镁合金等离子体微弧氧化过程控制的研究

研究AZ31镁合金微弧氧化过程中不同控制参数对膜性能的影响。镁合金微弧氧化中存在一个二次放电过程,它会对已长成的膜起破坏作用。通过改变溶液成分或浓度可对镁合金微弧氧化临界点的出现时间进行控制。在此基础上进一步研究一次放电不同控制过程对膜层性能的影响,发现采用渐进式升压方式能提高膜的致密层和疏松层的比例,但对膜的总厚度影响不大。合适的阴极匹配电压,可减小功耗,降低气孔率,改善膜的性能。     

镁合金等离子体微弧氧化膜层研究

研究了镁合金AZ31在磷酸盐和硅酸盐两种不同的溶液体系下生成氧化膜的性质,比较了多种因素,特别是负电压对于生成氧化膜的影响;并且通过X射线衍射(XRD)等方式分别确定了两种不同溶液条件下氧化膜的成分.结果表明:较低的负电压有利于氧化膜的生长,延缓二次放电现象的发生.在我们得到的氧化膜中,最主要的成分为高温相的MgO,不同于以往条件下得到的普通相MgO氧化膜,能提高镁合金的一部分性能.     

铸造镁合金微弧氧化机理

研究了ＺＭ５铸造镁合金微弧氧化过程中心膜生长规律和膜的相结构及形貌特征,并探讨了氧化膜生长机理。在初始一段时间内,氧化膜向外生长速度大于向内生长速度。氧化膜达到一定 度后,工件外部尺寸不再增加,而氧化膜完全转向基体内部生长。氧化膜具有表面疏松层和致密层２层结构,在ＮａＡｌ２Ｏ３溶液中氧化时,前者由ＭｇＯ和ＭｇＡｌ２Ｏ４相组成,后者主要由ＭｇＯ疏松层中富集来自溶液的铝元素。     

镁合金微弧氧化研究进展

介绍了镁合金微弧氧化直流电源、交流电源、脉冲电源、多种电源的发展现状。同时对酸性、碱性电解液体系以及添加剂对微弧氧化的影响进行了分析。通过几个应用实例阐述了制约镁合金微弧氧化发展的主要因素,对镁合金微弧氧化技术的未来发展方向进行了展望。     

负电压对2A50铝合金微弧氧化陶瓷层微观结构和耐磨性能的影响

目的 通过调节负电压参数,制备具有较高硬度与较好耐磨性的2A50铝合金微弧氧化陶瓷层。 方法 通过微弧氧化,利用双极性脉冲电源,在硅酸盐为主的电解液中,于2A50铝合金表面原位生成耐磨的高硬度陶瓷层。通过改变负电压,研究其对微弧氧化陶瓷层相组成、微观结构、显微硬度和摩擦磨损性能的影响规律。利用扫描电子显微镜、X射线衍射仪表征微弧氧化膜层的微观形貌、物相组成。利用显微硬度计测试微弧氧化膜层的硬度,并通过摩擦磨损试验机评价膜层的耐磨性。结果 涂层的主要相组成为γ-Al2O3。陶瓷层由内侧致密层和外部疏松层组成,随着负电压的提高,微孔的数量和尺寸先减少后增大。微弧氧化后,2A50铝合金得到明显强化,经–100 V负电压的微弧氧化,其显微硬度由未处理的75HV0.5提高至1321HV0.5。微弧氧化陶瓷层具有良好的耐磨性,摩擦系数在0.35~0.55之间,其磨损机制为磨粒磨损和粘着磨损共存。结论 正电压较高时,较低负电压可很好地抑制微弧氧化过程中的强放电现象,以获得较为致密、坚硬且耐磨的膜层。     

镁合金微弧氧化研究现状

综述了近年来国内外镁合金微弧氧化研究的进展和现状,介绍了电解液体系及电参数对镁合金微弧氧化陶瓷膜性能的影响,对今后镁合金微弧氧化的发展趋势进行了展望。     

镁合金微弧氧化技术的研究进展

介绍了镁合金微弧氧化技术的研究现状,重点介绍了电解液体系、添加剂、氧化时间和电解液温度等工艺参数对镁合金微弧氧化陶瓷膜层组织和性能的影响,分析指出对微弧氧化机理的研究和得到稳定的生产工艺条件是镁合金微弧氧化技术的研究重点。     

镁合金微弧氧化陶瓷层的生长过程及其耐蚀性

利用扫描电镜(SEM)和盐雾腐蚀试验等手段。研究了镁合金微弧氧化陶瓷层不同生长阶段的形貌特征及耐蚀性．结果表明：整个过程可分为三个阶段。即阳极沉积阶段、微弧阶段和局部弧光阶段．阳极沉积阶段是在阳极表面发生团絮氧化膜沉积与扩展的过程；微弧阶段是前期缺陷减少与消失并形成均匀膜层的过程，陶瓷层表面微孔孔径较小，膜层均匀致密；局部弧光阶段形成的放电微孔孔径较大，陶瓷层比较疏松．陶瓷层的耐蚀性则表现出先增后减的变化趋势．在微弧氧化处理8min～12min时，陶瓷层的耐蚀性最好．通过控制陶瓷层不同生长时期的能量分配，尽量延长陶瓷层的均匀生长过程。可以获得到均匀致密的陶瓷层．     

