Mg-Y-Sm-Ca-Sb合金的强度稳定机制研究

The strength stability of traditional magnesium alloys is unsatisfactory due to the sharp decrease of their strength with the increase of temperature, which is one of the main factors to restrict the applied scope of magnesium alloys. One of the key problems in the field of magnesium alloy is to develop new type heat resistant magnesium alloys and to improve the strength stability and safe reliability of magnesium alloys. Our research team found that from room temperature or 200℃ to 300℃,the strength stability of Mg-Y-Sm-Ca-Sb system alloys is superior to that of commercial heat resistant WE system alloys developed most successfully. On the basis of previous research, the microstructure and strength properties of Mg-Y-Sm-Ca-Sb system alloys and their changes with temperature are to be studied in this work. By means of intensive and careful micro-analysis, together with materials strength and fracture theory, the microstructure changes and their strengthening effects on the alloys during elevated temperature tensile tests are investigated. The strengthening effects of precipitate phases inside the grain and along the boundary at elevated temperature are researched especially. Based on the quantitative evaluation of strengthening effect, the models for microstructure, strength and temperature are established, and the mechanisms for strength stability of Mg-Y-Sm-Ca-Sb system alloys are revealed. The results can provide references for the development of new type heat resistant magnesium alloys.

传统镁合金的强度随着温度的升高迅速下降，导致镁合金的强度稳定性较差，这是制约镁合金应用范围的主要因素之一。开发新型耐热镁合金，改善镁合金的强度稳定性，进而增强镁合金应用时的安全可靠性，是目前镁合金研究的关键问题之一。本课题组前期研究发现，无论是从室温到300℃，还是从200℃到300℃，Mg-Y-Sm-Ca-Sb系合金的强度稳定性均优于目前发展最为成功的商用WE系耐热镁合金。本项目拟在前期研究的基础上，探讨Mg-Y-Sm-Ca-Sb系合金的显微组织、强度性能与温度的关系，通过深入、细致的材料微观分析，结合材料强度与断裂理论，研究合金在高温拉伸过程中的组织变化及其对合金的强化作用，尤其是晶界和晶内析出相的高温强化作用，基于强化作用的量化评估，建立组织、强度、温度三者间的关系模型，揭示 Mg-Y-Sm-Ca-Sb系合金强度稳定性的微观机制，为新型耐热镁合金的开发提供借鉴。

传统镁合金的强度随着温度的升高迅速下降，导致镁合金的强度稳定性较差。开发新型耐热镁合金并改善其强度稳定性具有重要意义，可增强镁合金零部件在高温下应用时的安全可靠性。采用合金制备、组织观察、拉伸试验和理论计算等，研究了Mg-Y-Sm-Ca、Mg-Y-Sm-Ca-Sb等系列镁合金的显微组织和力学性能，获得了强度稳定的Mg-5Y-3Sm-0.8Ca-0.5Sb(wt.%)合金，并对该合金的强度稳定机制进行了分析。研究结果表明：.Mg-5Y-(2-4)Sm-0.8Ca合金的铸态组织均由α-Mg基体和Mg24Y5、Mg41Sm5、Mg2Ca相组成；三种合金中，Mg-5Y-3Sm-0.8Ca合金的抗拉强度最高，为208MPa。Mg-5Y-3Sm-0.8Ca合金经525℃/6h固溶处理，析出相大部分溶入镁基体，再经225℃/12h时效处理，合金的时效强化效应明显。.Mg-5Y-3Sm-0.8Ca合金中加入0.1%-1.0%的元素Sb后，合金中有高熔点的Mg3Sb2相生成；随着Sb含量的增加，时效态合金的抗拉强度先增加后降低；Mg-5Y-3Sm-0.8Ca-0.5Sb合金的抗拉强度最高，室温时为266MPa，300℃时为208MPa，其抗拉强度稳定性优于目前发展最为成功的商用耐热镁合金WE43。.在室温和高温(200-300℃)下，时效态Mg-5Y-3Sm-0.8Ca-(0.1-1.0)Sb合金的断裂方式均为脆性断裂，强化机制主要为细晶强化、固溶强化、析出强化和弥散强化；随着温度的升高，合金的抗拉强度缓慢降低，其抗拉强度稳定性可主要归因于Mg24Y5等强化相硬度的稳定性。