Electrodeposition and corrosion behaviour of some Zn–Fe group metal alloys by pulsed current

Abstract

The corrosion and electrochemical behaviour of pulse plated Zn–Fe group metal alloy deposits obtained from chloride bath have been studied as a function of pulse parameters such as duty cycle, frequency and average current density. The frequencies of electric current, T _on, T _off, pulse duty cycles have large effects on the chemical composition and surface morphology of the deposits. Results of the electrochemical tests indicate that the corrosion resistance of pulse plated Zn–Fe group metal alloy coatings is superior to that of the alloy deposited by the direct current technique. The on time and off time had no significant influence on the deposit characteristics. Characterisations of deposits were carried out by cyclic voltammetry and the surface morphology was studied by scanning electron microscopy. The composition of the alloy deposits were analysed by spectrophotometry. Refinements in grain size and deposit composition have been made for better corrosion performance with the advent of pulse plating. A minimum corrosion rate was observed at 50% duty cycle and pulse frequency range of 100 Hz in all cases and is proposed as optimal conditions for development of a bright, smooth and uniform deposit of Zn–Fe group metal alloy over steel.     

镁合金化学转化膜上化学镀镍的研究

将化学转化和化学镀镍结合在一起,先对AZ91D镁合金进行化学转化处理,然后在转化膜上进行化学镀镍.并用扫描电镜(SEM)、X射线衍射技术(XRD)研究了镀层表面形貌和组织结构及处理后镁合金的耐蚀性能.结果表明:两种工艺结合得到的镀层使腐蚀电位正移0.83 V,腐蚀电流降低,有效的提高了镁合金耐腐蚀性能.     

Effects of low temperature thermal treatment on zinc and/or tin plated coatings of AZ91D magnesium alloy

A new method was investigated to obtain composite coatings on the AZ91D magnesium alloy by electrodeposition and low temperature thermal treatment. Zinc and tin were introduced to AZ91D Mg alloy surface by electroplating firstly. And a succedent thermal treatment was carried out at 190 ± 10 °C for 12 h. The surface and cross-section morphologies of the plated coatings with and without thermal treatment were studied by scanning electron microscopy (SEM). And the microstructure was determined by X-ray diffraction (XRD). The results reveal that it was difficult to obtain good adhesion plated Sn coating but easy to get well-adherent plated Zn coating. And the thermal treatment promoted the formation of Mg₂Sn in the plated Sn coating and the recrystallization in the plated Zn coating. The plated double Zn-Sn coating owned good adhesion and uniform surface. Furthermore, when the plated double Zn-Sn coating was treated at 190 ± 10 °C for 12 h, a three-layer structure coating was formed due to the diffusion of tin. The results of the anodic polarization behaviors in 5 wt.% NaCl solution show that the three-layer structure coating could provide better protection for AZ91D substrate than the plated Zn-Sn coating.     

Wear and corrosion resistance of AZ91 magnesium alloy coated by pulsed current electrodeposited Ni–Al2O3 nanocomposite

In this work, Ni and Ni–Al₂O₃ nanocomposite coatings were applied on AZ91 magnesium alloy using a pulse plating process and the corrosion resistance of coated samples was evaluated by means of the potentiodynamic polarisation method in 3.5?wt-% NaCl solution. Field emission scanning electron microscopy was employed to identify microstructure and morphology of the coatings. Vickers microhardness and pin-on-disc wear tests were also used to investigate mechanical properties of the coatings. The polarisation test revealed that the pure Ni coating on AZ91 along with the presence of nanoparticles were key factors leading to a reduction in the corrosion current density and the improvement of corrosion resistance so that the corrosion current density of 210.45?µA?cm^?2 for the substrate (AZ91) decreases to 31.92 and 1.54?µA?cm^?2 by applying pure Ni and Ni–Al₂O₃ nanocomposite coatings, respectively. Furthermore, Ni–Al₂O₃ nanocomposite coating increased the microhardness and wear resistance compared to the substrate up to 435 and 340%, respectively.     