镁合金微弧氧化陶瓷层形成及生长过程的研究

研究了MB8镁合金在硅酸盐溶液体系中微弧氧化陶瓷层形成及生长过程的形貌特征。结果表明：整个过程可分为3个阶段,即阳极沉积阶段、微弧阶段和局部弧光阶段。阳极沉积阶段是在阳极表面发生团絮氧化膜沉积与扩展的过程。微弧阶段是前期缺陷减少与消失并形成均匀膜层表面的过程,陶瓷层表面微孔孔径较小,膜层均匀致密。局部弧光阶段形成的放电微孔孔径较大,陶瓷层比较疏松。     

镁合金微弧氧化陶瓷层的耐蚀性

通过NaCl中性盐雾腐蚀试验定性地分析镁合金微弧氧化陶瓷层的耐蚀性，初步研究了陶瓷层表面微观结构对其耐蚀性的影响。结果表明：镁合金微弧氧化陶瓷层的微观组织结构的结合方式和生长方式直接影响其耐蚀性，微弧氧化试样的耐蚀性与陶瓷的厚度有关，陶瓷层厚度的增加并不一定能使其耐蚀性提高。     

溶质离子在镁合金微弧氧化膜形成过程中的作用

利用交流脉冲微弧氧化电源在NaF、NaCl和NaI三种电解液中对AZ31镁合金样品进行处理,采用SEM、XPD和XPS观察分析溶质离子对镁合金样品表面形貌、相组成及起弧前后微弧氧化膜层成分的变化。结果表明:微弧氧化现象只发生于NaF电解液中,起弧前样品表面的沉积膜为MgF2,起弧后膜层由MgF2和MgO两相组成;NaCl和NaI电解液中的两组样品既无微弧氧化现象发生,又未发现任何沉积膜层;微弧氧化初期阳极放电产生的金属阳离子与溶液中的阴离子形成沉积于样品表面的高阻抗膜层是微弧氧化过程进行的必要条件。     

Development of microarc oxidation process to improve corrosion resistance on AZ91HP magnesium alloy

A new anodizing process, which does not contain chromate but can improve the corrosion resistance of magnesium alloys significantly, was developed using a microarc power supply. Surface morphology was observed and the coating was compact and ceramic-like. In addition, the corrosion resistance of samples before and aider anodization by the new process and a method in US Patent 5470664 was compared by potentiodymaic polarization curves, electrochemical impedance spectroscopy （EIS） and salt spray test. The results show that the anodization can improve the corrosion resistance of magnesium alloy. The samples obtained by the new process and the method mentioned in the US Patent 5470664 achieve 9 and 7 rates aider 336 h salt spray test, respectively.     

电解质对AZ91D镁合金微弧氧化的影响

在Na2SiO3和NaAlO2为主成膜剂的硅铝复合电解液中,利用交流脉冲电源对AZ91D镁合金进行微弧氧化处理,研究主成膜剂含量的变化对微弧氧化过程及膜层特性的影响规律。利用扫描电镜(SEM)和膜层测厚仪分别研究了膜层的微观形貌和膜层厚度,通过电化学阻抗谱(EIS)测试膜层在3.5%NaCl中性溶液中的耐蚀性能。结果表明,随着主成膜剂含量的增加,微弧氧化过程中起弧电压和终止电压均呈下降的变化趋势,而膜层耐蚀性则基本呈先增大后降低的变化趋势,膜厚的变化趋势与其耐蚀性一致;Na2SiO3含量的变化对膜层内部致密层和外部疏松层的耐蚀性均有影响,而NaAlO2含量的变化则主要影响膜层内部致密层的耐蚀性;适量的主成膜剂含量是获得致密耐蚀膜层的关键。     

Effect of magnesium in aluminum alloys on characteristics of microarc oxidation coatings

Microarc oxidation（MAO） coatings were prepared on the surface of aluminum alloys with different contents of magnesium. The morphologies and surface roughness of the coatings were characterized by Confocal laser scanning microscopy（CLSM）. Phase and chemical composition of the MAO coatings were analyzed by X-ray diffractometry（XRD） and X-ray photoelectron spectroscopy（XPS）. The experimental results show that the coatings formed on different substrates have two-layer morphologies and are mainly composed of Al203 and Al-Si-O phases. In addition, the content of Al203 increases with increasing the content of magnesium. XPS results prove that magnesium from substrate indeed participates in the MAO process and is incorporated into the coating in the form of MgO. The coating formed on Al-3Mg substrate has the smallest mass loss and the lowest friction coefficient of 0.17--0.19.     

