behavior of Mg-3Li-1Sc alloys shows positive effect followed by negative effect within tested strain rate, 1350s^-1～2800s^-1. 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. And the stress of Mg-3Li-1Ce alloy is not sensitive to the strain rate at strain rate from 1000s^-1 to 2250s^-1. But under tested strain rate, 1350s^-1～2000s^-1, the stress-strain behavior of Mg-3Li-1Nd alloys just shows negative effect.