Influence of substrate composition on the formation of phytic acid conversion coatings

In this paper, the formation and corrosion resistance of the phytic acid conversion coatings on Mg, Al, and AZ91D magnesium alloy were contrastively investigated using scanning electronic microscopy (SEM), Auger electron spectroscopy (AES), Fourier transform infrared spectroscopy (FTIR), electronic probe microscopic analyzer (EPMA), electronic balance, and electrochemical methods. The influence of phytic acid conversion coating as a middle layer on the properties of the paint on magnesium alloys was also investigated. The results show that the formation process of the conversion coatings is evidently influenced by the compositions of the substrate. The coating on pure aluminum is thinner and compacter than that on pure magnesium and the coating formed on α phase in AZ91D magnesium alloy is thinner but denser than that on β phase. The phytic acid conversion coatings formed on Mg, Al, and AZ91D magnesium alloy can all increase their corrosion resistance. The active functional groups of hydroxyl and phosphate radical are rich in the conversion coatings, which can improve the bonding between the organic paint and magnesium alloy and then improve their corrosion resistance.     

镁合金磷酸盐 /氮化硅双层复合膜结构及耐蚀性能研究

目的针对传统镁合金化学转化膜裂纹尺寸大、耐腐蚀性差等问题,制备一种镁合金磷酸盐/氮化硅双层结构的抗腐蚀复合膜。方法先对镁合金进行传统磷酸盐转化处理,再运用等离子体增强化学气相沉积技术沉积氮化硅膜层,分析复合膜的形貌、元素分布、表面电位及极化曲线,并与磷酸盐转化膜进行对比。结果氮化硅膜层能在磷酸盐转化膜裂纹处选择性优先沉积,从而在相当程度上填补转化膜层的裂纹,形成致密的复合膜结构。具有复合膜结构的镁合金表面电位和腐蚀电位明显高于传统磷酸盐转化处理的镁合金。结论镁合金表面制备磷酸盐/氮化硅双层复合膜后,抗腐蚀能力明显高于传统磷酸盐转化处理的镁合金。     

Electrochemical behaviors of magnesium alloy with phosphate conversion coating in NaCl solutions

A composite conversion coating was prepared on magnesmm alloy by the only one-step immersion treatment.The characteristics of the conversion coating were investigated by scanning electron microscopy(SEM)and X-ray photoelectron spectroscopy(XPS).The results indicate that the composite conversion coating consists of magnesmm hydroxide,magnesmm phosphate and manganese phosphate.The electrochemical behavior of the conversion coating was investigated systematically by electrochemical impedance spectroscopy(EIS) and potentiodynamic polarization measurement in different NaCl solutions.Polarization measurements and EIS results reveal that the magnesium alloy with the conversion coating have better corrosion resistance compared to the bare magnesium alloy in these conditions.And the corrosion rate of the magnesium alloy with conversion coating increases consistently with the chloride ion concentration.In alkaline conditions,the magnesium alloy with conversion coating has superior corrosion resistance by the synergistic effects between Mg(OH)_2 film and conversion coating.Moreover,the electrochemical corrosion mechanism of the magnesium alloy was analyzed with respect to the conversion coating in a Cl~- containing environment.     

外加磁场下AZ31镁合金磷化膜结构及耐蚀性研究

为了获得优良的AZ31镁合金磷化膜,采用外加磁场作用于镁合金的磷化过程.利用SEM,AFM,XRD和电化学工作站等仪器,研究转化膜的表面形貌、结构及耐蚀性.研究结果表明:磁场方向垂直于镁合金样品情况下显著促进AZ31镁合金转化膜的形成,转化膜主要由晶态Zn3(PO4)2·4H2O与A1PO4和非晶态Mn化合物组成,外加...     

