高速铣削工艺对7055-T6I4铝合金表面质量和耐腐蚀性能的影响

发布时间：2019-03-01 12:28

【摘要】：7055铝合金具有高强度、低密度、高的断裂韧性及优异的抗疲劳裂纹扩展能力等诸多优点,在航空航天领域具有较大的应用潜力。航空零件大都是由高速铣削加工而成,铣削加工工艺对加工表面理化特征如表面硬化层、微裂纹等造成不同影响。这些理化特征会影响航空件在工作环境中的耐腐蚀性能,降低航空件的服役寿命,因此研究铝合金高速铣削工艺对表面加工质量和耐腐蚀性的影响有重要理论和实际意义。本文采用扫描电子显微镜、透射电镜、高速铣削试验、超景深显微镜、电化学腐蚀试验等手段,研究了7055-T6I4态铝合金高速铣削加工工艺对表面加工质量和耐腐蚀性的影响,得到如下结论:(1)相比于7055-T6铝合金,7055-T6I4铝合金析出相粒子更加细小密集,在切削加工过程中由于切削温度梯度更大,析出相更容易发生回溶,析出相对位错阻碍和晶界的钉扎作用减小,使得切削力减小,切削加工表面质量更高,7055-T6I4铝合金的机械加工性能优于7055-T6铝合金的机械加工性能。(2)在其他加工条件相同的情况下,增大切削速度,表面粗糙度Ra的值先增大后逐渐降低,表面切屑的粘连随切削速度的增大有增大的趋势;增大轴向切深,表面粗糙度Ra的值逐渐增大,裂纹的数量逐渐增多,裂纹垂直于加工表面,深入到基体内部。(3)铣削加工过程中由于后刀面对已加工表面的挤压强化作用改善了7055铝合金的耐腐蚀性能。随着切削速度的增大,自腐蚀电位呈现先向正极移动后向负极移动的变化规律;随着轴向切深的增大,自腐蚀电位逐渐向负极移动且电流密度呈现出增大的趋势;切削速度为1256m/min,轴向切深为0.25mm,进给量为0.1mm/r时,自腐蚀电流密度最低,加工表面的耐腐蚀性能最强。(4)材料耐腐蚀性能力与切削加工表面质量有密切关系,微裂纹的存在会加速材料表面氧化膜的破损,使其对合金表面的保护失效,导致腐蚀加剧。表面腐蚀优先发生在表面有缺陷的位置,在腐蚀初期主要以点蚀为主,随着腐蚀的进行,点蚀坑逐渐变大,最后出现均匀腐蚀,腐蚀产物主要为Al(OH)_3。
[Abstract]:7055 aluminum alloy has many advantages, such as high strength, low density, high fracture toughness and excellent anti-fatigue crack propagation ability, so it has great application potential in aerospace field. Most of the aeronautical parts are machined by high-speed milling. The milling process has different effects on the physical and chemical characteristics of the machined surface such as the hardened layer and the micro-cracks. These physical and chemical characteristics will affect the corrosion resistance of aeronautical parts in working environment and reduce the service life of aeronautical parts. Therefore, it is of great theoretical and practical significance to study the influence of aluminum alloy high-speed milling technology on surface processing quality and corrosion resistance. By means of scanning electron microscope, transmission electron microscope, high-speed milling test, ultra-depth of field microscope and electrochemical corrosion test, the effect of high-speed milling process on surface quality and corrosion resistance of 7055-T6I4 aluminum alloy was studied. The conclusions are as follows: (1) compared with 7055-T6 aluminum alloy, the precipitated phase particles of 7055-T6I4 aluminum alloy are finer and denser, and the precipitated phase is easier to dissolve in the cutting process due to the larger cutting temperature gradient. The relative dislocation hindrance of precipitation and the pinning effect of grain boundary decrease so that the cutting force decreases and the quality of machined surface is higher. The machinability of 7055-T6I4 aluminum alloy is better than that of 7055-T6 aluminum alloy. (2) under the same machining conditions, the Ra value of surface roughness increases first and then decreases gradually when the cutting speed is increased. The adhesion of surface chips increases with the increase of cutting speed. When the axial depth is increased, the Ra value of surface roughness increases gradually, and the number of cracks increases gradually. The crack is perpendicular to the machined surface. (3) during milling, the corrosion resistance of 7055 aluminum alloy is improved due to the extrusion strengthening effect of the back cutter on the machined surface. With the increase of cutting speed, the self-corrosion potential moves first to the positive pole and then to the negative pole, and with the increase of the axial cutting depth, the self-corrosion potential moves gradually to the negative pole and the current density increases. When the cutting speed is 1256 m / min, the axial cutting depth is 0.25 mm and the feed is 0.1mm/r, the self-corrosion current density is the lowest. The corrosion resistance of the machined surface is the strongest. (4) the corrosion resistance of the material is closely related to the quality of the machined surface. The existence of the micro-crack will accelerate the damage of the oxide film on the surface of the material and make it fail to protect the surface of the alloy. Leading to increased corrosion. The surface corrosion occurs first in the position where the surface is defective, and the pitting corrosion occurs mainly in the initial stage of corrosion. With the corrosion going on, the pitting pit becomes larger gradually, and finally uniform corrosion occurs. The corrosion product is mainly Al (OH) _ 3.
【学位授予单位】：湖南科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG54;TG146.21

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