Discharge Characteristic of Micro-Arc Oxidation on Aluminum Alloy under the Changing Electrolyte Temperature

The electrolyte temperature has a great influence on the performance of the coating prepared by micro-arc oxidation (MAO). The behavior of MAO discharge in the changing electrolyte temperature has been investigated. Compared to constant electrolyte temperature in conventional MAO process, the process has different discharge characteristics under the changing electrolyte temperature. The amplitude of pulse voltage was detected to study the change of discharge characteristic under the constant-current control of MAO power supply. Three successive discharge stages were differentiated by the variable the pulse voltage versus process time. Since there were significant changes in the sound, the sound signals were acquired and the audio analysis was used to describe the changing of the MAO discharge at different stages. Optical emission spectroscopy (OES) was employed in situ to unveil how the micro-discharge changed with the temperature increasing. Scanning electron microscopy (SEM) was used to characterize the morphology of the coatings on 6N01 aluminum alloy prepared by normal process with the constant-temperature control of the MAO electrolyte and by the process under the changing electrolyte temperature. A mode of film growth and micro-discharge was given to describe the effects of the changing electrolyte temperature in the whole MAO process.

Influence of oxidation heat on hard anodic film of aluminum alloy

The special experimental device and sulfuric acid electrolyte were adopted to study the influence of anodic oxidation heat on hard anodic film for 2024 aluminum alloy. Compared with the oxidation heat transferred to the electrolyte through anodic film, the heat transferred to the coolant through aluminum substrate is more beneficial to the growth of anodic film. The film forming speed, film thickness, density and hardness are significantly increased as the degree of undercooling of the coolant increases. The degree of undercooling of the coolant, which is necessary for the growth of anodic film, is related to the degree of undercooling of the electrolyte, thickness of aluminum substrate, thickness of anodic film, natural parameters of bubble covering and current density. The microstructure and performance of the oxidation film could be controlled by the temperature of the coolant.

Morphologies and Properties of Micro-Arc Oxidation on Plate and Cylinder 2024 Al Alloy

Samples with two different shapes of 2024 aluminum alloy were treated with micro-arc oxidation (MAO), and the formation process and mechanism of oxidation film was analyzed. The results show that different geometrical curvature of the material has an influence upon the uniformity of films and the corrosion-resistance.

Effect of Initial Oxide Film on the Formation and Performance of Plasma Electrolytic Oxidation Coating on 7075 Aluminum Alloy

In the early stage of plasma electrolytic oxidation(PEO),the quick formation of the initial oxide film on the surface of the aluminum substrate is necessary for the subsequent discharge spark process.Furthermore,the compactness of the initial oxide film greatly affects the quality of the PEO coating,but the related mechanisms are not investigated in detail.In this paper,the status of the initial oxide film was adjusted by adding the(NaPO)into the based electrolyte,and then the effect of initial oxide film on the formation of the PEO coating was compared.Microstructure and chemical composition were analyzed by scanning electron microscope,transmission electron microscopy and X-ray photoelectron spectrometer.The compactness of the initial oxide film was characterized by Mott-Schottky plots.The corrosion resistance was measured by electrochemical impedance spectroscopy.The results show that the addition of(NaPO)can promote the co-deposition of phosphide compound into the initial oxide film and improve the film compactness,which is beneficial for the more uniform spark discharge in the later stage.As a result,the addition of(NaPO)is helpful to obtain PEO coating with better performance.

Effect of electrolyte concentration o n the tribological performance of MAO coatings on aluminum alloys

Micro-arc oxidation(MAO)is an efficient approach to improve the hardness,wea r resistance,and other properties of aluminum alloys.In order to investigate the effect of the electrolyte concentration on the properties of MAO coatings for LY12 alloy,the voltage variation during the MAO process was recorded.The surface morphologies and phase compositions of the coatings produced with different electrolytes were investigated using scanning electron microscopy and X-ray diffraction,respectively.The roughness and thickness of the coatings were measured using a pocket roughness meter a nd an eddy-current thickness meter,respectively.The tribological performances of the coatings wer e investigated against GCr15 bearing steel on aball-on-disc wear tester in open air.The results showed that with an increase in the Na2SiO3 content,the working voltage of the MAO process decreased,the roughness a nd thickness of the coatings increased significantly,a nd the relative content of the α-Al2O3 phase decreased.With an increase in the KOH content,the working voltage decreased slightly,the roughness and thickness of the coatings increased slightly,and the α-and γ-Al2O3 phase contents remained unchanged.The friction coefficient and wear rate of the coatings increased with an increase in the Na2Sio3 and KoH concentrations.A decrease in the porosity and roughness and an increase in the α-Al2O3 content of the coatings reduced their wear mass loss.

