Na2WO4含量对镁合金微弧氧化膜层颜色和耐蚀性的影响

目的 研究电解液中的Na2WO4含量对AZ31B镁合金微弧氧化膜层的形成过程、颜色、微观结构、耐蚀性能的影响。方法 通过添加不同含量的NH4VO3和Na2WO4的碱性铝酸盐电解液体系,在AZ31B镁合金表面制备黑色的微弧氧化膜层。采用SEM、EDS分析加入不同含量的Na2WO4后膜层表面的微观形貌及元素组成,采用XRD分析物相组成,通过电化学实验表征膜层的耐腐蚀性能。结果 随着Na2WO4含量的增加,微弧氧化过程中的起弧电压下降,膜层的致密性提高,厚度呈先增加后减小的趋势。当Na2WO4的质量浓度为0.5 g/L时,膜层的厚度最大,且此时膜层表面微孔分布均匀,色度最低,耐蚀性最好,自腐蚀电位为−0.138 V,自腐蚀电流密度为2.36×10⁻⁷ A/cm²,相较于基体降低了3个数量级。结论 增加Na2WO4含量会使微弧氧化成膜过程中的电弧发生变化,适当增加Na2WO4会提高膜层的厚度,降低膜层的CIE色度,使陶瓷膜层表面的微孔分布得更加均匀致密,从而提高膜层的耐蚀性能。当Na2WO4含量过高时,会使膜层的离子浓度升高,电阻增大,介电击穿电压上升,导致膜层表面被烧蚀,耐腐蚀性能降低。     

铜锌合金表面CeO2颗粒掺杂微弧氧化复合膜层的制备及性能分析

目的 提高铜锌合金的耐蚀性,对黄铜表面进行颗粒掺杂微弧氧化(MAO),研究纳米颗粒CeO2对复合膜层性能的影响。方法 以Na2SiO3.9H2O、NaOH的混合溶液作为电解液,对铜锌合金进行微弧氧化,以膜层厚度和自腐蚀电流密度为评价指标,对氧化时间、正向电压、反向电压、占空比进行正交试验和极差分析,得到最佳微弧氧化电参数。将CeO2添加到混合电解液中,以制备颗粒掺杂微弧氧化复合膜层。通过SEM、EDS、XRD、动电位极化曲线和电化学交流阻抗测试等手段,研究CeO2纳米颗粒对膜层表面、横截面的微观形貌和成分组成及膜层表面的物相结构和耐蚀性能的影响。结果 以自腐蚀电流密度为主要评价指标,兼顾膜层厚度,通过正交试验和极差分析,得到了铜锌合金微弧氧化最佳电参数组合,氧化时间为80 min,占空比为20%,正向电压为550 V,反向电压为5 V。未添加CeO2的黄铜试件,微弧氧化膜层表面存在粗糙多孔的结构;掺杂纳米颗粒CeO2后,复合膜层表面变得更为平整,表面粗糙度Ra值从3.883 μm降至3.331 μm,孔隙率也由颗粒掺杂前的35.11%降至32.98%。随着CeO2颗粒的掺杂,膜层表面的C、O、Si、Ce元素增加,Cu、Zn元素下降,膜层表面的物相主要由CuO、ZnO、CeO2和SiO2组成。纳米颗粒CeO2掺杂前后,膜层均与黄铜基体结合紧密,无明显裂缝。沿着膜层表面向基体方向,Cu和Zn元素含量短暂上升后保持平稳,而O和Si元素含量变化情况为先增加、后减小至消失。颗粒掺杂前,MAO膜层的自腐蚀电流密度Jcorr为8.095×10^–4 A/cm²,掺杂纳米颗粒CeO2后,Jcorr为7.402×10^–5 A/cm²。两者与黄铜基体的Jcorr(1.236×10^–2 A/cm²)相比,分别下降了2、3个数量级。结论 对铜锌合金进行微弧氧化可以在合金表面制得多孔且有良好耐蚀性的陶瓷膜层。纳米颗粒CeO2的掺杂,能够有效改善铜锌合金微弧氧化膜层的多孔结构,降低孔隙率,阻碍外界腐蚀离子的侵入,增强膜层的耐腐蚀性能。     

