Research On Microalloying And Solidification Control With External Field Of Mg-Li Series Alloys

Mg-Li series alloys are so called ultra-light magnesium based alloys, and they are the lightest metal structural material. They have high specific strength and stiffness, good damping capacity, and electromagnetic shielding properties. Mg-Li alloy has a promising application prospect in aerospace, ordnance industry, automobile, electronics etc. With energy crisis and attention of environment protection, light-weight and recyclable materials are eagerly to be demanded, and the application of Mg-Li series alloys is becoming more and more widespread.In this paper, the effects of Gd, Ce, ultrasonic field and electromagnetic stirring on the microstructures and properties of Mg-Li series alloys were studied, and the effect of ultrasonic field on the fluid flow was studied by Particle Image Velocimetry (PIV) technology.Mg-8Li-3Al alloy consist of a dual phase structure of a andβphase, Gd and Ce can effectively improve the microstructures. After adding Gd, The white phase is observed at the phase boundary, and microstructure is refined and roundness. After adding Ce, Al2Ce is observed at the phase boundary andβphase, and microstructure can be refined.The result of PIV simulation indicates that there are two recirculation loops in the flow field on the left and the right, and the maximum speed is obtained in the front of the ultrasonic probe. The fluid flow rate increase with increasing of ultrasonic power, the effect of the increment of velocity is obvious in the front of the ultrasonic probe.Mg-8Li-3Al alloy melt was treated at different temperature with ultrasonic vibration. When the melt temperature was a litter higher than its liquidus, microstructure could be effectively improved when the melt was treated by ultrasonic field. It was supposed that the pressure-supercooling may be the major mechanism of refinement. The optimum refining effect is obtained in the front of the ultrasonic probe, and the refining efficiency decreases because of loss of ultrasonic energy with the distance increase.Ultrasonic vibration with different powers was introduced into the Mg-8Li-3Al alloy melt during the solidification process of the alloy. The experiment results show that the morphology of a phase is modified from coarse rosette-like structure to fine globular one after the application of ultrasonic vibration. The fine globular structure is obtained especially when the power is 170W, and the refining effect also gets better with prolonging the ultrasonic treatment time. The corrosion resistance and the mechanical properties of the alloy with 170W of ultrasonic vibration for 90s are improved apparently compared with the alloy without ultrasonic vibration, and the tensile strength and elongation are 184Mpa and 18.5% respectively. Compared with the Mg-8Li-3Al alloy without ultrasonic vibration, the tensile strength increases by 9.5%, and the elongation improves by 45.7%.Effects of electromagnetic stirring on microstructure and mechanical properties of the Mg-9Li-5Al-Zn alloy were simply studied in this paper. The results reveal that, the morphology of the a phase changes from the long blocky structure to somewhat globular one, the mechanical properties are increased significantly with electromagnetic stirring.