碳纳米管增强镁基复合材料导热性能研究

Study on Thermal Conductivity of Magnesium Matrix Composites Reinforced by Carbon Nano-Tubes

镁及其合金是目前最轻的金属结构材料,合金化虽然提升了镁合金的力学性能,但导致其导热性能严重下降,限制了镁合金的应用。碳纳米管(CNTs)因具有优异的力学、热学等性能,是最理想的增强体之一,可以用于改善镁合金的力学性能和热学性能。采用粉末冶金法分别以纯Mg、Mg-9Al合金、Mg-6Zn合金为基体制备了不同CNTs含量的镁基复合材料,利用光学显微镜、扫描电子显微镜、透射电子显微镜对复合材料微观组织、基体与增强体界面及析出相进行表征,并对复合材料的拉伸性能和热学性能进行测试。研究结果表明,当CNTs质量分数不超过1.0%时,可提高纯镁基复合材料的导热性能,力学性能仅有稍微降低;将CNTs添加到Mg-9Al合金中,可以促进纳米尺度β-Mg 17 Al 12相在CNTs周围析出,降低了Al在Mg基体中的固溶度,使CNTs/Mg-9Al复合材料的导热性能有所提高。此外,在CNTs/Mg-6Zn复合材料界面处存在C原子和Mg原子的相互嵌入区,这种嵌入型界面不仅有利于复合材料力学性能的提高,也使CNTs起到加速电子移动的“桥”的作用,有利于该复合材料热导率的提高。当CNTs质量分数为0.6%时,CNTs/Mg-6Zn复合材料具有较为优异的热学性能和力学性能,其热导率为127.0 W/(m·K),抗拉强度为303.0 MPa,屈服强度为204.0 MPa,伸长率为5.0%。

Currently,magnesium(Mg)and its alloys are the lightest structural metallic materials.Although the mechanical properties of Mg alloys can be improved by adding alloy elements,it causes a significant reduction of thermal property.Therefore,the application of Mg alloys is limited.Carbon nano-tubes(CNTs)are one of the most ideal reinforcements due to their excellent mechanical and thermal properties.They can be used to improve the mechanical and thermal properties of Mg alloys.Using pure Mg,Mg-9Al and Mg-6Zn as matrixes,the magnesium matrix composites with various CNTs contents were fabricated via the powder metallurgy method.The microstructures,interfaces between CNTs and matrix as well as precipitated phases of composites were characterized by OM,SEM and TEM.Moreover,the mechanical and thermal properties of composites were measured.Results indicate that the thermal conductivities of CNTs/Mg composites are enhanced with CNTs content less than 1.0wt%,while their mechanical properties only have a slight decrease.As CNTs are added into Mg-9Al alloy,a few nano-sizedβ-Mg 17 Al 12 phases precipitates around CNTs.It has reduced the solid solubility of Al atom in Mg matrix,so that the thermal conductivity of CNTs/Mg-9Al composite increases.In CNTs/Mg-6Zn composites,there is an area where C and Mg atoms have embedded in each other at the interface.On the one hand,the embedding area coud improve the mechanical properties of CNTs/Mg-6Zn composite.On the other hand,it could make CNTs as a“bridge”to accelerate the movement of electrons,accordingly increasing the thermal conductivity of composites.When the CNTs content is 0.6wt%,CNTs/Mg-6Zn composite has relatively excellent thermal and mechanical properties.Its thermal conductivity is 127.0 W/(m·K),and its ultimate tensile strength is 303.0 MPa,tensile yield strength is 204.0 MPa and elongation is 5.0%.