30CrMnSiA钢表面镉镀层化学转化膜的电化学特性

目的 通过研究镉镀层绿色化学转化膜的电化学性能,获得镉镀层最佳绿色化学钝化工艺。方法 采用无氰镀镉工艺,在30CrMnSiA钢表面电镀镉。采用植酸和钼酸钠在镉镀层表面进行绿色钝化处理,构建复合化学转化膜。通过研究钼酸钠浓度、处理时间和植酸浓度对绿色钝化处理镀镉层在质量分数为3.5%的NaCl溶液中电化学性能的影响,获得最佳的镀镉层绿色钝化工艺。结果 在处理时间为10 min、植酸的质量分数为1.0%的条件下,当钼酸钠的质量分数增至3%时,开路电压先从−0.741 9 V增至−0.739 7 V后,再降至−0.761 1 V,电荷转移电阻Rct从2.34 kΩ.cm²增至8.79 kΩ.cm²,腐蚀抑制率从72.9%增至92.8%,自腐蚀电流密度Jcorr从81.47 μA/cm²降至最低值(6.887 2 μA/cm²)。当钼酸钠和植酸的质量分数分别为2.0%和1.0%时,随着处理时间的延长,开路电压从−0.755 9 V增至−0.729 5 V,Rct先增至6.68 kΩ.cm²,然后降至5.28 kΩ.cm²,自腐蚀电流密度从16.26 μA/cm²降至4.527 μA/cm²。当钼酸钠的质量分数为2.0%、处理时间为10 min时,随着植酸浓度的增加,试样的开路电压从−0.739 3 V降至−0.756 1 V,Rct先增至6.68 kΩ.cm²,然后降低,自腐蚀电流密度Jcorr呈现先降至最小值后再增大的趋势。结论 与镉镀层相比,经化学转化膜处理后试样表现为高的开路电压、大的电荷转移电阻和低的自腐蚀电流。得到了耐蚀性好且成本较低的镉镀层表面绿色钝化工艺,钼酸钠和植酸的质量分数分别为2.0%和1.0%,处理时间为10 min。     

含氟聚氨酯防护涂层体系在模拟海洋环境下的防护性能

目的 考核评价Q345低合金钢表面“热喷锌铝基底”和“磷化膜基底”的含氟聚氨酯防护涂层体系在模拟海洋环境下的防护性能。方法 分别制备2类含氟聚氨酯防护涂层体系划痕和非划痕试样,采用实验室多因素组合循环试验方式对涂层试样进行模拟加速试验,分析涂层的外观、光泽、色差的变化情况;对比分析划痕部位涂层的耐腐蚀扩展性能,并采用金相法分析热喷锌铝层试验前后的截面变化;分别采用傅里叶变换红外光谱和电化学阻抗谱表征涂层的老化特征和电化学性能。结果 2类含氟聚氨酯防护涂层体系试验后的变色等级为1级,失光等级为2级,保护性漆膜综合老化性能等级为0级。磷化膜基底层试样划痕部位的含氟聚氨酯防护涂层出现了鼓泡、锈蚀等现象,单边腐蚀宽度为9.18 mm;热喷锌铝基底层试样划痕部位的含氟聚氨酯防护涂层未出现鼓泡现象,单边腐蚀宽度仅为2.58 mm。含氟聚氨酯防护涂层红外光谱特征峰的形状、位置、强度均未发生明显变化;磷化膜基底层试样涂层体系0.01 Hz阻抗模值(|Z|0.01 Hz)为2.3×10⁹ Ω.m²,热喷锌铝基底层试样涂层体系0.01 Hz阻抗模值(|Z|0.01 Hz)为4.6×10⁹ Ω.cm²。结论 含氟聚氨酯防护涂层具有较好的抗光老化和耐蚀性能。热喷锌铝基底层相较于磷化膜基底层,不仅可以提高涂层体系的持久耐蚀性能,而且能够有效缓解涂层破损后发生的腐蚀扩展现象。     

