High corrosion and wear resistant electroless Ni–P gradient coatings on aviation aluminum alloy parts

A Ni–P alloy gradient coating consisting of multiple electroless Ni–P layers with various phosphorus contents was prepared on the aviation aluminum alloy. Several characterization and electrochemical techniques were used to characterize the different Ni–P coatings’ morphologies, phase structures, elemental compositions, and corrosion protection. The gradient coating showed good adhesion and high corrosion and wear resistance, enabling the application of aluminum alloy in harsh environments. The results showed that the double zinc immersion was vital in obtaining excellent adhesion (81.2 N). The optimal coating was not peeled and shredded even after bending tests with angles higher than 90°and was not corroded visually after 500 h of neutral salt spray test at 35℃. The high corrosion resistance was attributed to the misaligning of these micro defects in the three different nickel alloy layers and the amorphous structure of the high P content in the outer layer. These findings guide the exploration of functional gradient coatings that meet the high application requirement of aluminum alloy parts in complicated and harsh aviation environments.

Tribological Behaviors of Electroless Nickel-Boron Coating on Titanium Alloy Surface

Titanium alloys are excellent structural materials in engineering fields,but their poor tribological properties limit their further applications.Electroless plating is an effective method to enhance the tribological performance of alloys,but it is difficult to efficiently apply to titanium alloys,due to titanium alloy’s strong chemical activity.In this work,the electroless Nickel-Boron(Ni-B)coating was successfully deposited on the surface of titanium alloy(Ti-6AL-4V)via a new pre-treatment process.Then,linearly reciprocating sliding wear tests were performed to evaluate the tribological behaviors of titanium alloy and its electroless Ni-B coatings.It was found that the Ni-B coatings can decrease the wear rate of the titanium alloy from 19.89×10^(−3)mm^(3)to 0.41×10^(−3)mm^(3),which attributes to the much higher hardness of Ni-B coatings.After heat treatment,the hardness of Ni-B coating further increases corresponding to coating crystallization and hard phase formation.However,heat treatment does not improve the tribological performance of Ni-B coating,due to the fact that higher brittleness and more severe oxidative wear exacerbate the damage of heat-treated coatings.Furthermore,the Ni-B coatings heat-treated both in air and nitrogen almost present the same tribological performance.The finding of this work on electroless coating would further extend the practical applications of titanium alloys in the engineering fields.

Microstructure and electrical conductivity of electroless copper plating layer on magnesium alloy micro-arc oxidation coating

In order to impart electrical conductivity to the magnesium alloy micro-arc oxidation(MAO)coating,the electroless copper plating was performed.Effects of plating temperature and complexing agent concentration on the properties of the electroless copper plating layers were studied by measuring their microstructure,corrosion resistance and electrical conductivity.It was found that the optimized plating temperature was 60°C,and the most suitable value of the complexing agent concentration was 30 g/L.Under this condition,a complete and dense plating layer could be obtained.The formation mechanism of the plating layer on magnesium alloy MAO coating was analyzed.A three-stage model of the plating process was proposed.The square resistance of the plated specimen was finally reduced to 0.03Ω/□after the third stage.Through electroless copper plating,the MAO coated sample obtained excellent electrical conductivity without significantly reducing its corrosion resistance.

Effects of zincate treatment on adhesion of electroless Ni-P coating onto various aluminum alloys

The effects of alloying elements on zincate treatment and adhesion of electroless Ni-P coating onto various aluminum alloy substrates were examined.Surface morphology of zinc deposits in the 1st zincate treatment and its adhesion were changed depending on the alloying element.The zinc deposits in the 2nd zincate treatment became thinly uniform,and the adhesion between aluminum alloy substrate and Ni-P coating was improved irrespective of the alloying element.XPS analysis revealed the existence of zinc on the surface of each aluminum alloy substrate after the pickling in 5% nitric acid.This zinc on the surface should be an important factor influencing the morphology of zinc deposit at the 2nd zincate treatment and its adhesion.