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。     

Preparation of Ni-Cu-Mo-Cr film deposited on AZ31magnesium alloy by double glow sputtering with Cu interlayer

For improving the corrosion resistance of AZ31magnesium alloy, a double glow sputtering deposited Ni-Cu-Mo-Cr film with brush plating Cu interlayer is applied to deposit a metal amorphous/nanocrystal film on AZ31magnesium alloy. Using a brush plated Cu interlayer, the content of noble elements, such as Ni, Cr, and Mo, is higher than that of a Ni-based film without Cu interlayer. The microstructure of the Ni-Cu-Mo-Cr alloy film with the brush plated Cu interlayer confirms that the film is classified into two regions, i.e., an amorphous layer on the outmost surface and an underlying nanocrystalline layer with a grain size of less than 5 nm. The Ni-based alloy amorphous film formed on AZ31magnesium alloy was investigated using an electrochemical polarization measurement. Compared with the AZ31 magnesium alloy, the sputter-deposited Ni-based alloy film and the sputter-depostion Ni-based alloy film with a brush plated Cu interlayer formed on AZ31 magnesium alloy exhibit obvious passivation phenomena.     

Progress of electroplating and electroless plating on magnesium alloy

The current research processes of electroplating and electroless Ni-P alloy plating on magnesium alloys were reviewed. Theoretically, the reason for difficulties in electroplating and electroless plating on magnesium alloys was given. The zinc immersion, copper immersion, direct electroless Ni-P alloy plating and electroplating and electroless plating on magnesium alloys prepared by chemical conversion coating were presented in detail. Especially, the research development of magnesium alloy AZ91 and AZ31 was discussed briefly. Based on the analysis, the existing problems and future research directions were then given.     

Effect of TiO2 nanoparticles on the microstructure and corrosion behavior of MAO coatings on magnesium alloy

The microstructure and corrosion behavior of the micro‐arc oxidation (MAO) coatings modified by TiO₂ on AZ91 magnesium alloys were investigated by SEM, EDS, XRD, electrochemical analysis and drop test, respectively. The modified MAO coatings were consisted of not only MgAl₂O₄ and MgO, which usually could be found in MAO coatings on the AZ91 alloys, but also a small quantity of Ti. With increasing the contents of TiO₂ nanoparticles from 0 to 4.8 g/L in the electrolyte, the coatings thickness increased from 19 to 24 µm, and the color of the MAO coating changed from light gray to dark. The addition of TiO₂ could effectively decrease the number of the pores and improve the density of the coatings. The corrosion potential of the modified coatings positively shifted about 180 mV and the corrosion current density declined and the drop time increased. The mechanism of the corrosion resistances of the modified coatings lay in the fact that TiO₂ nanoparticles could increase the thickness and the density of the coatings on the AZ91 magnesium alloys.     

磁控溅射Ti膜对AZ91镁合金耐磨耐蚀性能的影响

目的通过表面镀Ti膜提高AZ91镁合金的耐磨性能。方法通过直流磁控溅射方法在AZ91镁合金表面镀Ti膜,用拉伸实验法在电子万能实验机上测定薄膜的附着强度,用原子力显微镜观察薄膜与基体的界面形貌,并分析不同溅射参数时膜基的结合能力。通过湿摩擦实验分析两种试样的耐磨性能,采用Js M-670l F冷场发射型扫描电子显微镜观测两种试样磨损后的表面形貌。采用动电位极化曲线测试装置测得两试样的极化曲线,从而判定其耐腐蚀能力。结果通过直流磁控溅射方法制备的Ti膜和AZ91镁合金基体的结合能力与溅射时间有关,当溅射时间为6 min时,膜基结合能力最佳,但结合其他两项参数,所制备试样采用的时间应为4 min。AZ91镁合金镀Ti膜后磨损率降低,腐蚀电流降低,腐蚀电位升高。结论直流磁控溅射方法镀Ti膜提高了AZ91镁合金的耐磨耐蚀性能。     

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.     

