Effects of electrolytes variation on formation of oxide layers of 6061 Al alloys by plasma electrolytic oxidation

Plasma electrolytic oxidation(PEO) processes were carried out to produce ceramic layers on 6061 aluminum substrates in four kinds of electrolytes such as silicate and aluminate solution with and without sodium fluorosilicate.The PEO processes were carried out under a hybrid voltage(260 V DC combined with 200 V,60 Hz AC amplitude) at room temperature for 5 min.The composition,microstructure and element distribution analyses of the PEO-treated layers were carried out by XRD and SEM & EDS.The effect of the electrolyte contents on the growth mechanism,element distribution and properties of oxide layers were studied.It is obvious that the layers generated in aluminate solutions show smoother surfaces than those in silicate solutions.Moreover,an addition of fluorine ion can effectively control the layer porosity;therefore,it can enhance the properties of the layers.

Preparation of micro/nano-structured ceramic coatings on Ti6Al4V alloy by plasma electrolytic oxidation process

In order to improve the osseointegration and antibacterial activity of titanium alloys,micro/nano-structured ceramic coatings doped with antibacterial element F were prepared by plasma electrolytic oxidation(PEO)process on Ti6Al4V alloy in NaF electrolyte.The influence of NaF concentration(0.15-0.50 mol/L)on the PEO process,microstructure,phase composition,corrosion resistance and thickness of the coatings was investigated using scanning/transmission electron microscopy,energy dispersive spectroscopy,atomic force microscopy,X-ray diffractometer,and potentiodynamic polarization.The results demonstrated that Ti6Al4V alloy had low PEO voltage(less than 200 V)in NaF electrolyte,which decreased further as the NaF concentration increased.A micro/nano-structured coating with 10-15μm pits and 200-800 nm pores was formed in NaF electrolyte;the morphology was different from the typical pancake structure obtained with other electrolytes.The coating formed in NaF electrolyte had low surface roughness and was thin(<4μm).The NaF concentration had a small effect on the phase transition from metastable anatase phase to stable rutile phase,but greatly affected the corrosion resistance.In general,as the NaF concentration increased,the surface roughness,phase(anatase and rutile)contents,corrosion resistance,and thickness of the coating first increased and then decreased,reaching the maximum values at 0.25 mol/L NaF.

Incorporation mechanism of colloidal TiO_(2) nanoparticles and their effect on properties of coatings grown on 7075 Al alloy from silicate-based solution using plasma electrolytic oxidation

Plasma electrolytic oxidation(PEO)was applied using a pulsed unipolar waveform to produce Al_(2)O_(3)−TiO_(2) composite coatings from sol electrolytic solutions containing colloidal TiO_(2) nanoparticles.The sol solutions were produced by dissolving 1,3,and 5 g/L of potassium titanyl oxalate(PTO)in a silicate solution.Scanning electron microscopy,energy dispersive spectrometry,X-ray diffraction,and Raman spectroscopy were applied to characterizing the coatings.Corrosion behavior of the coatings was investigated using polarization and impedance techniques.The results indicated that TiO_(2) enters the coating through all types of micro-discharging and is doped into the alumina phase.The higher level of TiO_(2) incorporation results in the decrease of surface micro-pores,while the lower incorporation shows a reverse effect.It was revealed that the higher TiO_(2) content makes a more compact outer layer and increases the inner layer thickness of the coating.Electrochemical measurements revealed that the coating obtained from the solution containing 3 g/L PTO exhibits higher corrosion performance than that obtained in the absence of PTO.The coating produced in the absence of PTO consists of γ-Al_(2)O_(3),δ-Al_(2)O_(3) and amorphous phases,while α-Al_(2)O_(3) is promoted by the presence of PTO.

Effects of Yttrium Ion on Formation Mechanism of ZrO_2-Y_2O_3 Ceramic Coatings Formed by Plasma Electrolytic Oxidation on Al-12Si Alloy

ZrO2-Y2O3 ceramic coating was produced by plasma electrolytic oxidation （PEO） on ZAlSil2Cu3Ni2 alloy. The microstructure and phase composition of the coating were investigated by SEM and XRD.： The results show that adding an appropriate amount of yttrium ion can improve the growing rate of ceramic coating at different oxidation stages and decrease arc voltage. The thickness of ZrO2-Y2O3 coating is 16 μn thicker than that of ZrO2 coating and the maximum oxidation rate improves by 0.6 μm/min. In addition, the arc voltage decreases from 227 to 172 V. It can be seen that the rate of oxidation firstly increases to some extent and then decreases with the content of yttrium ion increasing. The growth rate reaches the maximum while the content of yttrium ion is 0.05 g-L-1The maximum thickness is 90 μm.Compared to ZrO2 coating, the micropores of ZrO2-Y2O3 coating are less and the ceramic layer is repeatedly deposited by ZrO2 and Y2O3 ceramic particles. Meanwhile, the binding force between coating and substrate is better and the coating is uniform and compact. The ceramic layer is mainly composed of c-Y0.15Zr0.85O1.93□0.07, m-ZrO2, α-Al2O3, ,γ-Al2O3 and Y2O3. It is indicated that ZrO2 has beert fully stabilized by yttrium ion through the formation of solid solution.

