镁合金微等离子体电解氧化陶瓷层生长及膜层微观形态和耐蚀性能的研究

通过对镁合金微等离子体电解氧化（Plasma Electrolytic Oxidation，PE0）沉积陶瓷层的生长过程、微观形貌及相组成的分析，研究探讨了镁合金微等离子体电解氧化沉积陶瓷层的生长过程与生长机理，并采用盐雾腐蚀试验对镁合金微等离子体氧化沉积陶瓷层耐蚀性进行了研究对比。实验结果表明，镁合金微等离子体电解氧化得到的陶瓷层分为3部分：外层为疏松层，表面有很多孔洞；中间层为紧密层，结构紧密；内层为过渡层，为陶瓷层与基体镁合金相互渗透的衔接部位，是经典的冶金结合；在微等离子体电解氧化处理过程中，由于在高压高温的等离子体环境下，促进了氧负离子和镁离子借助于放电通道向膜层深处的渗透和迁移，形成表面的盲孔，提高了防护膜的致密性和与镁合金基体结合的坚韧度。     

等离子体电解氧化膜的工艺优化及耐腐蚀性能评价

对镁合金等离子体电解氧化膜的表面制备工艺进行了研究.采用正交设计法优化实验方案,对最佳工艺条件下制备的氧化膜的微观形貌、相组成进行了研究;采用点滴腐蚀、动电位极化曲线、循环阳极极化曲线、电化学阻抗谱及浸泡腐蚀试验对AZ31镁合金及等离子体电解氧化膜的耐腐蚀性能进行了综合评价.结果表明,制备的等离子体电解氧化膜的最佳工艺为KOH 4g/L、硅酸盐20 g/L、氧化电压300 V、氧化时间30 min;氧化膜主要成分为MgSiO3和Mg2SiO4,经过等离子体电解氧化之后其显微硬度、耐点滴腐蚀、耐均匀腐蚀和耐点腐蚀性能较AZ31镁合金均有较大提高.     

Mg-9Gd-3Y镁合金PEO工艺制备复相陶瓷层电化学腐蚀行为

采用等离子体电解氧化(PEO)工艺在Mg-9Gd-3Y镁合金表面制备了复相陶瓷层。通过微观结构分析及电化学测试技术研究了PEO陶瓷层的微观组织及腐蚀行为。结果表明,偏铝酸盐体系中PEO法制备的陶瓷涂层主要由MgO和MgAl2O4相组成,还有少量MgF2相,其中MgAl2O4尖晶石相约占陶瓷层的19.87%,且由非贯通的等离子体放电微孔与喷射沉积复相氧化物组成。浸泡初期,PEO陶瓷层表现出较好的耐蚀性;浸泡后期,陶瓷层腐蚀电流密度Icorr逐渐增大,陶瓷层电阻Rct快速减小,144 h后陶瓷层的保护能力迅速下降,且陶瓷层表面出现点蚀及裂纹萌生;浸泡过程中,交流阻抗谱由浸泡0~72 h的两个容抗弧转变为浸泡144~300 h的单容抗弧和感抗弧组成,表明腐蚀介质已渗透整个陶瓷层,并萌生点蚀。腐蚀产物主要由Mg(OH)2相组成。陶瓷层的腐蚀主要由等离子体放电微孔开始,逐渐向四周蔓延并形成放射状裂纹而加速腐蚀。     