OH^(-)/F^(-)比与SiO_(3)^(2-)的关系对铝合金微弧氧化膜层的影响

目的探明不同氢氧化钠/氟化钾质量之比与硅酸钠浓度的关系对A356铝合金微弧氧化膜层耐蚀性的影响机制,寻找电解液中电解质之间的配比需求。方法利用SEM、EPMA、XRD分析所制得膜层的微观结构、元素分布及物相组成,并通过动电位极化曲线及电化学阻抗谱(EIS)研究膜层的电化学耐蚀性和腐蚀行为。结果当电解液中NaOH/KF之比(均为质量比)为0∶1、1∶2和2∶1时,均无法形成表观质量良好的微弧氧化膜层。而将NaOH/KF之比调整为1∶1时,便在基体表面得到了覆盖完整、均匀连续、光滑平整的膜层。但因此时电解液中主成膜剂Na_(2)SiO_(3)的不足,致使所获膜层与NaOH/KF之比为1∶0时相较而言,膜层表面的微孔尺寸增大,大尺寸的微孔个数也增加,在一定程度上削弱了膜层的抗腐蚀能力。继而保持NaOH/KF之比为1∶1但将主成膜剂Na_(2)SiO_(3)的浓度翻倍后,所制得膜层表面缺陷减少,厚度增加,致密度得到改善,膜层中α-Al_(2)O_(3)、γ-Al_(2)O_(3)、Mullite及AlF_(3)等优质耐蚀物相的含量也明显增多,进而提高了膜层在酸性腐蚀介质和中性Na Cl腐蚀介质中的耐蚀性。结论在硅酸盐电解液中,NaOH和KF都是微弧氧化成膜过程中的重要组分。NaOH促使A356铝合金基体表面形成充分的钝化膜,并显著提高了溶液的电导率,为微弧氧化反应的击穿发生创造了先决条件。KF可增进微弧氧化击穿发生后的放电效应,引发更多的放电火花产生,提高膜层的生长速率,加快成膜物质的沉积速率。NaOH与KF浓度相近,且二者浓度均小于Na_(2)SiO_(3)浓度时,SiO_(3)^(2-)、OH^(-)、F-三者之间交互作用对提高膜层的耐蚀性最为显著。

电解液参数对铝合金微弧氧化的影响

在氢氧化钠、铝酸钠、磷酸二氢钠体系电解液中用微弧氧化法制备铝氧化膜 ,并得到了电解液温度、浓度及氧化时间对铝氧化膜成膜的关系曲线。微弧氧化工艺处理后氧化膜的厚度可达 80 μm以上 ,显微硬度可达 1560HV。用X射线衍射 (XRD)和扫描电镜 (SEM)分析 ,观察了氧化膜层相结构和表面形貌。通过耐腐蚀试验可知 。

氢氧化钠电解液中铝合金的微弧氧化

叙述了在 Na OH电解液中进行铝合金表面微弧氧化处理。经微弧氧化制备的铝氧化膜 ,厚度可达 80 μm,显微硬度可达 HV1 2 0 0。通过 X射线衍射 ( XRD)分析和扫描电镜 ( SEM)分析观察可知 ,铝合金氧化膜层相结构为α- Al2 O3 和γ- Al2 O3 ,膜层与铝基体结合良好。通过热分析 ( TG、DSC)可知 。

电解液参数对铝合金微弧氧化膜层质量的影响

研究了在Na2S iO3系电解液中电解质浓度和添加剂浓度对铝合金微弧氧化膜层厚度和硬度的影响。结果表明:在本工艺条件下,膜层厚度随着电解质浓度的升高而增加,但硬度是先增加后减小;加入添加剂以后,膜层的厚度、硬度及手感细腻程度和均匀性都有明显提高。

铝合金阳极氧化膜着金色的研究

研究了以银盐为主盐的电解着金色工艺。研究了着色液中各成分及操作条件的影响 ,分析了影响着色效果的各因素 ,该着色工艺稳定性好 ,使用寿命长 ,着色膜耐蚀、耐磨。

电解液参数对铸造铝合金微弧氧化陶瓷层质量的影响

研究了在Na2SiO3体系中电解液组成和浓度对压铸铝合金微弧氧化陶瓷层厚度、硬度及外观均匀性的影响。结果表明:随着Na2SiO3和NaOH浓度的增加,膜层厚度和硬度先增加后减小,适宜的添加剂可以增加膜层厚度,提高膜层的均匀性。本实验条件下适宜压铸铝合金微弧氧化的电解液配方为Na2SiO310 g/L、NaOH 2 g/L、添加剂6 mL/L。

铝合金微弧氧化膜白色斑点成因分析

用硅酸盐体系电解液进行铝合金微弧氧化时,氧化膜表面出现白色斑点状物,影响零件质量和外观,对这种白色斑点状物进行EDS和XRD成分测试,同时还对形成原因进行分析。结果表明,白色斑点状物是由SiO2聚集而成。

铝合金A356微弧氧化电解液配方的优化

利用扫描电镜(SEM)、表面粗糙度测量仪等分析手段,研究了铝合金A356微弧氧化电解液配方对膜层性能的影响规律,优化了电解液配方:主电解质NaOH的质量浓度为4g/L及Na2SiO3的质量浓度为14g/L,添加剂KF的质量浓度为6g/L。KF对膜层性能有很大的改善,随着KF的加入,耐蚀时间从28.7min增大至36min,粗糙度从0.9μm减少到0.55μm。