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。     

络合剂对AZ31D镁合金化学镀Ni-P合金的影响

以AZ31D镁合金为研究材料,研究了化学镀Ni-P工艺配方中络合剂对镀层的沉积速度、镀层表面形貌与结构、镀层成分及其各种性能的影响,获得了最佳工艺参数.结果表明,可以实现在AZ31D镁合金上直接化学镀Ni-P合金,并且其镀层表面光亮、均匀致密,镀层的显微硬度比AZ31D镁合金基体有明显的提高,镀层与基底的结合力良好.     

无铬转化膜预处理提高AZ91D镁合金化学镀Ni-P的腐蚀性能(英文)

在化学镀Ni-P层和AZ91D镁合金之间生成磷酸锰、单宁酸或钒转化膜预处理层,以取代传统的铬酸盐加氢氟酸预处理工艺。电化学测试结果表明:与传统的铬酸盐处理加化学镀相比,镁合金上的无铬转化膜加化学镀镍磷具有低的腐蚀电流密度和更正的腐蚀电位,能够减少基体上化学镀层的腐蚀。因此,镀层具有致密的细晶结构,适当的磷含量、低孔隙度和良好的耐蚀性并且和基体结合良好的涂层可以取代传统的铬酐钝化加化学镀的工艺。     

Influence of pickling time on electroless Ni–P coating on magnesium alloy

In this study, a simple pickling process in H₃PO₄ and NH₄HF₂ solution was used for electroless Ni–P plating on AZ61 magnesium alloy. It is found that the corrosion rate of magnesium alloy during pickling significantly decreased because NH₄HF₂ was added into H₃PO₄ pickling solution. Ni–P coating plated only with pickling process shows poor adhesion because of the low F/O ratio of the substrate surface. However, F/O ratio, adhesion, and corrosion resistance of Ni–P coating are obviously enhanced after pickling followed by activation. The optimal pretreatment process is pickling for 120 s and activation for 4 min, under which the Ni–P coating has an optimum F/O ratio of 1.8 and the coating gets a dense structure, better adhesion, and higher corrosion resistance.     

Structure and wear resistance of TiN and TiAlN coatings on AZ91 alloy deposited by multi-arc ion plating

In order to investigate the microstructure of TiN and TiAlN coatings and their effect on the wear resistance of Mg alloy, TiN and TiAlN coatings were deposited on AZ91 magnesium alloy by multi-arc ion plating technology. TiN and Ti70Al30N coatings were prepared on the substrate, respectively, which exhibited dark golden color and compact microstructure. The microstructures of TiN and Ti70Al30N coatings were investigated by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The micro-hardness and wear resistance of TiN and Ti70Al30N coatings were investigated in comparison with the uncoated AZ91 alloy. The XRD peaks assigned to TiN and TiAlN phases are found. The hardness of TiN coatings is two times as high as that of AZ91 alloy, and Ti70Al30N coating exhibits the highest hardness. The wear resistance of the hard coatings increases obviously as result of their high hardness.     

A novel dual nickel coating on AZ91D magnesium alloy

Magnesium alloys covered with metal coating display excellent corrosion resistance,wear resistance,conductivity and electromagnetic shielding properties.The electroless plating Ni-P as bottom layer following the electroplating nickel as surface layer on AZ91D magnesium alloy was investigated.The coating surface morphology was observed with SEM and the structure was analyzed with XRD.Electrochemical tests and salt spray tests were carried out to study the corrosion resistance.The experimental results indi...     