钽在磷酸盐中等离子体电解氧化涂层耐腐蚀性能研究

目的 探究金属钽在磷酸盐中进行等离子体电解氧化(Plasma electrolytic oxidation,PEO)形成Ta2O5陶瓷涂层后的耐腐蚀性能.方法 在磷酸盐电解液中,采用等离子体电解氧化(PEO)方法,在金属钽表面形成Ta2O5陶瓷涂层.采用XRD、SEM和EDS等方法,表征涂层物相、形貌及元素组成,利用动电位极化曲线和电化学阻抗谱,测试涂层的耐腐蚀性能.结果 在磷酸盐电解液中,金属钽PEO处理形成了晶态Ta2O5陶瓷膜.氧化膜初期形貌为"瘤子状",后为"沟回状".在3.5％NaCl溶液中进行动电位极化测试,相比于基体,涂层的腐蚀电流密度降低约4个数量级.PEO处理600 s形成的涂层,相比于基体,自腐蚀电位提高了约1.3 V,腐蚀电流密度为3.7?10–10 A/cm2,保护效率为99.97％;PEO处理1200 s,自腐蚀电位提高了约1.4 V,电流密度为1.46?10–10 A/cm2,保护效率为99.99％.在3.5％NaCl溶液中浸泡160 d发现,在30 d左右,钽基体表面已形成一层极薄的氧化膜,导致阻抗值持续升高,表明对基体有一定的保护作用.然而,PEO处理600 s形成的涂层在浸泡3 d后,低频区域阻抗值大幅下降,且随浸泡时间的延长,阻抗值持续降低.在160 d腐蚀后,电荷转移电阻仍然比未经过处理的金属钽高1个数量级.结论 在磷酸盐电解液中,钽经PEO处理形成的陶瓷膜层具有较强的耐腐蚀性能,PEO处理可大幅度提高钽的耐腐蚀能力.     

甲醇对镁合金等离子体电解氧化过程的影响

以甲醇和水为混合溶剂,KOH、Na2SiO3为电解质,恒电压方式对AZ31镁合金进行等离子体电解氧化(PEO)处理,通过原子吸收分光光度计检测等离子体电解氧化处理后电解液中镁离子含量,研究甲醇对镁合金等离子体电解氧化过程的影响。结果表明,在等离子体电解氧化过程中,甲醇的加入影响镁合金PEO过程放电特性;随着甲醇浓度的增大,镁离子溶出量逐渐减少,耐点滴腐蚀、耐均匀腐蚀性能均有提高;甲醇的加入能有效降低PEO过程能耗,当溶剂中甲醇浓度为12%(体积分数)时,能耗比未加甲醇时降低42.9%。     

镁合金阳极氧化膜在NaCl溶液中的腐蚀行为

利用盐水浸泡实验研究了AZ91D镁合金阳极氧化膜层在3．5％NaCl溶液中的腐蚀行为。结果表明：AZ91D镁合金阳极氧化膜层不论封闭与否,在中性NaCl溶液中浸泡出现第一个腐蚀点后,膜层表面均很少再出现新的腐蚀点,而是原有的腐蚀点向纵、横两个方向扩展形成腐蚀坑,表面呈“树枝”状腐蚀形貌;浸泡溶液的pH值对阳极氧化膜层的耐蚀性影响很大,酸性溶液中的腐蚀速率明显大于中、碱性溶液的;随浸泡溶液温度的升高阳极氧化膜层的腐蚀速率加快。据此,提出了AZ91D镁合金阳极氧化膜层在NaCl溶液中腐蚀过程的模型。     

硅酸盐溶液中ZL101等离子体电解氧化膜形成过程的研究

以硅酸盐溶液为电解液,对ZL101合金进行等离子体电解氧化(PEO)处理,分析膜层的形成过程和膜层的组成和结构。结果表明,PEO初始阶段的膜层分别在初生α相和共晶体上独立形成,Si相上无等离子体放电产生,Si在临近α相的等离子体放电产生高温下氧化,形成SiO2进入膜层。初生α相的膜层以Al2O3为主,含有少量的SiO2。而共晶体的膜层中SiO2含量显著高于Al2O3。ZL101的PEO膜主要成分为γ-Al2O3、α-Al2O3,SiO2及莫来石(3Al2O3.2SiO2)。随着PEO处理时间的增加,γ-Al2O3逐渐向α-Al2O3转化,膜层中α-Al2O3量增加。     

镁合金表面聚苯胺膜层防腐性能的研究

用循环伏安法在镁合金表面制备了聚苯胺膜层,并用扫描电子显微镜(SEM)和电极电位研究了聚苯胺膜的表面形貌和腐蚀防护性能.研究表明:聚苯胺膜层并不是均匀覆盖在基体表面,而且膜层表面存在很多的微孔;聚苯胺改变了膜层的电极电位;在腐蚀介质中聚苯胺膜以点蚀或剥离的方式进行腐蚀.     