Electroless Ni-P plating on Mg-Li alloy by two-step method

Pretreated Mg-Li alloy sheets were pre-plated in a NiCO3？2Ni（OH）2？4H2O solution to form a thin Ni-P alloy film and then plating in a NiSO4？6H2O solution was carried out to obtain a protective coating.The surface morphology,structure and corrosion resistance of the coating were studied.The results showed that a flat,bright and compact plating layer,which was integrated into the matrix metal,was obtained.The P content of the Ni-P coating reached 13.56%（mass fraction）.The hardness value of the Ni-P coating was about HV 549.The polarization curve showed that the corrosion potential of the Ni-P coating reached ？0.249 V（vs SCE）.A long passivation region was found on the polarization curve,and this phenomenon indicated that the coating has an excellent anti-corrosion property.

An in situ measure method to study deposition mechanism of electroless Ni-P plating on AZ31 magnesium alloy

An in situ method was designed to measure a continuous open circuit potential （OCP） curve of AZ31 magnesium alloy and to observe the morphology variation of Ni-P coating during the process of the electroless plating. The deposition mechanism of the electroless Ni-P plating on AZ31 Mg alloy was studied by OCP curve, scanning electron microscopy （SEM）, and energy dispersion spectroscopy （EDS）. The process of electroless Ni-P plating contains the coating formation stage and the coating growth stage. The formation stage includes three procedures, i.e., the nucleation and growth of Ni crystallites, the extension of the coating in two-dimensional （2D） direction and the coalescence of the coating along three-dimensional （3D） direction. SEM investigations demonstrate that the spherical nodules of the Ni-P coating are not only formed during the coating growth stage, but also generated in the initial deposition stage of electroless Ni-P plating. The variation of the coating rates at different deposition stages corresponds to the deposition mechanism of their respective deposition stage.

Effect of novel ternary ligand system on acidic electroless Ni-P plating on AZ91D magnesium alloy

The electroless Ni-P coatings on AZ91 D magnesium alloy substrate were prepared using the acidic hypophosphite-reduced electroless nickel bath containing the novel ternary ligand system. The results indicate that the deposition rate varies with the ternary ligand concentration in plating solution. The structural and morphological characteristics of the coatings were analyzed by XRD and SEM. The anticorrosion properties of the Ni-P coatings were evaluated in 3.5% NaCl solution by electrochemical impedance and potentiodynamic polarization methods. The amount of ternary ligands in electroless plating bath has an significant effect on the surface morphology and structure of Ni-P coatings. The decrease of crystallization temperature and increase of crystallization heat of all the deposits with an increase in ternary ligand concentration are found by DSC measurements. The coating obtained with 0.035 mol/L ternary ligand additive in plating bath can offer a better surface homogeneity and improve corrosion resistance.

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.

Influence of pH values on electroless Ni-P-SiC plating on AZ91D magnesium alloy

A novel Ni-P-SiC composite coating was prepared by electroless plating in order to improve the corrosion capacity and wear resistance of AZ91D magnesium alloy.The influence of pH values on deposition rates and properties of the coatings was studied.The microstructure and phase structure of the Ni-P-SiC coatings were analyzed by scanning electron microscopy(SEM)and X-ray diffractometry(XRD).The corrosion and wear resistance performances of the coatings were also investigated through electrochemical technique and pin-on-disk tribometer,respectively.The results indicate that the composite coating is composed of Ni, P and SiC.It exhibits an amorphous structure and good adhesion to the substrate.The coatings have higher open circuit potential than that of the substrate.The composite coating obtained at pH value of 5.2 possesses optimal integrated properties,which shows similar corrosion resistance and ascendant wear resistance properties to the substrate.

High-temperature Compressive Performance of Mg Alloy Foams Coated with Ni-P Layer

Mg/Ni hybrid foams were fabricated by the electroless method.The Ni-P(Nickel-Phosphorous)coatings were deposited on the surface of closed-cell Mg alloy foams.The composition,microstructure and phases of the Ni-P coatings were characterized by scanning electron microscopy(SEM),energy-dispersive X-ray spectroscopy(EDS)and X-ray diffraction(XRD),respectively.The compressive tests were performed on the Mg/Ni hybrid foams at 400℃using the Mg alloy foams as a reference.The experimental results show that the yield strength,plateau stress and energy absorption capacity of the closed-cell Mg alloy foams at high temperature were improved by the Ni-P coating.And there are four main modes for the Mg/Ni hybrid foam failure at 400℃,i e,shearing in cell wall,bending in cell edge,shedding and cracking in Ni-P coating.