A new method for electroless Ni-P plating on AZ31 magnesium alloy

Coating Ni-P films on AZ31 magnesium alloys via electroless plating and organic coatings (organsilicon heat-resisting varnish), was studied. An organic coating was proposed as the interlayer between Ni-P coating and AZ31magnesium alloy substrate, to replace the traditional chromium oxide plus HF pretreatment. The Ni-P deposited on the interlayer was also characterized by its structure, morphology and corrosion-resistance. The interlayer on the substrate not only reduces the corrosion of magnesium during Ni-P plating process, but also reduces the potential difference between the matrix and the second phase. The result of the cross-cut test indicates the adhesion between the substrate and the interlayer is good enough. A Ni-P film with fine and dense structure was obtained on the AZ31 magnesium alloy. The electrochemical measurements show that the sample with Ni-P film exhibits lower corrosion current density and more positive corrosion potential than the substrate. Furthermore, the Ni-P coating on the AZ31 magnesium alloy exhibits high corrosion resistance in the rapid corrosion test illustrated in this paper. The method proposed in this work is environmentally friendly: no fluoride or hexacalent chromium compounds are used. In addition, it provides a new concept for plating the metals, which are considered difficult to plate due to high reactivity.     

Zn-Ni合金镀层中添加第三种元素和纳米颗粒的研究新进展

介绍了在汽车、航空航天等行业中得到广泛应用的钢铁零件电镀Zn-Ni合金镀层,以及往碱性、氯化物等锌镍合金镀液中加入Fe、Co、Mn、Ce、P等第三种元素所获得的锌镍三元合金镀层,具有更优良的耐腐蚀性、催化性等性能的情况。介绍了往Zn-Ni合金镀液里加入氧化硅、氧化铈、氧化钛、氧化铝、碳化硅等纳米颗粒的进展情况,发现含有纳米颗粒的锌镍复合镀层具有耐腐蚀性、耐磨损性、热稳定性更好,硬度更高等优点。梳理了2016年以来在Zn-Ni合金电镀中添加第三种元素和纳米颗粒的多层镀层研究新进展。从Zn-Ni单一镀液中沉积Ni-P和Zn-Ni合金多层镀层时,在低电流密度下沉积出Ni-P层;在较高电流密度下,沉积出含3.2%P的Zn-Ni-P合金镀层,这种多层镀层可以大幅度提高钢铁零件的防腐蚀性能。介绍了在含12%Ni的Zn-Ni镀层上镀覆Ni-Co-SiC纳米复合镀层的情况,这种多层结构既可以提高镀层的结合力,又可提高其在3.5%NaCl溶液中的耐腐蚀性能。该复合镀层是一种硬度高、磨损量低的新型Zn-Ni合金复合镀层。     

镁合金在硅酸盐体系中微弧氧化膜层的性能研究

利用交流微弧氧化装置对AZ91D镁合金在硅酸盐体系中进行了微弧氧化处理,并通过扫描电镜、电化学测试技术和表面性能测试仪等研究了氧化时间和电流密度对微弧氧化膜层表面形貌、厚度、耐蚀性、摩擦磨损性能和结合力的影响.结果表明：随氧化时间和电流密度的增大,镁合金微弧氧化膜层中微孔的数量减少,但微孔的直径和表面粗糙度增大.膜层厚度随氧化时间和电流密度的增加呈线性增大,但与基体的结合力明显降低.镁合金微弧氧化膜层的耐蚀性和耐磨性随氧化时间和电流密度的增大呈先增大后减小的趋势.镁合金在硅酸盐体系中微弧氧化处理的最佳工艺为氧化时间40min、电流密度0.20A/cm2.     

AZ91D镁合金表面聚氨酯涂层耐腐蚀性能

利用附着力及铅笔硬度测试、浸泡试验、盐雾试验、电化学试验等方法对AZ91D镁合金表面的聚氨酯涂层及环氧聚氨酯涂层形貌和性能进行了研究,并对两种涂层的腐蚀保护效果及机理进行了探讨。结果表明,这两种涂层都能显著提高镁合金的耐腐蚀性能,与基材附着良好且硬度高。与聚氨酯涂层PU相比,环氧聚氨酯涂层ER/PU的耐腐蚀效果更好。