微弧氧化膜层的组分质量比率、结构与性能

为了同时提高AZ61的MgF₂+MgO微弧氧化膜层的电化学腐蚀与磨损性能,本文运用复合电介质顺序放电学术思想,通过减弱击穿熔体的喷发,使膜层进一步致密,进而使其性能得到提高。膜层的MgF₂-MgO质量比率α、微观组织、电化学腐蚀与磨损性能的研究结果表明：α=1.2时,减弱击穿熔体喷发的效果显著好于α=0.1和11.8,膜层的内部致密层厚度可提高到3.6 μm,是现有微弧氧化膜层的3倍,外部疏松层的阻抗可提高到13555 Ω cm^₂,比α=0.1和11.8的大30%。该膜层可将AZ61的自腐蚀电压Ecorr由-1.912提高到-0.455 V_SCE、自腐蚀电流Icorr由378.6减小到0.453(10^_-6 A/cm^₂)、磨损率由921降低到0.5(10^_-5 mm^₃/N.m)。本研究为制备高性能微弧氧化膜层提供了一种新模式。     

钐盐含量对AZ31B镁合金表面铁氰化物转化膜耐蚀性的影响

目的 改善AZ31B镁合金表面单一铁氰化钾转化膜附着力以及提高单一膜层的耐腐蚀性能。方法 选用钐盐对镁合金单一膜层进行处理,着重探讨不同钐盐含量对膜层的影响。利用两步法进行化学浸渍成膜,并且利用扫描电镜(SEM)、X射线衍射仪(XRD)、能谱仪(EDS)和X射线光电子能谱(XPS)对复合膜层表面形貌和组成成分进行表征。采用动电位极化曲线和电化学交流阻抗对复合膜层在3.5%NaCl溶液中的腐蚀行为进行探究。结果 经过钐盐处理的镁合金铁氰化钾转化膜表面生成了新的膜层,该复合膜层主要成分为SmFe(CN)6和Sm(OH)3。其不仅具有比单一膜层更优异的耐蚀性能以及膜层与基体的结合力也有所提高,而且形成的复合膜层也较稳定,可以对基体起到更好的保护作用。另外,钐盐含量为5 g/L时处理的膜层最为致密平整,自腐蚀电流密度最低,为2.129×10^?9 A/cm²,电荷转移电阻和膜层电阻最大,分别为8.164×10⁴ Ω.cm²和1.293×10⁷ Ω.cm²,耐蚀性能最好。结论 使用钐盐对镁合金表面铁氰化钾膜层进行改性,可以进一步提高单一膜层的耐蚀性,并且最佳钐盐含量为5 g/L。     

基于磁过滤技术制备亚微米级TiAlN/TiAlCN/TiAlC复合涂层的耐腐蚀性能

海洋环境中长期服役的船舶、舰载机关键部件存在严重的腐蚀问题。为提高其耐腐蚀性能,采用磁过滤真空弧（FCVA）技术制备不同Al/Ti含量比的亚微米级Ti （Al） N/Ti （Al） CN/Ti （Al） C多元复合多层膜（以下简称TANC）。通过扫描电子显微镜、X射线衍射仪、电化学工作站和盐雾试验机等表征薄膜的形貌、结构和腐蚀性能。结果表明：在盐雾试验中腐蚀形态主要以点蚀为主,随着膜层中Al/Ti含量比的增大,耐腐蚀性提高;电化学腐蚀试验中,亚微米级膜层的自腐蚀电流密度可达到10^-7 A/cm²数量级,且随着膜层Al/Ti含量比的增大,腐蚀电流密度从7.73×10^-7减小到3.83×10^-7 A/cm²,低频区阻抗值从1.19×10⁵增大到4.70×10⁵ Ω·cm²,较基底提高了2个数量级,耐腐蚀性能不断提高;盐雾腐蚀和电化学腐蚀结果一致,高Al含量的TANC耐腐蚀性能最优。通过FCVA技术能实现亚微米级TANC涂层的强防腐效果,该涂层具有发展成为关键部件耐海洋腐蚀涂层的潜力。     