A novel electroless silver depositing method for magnesium alloys

Depositing silver on magnesium alloy by both electroless plating and organic coatings was studied. The organic coating was made by immersing samples in organosilicon heat-resisting varnish. In this method the organic coating acts as interlayer between the substrate and silver film. When the reaction starts, silver deposits directly on the interlayer. X-ray diffraction and SEM analysis were used to determine the composition and morphology of the interlayer and silver film. The potentiodynamic polarization curves for corrosion studies of coated magnesium alloys were performed in a corrosive environment of 3.5% NaCl(mass fraction) at neutral pH (6.9). The results indicate that compared with the substrate, the corrosion resistance of coated magnesium alloys increases greatly. Moreover, the method proposed in this work is environmentally friendly, non-toxic chemicals were used. In addition, it provides a new concept for the corrosion inhibition of magnesium alloys.

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 indicate that the dual coating is uniform,compact and pore-free.The adhesion strength between magnesium alloy substrate and electroless plating Ni-P bottom layer and electroplating nickel surface layer is perfect.The corrosion resistance of AZ91D magnesium alloy is greatly improved after being protected with the dual coating.

稳定剂KI对化学镀Ni-Fe-P-B合金性能的影响

利用化学镀方法沉积铁合金系镀层，具有诱人的软磁性能，应用于计算机以及磁头材料等领域。近期研究较多的镀层主要有：Fe—P、Fe—Ni-P、Fe-Mo-B、Fe-W—B、Fe—Sn—B、Fe—Mo—W—B和Fe—Ni-P-B等体系，并取得了可喜的成果。但也存在不少问题，化学镀液本身处于热力学不稳定状态，常要加入稳定剂，阻止H2PO2^-分解。目前常用稳定剂：（1）重金属离子，如Pb^2＋等；（2）无机含氧酸根离子，如IO3^-等；（3）有机酸，如柠檬酸等；

Pretreatment-free Ni-P plating on magnesium alloy at low temperatures

Electrochemically promoted electroless plating(EPEP)was used for the application of pretreatment-free Ni-P coating on AM60B magnesium alloy at low temperatures and the obtained coating was characterized by SEM,AFM,EDS and XRD techniques.Compact,uniform,and medium-phosphorus Ni-P coating with mixed crystalline-amorphous microstructure was obtained by applying a cathodic current density of4mA/cm^2at50℃.Also,island-like nickel clusters were deposited on the alloy surface under the same plating condition but without applying the cathodic current.In addition,the durability of the magnesium alloy against corrosion was strongly improved after plating via EPEP technique which was revealed by electrochemical examinations in3.5%NaCl(mass fraction)corrosive electrolyte.The results of the electrochemical examinations were confirmed by microscopic observations.Thickness,microhardness,porosity and adhesive strength of the deposits were also qualified.

医用Co-Cr合金表面化学镀铜抗菌涂层的制备及性能

钴铬合金具有良好的耐磨性、耐菌性及生物性能,是理想的医用金属材料,但钴铬合金对细菌的粘附往往比较敏感,容易引发口腔细菌感染,因而采用化学镀方法在钴铬合金上镀铜,对镀铜工艺参数进行单因素变量研究,得出化学镀铜最佳实验方案为:硫酸铜质量浓度为16 g/L,酒石酸钾钠质量浓度为46 g/L,NaOH质量浓度为15 g/L,甲醛为15 g/L,pH为12.9。通过采用XRD分析和SEM表征结果表明,化学镀铜后表面化学成分大部分为Cu,且分布密集,厚度约为6~7μm。涂层和基体结合稳定,不易脱落,镀铜后的钴铬合金抗菌性能明显得到提高。

