搅拌摩擦通道挤压制备碳纳米管增强7075铝基复合材料

搅拌摩擦通道挤压是作者基于搅拌摩擦焊接和等通道转角挤压提出的一种固相状态制备金属基复合材料的新方法。采用搅拌摩擦通道挤压方法，通过添加不同体积分数的碳纳米管（CNTs）(0%、2%和4%)，制备了碳纳米管增强7075铝合金基复合材料（CNTs/Al-7075）。通过光学显微镜、扫描电子显微镜和透射电子显微镜观察并分析了CNTs在Al-7075基体中的分布特征，以及复合材料的细晶组织和第二相颗粒特征。采用固溶和时效处理改善CNTs/Al-7075复合材料的组织和力学性能。结果表明，采用搅拌摩擦通道挤压方法可以制备CNTs分布均匀的CNTs/Al-7075复合材料，实现7075铝合金基体晶粒细化，通过引入CNTs增强相可获得更为细小的晶粒组织。随着CNTs体积分数增加，CNTs/Al-7075复合材料的晶粒更加细化。固溶和时效处理改善了搅拌摩擦通道挤压制备的7075铝合金和CNTs/Al-7075复合材料的第二相析出行为，使材料的显微硬度得到提高。CNTs/Al-7075复合材料的强化机制综合了细晶强化、位错强化、载荷传递和第二相强化，其中以第二相强化为主。

Friction Stir Channel Pressing of Carbon Nanotubes Reinforced 7075 Aluminum Alloy Composites

Friction stir channel pressing (FSCP) is a new solid-state method for producing metal matrix composite, which was invented by the authors based on the principles of friction stir welding and equal channel angular pressing. The carbon nanotubes (CNTs) reinforced 7075 aluminum alloy composites (CNTs/Al-7075) were fabricated by FSCP, with different volume percentages of CNTs (0%, 2% and 4%). The distribution of CNTs in Al-7075 matrix and the microstructures including fine grains and second-phase particles were analyzed by optical microscope, scanning electron microscope and transmission electron microscope. The solution and aging treatments were used for improving the microstructures and the mechanical properties of the CNTs/Al-7075 composites. The results show that the CNTs/Al-7075 composite with a uniform distribution of CNTs is fabricated by FSCP. The grain refinement of Al-7075 is realized by FSCP, and further finer grains are obtained by introduction of CNTs. The grains of CNTs/Al-7075 composite become finer with increasing the volume percentage of CNTs. The precipitation behavior of second-phase particles of the Al-7075 produced by FSCP and the CNTs/Al-7075 composite is improved by the solution and aging treatments, resulting in an increase in micro-hardness. The strengthening mechanisms of the CNTs/Al-7075 composite include fine-grain strengthening, dislocation strengthening, load transfer mechanism and second-phase strengthening, among which the second-phase strengthening plays a leading role.