【作者】 李丹；

【导师】 谢治辉；

【作者基本信息】 西华师范大学 ， 物理化学， 2017， 硕士

【摘要】 镁合金因具有低密度、高强度、高刚性、和较强的消震性及韧性等优异性能,而广泛用于国防、航空航天、运输、电子领域等,在机械零件制造领域,甚至有望取代铝和钢。但是,镁合金的耐腐蚀性差、化学反应活性高,限制了它在工业生产中的更广泛应用。本文将制备好的化学镀镍层浸入质量分数为3.5%的NaCl溶液中浸泡,对镀层做初步评估。镀层与基底间的结合力用GB/T 5270—2005和ISO 2819推荐的划线和划格试验方法进行测定。实验采用扫描电子显微镜(SEM,Hitachi S-4800,日本)表征镀层的表面及截面形貌。用X射线能谱仪(EDX,Horiba,EX-350)进行镀层成分分析。镀层晶形结构使用X射线衍射仪(XRD,D8 Advance,德国)X射线光电子能谱(XPS,PHI5000,Versaprobe)测定。将制备好的镀层浸泡在一定浓度的NaCl溶液中,用电化学测试方法对镁合金上的镀层的腐蚀电位Ecorr,腐蚀电流ic等参数进行了测试。通过实验和讨论,得到如下结论:(1)研究了一种制备高耐蚀纳米复合镀层的方法——两步化学镀。采用两步化学镀方法,在AZ31镁合金最外层镀层中引入二氧化硅纳米颗粒(NSPs),会形成一种功能化复合涂层,使镀层的表面更平滑,均匀,并且具有很强的耐腐蚀性能。NSPs的掺入不会对复合镀层Ni-P/Ni-P-nano-SiO2(NNNS)的晶态结构产生影响,整体镀层都保持非晶态结构。最佳镀层在NaCl溶液中的缓蚀效果高于HCl溶液。新制备的镀层性能提高的主要原因是涂层缺陷的错位和腐蚀过程中NSPs的“屏障效应”。(2)研究了镁合金上均匀分散F@MSNs(Mesoporous Si nanocontainers)的具有自愈功能的镍涂层的制备。所制备的F@MSNs镀层具有良好的耐腐蚀性能的原因为F@MSNs释放的氟离子与镁离子之间发生反应生成了MgF2保护膜。氟离子的释放和MgF2薄膜的形成可以有效的修复镁合金表面的自然氧化膜缺陷,从而改变腐蚀机理并且降低镁合金的腐蚀速率。镁合金浸泡在腐蚀介质中,随着时间的增大,腐蚀电位Ecorr趋向稳定,腐蚀电流ic减小,电极阻抗Rp增大都可以进一步证实纳米复合镀层的自愈功能。更多还原

【Abstract】 Magnesium alloys have excellent properties such as low density,high strength,high rigidity,strong shock resistance and toughness.Based on these properties,magnesium alloys are mainly used in the fields of national defense,aerospace,transportation,electronics and so on.In the manufacture of mechanical parts,it will be expected to replace aluminum and steel.However,magnesium alloy has poor corrosion resistance and high chemical reactivity,which limits its wide application in industrial production.The corrosion resistance of the electroless nickel plating(ENP)coating was preliminary evaluated through immersion in 3.5%(wt.%)NaCl solution.Adhesion of ENP coating was tested by scribe and grid measurement according to GB/T5270-2005 and ISO 2819.The surface and cross-sectional morphologies as well as the elemental composition of the coatings were observed and inspected,respectively,by scanning electron microscopy(SEM,Hitachi S-4800,Japan)and energy-dispersive X-ray(EDX,HORIBA EX-350).X-ray diffractometer(XRD,D8 Advance,Germany)was used to characterize the crystal microstructure of the coating.The as-prepared coating was immersed in a certain concentration of NaCl solution.The corrsion potential(Ecorr),corrosion current density(ic)of the coating were estimated from the electrochemical data.The experimental results are shown as follows:(1)The coatings deposited by adding nano silica oxide particles(NSPs)directly into the fluoride-containing ENP bath were shown to display poor adhesion and corrosion resistance,which results from the formation of byproduct due to the reaction between fluoride and NSPs.In contrast,using a two-step deposition method,a functionalized duplex coating with smoother and more uniform surface was shown to exhibit enhanced corrosion resistance on AZ31 Mg alloy because of the introduction of NSPs in the outer layer of the coating.The incorporation of NSPs does not influence on the crystalline state structure of the NNNS(Ni-P/Ni-P-nano-SiO2)coatings,all of which remain amorphous structures.The corrosion inhibition effectiveness of the optimum coating in NaCl solution was higher than that in HCl solution.The enhancement of the as-prepared coatings is attributed to the mismatch of coating defects and the “barrier effect” of NSPs during corrosion.(2)We have demonstrated the preparation of a self-healing metallic Ni coating containing uniformly dispersed F@MSNs(mesoporous Si nanocontainers)on Mg alloy towards enhanced corrosion resistance.The as-prepared F@MSNs have been shown to enhance corrosion-resistant capability of bare Mg alloy after exposure in corrosive media for a long period of time.This is ascribed to the formation of a protective film,MgF2,arising from the reaction between the Mg ions and the fluoride ions released from F@MSNs.The release of fluoride ions and formation of MgF2 film are important for repairing defects in the natural oxide film on Mg alloy surface,thereby changing the corrosion mechanism and decreasing the corrosion rate of Mg alloy.The self-healing functionality of the nanocomposite Ni coating has been further substantiated by the observation of stable Ecorr and the decrease of ic and increase of Rct with increasing immersion time in the corrosive media.更多还原