GW93镁合金表面锡酸盐化学转化膜工艺研究

以锡酸钠为转化液主要成分对Mg-8.8Gd-3.1Y-0.6Zn-0.5Zr(GW93)镁合金进行无铬化学转化表面处理,通过全浸法评价转化膜在pH为中性的3.5%NaCl(质量分数)溶液中的腐蚀性能,利用光学显微镜、X射线衍射仪和扫描电子显微镜分析转化膜的微观形貌和相组成。结果表明,适用于GW93镁合金的锡酸盐转化膜的最佳工艺条件为:锡酸钠50 g/L,焦磷酸钠50 g/L,乙酸钠15 g/L,氢氧化钠5 g/L,柠檬酸3 g/L,碳酸钠20 g/L,转化温度80℃,转化时间15 min。转化膜主要组成为MgSnO3·3H2O。该工艺下形成的膜层为细小的、近球状颗粒堆积而成,表面均匀平整。腐蚀性能评价结果表明,未经锡酸盐化学转化的镁合金的平均腐蚀速率为6.1083 g·a-1·cm-2,经最佳化学转化成膜工艺处理后,该镁合金的平均腐蚀速率为0.1264 g·a-1·cm-2。抗腐蚀性能被提高了97.9%,说明该锡酸盐化学转化膜层可以有效地提高镁合金的耐腐蚀性能。     

AZ31镁合金表面锡酸盐化学转化膜的研究

对AZ31镁合金表面采取锡酸盐化学转化处理,采用对比试验测定了转化膜在质量分数3.5%NaCl溶液中的腐蚀率,利用扫描电镜(SEM)及能谱(EDS)观察分析了转化膜的形貌和元素含量.结果表明:经锡酸盐转化后的AZ31镁合金的腐蚀率为2.65mm/a,未经转化的AZ31镁合金的腐蚀率为30.36mm/a,耐蚀性有明显提高;锡酸盐转化液pH值在3.5～12范围时对AZ31镁合金均形成了转化膜保护层.     

镁合金锡酸盐化学转化膜生长过程研究

采用环保型锡酸盐化学转化工艺,并利用扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射(XRD)和全浸腐蚀试验等手段,研究了AZ91D镁合金锡酸盐化学转化膜不同生长阶段的形貌特征及其耐蚀性.结果表明,整个过程可分为3个阶段,成膜初期,膜重迅速增加,在α相上生成MgSnO3;约10 min后膜的生长速度减小,锡酸盐开始在β相上沉积.此后,膜溶解速度加快,由于α相上的锡酸盐颗粒间隙远大于β相上的颗粒间隙,金属的溶解主要发生在α相上.同时新的膜不断生成,达到动态平衡.此后,随时间延长,膜溶解速度大于成膜速度,膜重减小.经化学处理30 min左右,锡酸盐膜层的耐蚀性最好.     

镁合金表面化学转化膜的研究进展

综述镁合金化学转化膜:铬酸盐转化膜、磷酸盐转化膜、磷酸盐-高锰酸盐转化膜、锡酸盐转化膜、稀土转化膜、植酸转化膜等处理方法的工艺特点.讨论磷酸盐转化膜的成膜原理及工艺,分析这些化学转化工艺存在的不足,并展望镁合金化学转化膜的研究前景.     

ZK60镁合金磷酸盐及锡酸盐化学转化膜

为了提高ZK60镁合金的耐腐蚀性能,利用磷酸盐溶液或锡酸盐溶液,考察了在ZK60镁合金上形成磷酸盐或锡酸盐化学转换膜的工艺条件及膜层的耐蚀性能。通过改变处理时间和温度,可以得到性能不同的转换膜。通过电化学阻抗谱技术和极化曲线技术研究转化膜的耐腐蚀性能,利用扫描电镜研究其微观结构。结果表明:在磷酸盐溶液中,当处理温度为50℃时,磷化30min后试样的电荷转移电阻(Rct)为224.03Ω·cm2;当温度为80℃,反应时间为45min时,所得转换膜的Rct为377.67Ω·cm2,阻值最大,耐腐蚀性能最好;对于锡酸盐化学转化膜,90℃下,处理60min的膜层耐蚀性能最好,其Rct为388.32Ω·cm2,与磷酸盐化学转化膜相比,两种膜的保护性能相差不大。     

镁合金锡酸盐化学转化表面处理工艺研究

研究了AZ91D镁合金的锡酸盐化学转化表面处理工艺,利用中性盐雾试验和极化曲线法测试了转化膜的耐蚀性,使用划格法测试了转化膜对有机涂层的附着力,采用扫描电镜、能谱仪、射线衍射仪分析了转化膜的微观形貌、成分和结构并讨论了成膜机理.结果表明,最佳工艺条件下的锡酸盐转化膜为致密的MgSnO3·3H2O晶粒所构成,盐雾腐蚀评级达到了8级,自腐蚀电位降低了40 mV,对铁红漆的附着力达到了3B级.     