镁合金铈转化膜在NaCl溶液中的腐蚀行为及腐蚀机理

通过静态浸泡腐蚀实验,采用扫描电子显微镜、X射线能谱仪、电化学实验等研究镁合金铈转化膜在0.05mol/L Na Cl溶液中的腐蚀行为,探讨膜层腐蚀机理。结果表明:随着浸泡时间的延长,膜层发生腐蚀和遭到破坏的程度也随之增强,浸泡初级腐蚀产物组织疏松,腐蚀后期腐蚀产物的致密性和紧实度增加;腐蚀产物主要由镁、氧等元素组成。随浸泡时间的延长,膜层电阻和腐蚀电位先增大后减小,腐蚀电流密度呈现先减小后增大的趋势。     

镁合金黑色微弧氧化膜在NaCl溶液中腐蚀电化学演变

目的 评价镁合金黑色微弧氧化热控膜层在氯离子作用下的腐蚀演变行为.方法 在电解液中添加不同浓度的添加剂制备微弧氧化膜层,分析不同微弧氧化膜试样在0.1 mol/L NaCl溶液中的电化学演变过程.采用电化学极化、电化学交流阻抗表征和拟合,结合扫描电镜等方法,对膜层演变规律及机理进行了探讨.结果 未经微弧氧化的镁合金自腐蚀电流密度为17.7 μA/cm2,自腐蚀电位为-1.464 V;经微弧氧化后,试样自腐蚀电流密度减小至0.09 μA/cm2,自腐蚀电位下降至-1.628 V.添加剂加入后制备的微弧氧化膜相比于镁合金基体,其耐蚀性能提高,且随着添加剂浓度的增加,耐蚀效果呈现先增加、后减弱的趋势,添加剂质量浓度在10 g/L时制备的膜层具有最好的防腐效果.镁合金微弧氧化热控膜层在NaCl溶液中腐蚀过程分为三个阶段:一是腐蚀性离子进入多孔膜层,引起界面熔融层变化;二是MgO与水分子反应造成内层膜更加致密,阻抗有所增加;三是腐蚀溶液接触到部分镁合金基底,发生电化学腐蚀,形成楔形效应,引发裂纹,最终导致局部腐蚀失效.结论 微弧氧化提高了膜层的耐蚀性能,其在0.1 mol/L NaCl溶液中的腐蚀过程可分为介质进入孔内、水合反应和局部腐蚀三个阶段.     

等离子电解渗入工艺和渗层组织

介绍了液相等离子体电解渗入技术,即利用液相中的等离子放电实现渗碳、渗氮、渗硼及多元共渗的基本工作原理、工艺特点和电解液成分等。论述了液相等离子体电解渗入过程中的电流-电压特性和物理化学效应。介绍了经液相等离子体电解渗入处理的20CrMnTi和40Cr钢的表面形貌、渗层显微组织和硬度分布。     

甘油体系中不锈钢表面液相等离子体电解渗碳工艺

采用液相等离子体电解渗方法,在80%甘油水溶液中实现了304不锈钢表面快速渗碳。研究施加电压和放电时间对渗碳过程的影响,分析了渗碳层的显微组织,并比较了不同工艺条件下渗碳层显微硬度分布。结果表明:经过5 min的快速放电处理,渗碳层厚度接近100μm,硬度达到880 HV。在350 V和3 min渗透条件下渗碳层质量较好。     

Surface modification of die casting mold steel by a composite technique of hot-dipping and plasma electrolytic oxidation

The hot dipping process of pure aluminum on H13 steel substrates followed by plasma electrolytic oxidation（PEO） was studied to form alumina ceramic coatings for protective purpose.H13 steel bars were first dipped in pure aluminum melts,and then,a reactive iron-aluminum intermetallic layer grew at the interface between the melt and the steel substrate.The reactive layer was mainly composed of intermetallic Fe-Al（Fe₂Al₅）;the thickness of aluminum layer and Fe-Al intermetallic layer were mainly influenced by dipping time（1.5～12.0 min） and dipping temperature（710～760 ℃）.After PEO process,uniform Al₂O₃ ceramic coatings were deposited on the surface of aluminized steel.The element distribution,phase composition and morphology of the aluminized layer,and the ceramic coatings were characterized by SEM/EDS and XRD.The distribution of hardness across the composite coating is demonstrated,and the maximum value reaches 1864 HV.The thermal shock resistance of the coated sample is also well improved.     

