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以镁合金专用熔炼炉为设备,在SF6+N2保护气氛下对熔炼过程中熔炼温度、物料加入速率、熔炼时间、浇铸温度以及保护气中SF6浓度对合金收率、合金元素La收率、合金元素La偏析程度等制备工艺技术指标的影响进行研究,确定Mg-25La中间合金的高品质制备工艺条件为:熔炼温度685~695℃、物料加入速率为30 g·min-1、熔炼时间90 min、浇铸温度680℃以及保护气中SF6浓度为0.1%(体积分数)。基于以上工艺条件所获得合金元素收率大于98%,上部及下部的稀土元素成分比为0.99∶1.00,偏析程度为±0.3%~0.6%(质量分数);组分中稀土元素含量为25.0%±0.5%(质量分数),合金内部无氧化缺陷、气孔,合金组分均一,成分稳定。通过对合金所进行的X射线衍射(XRD),能谱(EDS)及扫描电镜(SEM)分析可知,当镧元素含量为25.0%时,合金中出现连续分布的Mg17La2共晶相,近似网状分布,且尺寸粗大。同时在晶粒内部及晶界之上出现一定数量的、分布不均匀细小第二相颗粒Mg2La相,该相与Mg17La2相同为Mg-25La中间合金的重要强化相。
Taking the special magnesium alloy melting furnace as equipment, the effects of SF6 + N2 atmosphere, such as melting temperature, material addition rate, melting time, casting temperature and SF6 concentration in protective gas, on the yield of alloy, yield of alloying element La, Elemental La segregation degree of the preparation process technical indicators of the study to determine the quality of Mg-25La master alloy preparation process conditions: melting temperature 685 ~ 695 ℃, the material added rate of 30 g · min-1, the melting time of 90 min , The casting temperature is 680 ℃ and the concentration of SF6 in protective gas is 0.1% (volume fraction). Based on the above process conditions, the yield of the alloying element is more than 98%, the ratio of the rare earth elements in the upper part and the lower part is 0.99: 1.00, and the degree of segregation is ± 0.3% to 0.6% (mass fraction); the rare earth element content in the component is 25.0% ± 0.5% (mass fraction), no oxidation defects inside the alloy, porosity, uniform alloy composition, composition and stability. The results of XRD, EDS and SEM showed that when the content of Lanthanum is 25.0%, the continuous distribution of Mg17La2 eutectic phase appears in the alloy and the approximate network Distribution, and size. At the same time, a certain amount of Mg2La phase with a small number of second phase particles, which is the same as Mg17La2, appears as an important strengthening phase in the middle of Mg-25La master alloy.