稀土氧化物直接还原制备含稀土AZ31镁合金组织及性能的研究

发布时间：2018-05-18 04:15

  本文选题：稀土变形镁合金 + 稀土氧化物　； 参考：《吉林大学》2016年博士论文

【摘要】：稀土变形镁合金的制备一般采用添加镁-稀土中间合金的方法,因此需要对稀土资源进行提纯,在这一过程中产生的氟化物等有毒物质对环境的污染十分严重。而稀土氧化物既是稀土的自然存在形式,又是制备稀土金属和镁-稀土中间合金的前置产物,提纯容易且市场价格十分低廉。因此稀土氧化物直接还原制备稀土变形镁合金可以减少稀土提纯和中间合金的制备,减轻有毒产物对环境的危害,降低稀土变形镁合金的制造成本。本文选用AZ31镁合金为研究载体,按预先设计的正交方案,研究稀土氧化物直接还原制备含稀土AZ31镁合金,确定了不同参数下稀土氧化物的还原率。深入探讨了稀土氧化物还原反应的热力学原理及影响稀土氧化物还原率的动力学因素。比较了稀土氧化物还原制备的含稀土AZ31合金与采用镁-稀土中间合金制备的相同稀土含量的AZ31合金的组织、抗拉强度、轧制变形能力和抗氧化性,并得到了如下结论:(1)进行了单一CeO_2和La_2O_3及混合稀土氧化物还原制备含稀土AZ31合金的研究,确定了不同参数下单一CeO_2的还原率最高可达11.50%,单一La_2O_3的还原率最高可达26.85%;混合稀土氧化物中CeO_2的最大还原率为9.45%,La_2O_3的最大还原率为21.08%。(2)单一CeO_2的还原反应主要以2Mg+CeO_2=Ce+2MgO为主。单一La_2O_3的还原反应主要有三种,分别为:a.先发生反应:La_2O_3+3CaF_2=2LaF_3+3Ca O,之后进行还原反应:LaF_3+Mg=La+M F_2;b.先发生络合反应:(La_2O_3)+(F~-)→(LaOF)n~(x-)),之后与Al进行还原反应:(LaOF)n~(x-))+[Al]→[La]+(AlF_6~(3-))or(Al OF);c.先发生反应:La_2O_3+3Mg Cl_2=2LaCl_3+3MgO,之后发生电解:LaCl_3(?) La+Cl_2.。混合稀土氧化物的还原按CeO_2和La_2O_3的还原分别进行,二者之间不发生交互反应。(3)影响稀土氧化物还原率的正交因素最优水平分析表明:稀土氧化物的添加量搅拌时间与稀土氧化物的还原率呈正比,而最佳熔炼温度为710℃。影响单一CeO_2和La_2O_3还原率的最主要因素为搅拌时间,影响混合稀土氧化物还原率的最主要因素为稀土氧化物添加量。按最小二乘法计算得到关于AZ31合金中稀土含量与稀土氧化物添加量、搅拌时间之间的回归方程。对单一CeO_2有:Φ_(Ce_=0.093x+0.067y-2.87;对单一La_2O_3有:Φ_(La)=0.24x+0.068y-2.97;对混合稀土氧化物中的CeO_2和La_2O_3分别有:Φ_(Ce)=0.084x+0.001y-0.341和Φ_(La)=0.61x+0.041y-5.698。其中Φ_(Ce)和Φ_(La)为AZ31合金中的Ce和La的含量,x为稀土氧化物的添加量,y为搅拌时间。(4)实验表明,稀土氧化物还原制备的AZ31合金随稀土含量增加,其晶粒尺寸减小,抗拉强度、轧制变形能力和抗氧化性提高。但当稀土含量增加至一极值时,晶粒尺寸开始增加,各项性能呈下降趋势变化。与采用镁-稀土中间合金制备的AZ31合金相比较,二者在稀土含量相同时其组织及性能基本相近,因此还原法制备的含稀土AZ31合金具有可替代性。
[Abstract]:Rare earth wrought magnesium alloys are usually prepared by adding magnesium-rare earth master alloys, so it is necessary to purify rare earth resources. The toxic substances such as fluoride produced in this process pollute the environment very seriously. Rare earth oxides are not only the natural forms of rare earths but also the preproducts of preparing rare earth metals and Mg-rare earth master alloys. It is easy to purify and the market price is very low. So the preparation of rare-earth wrought magnesium alloys by direct reduction of rare earth oxides can reduce the purification of rare earths and the preparation of master alloys, reduce the harm of toxic products to the environment, and reduce the manufacturing cost of rare-earth wrought magnesium alloys. In this paper, AZ31 magnesium alloy was selected as the carrier to study the preparation of rare earth containing AZ31 magnesium alloy by direct reduction of rare earth oxide according to the orthogonal scheme designed in advance. The reduction rate of rare earth oxide under different parameters was determined. The thermodynamic principle of rare earth oxide reduction reaction and the kinetic factors affecting the reduction rate of rare earth oxide were discussed. The microstructure, tensile strength, rolling deformation and oxidation resistance of rare earth AZ31 alloy prepared by rare earth oxide reduction and AZ31 alloy with the same rare earth content prepared by magnesium rare earth master alloy were compared. The following conclusions have been obtained: (1) the preparation of rare earth containing AZ31 alloy by single CeO_2 and La_2O_3 and mixed rare earth oxide reduction has been studied. The maximum reduction rate of single CeO_2 is 11.50, that of single La_2O_3 is 26.85, that of CeO_2 in mixed rare earth oxides is 9.45%. The maximum reduction rate of CeO_2 is 21.08% and 21.08% respectively. The main reduction rate of single CeO_2 is 2Mg CeO_2=Ce 2MgO. There are three kinds of reduction reactions of a single La_2O_3, which are respectively: a. There was a reaction of: La _ 2O _ 3 3CaF_2=2LaF_3 3Ca O, and then a reduction reaction: Laf _ 3 Mg=La M _ T _ 2b. First, there is a complexation reaction: 1 / L / L _ 2O _ 3 / F ~ (-) / A / O / F / N / C / C / L / L / L / L / L / L / T / L / L / L / L / L / L / L / L / L / L / L / C / L / L / L / L / C / L / L / L / L / L / L / L / C / L / O / O / C / Al / O / O / C First there was a reaction: La2O3 3Mg Cl_2=2LaCl_3 3MgO, and then there was an electrolytic reaction: LaCl3. La Cl_2.. The reduction of mixed rare earth oxides was carried out according to the reduction of CeO_2 and La_2O_3 respectively. The optimum level analysis of orthogonal factors affecting the reduction rate of rare earth oxides shows that the mixing time of rare earth oxides is proportional to the reduction rate of rare earth oxides, and the optimum melting temperature is 710 鈩，

本文编号：1904323