高能球磨结合粉末冶金法制备碳纳米管增强7055Al复合材料的微观组织和力学性能

采用高能球磨结合粉末冶金工艺制备了碳纳米管(CNT)含量(体积分数)分别为0、1%和3%的CNT/7055Al复合材料。采用OM、SEM、TEM以及拉伸实验等方法研究了CNT/7055Al复合材料的CNT分布、晶粒结构、近界面结构及力学性能,分析了复合材料的强化机制和各向异性。结果表明,CNT/7055Al复合材料为无CNT的粗晶区与富集CNT的超细晶区组成的双模态晶粒结构;CNT在Al基体的超细晶区中分散良好,CNT-Al界面干净清洁,界面反应产物少;3%CNT/7055Al复合材料沿挤压方向的抗拉强度达到816 MPa,但延伸率仅为0.5%。细晶强化和Orowan强化是CNT/7055Al复合材料主要的强化机制。由于CNT沿不同方向的增强效率不同以及粗晶条带组织的存在,复合材料表现出比基体合金更强烈的各向异性,在垂直挤压方向的拉伸性能要弱于沿挤压方向的拉伸性能。

Microstructure and Mechanical Properties of Carbon Nanotubes-Reinforced 7055Al Composites Fabricated by High-Energy Ball Milling and Powder Metallurgy Processing

In the recent years,lightweight and high-strength structural materials have gained much attention in engineering applications.Carbon nanotube(CNT)-reinforced Al(CNT/Al)composites are promising structural materials owing to the good mechanical properties and high reinforcing efficiency of CNTs.Previous studies on these composites mainly focused on fabricating CNT-reinforced low-strength or medium-high-strength Al alloys(such as pure Al,or 2xxx series or 6xxx series Al alloys)composites via various dispersion methods.However,only few studies investigated composites with super-high-strength Al alloys as the matrices.In the present work,CNT/7055Al composites with CNT volume fractions of 0%,1%,and 3%were prepared by high-energy ball milling combined with powder metallurgy.The CNT distribution,grain structure,interface,and mechanical properties of the CNT/7055Al composite were investigated using OM,SEM,TEM,and tensile tests.The strengthening mechanism and anisotropy of the composite were analyzed.The results indicated that the composite had a bimodal grain structure consisting of CNT-free coarse grain zones and CNT-enriched ultrafine grain zones.CNTs were well dispersed in the ultrafine grain zones of the Al matrix,and the CNT/Al interface was clean.There were only few reaction products at the interface.The tensile strength of the 3%CNT/7055Al composite reached 816 MPa,but the elongation was only 0.5%.Grain refinement and Orowan strengthening were the main strengthening mechanisms of the CNT/7055Al composite.Because of the load transfer efficiency of CNTs and a coarse grain band structure,the composite exhibited stronger anisotropy than the matrix alloy.The tensile properties of the CNT/7055Al composite normal to the extrusion direction were weaker than those in the extrusion direction.