植酸修饰改性对TC4钛合金微弧氧化膜层性能的影响

通过向电解液中添加有机酸植酸,提升了TC4钛合金微弧氧化涂层的耐腐蚀性能和热稳定性。通过扫描电子显微镜、X射线衍射仪、X射线光电子能谱仪和热冲击实验等技术手段,分析了植酸对涂层形成、形貌和性能的影响。结果显示,植酸的添加使放电微孔更加细小,提高了涂层的形成效率并优化了相结构。通过动电位极化测试,发现添加植酸显著提高了微弧氧化涂层的耐腐蚀性能。将电解液中的植酸浓度调整为12 mL/L（最佳植酸浓度）后,腐蚀电流密度由8.406×10^-5 A·cm^-2降低至2.580×10^-6 A·cm^-2。循环高温氧化试验结果表明,TC4钛合金的耐热冲击性能和高温抗氧化性能得到了改善。     

超高频脉冲电流作用下纳米Al2O3颗粒对Mg-Gd-Y-Zr合金微弧氧化涂层的影响

目的 进一步提高Mg-Gd-Y-Zr合金微弧氧化涂层的耐腐蚀性能。方法 采用超高频微弧氧化技术在含有Al2O3纳米颗粒的溶液中制备了微弧氧化涂层。利用扫描电子显微镜(FESEM)、能谱仪(EDS)和X射线衍射仪(XRD)对微弧氧化涂层的表面形貌、截面形貌、成分和晶体结构进行分析。利用极化曲线和电化学阻抗谱(EIS)测试了涂层的耐腐蚀性能。结果 频率由0.5 kHz提升至20 kHz后,涂层表面放电孔洞面积由0.07~24.4 μm²降低至0.08~6.3 μm²,涂层的孔隙率由6.47%减小至3.35%。Al2O3纳米颗粒的添加使超高频涂层表面形成大量自封闭孔洞结构,进而进一步降低了涂层表面的孔径面积(0.1~ 4.63 μm²)和孔隙率(0.97%)。极化试验表明,提高频率至20 kHz,涂层的自腐蚀电流密度由4.7×10^‒6 A/cm²降低至4.7×10^‒7 A/cm² ,添加 Al2O3纳米颗粒,涂层的自腐蚀电流密度进一步降低至1.7×10^‒7 A/cm²,表明其耐蚀性能显著提高。阻抗谱显示,20 kHz-Al涂层具有最大的阻抗,说明该工艺可有效提高微弧氧化涂层的耐蚀性能。 结论 超高频可有效降低放电孔洞尺寸,提高微弧氧化涂层的致密性,改善涂层的耐腐蚀性能。超高频与Al2O3纳米粒子的协同作用使涂层表面形成自封闭孔洞结构,进一步提高微弧氧化涂层的致密性和耐腐蚀性能。     

电流密度对ZK60镁合金表面超疏水涂层的制备及耐腐蚀性的影响

为了提高镁合金的耐腐蚀性能,基于层状双氢氧化物（LDHs）膜在ZK60镁合金表面制备了超疏水（SH）涂层。涂层制备过程中引入电场辅助,研究了工作电流密度对涂层性能的影响。结果表明,工作电流密度显著影响LDHs膜的微观结构,这对SH涂层的疏水性具有重要影响。当工作电流密度为25 mA/cm²时,SH涂层表面呈现均匀的微纳米结构,并表现出超疏水性。超疏水涂层的腐蚀电流密度（I_corr=9×10^-7 A·cm^-2）比ZK60基体的腐蚀电流密度（I_corr=3×10^-5 A·cm^-2）低了2个数量级,表现出优异的耐腐蚀性。     

