铝合金表面扫描式微弧氧化陶瓷膜的制备与形成机理

发布时间：2018-04-06 06:26

本文选题：扫描式微弧氧化　切入点：工艺参数　出处：《北京交通大学》2017年博士论文

【摘要】：槽式微弧氧化技术(MAO)作为阀金属表面改性的重要技术,在提高材料防腐、耐磨、绝缘等方面展现出了广阔的应用前景。然而在大面积工件的处理、零件陶瓷膜局部修复等方面,槽式微弧氧化处理在装备、效率和经济性上均存在较大的局限性。基于此,本文提出了扫描式微弧氧化(SMAO)技术方法,并对SMAO陶瓷膜的制备工艺、放电特性、陶瓷膜生长机制、组织结构及服役性能开展了深入系统的研究。借鉴电刷镀技术的工作原理和工艺方法,研发了成膜轨迹可控的SMAO装备和工艺方法,探讨了电极间距、扫描转角、扫描速度、扫描道次等关键工艺参数对铝合金表面陶瓷膜生长规律、粗糙度及显微硬度等膜层特性的影响,揭示了工艺参数对膜层特性的作用规律。研究表明:电极间距越短,成膜效率越高;扫描转角0°时成膜效率最高;陶瓷膜厚度低于40 μm时,单次成膜更经济,陶瓷膜厚度大于40 μm,则多次成膜效率更高。针对A356合金,研究了工艺参数对SMAO微弧放电特征的影响规律,建立了 A356铝合金SMAO复合放电模型。研究表明,缩短电极间距将有效地降低击穿电压,降低扫描速度有利于增加单个火花的能量,SMAO发生A型放电的基本条件为电压达到临界击穿电压,发生B型放电的基本条件为单个微弧能量和电压都达到临界值;并通过分析SMAO过程中SiC颗粒的演变机制,证实了 SMAO过程中陶瓷膜内部存在D型放电。基于SMAO陶瓷膜的表面截面形貌、组织结构等膜层特性研究,建立了 SMAO陶瓷膜的生长模型。SMAO陶瓷膜外层存在不连续的"紧密重熔层",陶瓷膜生长是"成膜→原位生长、表层重熔→再成膜"的多次循环的过程。SMAO陶瓷膜的组成和成膜机理与定点喷射处理和传统槽式处理具有明显的区别。铝合金SMAO陶瓷膜的服役性能研究表明:陶瓷膜的硬度约为1000～1400 HV0.1,膜/基结合强度可达80 MPa;电化学分析显示陶瓷膜的腐蚀电流密度较铝合金降低4～5个数量级,陶瓷膜具有优异的耐腐蚀性能;干摩擦条件下,SMAO陶瓷膜具有良好的摩擦磨损性能,其厚度大于50 μm时磨损机制以机械抛光和脆性微断裂为主,厚度低于20 μm时因陶瓷膜的挤压破碎,磨损机制变为磨粒磨损。扫描式微弧氧化技术是传统槽式微弧氧化技术的补充,本文的研究工作对SMAO技术的推广应用具有重要的理论指导意义和工程应用价值。
[Abstract]:As an important technology of metal surface modification, trough micro arc oxidation (MAO) has shown a broad application prospect in improving material corrosion, wear resistance, insulation and so on.However, in the treatment of large areas of workpieces and the partial restoration of ceramic film, slot micro-arc oxidation treatment has great limitations in equipment, efficiency and economy.Based on this, a scanning arc oxidation (SMAO) technique was proposed, and the preparation process, discharge characteristics, growth mechanism, structure and service performance of SMAO ceramic membrane were studied systematically.Based on the working principle and technology of brush plating technology, the SMAO equipment and process method with controllable film-forming trajectory are developed, and the electrode spacing, scanning angle, scanning speed are discussed.The effects of the key process parameters such as scanning pass order on the growth rule, roughness and microhardness of ceramic film on aluminum alloy surface are discussed. The effects of process parameters on the film characteristics are revealed.The results show that the shorter the electrode spacing, the higher the film-forming efficiency, the higher the film-forming efficiency is when the scanning angle is 0 掳, and when the thickness of ceramic film is less than 40 渭 m, the single film formation is more economical, the thickness of ceramic film is more than 40 渭 m, and the multiple film-forming efficiency is higher.For A356 alloy, the influence of process parameters on the characteristics of SMAO microarc discharge was studied, and the composite discharge model of A356 aluminum alloy SMAO was established.The results show that the reduction of electrode spacing will effectively reduce the breakdown voltage and the scanning speed will increase the energy of a single spark. The basic condition for the type A discharge of SMAO is that the voltage reaches the critical breakdown voltage.The basic condition of B type discharge is that the single arc energy and voltage reach the critical value, and by analyzing the evolution mechanism of SiC particles in the SMAO process, it is proved that the D type discharge exists in the ceramic film in the SMAO process.Based on the study of the surface cross-section morphology and microstructure of SMAO ceramic film, the growth model of SMAO ceramic membrane was established. There was a discontinuous "compact remelting layer" in the outer layer of SMAO ceramic film.The composition and film forming mechanism of SMAO ceramic membrane are different from that of fixed point spray treatment and traditional trough treatment.The study on the service performance of aluminum alloy SMAO ceramic film shows that the hardness of ceramic film is about 1 000 ~ 1 400 HV0.1, the bonding strength of the film / substrate can reach 80 MPA, and the electrochemical analysis shows that the corrosion current density of ceramic film is 4 ~ 5 orders of magnitude lower than that of aluminum alloy.The ceramic film has excellent corrosion resistance, and SMAO ceramic film has good friction and wear performance under dry friction condition, and the wear mechanism is mainly mechanical polishing and brittle micro-fracture when its thickness is more than 50 渭 m.When the thickness is less than 20 渭 m, the wear mechanism becomes abrasive wear due to the crushing of ceramic film.Scanning micro-arc oxidation (SMAO) technology is a supplement to the traditional trough micro-arc oxidation technology. The research work in this paper has important theoretical guiding significance and engineering application value for the popularization and application of SMAO technology.
【学位授予单位】：北京交通大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG174.453

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