论文部分内容阅读
普通钢热浸铝后,形成了具有耐热及耐蚀双重性能的复合新材料。本研究首先针对钢材熔剂法热浸铝工艺中助镀剂存在的问题,提出一种低温预镀的三元助镀剂。在此基础上深入分析了浸铝表层厚度变化的动力学过程、形成机理及组织结构。同时系统地研究了浸铝后扩散(浸扩铝)对表层组织结构及抗氧化性的影响规律。 在表层动力学过程研究中,首次发现表面层厚度随时间的变化经历了先减薄达到谷值,然后又增加达到峰值,再减薄、最后趋于稳定的三个阶段。而过渡层的厚度变化大致符合抛线增长规律,其扩散激活能为139.6kJ/mol。通过对镀层形成机理分析,得出表面层厚度变化的第Ⅰ阶段为铝液的凝固—重熔过程,而第Ⅱ及第Ⅲ阶段则为铝液与试样表面浸润及凝固过程,并提出了耐蚀性浸铝工艺的优化准则。 通过高温氧化及组织观察查明,浸铝层直接用于高温环境时,当表面层通过扩散消失后,钢表面形成脆性Fe_2Al_5相柱状晶,在氧化过程中极易开裂产生内氧化。对此,本研究首次提出对浸铝层表面保护后预扩散处理的新工艺。研究发现,预扩散处理温度对表层的结构及抗氧化性有明显影响。在750℃扩散时,镀层结构由较厚的外表层(Fe_2Al_5+FeAl_2)及内层(FeAl+条状FeAl_2)组成,由于内层条状FeAl_2平行排列的结构进一步增加了氧向内传输的速度
Ordinary steel hot-dip aluminum, forming a composite with heat and corrosion resistance of new materials. In this study, aiming at the problems existing in the fluxing agent in the hot-dip aluminum process by the steel flux method, a low-temperature pre-plating ternary fluxing agent was proposed. On this basis, the dynamic process, formation mechanism and organizational structure of the surface thickness of immersed aluminum are analyzed in depth. At the same time systematically studied the diffusion after immersion (dip aluminum) on the surface structure and anti-oxidation of the law. In the study of surface kinetic process, it was first found out that the change of surface layer thickness over time experienced the first decrease to the valley value, and then increased to the peak, then thinned, finally stabilized in three stages. The thickness of the transitional layer is roughly consistent with the law of the growth of the line, and its diffusion activation energy is 139.6kJ / mol. Through the analysis of the forming mechanism of the coating, the first phase of the change of the surface layer thickness is the solidification-remelting process of the aluminum liquid, while the second and the third phase are the infiltration and solidification process of the aluminum liquid and the sample surface, Corrosion resistance of aluminum plating process optimization guidelines. Through the high temperature oxidation and microstructure observation, when the aluminum immersion layer is directly used in the high temperature environment, when the surface layer disappears by diffusion, the brittle Fe 2 Al 5 phase columnar crystal forms on the steel surface, and the internal oxidation easily occurs during the oxidation. In this regard, this study for the first time put forward a new process of pre-diffusion treatment of the surface of the aluminum-impregnated layer. The study found that pre-diffusion treatment temperature on the surface structure and oxidation resistance significantly affected. When diffused at 750 ℃, the structure of the coating consists of a thicker outer layer (Fe_2Al_5 + FeAl_2) and an inner layer (FeAl + strip FeAl_2). Due to the arrangement of the inner strip-like FeAl_2 in parallel, the oxygen transport rate is further increased