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AlSi10Mg材料空蚀性能研究

发布时间:2018-10-05 18:49
【摘要】:空化发生在液体内部,与液体压强的变化息息相关,是空泡初生、长大与溃灭的过程。空蚀是空化对固体材料造成的损伤与破坏,是空化的结果。对于工作在液体环境下的液压元件、水利设施等,在液体压强变化时,表面材料容易受到空蚀的作用。AlSi10Mg材料具备耐磨损侵蚀、热膨胀系数低、强度与刚度高、导热性好等优点,应用十分广泛,但对其空蚀性能的研究还相对较少。基于AlSi10Mg材料在液体环境下的应用背景,有必要对其空蚀性能展开研究。本文各章内容分述如下第一章,介绍了空化、空蚀的物理背景以及基于空化射流的材料空蚀性能标准实验,介绍了表面形貌对于空蚀的影响规律与机理,介绍了选择性激光熔化(SLM)技术及在铝合金上的研究与应用背景,最终确定了论文研究内容。第二章,以ASTMG134为标准,搭建了空化射流实验平台,并加工制造了符合标准的空化射流喷嘴,为空蚀实验的进行奠定实验装置的基础,另外结合表面形貌、硬度测试、密度测试、物相分析、金相分析等手段,介绍了相关实验设备。第三章,探究不同表面加工方式(激光织构、车削、磨削和抛光)造成的原始表面形貌差异对于锻造AlSi10Mg试件空蚀性能的影响,发现:表面更粗糙的激光织构试件和车削试件的质量损失大于其他两种试件;在具有一种类似形貌特征的激光织构试件和车削试件表现出水平方向上的塑性变形,其他两种试件没有出现这种现象;通过两种三维表面高度参数,可以预测表面加工痕迹受空蚀作用后消失的时间。第四章,探究选择性激光熔化(SLM)过程中不同的激光扫描速度对SLM试件空蚀性能的影响,并与锻造试件做出对比,发现:SLM试件在加速阶段的质量损失远大于锻造试件,这主要是由于SLM试件表面的气孔缺陷和气孔内的残余合金颗粒造成的,过快或者过慢的激光扫描速度会加大气孔的尺寸和残余合金颗粒的数量,导致空蚀加速阶段中更大的质量损失及速率;进入稳定期后,三种选择性激光熔化试件的质量损失速率远远小于锻造试件,但选择性激光熔化试件之间差别不大,激光扫描速度对其影响基本可忽略不计;SLM试件显微金相表现为树枝状的Si相将A1基体分割为小岛状,这种组织均匀、晶粒细小的结构提高了 SLM试件的硬度和抗空蚀能力。第五章,总结了本文主要研究工作与成果,展望了今后有待进一步开展的研究内容。
[Abstract]:Cavitation occurs in the liquid and is closely related to the change of liquid pressure. It is the process of cavitation, growth and collapse. Cavitation erosion is the result of cavitation and damage to solid material caused by cavitation. For hydraulic components and water conservancy facilities working in liquid environment, when the liquid pressure changes, the surface material is vulnerable to cavitation erosion. AlSi10mg material has the advantages of abrasion resistance, low thermal expansion coefficient, high strength and stiffness, good thermal conductivity, etc. It is widely used, but the study of cavitation corrosion performance is relatively rare. Based on the application background of AlSi10Mg material in liquid environment, it is necessary to study its cavitation corrosion property. In the first chapter, the physical background of cavitation and cavitation erosion and the standard experiment of cavitation performance based on cavitation jet are introduced, and the influence law and mechanism of surface morphology on cavitation erosion are introduced. The selective laser melting (SLM) technology and its research and application background on aluminum alloy are introduced. Finally, the research content of this paper is determined. In the second chapter, the cavitation jet experimental platform is set up with ASTMG134 as the standard, and the cavitation jet nozzle is manufactured according to the standard, which lays the foundation of the experimental device for the cavitation corrosion experiment. In addition, it combines the surface morphology, hardness test and density test. The related experimental equipment is introduced by means of phase analysis and metallographic analysis. In chapter 3, the effects of different surface processing methods (laser textures, turning, grinding and polishing) on the cavitation corrosion properties of forged AlSi10Mg specimens are investigated. It is found that the mass loss of the laser textured and turning specimens with rougher surface is larger than that of the other two, and that the laser texture and turning specimens with a similar morphologic feature exhibit a horizontal plastic deformation. There is no such phenomenon in the other two kinds of specimens, and the time of surface machining trace disappearing after cavitation erosion can be predicted by two three dimensional surface height parameters. In chapter 4, the effects of different laser scanning speeds on the cavitation corrosion properties of SLM specimens during the selective laser melting process are investigated, and compared with the forged specimens, it is found that the mass loss of the SLM specimens at the acceleration stage is much greater than that of the forged specimens. This is mainly due to the porosity defects on the surface of SLM specimens and the residual alloy particles in the pores. Too fast or too slow laser scanning speed will increase the size of the pores and the number of residual alloy particles. The mass loss rate of the three kinds of selective laser melting specimen is much smaller than that of the forged specimen, but the difference between the three selective laser melting specimens is not significant. The effect of laser scanning speed on the microstructure of SLM specimens is negligible. The microstructure of SLM specimens is characterized by dendritic Si phase, which divides A1 matrix into small islands. The microstructure of the samples is uniform and the fine grain structure improves the hardness and cavitation resistance of SLM specimens. In the fifth chapter, the main research work and results are summarized, and the future research contents are prospected.
【学位授予单位】:浙江大学
【学位级别】:硕士
【学位授予年份】:2017
【分类号】:TG146.21

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