Effects of sodium tungstate on characteristics of microarc oxidation coatings formed on magnesium alloy in silicate-KOH electrolyte

Oxide coatings on AM60B magnesium alloy were prepared using the microarc oxidation（MAO） technique in silicate-KOH electrolyte with addition of 0-6.0 g/L Na2WO4. The MAO processes in base electrolyte with different concentrations of Na2WO4 were studied. The microstructure, compositions and mechanical tribological characteristics of the oxide coatings were also investigated by SEM, XRD, XPS, microhardness analysis and ball-on-disc friction testing, respectively. It is found that the addition of Na2WO4 into the base electrolyte has direct effect on the characteristics of voltage-time curves and breakdown voltage in MAO process. The number of micropores at top of the coating surface is increased by the addition of Na2WO4. The fraction of forsterite Mg2SiO4 in the oxide coating increases with increasing concentration of Na2WO4 in base electrolytes. Furthermore, the microhardness and wear resistance of oxide coatings are enhanced as well.     

Effects of rare earths on the microarc oxidation of a magnesium alloy

The effects of rare earths on the properties of the microarc oxidation（MAO） coating on a magnesium alloy were investigated by means of scanning electron microscopy（SEM）,energy dispersive X-ray spectroscopy（EDS）,and electrochemistry methods.The results show that a nice and compact MAO coating was successfully obtained when the magnesium alloy was treated in nitrate solutions as the pre-treatment of MAO.However,the MAO was not successfully completed for the silicate electrolytes with the addition of rare earths.After the magnesium alloy being treated by rare earth nitrate,the obtained MAO coating has advantages such as uniform distribution of thickness,improved corrosion resistance,and nice-uniform surface,as compared with the untreated magnesium alloy.In addition,the time of non-ESP,the voltage and current density of the MAO process obviously decrease.Cerium oxide doped on the surface of the magnesium alloy can significantly improve the corrosion resistance of the MAO coating and decrease the current density of the MAO process,as compared with lanthanum oxide,whereas the doped rare earths have no significant effect on the components of the MAO coating.     

Structure and tensile／wear properties of microarc oxidation ceramic coatings on aluminium alloy

Thick and hard ceramic coatings were prepared on the Al-Cu-Mg alloy by microarc oxidation in alkali-silicate electrolytic solution. The thickness and microhardness of the oxide coatings were measured. The influence of current density on the growth rate of the coating was examined. The rnicrostructure and phase composition of the coatings were investigated by means of scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. Moreover, the tensile strength of the AI alloy before and after microarc oxidation treatment were tested, and the fractography and morphology of the oxide coatings were observed using scanning electron microscope. It is found that the current density considerably influences the growth rate of the microarc oxidation coatings. The oxide coating is mainly composed of α-Al2 O3 and γ-Al2O3, while high content of Si is observed in the superficial layer of the coating. The cross-section microhardness of 120μm thick coating reaches the maximum at distance of 35μm from the substrate/coating interface. The tensile strength and elongation of the coated AI alloy significantly decrease with increasing coating thickness. The rnicroarc oxidation coatings greatly improve the wear resistance of AI alloy, but have high friction coefficient which changes in the range of 0.7-0.8. Under grease lubricating, friction coefficient is only 0. 15 and wear loss is less than 1/10 of the loss under dry friction.     

磷酸盐系溶液中钛合金微弧氧化涂层生长与组织结构

采用常流脉冲控制方式于(NaPO3)6-NaF-NaAlO2溶液中用微弧氧化法在Ti6Al4V表面制备了陶瓷化涂层, 研究了涂层的生长过程及组织结构变化.结果表明: 氧化过程中涂层的生长经历了由快到慢的过程, 在前10min涂层以较快速度生长(约3μm/min), 随着时间的延长涂层生长速度逐渐减慢; 生长过程中涂层表面微孔数目减少, 微孔孔径增大, 涂层表面气孔率增大; 涂层主要由二氧化钛的两种不同变体(锐钛矿及金红石)以及磷化物相AlPO4组成; 随着氧化的进行, 锐钛矿含量降低, 金红石含量增加, 氧化过程中发生了锐钛矿相到金红石相的相转变; 结晶AlPO4相是通过水合多聚磷酸铝在放电区附近发生高温热解反应而进入涂层.     

Preparation and structure of microarc oxidation ceramic coatings containing ZrO2 grown on LY12 Al alloy

Ceramic coatings containing ZrO2 were prepared in situ on LY12 aluminum alloy by microarc oxidation（MAO） in the mixed solution of zirconate and phosphate solution.The phase composition and morphology of the coatings were studied by XRD and SEM,respectively.The growing mechanism of ceramic coatings was discussed in a preliminary manner.The results show that with an increase in MAO time,the compactness of the coating improved and the thickness increased.From the inner layer to the coating surface,the content of Zr increased,while the content of Al decreased.In addition,the coating was composed of m-ZrO2,t-ZrO2,and a little amount of γ-Al2O3.With an increase in reaction time,the relative content of t-ZrO2 within the coating sharply decreased while the relative content of m-ZrO2 sharply increased,and then both generally kept at a constant level after 60 min.