Comparison of electrochemical corrosion behaviour of MgO and ZrO2 coatings on AM50 magnesium alloy formed by plasma electrolytic oxidation

Two types of PEO coatings were produced on AM50 magnesium alloy using pulsed DC plasma electrolytic oxidation process in an alkaline phosphate and acidic fluozirconate electrolytes, respectively. The phase composition and microstructure of these PEO coatings were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The corrosion behaviour of the coated samples was evaluated by open circuit potential (OCP) measurements, potentiodynamic polarization tests, and electrochemical impedance spectroscopy (EIS) in neutral 0.1 M NaCl solution. The results showed that PEO coating prepared from alkaline phosphate electrolyte consisted of only MgO and on the other hand the one formed in acidic fluozirconate solution was mainly composed of ZrO₂, MgF₂. Electrochemical corrosion tests indicated that the phase composition of PEO coating has a significant effect on the deterioration process of coated magnesium alloy in this corrosive environment. The PEO coating that was composed of only MgO suffered from localized corrosion in the 50 h exposure studies, whereas the PEO coating with ZrO₂ compounds showed a much superior stability during the corrosion tests and provided an efficient corrosion protection. The results showed that the preparation of PEO coating with higher chemical stability compounds offers an opportunity to produce layers that could provide better corrosion protection to magnesium alloys.     

Corrosion electrochemical behaviors of silane coating coated magnesium alloy in NaCl solution containing cerium nitrate

Sol–gel coatings cannot provide adequate corrosion protection for metal/alloys in the corrosive environments due to their high crack‐forming potential. This paper demonstrates the possibility to employ cerium nitrate as inhibitor to decrease the corrosion development of sol–gel‐based silane coating on the magnesium alloy in NaCl solution. Cerium nitrate was added into the NaCl solution where the silane coating coated magnesium alloy was immersed. Scanning electron microcopy (SEM) was used to examine surface morphology of the silane coating coated magnesium alloy immersed in NaCl solutions doped and undoped with cerium nitrate. The corrosion electrochemical behaviors were investigated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests. The results showed that the introduction of cerium nitrate into NaCl solution could effectively inhibit the corrosion of the silane coating coated magnesium alloy. Moreover, the influence of concentration of cerium nitrate on the corrosion inhibition and the possible inhibiting mechanism were also discussed in detail.     

SiO2 对镁合金阴极电泳涂层耐磨性的影响

目的提高镁合金有机涂层的耐磨性能。方法用KH450硅烷改性Si O2粉体,并充分分散于电泳漆中。用KH460硅烷预处理镁合金表面,并阴极电泳复合涂层。通过铅笔硬度测试、摩擦磨损实验、画圈附着力测试、NMP(N甲基吡咯烷酮)试验和Machu试验,分别评价阴极电泳涂层的硬度、耐磨性能、附着力、抗NMP溶胀性能和耐蚀性,并通过扫描电子显微镜和光学显微镜对磨痕形貌进行分析。结果在镁合金用KH460预处理的前提下,添加Si O2粉体使涂层硬度由4H上升为5H,同时也提高了涂层的耐蚀性,并且涂层的附着力保持为1级,抗NMP溶胀性能仍120 h。在预处理镁合金基体上制得的原漆涂层和添加纳米Si O2的涂层耐磨性较好,磨痕深度与涂层厚度的比值分别为0.47和0.475,摩擦系数均低于0.4;在未预处理镁合金基体上制备的原漆涂层和在预处理镁合金基体上制备的添加微米Si O2的涂层耐磨性较差,磨痕深度与涂层厚度的比值分别为0.665和0.673,摩擦系数均大于0.7。四种涂层磨损破坏的机制主要为疲劳破坏。结论 Si O2粉体的加入可以有效提高涂层的耐蚀性和铅笔硬度,同时不降低涂层的附着力和抗NMP溶胀性能。用硅烷对镁合金进行预处理,向电泳漆中添加硅烷处理的纳米Si O2,可有效提高阴极电泳涂层的耐磨性。     

镁合金水基金属耐蚀涂层的研究

针对镁合金化学性质活泼、不易直接涂装等特点,研究开发了一种主要由微米金属粉、有机硅烷等组成的新型环保水基金属防护涂层.中性盐雾试验、3.5%NaCl溶液浸泡、电化学阻抗和附着力测试等研究结果表明,该涂层具有良好的结合力、耐热性以及对基体的防护性能.用扫描电子显微镜(SEM)等分析手段研究了涂层的片状层叠组织结构,并探讨了涂层的成膜机理与防护作用.     

