【作者】 姚磊；

【导师】 郝海；

【作者基本信息】 大连理工大学 ， 材料加工工程， 2010， 硕士

【摘要】 镁锂合金被称为超轻镁合金,是最轻的金属结构材料,具有较高的比强度、比刚度,良好的塑性,以及优异的电磁屏蔽性能等优点,在宇航、兵器工业、汽车、电子等领域有着良好的发展前景。随着能源危机以及人们环保意识的增强,对轻质、可回收材料的需求更为迫切,镁锂合金的应用领域也将越来越广泛。本文主要研究了稀土元素Gd、Ce以及超声场、电磁场对镁锂合金凝固组织及其性能的影响,并利用PIV物理模拟技术,模拟了超声场对流场的影响,得到了以下结果：Mg-8Li-3Al合金组织由α和β两相组成,添加稀土元素Gd及元素Ce可以有效地改盖Mg-8Li-3Al合金的凝固组织。添加元素Gd后,在相界处有白色析出相,组织得到细化且相对圆整化；添加元素Ce后,在β相及相界处有Al2Ce相析出,细化了合金的显微组织。PIV对超声作用下流场结构的模拟结果表明,超声作用下,流场内存在左右两个环流状结构,靠近超声工具头前端位置,流场有较大的速度。随着超声振动功率的增加,流场的流速增大,在工具头前端位置速度增大效果比较明显。对不同温度下的Mg-8Li-3Al合金熔体施加超声场。研究表明,在液相线以上稍高温度施加超声场时,可显著改善合金的凝固组织,这说明了压强-过冷机制可能是主要的超声细化机制。超声工具头前端位置有最为细化的凝固组织,随着距超声工具头距离的增大,超声能量发生衰减,作用效果变小,凝固组织细化程度减弱。对Mg-8Li-3Al合金施加不同功率的超声振动。结果表明,当超声作用功率为170W时,能显著改善Mg-8Li-3Al合金的凝固组织,α相形貌从蔷薇状结构转变为细小的近球状结构,并随着超声作用时间的延长细化效果也变得越来越好。经170W超声处理90s后的合金试样,抗腐蚀性能与力学性能都有了明显提高,其中抗拉强度与伸长率分别为184MPa与18.5%,相比不经超声处理的试样,提高了9.5%与45.7%。初步研究了电磁场对Mg-9Li-5Al-Zn合金的影响,结果显示,施加电磁场后,凝固组织中,α相形貌由长条状结构转变为近球状结构,合金的力学性能得到明显提高。更多还原

【Abstract】 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.更多还原