中文摘要：

在Mg-9Li双相合金中添加0.5%（质量分数,下同）Ca元素,通过磁悬浮熔炼及铜模吸铸方法熔炼制备了共晶型Mg-9Li-0.5Ca合金。组织观察表明,常规Mg-9Li双相合金中形成的α-Mg相为粗大短板条状,取向随机、均匀无序分布于β-Li基体中。而Mg-9Li-0.5Ca合金中形成了棒状交替排列的（α-Mg＋β-Li）共晶团组织,在共晶团内,α-Mg相呈长纤维状（长宽比约为100）、并以一定取向定向排列;相比于Mg-9Li合金,共晶a-Mg相纤维间距及纤维直径显著减小、组织明显细化,a-Mg相体积分数显著增加;同时,大量纳米、亚微米级Mg_2Ca颗粒均匀弥散分布于α-Mg、β-Li晶粒内及两相界面上。由此导致具有该共晶组织的Mg-9Li-0.5Ca合金相比于Mg-9Li合金力学性能显著增加,室温拉伸屈服强度提高3%、抗拉强度提高3.5%,伸长率提高50%。分析表明,微量Ca元素的添加和铜模吸铸产生的较快的冷却速度,诱发Mg-9Li双相中细小（α-Mg＋β-Li）共晶组织的形成,显著提高力学性能。

英文摘要：

Mg-9Li-0.5Ca alloy with a eutectic structure was prepared by alloying Mg-9Li alloys with 0.5 wt% Ca element and employing the magnetic levitation melting and copper mould suction casting method. Microstructure observation results show that α-Mg phase in the conventional Mg-9Li alloy are coarse plates, oriented randomly and distributed homogeneously in the β-Li matrix. While a eutectic structure consisting of alternating lamellae of α-Mg and β-Li phases is formed in Mg-9Li-0.5Ca alloy, which exists as grains, i.e. eutectic colonies. Within each colony, α-Mg phases are present in the form of long fibers（the length-to-diameter ratio of ~100） and such lamellaes are oriented essentially in the specific direction. Also, large amounts of nano- or ultrafine-scale Mg2_ Ca particles are dispersed uniformly inα-Mg and β-Li grains and the α-Mg/β-Li phase interface. As a consequence, Mg-9Li-0.5Ca alloy with such eutectic structure exhibits significantly enhanced mechanical properties with the yield strength increased by 3%, the tensile strength by 3.5% and the elongation by50% compared to Mg-9Li alloy. It is inferred that a small amount of Ca addition and a relatively fast cooling rate from the copper mould suction casting result in the formation of fine（ α-Mg＋β-Li） eutectic structure which greatly improves the mechanical properties of Mg-9Li-0.5Ca alloy.