AZ31镁合金表面含纳米SiC氟化镁膜层的制备及耐腐蚀性能

为了提高 MgF2 膜层的耐腐蚀性能,利用微弧氧化工艺,通过在 NH4F-EG 电解液中添加纳米 SiC 颗粒,在 AZ31 镁合金表面制备含 SiC 的 MgF2 -SiC 膜层,并探究纳米 SiC 颗粒的浓度对 MgF2 膜层组成、结构和耐腐蚀性能的影响。 采用 SEM、EDS、XRD、XPS 等测试方法对含 SiC 的 MgF2 膜层的微观组织、元素含量和物相组成进行分析,利用电化学工作站对膜层的耐腐蚀性能进行测试。 结果表明:电解液中的纳米 SiC 颗粒成功进入 MgF2 膜层中。 随着电解液中纳米 SiC 浓度的增加,膜层中的 Si、C 元素含量增加,Mg、F 元素含量减少,膜层变得致密平整,孔隙率减少,膜层缺陷得到有效改善,膜层厚度减小;MgF2 膜层的耐腐蚀性能先增大后减小,当电解液中纳米 SiC 的浓度为 5 g / L 时,膜层的耐腐蚀性能最优。 因此,在 NH4F-EG 电解液中添加纳米 SiC 颗粒,可以在 AZ31 镁合金表面制备出含 SiC 的 MgF2 -SiC 膜层, 且耐腐蚀性能优于不含 SiC 的 MgF2 膜层。     

Microstructure and corrosion behavior of plasma electrolytic oxidation coated magnesium alloy pre-treated by laser surface melting

An AZ91D magnesium alloy was treated using duplex techniques of laser surface melting (LSM) and plasma electrolytic oxidation (PEO). The microstructure, composition and corrosion behavior of the laser melted surface, PEO coatings, LSM–PEO duplex coatings as well as the as-received specimen were characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) and electrochemical corrosion tests, respectively. Especially, the effect of LSM pre-treatment on the microstructure, composition and corrosion resistance of the PEO coatings was investigated. Results showed that the corrosion resistance of AZ91D alloy was marginally improved by LSM due to the refinement of grains, redistribution of β-phase (Mg₁₇Al₁₂) and increase of Al on the surface. Both the PEO and duplex (LSM–PEO) coatings improved significantly the corrosion resistance of the AZ91D alloys, while the duplex (LSM–PEO) coating exhibited better corrosion resistance compared with the PEO coating.     

Corrosion and wear resistance of AZ31 Mg alloy treated by duplex process of magnetron sputtering and plasma electrolytic oxidation

In order to improve the wear and corrosion resistance of AZ31 magnesium alloy, a magnetron-sputtered Al layer with a thickness of 11 μm was firstly applied on the alloy, and then treated by plasma electrolytic oxidation (PEO) in an aluminate and silicate electrolytes, respectively. The performance of PEO coatings was investigated by dry sliding wear and electrochemical corrosion tests. The aluminate coating exhibits excellent wear resistance under both 10 and 20 N loads. The silicate coating only shows low wear rate under 10 N, but it was destroyed under 20 N. Corrosion tests show that the Al layer after magnetron sputtering treatment alone cannot afford good protection to the Mg substrate. However, the duplex layer of PEO/Al can significantly improve the corrosion resistance of AZ31 alloy. Electrochemical tests show that the aluminate and silicate coatings have corrosion current densities of ∼1.6×10⁻⁶ and ∼1.1×10⁻⁶ A/cm², respectively, which are two orders lower than that of the un-coated AZ31 alloy. However, immersion tests and electrochemical impedance spectroscopy (EIS) show that the aluminate coating exhibits better long-term corrosion protection than silicate coating.     