Electrolytic Codeposition of Y(Ⅲ) and Al(Ⅲ) and Surface Metalliding in Molten Fluorides—Oxides Systems

The mechanism of the electrolytic codeposition of Y Al alloy in molten LiF AlF 3 Al 2O 3 YF 3, LiF YF 3 Y 2O 3 AlF 3 and LiF YF 3 Y 2O 3 Al 2O 3 systems was investigated by means of cyclic voltammetry. The electrodeposited products were analysed by X ray diffraction. The results show that the electrolytic codeposition of Y Al alloy in the LiF YF 3 Y 2O 3 Al 2O 3 system without AlF 3 can be achieved at the same potential for Y(Ⅲ) and Al(Ⅲ) which have great difference in deposition potential. It is beneficial to codeposition of Y(Ⅲ) and Al(Ⅲ) when temperature rises. The potential of beginning codeposition is about -0.85 V ( vs Pt reference electrode), but only at the potential of -0.95 V or more negative can Y based Al alloy containing a great amount of yttrium be obtained.

Influence of anions in phosphate and tetraborate electrolytes on growth kinetics of microarc oxidation coatings on Ti6Al4V alloy

The growth kinetics of microarc oxidation(MAO)coatings on Ti6Al4V alloy was studied by designing an electrolyte with low PO_(4)^(3−)content and high B_(4)O_(7)^(2−)content,using scanning electron microscopy,transmission electron microscopy,X-ray diffraction,and potentiodynamic polarization.The results showed that B_(4)O_(7)^(2−)increased the spark intensity and dissolved most of the oxides at high temperatures.Then,a thicker barrier layer at the coating/substrate interface was produced,which increased the polarization resistance of the coating.PO_(4)^(3−)at a low concentration also promoted the uniform growth of the MAO coating and the formation of hat-shaped holes in the outer deposition layer.The thickness of the MAO coatings obtained in Na_(2)B_(4)O_(7) electrolytes exhibited an exponential increase with time at spark discharge stage,while that of the MAO coating obtained in phosphate–tetraborate electrolytes showed a linear trend as the PO_(4)^(3−)content increased.

DETERMINATION OF ACTIVITY OF AI IN SOLID Cu-Al ALLOYS

Activities and activity coefficients of Al in solid Cu-AI alloys have been determined by means of solid electorlyte galvanic cells Al(a_1 , in alloy), Al_2O_3 | ZrO_2· Y_2O_3 | Ni, NiO and Al(a_1 , in alloy), Al_2O_3 | Na, βAl_2O_3 | Al(a_2 , in alloy), Al_2O_3

Al-Mg合金镀层的制备与性能

利用AlCl3＋LiAlH4＋MgBr2有机溶剂体系在碳钢基体上电沉积出Al—Mg合金镀层，并对不同沉积电流密度下Al—Mg镀层的表面形貌、成分、结构、厚度、结合力和耐蚀性进行了研究。结果表明：沉积出的铝镁合金镀层表面光滑、均匀、致密；膜层中的镁含量随沉积电流密度的增加而增大，且以Al—Mg固溶体形式存在，并按（200）面的结构生长；随沉积电流密度的增加，铝镁合金镀层的厚度与晶格常数呈线性增大;在3．5％NaCl溶液中的耐蚀性呈先增大后减小的规律；Al—Mg镀层与碳钢基体的结合力良好，均大于50N；Al—Mg镀层的沉积速率、结合力和耐蚀性均高于相同沉积条件下的纯铝镀层；Al—Mg合金镀层沉积的最佳电流密度为0．75～1．50A／dm^2。

Al-Mn合金镀层的制备与性能

利用AlCl3+LiAlH4+MnCl2有机溶剂体系在低碳钢基体上进行了电镀Al-Mn合金的实验,并对不同电镀工艺下Al-Mn合金镀层的表面形貌、成分、结构、厚度、结合力和耐蚀性等进行了研究.实验结果表明,沉积出的Al-Mn合金镀层表面光滑并呈网状分布;镀层中的Mn含量(原子分数)在30/0-80/0间变化,其中Mn以Al-Mn过饱和固溶体形式存在,且按(200)面的结构进行生长.随电镀时间和电流密度的增加,Al-Mn合金镀层的厚度呈线性增大,但膜层与基体的结合力逐渐降低.Al-Mn合金镀层的耐蚀性随沉积电流密度的增加而减小,随电镀时间的延长呈先增大后减小的规律.Al-Mn合金镀层的沉积速率、结合力和耐蚀性均高于相同沉积条件下的纯铝镀层。Al-Mn合金镀层在AlCl3+LiAlH4+MnCl2有机溶剂体系中的最佳沉积工艺为电流密度0.15-0.50 A/dm2、电镀时间30-45 min.