Preparation and Characterization of Amorphous Layer on Aluminum Alloy Formed by Plasma Electrolytic Deposition (PED)

PLASMA Electrolytic Deposition(PED)is a relativelynew technology to form ceramic layers on somenon-ferrous metal and their alloys such as aluminum,magnesium and titanium'1'21.By apply high electricalpotential between the work-piece and another counterelectrode in certain electrolysis,the breakdown of thepassive film or the gas envelope surrounding theworkpiece lead to electrical discharge in the interfacebetween the workpiece surface and the electrolysis.Ceramic layers and/or diffusion lay…     

Microstructural,corrosion and mechanical behavior of two-step plasma electrolyte oxidation ceramic coatings

Plasma electrolytic oxidation (PEO) is considered as a cost effective and environmentally friendly surface treatment process for improving surface properties of light alloys. The formation of ceramic coatings on Ti6Al4V alloy was reported by two-step PEO process and its structural, electrochemical and mechanical properties with the coated samples were compared by one-step PEO process in an alkaline electrolyte. The structural properties were studied using field-emission scanning microscope (FESEM) and X-ray diffraction (XRD). Electrochemical studies were carried out using linear polarization method and in addition mechanical behaviors were investigated by means of Knoop microhardness and nanoindentation method. Results showed that the second step process resulted in an increase of both porosity percentage and average pore diameter on the surface. The two-step process resulted in a small increase of thickness from about 12.5 to 13.0 µm. Electrochemical test results showed that applying the second step resulted in the decrease of both polarization resistance from 1800.2 to 412.5 kΩ/cm² and protection efficiency from 97.8% to 90.5%. Finally, the nanoindentation results indicated that the PEO coatings became softer but more ductile after applying the second processing step in acidic electrolyte.     

等离子体电解氧化过程中参数控制模式分析

在分析有关等离子体电解氧化（Plasma Electrolytic Oxidation—PEO）系统模型的基础上，推导了一个用于描述PEO处理过程中各参数之间联系的系统方程，并在恒流与恒压条件下对该方程进行了讨论。磷酸盐电解液中镁合金PEO处理的验证试验表明：在恒压条件下利用该方程计算所得的后期电流值与试验结果具有较好的一致性，而恒流条件下具有较大的偏差，这与推导方程过程中所做的假设和简化有关。另外，在恒流控制的基础上，提出了阶梯降流法的控制成膜方式，并研究了其在磷酸盐系电解液中具体的实现方法及其在成膜过程中的作用。     

Amorphous coatings deposited on aluminum alloy by plasma electrolytic oxidation

Amorphous [Al-Si-O] coatings were deposited on aluminum alloy by plasma electrolytic oxidation (PEO). The process parameters, composition, micrograph, and mechanical property of PEO amorphous coatings were investigated. It is found that the growth rate of PEO coatings reaches 4.44μm/min if the current density is 0.9 mA/mm^2. XRD results show that the PEO coatings are amorphous in the current density range of 0.3 - 0.9 mA/mm^2. EDS results show that the coatings are composed of O, Si and A1 elements. SEM results show that the coatings are porous. Nano indentation results show that the hardness of the coatings is about 3 - 4 times of that of the substrate, while the elastic modulus is about the same with the substrate. Furthermore, a formation mechanism of amorphous PEO coatings was proposed.     

Evolution of active species and discharge sparks in Na2SiO3 electrolyte during PEO process

For the plasma electrolytic oxidation (PEO) of Mg alloy in Na₂SiO₃ electrolyte, optical emission spectroscopy (OES) was adopted to identify the active plasma species at the four stages and the evolution of the discharge sparks in the PEO process was analyzed. At the conventional anodic oxidation stage the emitting-light was correlated to the “flaws” in the oxide films. At the transition stage the active species were O₂ and H₂O. At the transition stage, the collapse and ionization of the bubble layer happened. At the plasma discharge stage, the active plasma species transited and emitted light. The main active plasma species of the micro-discharges were Na, K, Mg, H_α, O₂⁺ and OH. At the arc discharge stage, the energy was not uniform and the discharge was uneven, the light intensity increased sharply, O⁺ and O were excited.