AZ31镁合金表面化学镀镍工艺研究

    研究了在AZ31镁合金表面直接化学镀镍工艺,得到了镀液的最佳配方,镀液的成分为25 g/L NiSO₄•6H₂O、25 g/L次亚磷酸钠、15 g/L柠檬酸、10 g/L NH4F、1 mg/L硫脲.在温度为85℃、pH=9.0、反应时间1小时条件下可以在AZ31镁合金表面得到性能良好的Ni P合金化学镀层,镀层厚度超过10 μm.用SEM、XRD和EDS研究了镀层的形貌和物相组成;在3.5%NaCl水溶液中通过测定Tafel极化曲线研究了镀层的耐腐蚀性能.结果表明,Ni-P镀层比基体AZ31镁合金的耐腐蚀性能有极大的提高.     

Environmentally assisted cracking behaviour of plasma electrolytic oxidation coated AZ31 magnesium alloy

Abstract

A wrought AZ31 magnesium alloy was plasma electrolytic oxidation (PEO) coated in phosphate and silicate based alkaline electrolytes. The effect of these PEO coatings on the stress corrosion cracking (SCC) behaviour of the alloy was investigated by slow strain rate tensile (SSRT) tests in ASTM D1384 solution. The untreated and PEO coated AZ31 magnesium alloy specimens were found to be susceptible to SCC, despite the fact that the PEO coatings offered an excellent general corrosion resistance. The results of the polarisation tests on the untreated AZ31 alloy specimen after prolonged immersion in ASTM D1384 electrolyte suggested the formation of a film on the surface constituted by the corrosion products. The cracking of this film and the evolution/ingress of hydrogen at these defective sites during the SSRT tests in the corrosive environment was believed to be responsible for the SCC of the untreated alloy. Similarly, the cracking of the PEO coatings during the SSRT test, the consequent exposure of the underneath magnesium alloy substrate and the associated electrochemical reactions were attributed as reasons for the SCC of the PEO coated specimens. The transgranular mode of fracture in all the cases avowed that the hydrogen induced cracking was the mechanism of SCC.     

Tribological and Electrochemical Corrosion Properties of CNT-Incorporated Plasma Electrolytic Oxidation (PEO) Coatings on AZ80 Magnesium Alloy

Plasma electrolytic oxidation (PEO) coatings were carried out in silicate-based electrolyte embedded with various amounts of carbon nanotube (CNT) additives (0, 0.5, 1, 2 and 4 g/L) on AZ80 magnesium alloy substrate. Microstructure, tribological and electrochemical corrosion properties of the coated specimens were investigated. The results demonstrated that the increasing CNT additions into the electrolyte resulted in a gradual increase in the thickness of PEO-coating layer. The CNT addition to the electrolyte by 0.5 g/L resulted in a slight decrease in the roughness of PEO-coating above which it continually increased. Wear resistance of the PEO-coated specimens showed a gradual improvement with increasing CNT-incorporation within the coating. The electrochemical corrosion tests revealed that the best corrosion resistance was found after the CNT addition into the electrolyte by 0.5 g/L due to the better roughness values, more homogenous coating layers and less pore formation.     

The effect of substrate composition on the electrochemical and mechanical properties of PEO coatings on Mg alloys

Plasma electrolytic oxidation (PEO) is a unique surface treatment technology which is based on anodic oxidation forming ceramic oxide coatings on the surface of light alloys such as Mg, Al and Ti. In the present study, PEO coatings prepared on AZ91D, AZ31B, AM60B and AM50B Mg alloys have been investigated. Surface morphology and elemental composition of coatings were determined using scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS). SEM results showed that the coating exhibited a porous top surface layer and a subsequent dense layer with micro-pores and shrinkage cracks. Phase analysis of coatings was carried out by X-ray diffraction (XRD). XRD analyses indicated that PEO coatings on AZ alloys had higher amount of Periclase (MgO) followed by the presence of Spinel (MgAl₂O₄) e.g. on the AZ91D alloy compared to that on AM series alloys. In order to examine the effect of substrate composition on adhesion strength of PEO coating scratch tests were carried out. Electrochemical corrosion tests were undertaken by means of potentiodynamic polarization technique in 3.5% NaCl solution at room temperature (20 ± 2 °C). Corrosion test results indicated that the corrosion rates of coated Mg alloys decreased by nearly two orders of magnitude as compared to bare Mg alloys. PEO coatings on AZ series alloys showed better corrosion resistance and higher adhesion properties than AM series alloys. In addition to the PEO processing parameters, such are mainly attributes of the compositional variations of the substrate alloys which are responsible for the formation, phase contents and structural properties of the PEO coatings.     