Al基合金原位Ti合金化及自身晶粒细化

利用电解工艺 ,向氧化铝中掺入数量很少的TiO2 粉 ,通过电解使阴极Al液含质量分数为 0 .1%～ 0 .3 %的Ti。实现了铝基合金原位钛合金化及自身晶粒细化 ,获得了等轴的细晶Al锭 ,晶粒尺寸细化到 13 0 μm。该合金直接用于 60 63变形铝合金 ,取得了明显的晶粒细化效果 ,使原来的 4级细化到 1～ 2级。电解加Ti优于熔配加Ti ,能使 60 63变形合金产生自身晶粒细化作用。

磁控溅射镀铝AZ31镁合金等离子体电解氧化揭示的放电通道结构及其腐蚀行为

在硅酸盐-六偏磷酸盐电解液中对覆盖薄磁控溅射铝层的AZ31镁合金进行等离子体电解氧化(PEO),以研究PEO机理并提高合金的耐腐蚀性。使用SEM和EDS检测涂层形貌并追踪涂层中Mg和Al元素的分布。新的涂层主要在靠近涂层/金属基体界面的放电通道下部形成。在放电通道上部先前形成的氧化物大部分以固态形式保留在原先的位置,只有少部分熔融氧化物通过涂层的微孔流出,到达表层。阴离子可以通过涂层充满电解液的孔传输,自由地进入涂层的最深部位。在3.5%NaCl (质量分数)中进行开路电位、极化曲线和EIS测试。结果表明,致密的磁控溅射Al层可以显着提高AZ31镁合金的耐腐蚀性,其耐腐蚀性甚至优于PEO处理后的样品。

NaCl－AlCl_3融盐电解中MnCl_2对改善Al－Mn合金电沉积层的作用

在１７５℃下实验测得ＭｎＣｌ２在ＮａＡｌＣｌ４熔体中的溶解度为０．０８６±０．００６ｍｏｌ％。锰可以在阴极上与铝发生共电沉积，生成含锰量为８ａｔｏｍ％～１０ａｔｏｍ％的二元合金。铝锰共电沉积可以显著地加快电化学成核步骤，从而完全消除低电流密度下絮状沉积产物的生成，且对高电流密度下枝晶产物的生成也有抑制作用。

ZrO2纳米粉对Al-Si合金微弧氧化陶瓷层组织和性能的影响

为提高铝硅合金在高温环境下的服役寿命,文中通过微弧氧化技术在硅酸盐体系电解液中于Al-Si合金表面制备ZrO2-Al2O3陶瓷层。采用扫描电子显微镜和X射线衍射仪分别对陶瓷层进行了表面、截面形貌以及物相组成分析。利用涡流测厚仪测量不同ZrO2加入量的膜厚,分析ZrO2-Al2O3体系陶瓷层的生长速率,通过自制隔热装置对陶瓷层进行隔热性能测试。研究结果表明:Al2O3陶瓷层表面由许多胞状熔融物烧结而成,粗糙度较大,并分布着孔洞较大的放电通道,膜厚约10μm;ZrO2-Al2O3陶瓷层表面除了胞状熔融物还有细小的颗粒,粗糙度较小,且陶瓷层更加致密,膜层厚度达到25μm。两种体系陶瓷层均形成了Al2O3及SiO2相,且在15°~50°范围内出现"馒头包"现象,说明陶瓷层中有非晶成分,但ZrO2-Al2O3陶瓷层中衍射峰"馒头包"的现象更为严重,非晶成分含量更高,说明在微弧氧化过程中ZrO2纳米粉的加入有利于亚稳相γ-Al2O3的形成。陶瓷层生长速度研究结果表明,电解液中ZrO2的浓度越大,陶瓷层厚度越厚,生长速度先增大后减小。隔热性能测试结果显示,随ZrO2含量的增多,陶瓷层的隔热温度升高,ZrO2的加入对涂层的隔热起到增强的作用。

熔盐电解法制备Al-Cu中间合金

以Na3Al F6-Al F3-Mg F2-Li F为电解质,Al2O3、Cu O为原料,对熔盐电解共沉积制备Al-Cu中间合金进行了研究,采用扫描电子显微镜（SEM）、能谱（EDS）及X射线衍射（XRD）分析合金表面形貌及元素分布.结果表明：施加外电压为2.6-3.5 V时,合金形成速率随电压的增加先增加后降低,施加外电压为3.3 V时,合金形成速率可达最大值;温度为895-955℃时,合金的形成速率随温度升高先增加后降低,温度为935℃时可达最大值;恒压3.3 V,温度为935℃,可制得Cu质量分数为11.51%、纯度为97.2%的Al-Cu合金,且合金中的铜与铝合金化过程中主要是以环状的Al2Cu相分布在晶界上;XRD分析表明合金中Cu主要是以Al2Cu相存在于合金组织中.