钛铜合金接插件连续电镀及化学镀高磷镍工艺优化

针对智能手机零件的无磁性要求,采用钛铜合金为基材进行电镀和化学镀高磷镍。通过正交试验对镀前阳极电解脱脂、阴极电化学浸蚀、冲击镀镍,电镀高磷镍和化学镀高磷镍,以及镀后封孔工艺进行优化。研究了镀层P含量对其磁导率的影响,得出镀层P质量分数至少为11%方可满足静态磁导率小于1.003 H/m的要求。目前该连续电镀及化学镀高磷镍工艺已用于实际生产,产品合格率高达99.8%以上。

Coupling a titanium dioxide based heterostructure photoanode with electroless-deposited nickel-phosphorus alloy coating on magnesium alloy for enhanced corrosion protection

The utilization of photoelectrochemical cathodic protection(PECCP)enables an indirect corrosion pro-tection of metals with low self-corrosion potential by introducing a metallic nickel interlayer.However,the ability to enhance the PECCP efficiency remains challenging because of the inherent property of the semiconductor.Herein,this ability is demonstrated by coupling a covalent organic framework(TpBD)dec-orated TiO 2 photoanode(TiO 2/TpBD)with nickel coating on magnesium alloy for an effective corrosion protection.The composite photoanode showed direct PECCP for the nickel interlayer and indirect corro-sion protection of the magnesium alloy.The composite structure of the nanotube array and the covalent organic framework for the photoanode were confirmed by field emission scanning electron microscopy(FESEM),transmission electron microscopy(TEM),and X-ray photoelectron spectroscopy(XPS).The en-hanced photoelectrochemical conversion capability and PECCP performance of the nickel-coated Mg alloy were evidenced by the results from electrochemical and photoelectrochemical measurements including Mott-Schottky curves,photoinduced potential variations,and electrochemical impedance spectroscopy(EIS).Lastly,a corrosion protection mechanism is proposed,where the enhanced PECCP efficiency is at-tributed to the formation of a direct Z-scheme heterojunction,which is substantiated by the results from valence band(VB)XPS and electron spin resonance characterizations.

化学镀Ni-P镀层晶化过程研究

化学镀Ni-P镀层的显微组织对其服役性能有重要影响.通过SEM、TEM、XRD和DTA等分析手段,研究了压铸镁合金表面Ni-P镀层的晶化过程.结果表明,初始化学镀层不仅有非晶,还有亚稳态纳米晶;镀层的初始晶化温度大约为300℃,450℃晶化过程完成;升温过程中的原子扩散和纳米晶的长大导致有新的亚稳态相析出和转变;有序畴和析出物一起长大最终产生晶界.

化学镀Ni-P合金工艺的优化

用五种化学镀工艺制备了Ni-P合金镀层。用动电位极化曲线法比较镀层的耐均匀腐蚀性能,用溶液浇浸法测定了镀层的耐孔蚀性能,并用X-射线衍射仪和扫描电子显微镜分别研究镀层结构和表面形貌。结果表明:工艺2制备的镀层具有较高的耐均匀腐蚀和耐孔蚀性能,属于非晶和微晶组成的混晶结构。并对该工艺进行了正交试验,得到了最优工艺条件。

温度对化学镀Ni-P合金层形貌、硬度及耐蚀性的影响

目的揭示在70-95℃施镀温度范围,Ni-P合金镀层显微形貌的变化规律,并探讨表面形貌结构、合金硬度及耐蚀性能的相关性。方法以施镀温度为变量,通过化学沉积的方法制备Ni-P合金镀层。对镀层表面形貌进行表征,测试镀层硬度,并采用盐酸为腐蚀介质进行浸泡,以相对腐蚀速率表征镀层的耐蚀性。结果在70-95℃的施镀温度范围内,随着温度升高,镀层形貌先趋于致密和平整,而后表面粗化,镀层的硬度和耐蚀性均呈现先提高、后降低的趋势。最佳镀层形貌和硬度值出现在85℃,耐蚀性最好的施镀温度区间为85-90℃。结论当镀液p H值为4.5±0.1,施镀时间为3 h时,施镀的最佳温度为85℃。此条件下制备的镀层表面平整且均匀致密,硬度高,耐蚀性能优异。