一步电沉积Ca-P/CTS复合涂层的制备及其耐蚀性

通过一步电沉积法在AZ31镁合金基体表面上沉积钙磷/壳聚糖(Ca-P/CTS)复合涂层,通过共聚焦显微镜(CLSM)、扫描电镜(SEM)和红外光谱分析仪(FT-IR)对Ca-P/CTS复合涂层的形貌、结构以及成分进行分析,采用电化学测试研究了其耐蚀性。结果表明:Ca-P/CTS复合涂层能够有效提高AZ31镁合金基体的耐蚀性,当壳聚糖的质量浓度为0.2g/L时,复合涂层的耐蚀性最好。     

Influence of pH on the deterioration of plasma electrolytic oxidation coated AM50 magnesium alloy in NaCl solutions

The corrosion deterioration process of plasma electrolytic oxidation (PEO) coatings on AM50 magnesium alloy prepared from two different based electrolytes, i.e., an alkaline phosphate electrolyte and an acidic fluozirconate electrolyte, were investigated using electrochemical impedance spectroscopy (EIS) in a 0.1 M NaCl solution with pH of 3, 7 and 11, respectively. It was found that the PEO coating formed in alkaline phosphate electrolyte, which was composed mainly of MgO, suffered from rapid chemical dissolution and lost its protection capability very quickly in acidic NaCl solution (pH 3). The chemical dissolution of this PEO coating was retarded in neutral NaCl solution (pH 7) and the corrosion damage was localized in this environment. On the other hand, in the alkaline NaCl solution (pH 11), the MgO coating underwent only slight degradation. The PEO coating produced in acidic fluozirconate electrolyte, the failure was marked by the flaking-off of the large areas of coating in acidic NaCl solution (pH 3). However, in the neutral and alkaline NaCl solutions, the coating underwent only a slight degradation without any observable corrosion damage in the 50 h test. The results showed that the deterioration process of PEO coated magnesium alloy was governed mostly by the pH of NaCl solution and it was also strongly related to the microstructure and composition of the PEO coatings.     

镁合金化学镀中预处理氟化镁膜的特征与作用

对镁合金的表面前处理工艺进行研究,探讨氟化镁在化学镀层中的存在形式及作用。结果表明：酸浸使镁合金表面形成一层氧化物膜;活化过程生成的氟化镁不具备反应活性,对镁合金基体有保护作用,使之免于受镀液的过度腐蚀;对化学镀层断口进行SEM元素分布分析显示氟化镁层集中存在于镁合金基体与Ni-P镀层之间;但过度活化会导致化学镀层孔隙率升高,以3.5%NaCl溶液为介质的动电位极化测试表明,过度活化会导致化学镀层耐蚀性下降。     

以硫酸镍为主盐的AZ91D镁合金化学镀镍研究

研究了以硫酸镍为主盐的AZ91D镁合金化学镀镍.采用无铬前处理在AZ91D镁合金表面形成高锰酸盐和磷酸盐化学转化膜,用SEM、EDX、XRD和极化曲线等方法研究化学转化膜和化学镀镍层的形貌、组成及在3.5%的NaCl溶液中的耐腐蚀性能.结果表明,在高锰酸盐转化膜表面形成的化学镀镍层呈胞状,较致密,有微裂纹;在磷酸盐转化膜上形成的化学镀镍层也呈胞状,晶胞大小不均匀,没有微裂纹.镀层厚度均匀,致密,无孔隙.在3.5%的NaCl溶液中的极化曲线表明化学转化膜对镁合金基体的耐腐蚀性能提高不大,经高锰酸盐和磷酸盐前处理的化学镀镍层腐蚀电位分别为-0.48V_(SCE)和-1.12 V_(SCE).以硫酸镍为主盐的经磷酸盐前处理的化学镀镍层较好地提高了镁合金的耐腐蚀性能.     

