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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。
In the Mg-9Li duplex alloy, 0.5% (mass fraction) of Ca is added, and the eutectic Mg-9Li-0.5Ca alloy is prepared by melting and casting by magnetic levitation and copper die suction. The microstructure observation shows that the α-Mg phase formed in the conventional Mg-9Li duplex alloy is coarse and short strips with random and uniform disordered distribution in the β-Li matrix. In the Mg-9Li-0.5Ca alloy, α-Mg + β-Li eutectic clusters were formed. In the eutectic phase, α-Mg phases were long-fibrous (the aspect ratio was about 100 ), And aligned with a certain orientation; compared to the Mg-9Li alloy, the eutectic a-Mg phase spacing and fiber diameter significantly reduced, the organization was significantly refined, a-Mg phase volume fraction increased significantly; the same time, a large number of nano , Submicron Mg_2Ca particles are uniformly dispersed in α-Mg, β-Li grains and two-phase interface. As a result, the mechanical properties of Mg-9Li-0.5Ca alloy with this eutectic structure were significantly increased compared to that of Mg-9Li alloy, the yield strength at room temperature was increased by 3%, the tensile strength by 3.5% and the elongation by 50% . The analysis shows that the addition of trace Ca and the rapid cooling rate induced by copper die casting can induce the formation of small (α-Mg + β-Li) eutectic microstructure in Mg-9Li duplex and improve the mechanical properties remarkably.