锡酸盐转化前处理对镁合金化学镀镍镀层的影响

目的利用锡酸盐转化膜中间层避免化学镀镍镀层与金属基体的直接接触,降低其产生原电池腐蚀的趋势,提高镁合金化学镀镍层的耐蚀性及稳定性。方法采用锡酸盐化学转化膜技术在AZ31镁合金表面制备锡酸盐转化膜层,然后通过直接化学镀镍技术在该膜层上沉积Ni-P镀层。利用SEM、EDS、浸泡析氢、电化学测试等手段,研究了复合镀层的显微结构、相组成、耐蚀性。结果锡酸盐转化膜由细小均匀的球形颗粒堆积而成,颗粒之间存在空隙,为直接化学镀镍时镍磷的初始沉积提供了可能。化学转化膜表面沉积的化学镀镍层均匀致密,形成典型的胞状结构。基体-化学转化膜-化学镀Ni-P合金层三者之间的结合良好,保证了复合镀层优良的耐蚀性能。结论化学镀Ni-P层能够在不经过钯活化处理的条件下直接在锡酸盐转化膜上沉积,锡酸盐转化膜中间层避免了Ni-P阴极性镀层与阳极性镁基体的直接接触,降低了Ni-P镀层局部缺陷对整体防护效果的影响,提高了镀层的耐蚀性及耐久性。     

镁合金环保型化学转化膜工艺研究

采用环保型化学转化工艺,利用扫描电镜、X射线衍射和全浸蚀等分析试验手段,研究了AZ91D镁合金锡酸盐化学转化膜的形貌、相结构及耐腐蚀性.结果表明,转化膜主要由镁的α相、β相和MgSnO2·3H2O组成;该环保型化学转化工艺可获得由近球状微粒构成的银白色膜层,表面均匀平整.该膜层的耐蚀性能优于传统含铬DOW7工艺形成的防护膜,且所用成膜液无铬,符合环保要求.     

AZ31镁合金钼酸盐转化膜

利用钼酸盐溶液在AZ31镁合金表面获得棕黄色的转化膜。用扫描电镜（SEM）和X射线光电子能谱（XPS）对膜层的形貌和组分进行研究,采用动电位极化曲线测试对膜层的耐蚀性进行研究。结果表明：膜的微观形态由球形颗粒构成,膜层厚度约12 μm,对镁合金的覆盖作用良好;转化膜表层中Mo元素主要以MoO3形式存在,在膜的内部钼主要以MoO2和MoO（OH）2存在,并含有部分MoO3;钼酸盐转化膜在阳极极化过程中发生明显的钝化,腐蚀电位正移683 mV,腐蚀电流密度降低2个数量级,明显提高AZ31镁合金的耐蚀性能。同时对镁合金表面钼酸盐转化膜的成膜机理进行初步探讨。     

化学转化膜对镁合金抗腐蚀性的影响

利用扫描电镜、X射线衍射和质量损失等手段,研究预处理前后的表面形貌及质量变化和锡酸盐化学转化膜层表面形貌及其相组成,采用盐雾和湿热实验箱检验膜层的抗腐蚀性能。结果表明:预处理前后镁合金表面相组成基本不变,质量减少主要发生在酸洗阶段,但变化不大;由于发生化学腐蚀和电化学腐蚀,预处理后表面在相界处出现较深的狭缝。化学转化膜层主要由Mg、Al12Mg17和MgSnO3.3H2O组成,表面由细小近球形颗粒密积而成,颗粒之间存在缝隙。经盐雾和湿热检测,化学转化膜层可以大大提高镁合金基体的抗腐蚀性。     

Electrodeposition of zinc on AZ91D magnesium alloy pre‐treated by stannate conversion coatings

A stannate chemical conversion process followed by an activation procedure was employed as the pre‐treatment process for AZ91D magnesium alloy substrate. Zn was electroplated onto the pre‐treated AZ91D magnesium alloy surface from pyrophosphate bath to improve the corrosion resistance and the solderability. The surface morphologies of conversion coating and zinc coating were examined with scanning electron microscope (SEM). The phase composition of conversion coating was investigated by X‐ray diffraction (XRD). The electrochemical corrosion behavior of the coatings in the corrosive solution was investigated by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). The experimental results showed that the activated stannate chemical conversion coating provided a suitable interface between zinc coating and the AZ91D magnesium alloy substrate. The corrosion resistance of the AZ91D substrate was improved by the zinc coating.     