Al-12.5%Si合金表面ZrO2溶胶改性PEO陶瓷层的形成机制

采用ZrO2溶胶改性的等离子体电解氧化(PEO)技术在Al-12.5%Si合金表面制备Al2O3-ZrO2陶瓷层,研究ZrO2溶胶对PEO陶瓷层形成机制的影响。采用扫描电镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)、红外光谱仪(FTIR)和激光粒度仪等研究了ZrO2溶胶的微观组织结构、粒径及荷电性以及陶瓷层的微观形貌、成分及物相。结果表明:荷负电的ZrO2溶胶粒径为50~60 nm,烧结后以四方相t-ZrO2存在,含有少量m-ZrO2。ZrO2溶胶改性的PEO涂层较未改性的涂层均匀、致密,并且生长速率提高。由于ZrO2溶胶吸附在基体表面形成凝胶层,凝胶层的高电阻使PEO初期更易产生火花放电,促进了Al2O3膜的形成。ZrO2溶胶改性的PEO涂层由Al2O3、c-ZrO2、t-ZrO2和少量的SiO2组成,而溶胶改性前SiO2的含量较高。ZrO2凝胶颗粒在等离子体放电产生的高温下进入放电通道,与电化学反应形成的Al2O3烧结形成Al2O3-ZrO2复合陶瓷层。

固态Cu-Al合金中Al活度的测定

用固体电解质电池在1000℃下研究了固态Cu-Al二元系中Al的活度,Al的摩尔分数为0.0234到0.327。

Al-B中间合金对用电解低钛铝制备的Al-Mg-Si变形合金的晶粒细化作用

研究了Al-B中间合金对用电解低钛铝合金制备的Al-Mg-Si变形合金的晶粒细化作用。结果表明,按硼钛质量比1:5的比例加入Al-B中间合金,可获得理想的晶粒细化效果。研究结果扩大了Al-B中间合金作为晶粒细化剂的使用范围,也为Al-Mg-Si变形合金的制备与晶粒细化处理提供了一条新的途径。

2A97 Al-Cu-Li合金在铝酸盐和磷酸盐电解液中等离子电解氧化膜的性能

采用交流双脉冲电流制度对2A97 Al-Cu-Li合金分别在铝酸盐和磷酸盐电解液中进行等离子电解氧化处理的研究,分析所得膜层的微观结构和相组成,并采用电化学极化曲线和摩擦试验对两种电解液中所得膜层的耐腐蚀性能和耐磨性能进行评价。结果表明:在两种电解液中所得膜层表面存在大量饼状结构,膜层由内外两层构成,两层之间分布大量微孔,膜层的相组成主要为α、γ、δ-Al2O3,铝酸盐电解液中所得膜层有较多的α-Al2O3。磷酸盐电解液中所得膜层的耐腐蚀性高于相应的铝酸盐中所得膜层的耐腐蚀性。磷酸盐电解液中所得膜层具有较低的摩擦因数,与膜层中含有的P元素有关。然而,铝酸盐电解液中所得膜层具有更高的耐磨性,是因为铝酸盐膜层中含有更多硬度较高的α-Al2O3。

电解低钛铝制备Al-9%Si合金的晶粒细化

分别以纯铝和电解低钛铝为母材制备Al-9%Si合金,对Al-5%Ti、Al-5%Ti-1%B和Al-4%B中间合金对纯铝制备合金的晶粒细化效果与Al-4%B对电解低钛铝制备合金的晶粒细化效果进行了对比试验研究。结果表明:Al-5%Ti-1%B中间合金的细化效果明显优于Al-5%Ti中间合金,向电解低钛铝制备的Al-9%Si合金中按51∶钛硼质量比添加Al-4%B中间合金,可获得比Al-5%Ti-1%B中间合金更好的细化效果;在硼添加量较低时,细化效果也优于Al-4%B细化纯铝制备合金。对试验结果进行了讨论,对铝硅合金的细化机理进行了分析。

电解Al-Si合金自变质显微组织及力学性能

电解Al-Si合金是一种符合我国矿产资源特点,能耗少、能减轻环境污染的轻质金属。电解Al-Si合金具有自变质的特性,Si相、Fe相及Ti相细小弯曲,共晶合金也具有相当数量的初生Al枝晶。合金组织对冷却速度不敏感,具有遗传性,合金具有良好的韧性和塑性。电解Al-Si合金熔体为均质熔体,凝固时出现大的过冷度是形成变质组织的原因。