Investigation of wear and corrosion resistance of nanocomposite coating formed on AZ31B Mg alloy by plasma electrolytic oxidation

Ceramic-WC coatings were prepared on AZ31 B Mg alloy by plasma electrolytic oxidation (PEO) from a phosphate based bath containing suspended tungsten carbide nanoparticles at various process times. Scanning electron microscope results indicated that increase of coating time and incorporation of tungsten carbide into the ceramic coating during the PEO process led to a decrease in the number and diameter of coating pores. Phase analysis showed that the nanocomposite coating was composed of MgO, Mg₃(PO₄)₂ and WC. Tribological properties and corrosion behaviour of uncoated AZ31 B Mg alloy and ceramic coatings were evaluated using a pin-on-disc tribometer and potentiodynamic polarisation technique in 3.5% NaCl solution, respectively. The wear and electrochemical tests showed that wear and corrosion resistance of ceramic-WC nanocomposite coatings were better than ceramic only ones. In addition, wear and corrosion behaviour of coatings improved with increasing the coating time.     

镁合金等离子喷涂Al/Al_2O_3涂层的耐腐蚀性能

采用等离子喷涂技术在AZ31镁合金表面制备Al/Al_2O_3复合涂层,测试了镁合金及表面喷涂有Al/Al_2O_3复合涂层的镁合金试样的极化曲线,研究了没有涂层、经封孔处理和未经封孔处理的喷涂有复合涂层的镁合金三种试样在浸泡腐蚀和5%NaCl盐雾腐蚀情况下的耐腐蚀性能及其腐蚀行为.结果表明,经封孔处理的Al/Al_2O_3复合涂层镁合金试样在上述腐蚀条件下的耐腐蚀性均优于镁合金和涂层未封孔处理的试样,在浸泡试验中未封孔处理的涂层试样比镁合金腐蚀更加严重,在盐雾试验中却优于镁合金.     

镁合金化学镀Ni-Cu-P/Ni-P复合镀层及腐蚀防护机理研究

目的为提高镁合金化学镀Ni-P合金镀层的腐蚀防护性能。方法在AZ31B镁合金表面,先化学镀Ni-Cu-P,再化学镀Ni-P,制备Ni-Cu-P/Ni-P复合镀层。研究复合镀层的表面形貌、成分、厚度和腐蚀电流密度随镀液硫酸铜浓度的变化规律,表征1.0 g/L硫酸铜质量浓度下,复合镀层的截面形貌、成分和晶态结构。结合动电位极化曲线和盐雾试验,分析复合镀层的耐蚀性能和腐蚀防护机理。结果复合镀层中的铜含量随硫酸铜浓度的增加而升高,铜对复合镀层的结构和性能影响很大。通过抑制镀层表面胞状物的生长和增加形核点数量,铜的共沉积能够大幅提高复合镀层的致密性。随硫酸铜浓度的增加,样品表面的催化活性下降,镀液稳定性升高,由此导致复合镀层的厚度随硫酸铜浓度的增加而明显下降。硫酸铜质量浓度为1.0 g/L时,复合镀层均匀致密,并具有可钝化性,按照ISO 9227,其耐盐雾腐蚀时间超过180 h。结论化学镀Ni-Cu-P/Ni-P复合镀层能够赋予镁合金表面优异的耐蚀性能,复合镀层所具有的可钝化性和均匀致密的镀层结构,是镀层腐蚀防护性能提升的主要原因。