Chemical conversion coating on AZ31B magnesium alloy and its corrosion tendency

The morphology change of the magnesium matrix after pre-treatment and the mor-phology as well as the phase composition of chemical conversion coating formed by phosphate were studied using scanning electron microscope and X-ray diffraction. The corrosion resistance of the coating was studied by salt spray and damp test, and the corrosion tendency during salt immersion test was analyzed. The results show that the phase composition before and after pre-treatment is almost change- less, and the deep microflaw appears between α and β phases during acidic pickling. The phosphate conversion coating is mainly composed of Mg, MgO, and some amor-phous phase, and it can provide a good protection for the AZ31B alloy. Results from corrosive morphology indicate that the growth and the corrosion resistance of the phosphate conversion coating are related to the forming process of the AZ31B matrix.     

水性Al-Zn-Si合金涂层微观组织及腐蚀性能研究

用Al-Zn-Si合金粉末制备热烧结铝锌硅合金涂层,通过盐水浸泡实验和电化学测试研究其耐蚀性能,并结合扫描电镜和X射线衍射分析等手段观察Al-Zn-Si合金涂层显微组织及其在盐水中的腐蚀产物形貌,分析涂层的耐蚀机理。结果表明,Al-Zn-Si合金涂层也具有阴极保护作用,且Al-Zn-Si合金延缓涂层金属粉末的消耗,使牺牲阳极的腐蚀速率减慢。     

海洋工程用结构铝合金无铬化学转化膜耐腐蚀及涂装配套性能

为改善服役于海洋环境下的结构铝合金的耐腐蚀性及其与底漆的配套性能,在两种典型海洋工程用结构铝合金(5083-H116和6061-T6)基体上制备了一种无铬钛/锆基化学转化膜———Alum-nanoceramic coating。采用扫描电子显微镜(SEM)和能谱仪(EDS)对膜层形貌及组成进行了表征,通过动电位极化曲线和电化学阻抗谱研究了膜层的电化学性能,利用中性盐雾试验及胶带剥离试验分别对膜层耐蚀性及其与环氧厚浆底漆的配套性进行了考察。结果表明:5083和6061铝合金Alum-nanoceramic无铬化学转化膜中性盐雾试验白锈面积达到5%所需时间分别为240h和168h;5083铝合金Alum-nanoceramic膜层比后者显示出更好的与环氧厚浆底漆的配套性能。     

模拟海洋环境中Ni-Co合金镀层对AZ91D镁合金的腐蚀防护研究

目的提高AZ91D镁合金的腐蚀防护性能。方法采用化学镀前处理在AZ91D镁合金表面制备一种保护性的Ni-Co合金镀层。分别采用环境扫描电镜(ESEM)、X射线衍射(XRD)和能量散射谱(EDS)分析合金镀层的表面形貌、微结构特点和化学成分。采用动电位极化(PC)和电化学阻抗谱(EIS),分析测试在模拟海洋环境(中性3.5%Na Cl溶液)中Ni-Co合金镀层对AZ91D镁合金的腐蚀防护性能。结果镁合金表面化学镀Ni-P镀层均匀覆盖,晶粒生长较致密,表面呈菜花状形貌,Ni-P镀层中P质量分数约为5.6%。Ni-Co合金镀层表面均匀且呈金字塔状形貌,形成了面心固溶体(FCC),镀层中Co质量分数约为31%。Ni-P镀层和Ni-Co合金镀层的厚度分别约为11μm和19μm。在模拟海洋(中性3.5%Na Cl溶液)环境中,镁合金裸基体、化学镀前处理Ni-P镀层、Ni-Co合金镀层的腐蚀电位分别为-1485、-372、-284 m V,其腐蚀电流密度分别是3.4×10-5、1.8×10-6、2.9×10~(-7) A/cm2,所拟合的电荷转移电阻分别为4.72×103、1.70×104、2.06×106?/cm2。结论化学镀前处理Ni-P镀层可为镁合金提供较好的腐蚀防护,Ni-Co合金镀层能够为镁合金提供更显著的腐蚀防护。     