Corrosion of AZ91D magnesium alloy with a chemical conversion coating and electroless nickel layer

A chemical conversion treatment and an electroless nickel plating were applied to AZ91D alloy to improve its corrosion resistance. By conversion treatment in alkaline stannate solution, the corrosion resistance of the alloy was improved to some extent as verified by immersion test and potentiodynamic polarization test in 3.5 wt.% NaCl solution at pH 7.0. X-ray diffraction patterns of the stannate treated AZ91D alloy showed the presence of MgSnO₃ · H₂O, and SEM images indicated a porous structure, which provided advantage for the adsorption during sensitisation treatment prior to electroless nickel plating. A nickel coating with high phosphorus content was successfully deposited on the chemical conversion coating pre-applied to AZ91D alloy. The presence of the conversion coating between the nickel coating and the substrate reduced the potential difference between them and enhanced the corrosion resistance of the alloy. An obvious passivation occurred for the nickel coating during anodic polarization in 3.5 wt.% NaCl solution.     

AZ91D镁合金表面转化膜腐蚀及防护涂层性能研究

采用高锰酸盐、钼酸盐、锡酸盐转化液分别对AZ91D镁合金进行表面化学转化,得到三种不同的化学转化膜。分别通过SEM、EDS和全浸试验研究不同转化膜的表面微观形貌、成分和腐蚀率,通过划格法和中性盐雾试验法研究转化膜外部有机涂层的附着性能和耐蚀性能。结果表明,高锰酸盐和钼酸盐转化膜表面具有大量微细裂纹,锡酸盐转化膜表面呈鱼鳞状,均为后续涂装提供了具有一定粗糙度的表面。锡酸盐转化膜的耐蚀性最好,高锰酸盐转化后并涂层的附着力和耐蚀性能最好。     

Ceria/stannate multilayer coatings on AZ91D Mg alloy

In this work, CeO₂/stannate multilayer coatings on AZ91D magnesium alloy were successfully obtained by chemical conversion and sol–gel dip coating. The stannate conversion coatings were prepared from a stannate aqueous bath containing Na₂SnO₃, CH₃COONa, Na₃PO₄ and NaOH at different temperatures and immersion times. Ceria films were produced on stannate/AZ91D starting from Ce(III) nitrate solutions in H₂O. In some cases, the PVA was added as chelating agent. Ceria top coatings were fired at 200 °C for 1 h. Coating microstructure was examined by FE-SEM. Finally, the corrosion resistance features of the coatings were tested by the electrochemical impedance spectroscopy (EIS) in 3 wt.% NaCl solution. The effect of PVA addition was evaluated in terms of microstructure and corrosion resistance features. CeO₂/stannate multilayer films, 3 μm thick, uniform, well adherent and nearly crack free were obtained. The formation of CeO₂ phase was confirmed by XRD and XPS analyses. The XPS depth profiles showed a limited diffusion of Mg towards the ceramic film. The EIS tests showed a significant improvement of corrosion resistance of the multilayer coatings (~ 16.6 kΩ after 48 h in NaCl solution) with respect to the blank alloy (~ 2.4 kΩ after 48 h in NaCl solution).     

有机添加剂对AZ91D镁合金锡酸盐转化膜性能的影响

采用化学转化法在镁合金表面制备锡酸盐转化膜。采用硫酸铜点滴实验、电化学交流阻抗(EIS)测试和Tafel曲线、扫描电子显微镜(SEM)测试和X射线衍射分析(XRD)等方法检测膜层的性能。研究了几种有机添加剂(Tartaric acid、Citric acid、Phytic acid、EDTA、Sodium dodecyl sulfate)对膜层耐蚀性的影响,结果表明溶液中添加SDS后,转化膜的硫酸铜点滴时间由35 s提高到了86 s,明显提高转化膜的耐腐蚀性能,膜层的形貌为呈"颗粒"状紧凑的连接到一起,该膜层的主要成分为Mg Sn(OH)6、Mg(OH)2。     

Stannate and permanganate conversion coatings on AZ31 magnesium alloy

The formation of stannate and permanganate–phosphate conversion coatings on AZ31 magnesium alloy was investigated in situ by EIS measurements and their protective performances were studied by different electrochemical techniques in diluted (0.05 M) sodium sulphate solution.The influence that short or long treatment times exert on the performances of such conversion coatings is discussed. While permanganate–phosphate baths always built layers characterized by penetrating cracks, long stannate baths produced layers without interconnected porosity, but were defective. This accounted for the initial greater protectiveness achieved with the stannate treatment; nevertheless, the easy penetration of the electrolytic solution through such a layer quickly decreased its corrosion resistance.     

压铸镁合金AZ91D无铬转化膜

以压铸镁合金AZ91D为基底，用乙酸盐高锰酸盐在其表面制备出无铬化学转化膜，用扫描电镜和能谱仪研究了转化膜的形貌和成分，极化曲线法测定转化膜的耐蚀性能。结果表明，该无铬转化膜为黄色鳞片状，由锰、镁氧化物和镁锰氧化物组成，耐蚀性能高于压铸镁合金基体。