基于双纳米化镁合金表面连续 Mg-Al 金属间化合物基扩渗层形成机制与结构性能

Aim at the two key problems of the high diffusion temperature and low wear resistance of Mg-Al intermetallics diffusion layer on magnesium alloy surface, a method is proposed to prepare the continuous Mg-Al intermetallic matrix diffusion layer at low diffusion temperature. Firstly, surface nano-crystallization of magnesium alloy is induced by supersonic fine particles bombardment (SFPB) based on the modified cold spraying technology; Secondly, ceramic reinforced aluminum matrix nanocomposite powder is prepared by mechanical alloying process. Thirdly, a aluminum matrix nanocomposite coating is deposited on the nano-crystallization surface of magnesium alloys through cold spraying process due to its in-situ material transplantation characteristics. Finally, the dense Mg-Al intermetallic matrix diffusion layer is produced on the magnesium alloys surface through diffusion treatment at low temperature based on the high activity of “dual nanostructures”. At the same time, the wear resistance of the Mg-Al diffusion layer is significantly improved based on the synergistic strengthened effect of the interface bodings between magnesium alloy and diffusion layer and between ceramic reinforced particles and Mg-Al substrate. In this project, the microstructure features of surface deformation layer on magnesium alloys resulted from the supersonic particles collide is investigated in order to clarify its surface nano-crystallization process and mechanism. The plastic deformation behavior of aluminum matrix nanocomposite particle and the flow characteristics of ceramic hard phase in the composite powder at the moment of collision between single aluminum-ceramic composite particle and substrate are studied. The deposit behavior and microstructure formation mechanism of cold-sprayed aluminum matrix nanocomposite coating are examined. The influence of the nanostructure characteristics of magnesium substrate and cold-sprayed aluminum matrix naocomposite coatings and diffusion parameters on the microstructure evolution and properties of Mg-Al intermetallic matrix diffusion layer are studied. The macro-trends and micro-mechanism of microstructure formation of the Mg-Al intermetallic matrix diffusion layer during diffusion process are investigated. A theoretical basis for the preparation of high corrosion and wear resistant Mg-Al intermetallic matrix composite coating diffusion layer on magnesium alloy surface is provided.

针对镁合金表面连续Mg-Al金属间化合物扩渗层形成温度过高及耐磨性不足的关键问题，采用冷喷超音速微粒碰撞诱导镁合金表面纳米化，通过机械合金化制备陶瓷增强Al基纳米复合粉末，利用冷喷材料原位移植特性，实现镁合金纳米化表面Al基纳米复合涂层的可控沉积，基于“双纳米化”高活性实现镁合金表面连续Mg-Al金属间化合物基扩渗层的低温形成，同时，通过Mg-Al扩渗层与镁合金及Mg-Al扩渗层内陶瓷颗粒与基体相间“双界面”协同强化，提高扩渗层耐磨损性能。研究冷喷微粒碰撞镁合金表面变形层的结构特征，阐明纳米化过程和机制，研究Al基纳米复合粒子碰撞瞬间的塑性变形机理及内部陶瓷颗粒流动特征，揭示其沉积行为及影响涂层可控沉积的因素，研究纳米晶尺寸及热扩渗工艺对Mg-Al金属间化合物基扩渗层结构及性能的影响，阐明其形成的宏观趋势和微观机制，为镁合金表面抗腐耐磨连续Mg-Al金属间化合物基扩渗层的制备提供理论基础。

镁合金在航空航天、电子、汽车、交通及国防等领域具有重要应用价值，但其抗腐蚀和耐磨损性能差限制了其广泛应用。在镁合金表面热扩渗连续Mg-Al金属间化合物合金层是提高其抗腐耐磨性能的有效方法，但扩渗温度过高及耐磨性能不足限制了其性能发挥。本项目采用冷喷超音速微粒碰撞实现了AZ91D镁合金表面纳米化并利用冷喷低温移植特性，在纳米化表面制备了致密Al基纳米复合涂层，基于“双纳米化”高活性，实现了AZ91D镁合金表面连续Mg-Al扩渗层的低温形成并提高其耐腐蚀磨损性能，为镁合金表面抗腐耐磨连续Mg-Al金属间化合物基扩渗层的制备提供理论基础。通过项目研究，获得以下主要结果：1）冷喷超音速微粒碰撞可实现AZ91D表面纳米化，纳米化机制为强烈塑性变形中晶粒细化，纳米层厚度约50um、晶粒尺寸50-80nm，随后为滑移和孪晶层，纳米化层热稳定性可维持到280℃，并呈现梯度硬度和较好耐磨损性能；2）球磨可获得陶瓷颗粒弥散分布的Al基纳米复合粉末，合适的过程控制剂（PCA）和陶瓷含量可避免粘罐粘球并控制粉末尺寸，获得粉末粒子参数适合冷喷涂的Al基纳米复合粉末；3）AZ91D镁合金表面Al颗粒碰撞变形行为过程中，随着气体压力和温度增大，不仅Al颗粒自身扁平化加剧，也导致镁合金基体发生强烈塑性变形，在碰撞凹坑四周出现材料塑性变形堆积；4）在喷涂粉末中引入刚性颗粒，通过其在冷喷涂沉积过程中的反弹碰撞作用，实现了多孔Al涂层“原位”致密化，并对基体表面产生了类似“喷丸纳米化”的作用；5）AZ91D镁合金表面冷喷Al/SiC纳米复合涂层均组织致密，随着SiC增加涂层硬度显著增加，50%SiC/Al涂层硬度高达515Hv0.3±28，呈现优异耐磨性能。6）AZ91D镁合金表面冷喷Al-Al2O3纳米复合涂层呈现优异耐磨损性能和抗耐腐蚀性能，对比AZ91D镁合金，其电化学极化中存在稳定钝化区，自腐蚀电位提高约450ｍV而腐蚀电流密度减小为1/6；7）镁合金表面纳米化和涂层组织结构纳米化协同作用，可显著降低其相互热扩散温度。200℃热处理后Al涂层与AZ91D基体界面就开始形成连续Mg-Al金属间化合物扩散层，240℃之前，随着热处理温度升高，扩散层厚度增加缓慢，但之后增加显著，360℃热处理后扩散层厚度约80um并由Mg3Al2相和Mg17Al12相两层构成。