Plasma-Sprayed Hydroxyapatite Coating for Improved Corrosion Resistance and Bioactivity of Magnesium Alloy

In the present study, the corrosion resistance and bioactivity of AZ91HP magnesium alloy were improved by plasma spraying hydroxyapatite (HA) coating. X-ray diffraction measurements indicated that the coating formed amorphous and little β-Ca₃ (PO₄)₂ besides of HA. The corrosion resistance and bioactivity of the coating and magnesium alloy in simulated body fluid were investigated using immersion test. The coating showed lower corrosion rate and better bioactivity than magnesium alloy. The coating significantly improved the hydrophilicity of Mg alloy. The prothrombin time of the coating was 18 s, and the prothrombin time of Mg alloy was 11 s, so the coating had better anticoagulant activity.     

pH值对AZ91D镁合金表面植酸转化膜的影响

在pH值不同的几种植酸转化液中对AZ91D镁合金进行表面转化处理,利用扫描电镜及自带能谱仪、Tafel曲线和阻抗谱等分析手段,结合NaCl水溶液点滴实验,研究了pH值对植酸转化膜表面成分及耐蚀性的影响.结果表明:在酸性条件下形成的植酸转化膜的耐蚀性较好;转化液的pH值会影响植酸螯合物的形成和转化膜的物质组成,进而影响转化膜的耐蚀性能;在酸性条件下,镁合金表面形成的植酸转化膜应属于电子导体膜,它阻碍了腐蚀介质与基体的接触,同时抑制腐蚀产物的扩散,对镁合金起到防护作用.     

AZ91D 镁合金表面 Ni-P / Ni-Sn-P 双镀层的制备与性能研究

目的提高AZ91D镁合金的耐腐蚀性能,扩大其应用范围。方法先在AZ91D镁合金表面化学镀Ni-P镀层,再化学镀Ni-Sn-P镀层,形成Ni-P/Ni-Sn-P双镀层。研究Ni-P/Ni-Sn-P双镀层的表面形貌和耐腐蚀性能,并与Ni-P单镀层进行对比。结果 Ni-P/Ni-Sn-P双镀层表面分布更均匀平整,缺陷较少,孔隙率较低,具有无定形结构。二次Ni-Sn-P镀层的腐蚀电位约为-0.77 V,略低于一次化学镀Ni-P层(约-0.68 V),两镀层间的电位差使得其构成了微腐蚀电偶,Ni-P层作为阴极,Ni-Sn-P层作为阳极,阳极优先被腐蚀。结论 Ni-P/Ni-Sn-P双镀层的Ni-Sn-P外层能为Ni-P内层提供阴极保护,较好地横向分散腐蚀电流,从而增强AZ91D镁合金基底的耐腐蚀性能。     

Enhanced corrosion performance of magnesium phosphate conversion coating on AZ31 magnesium alloy

Magnesium phosphate conversion coating (MPCC) was fabricated on AZ31 magnesium alloy for corrosion protection by immersion treatment in a simple MPCC solution containing Mg²⁺ and PO^3?₄ ions. The MPCC on AZ31 Mg alloy showed micro-cracks structure and a uniform thickness with the thickness of about 2.5 µm after 20 min of phosphating treatment. The composition analyzed by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy revealed that the coating consisted of magnesium phosphate and magnesium hydroxide/oxide compounds. The MPCC showed a significant protective effect on AZ31 Mg alloy. The corrosion current of MPCC was reduced to about 3% of that of the uncoated surface and the time for the deterioration process during immersion in 0.5 mol/L NaCl solution improved from about 10 min to about 24 h.