Characterization of Electroless Ni-P Deposits on Surface of AZ91D Magnesium Alloy

Characterization of electroless nickel deposits on magnesium alloys was investigated by X-ray diffraction(XRD),scanning electron microscope(SEM),energy dispersive spectrometer(EDS)and electrochemical potentiodynamic polarization analysis.The result of XRD showed that the electroless nickel deposits on magnesium alloys were composed mostly of amorphous Ni-P and partially of microcrystalline nickel.The phosphorus content in the Ni-P deposits was 10.8%by the calculation of EDS.SEM micrographs showed that morphology of electroless nickel deposits on magnesium alloys was a typical cellular structure,and the growth of cellular structure was influenced by surface condition of substrate.Zinc layer between substrate and electroless nickel deposits was not found by the results of SEM and EDS,which indicated that the zinc layer on the surface of magnesium alloy was very thin,and the zinc would dissolved while being immersed in electroless nickel plating solution.The thin zinc layer was almost dissolved completely before Ni-P plating.The result of electrochemical potentiodynamic polarization analysis showed that the corrosion potential Ecorr of electroless nickel deposits in 3.5%NaCl solution was about-0.53 V,which was 1 V higher than that of magnesium alloys substrate.And corrosion current density of Ni-P deposits in 3.5%NaCl solution was much smaller than that of magnesium alloys substrate at the same potential value,which indicated that corrosion resistance of electroless Ni-P deposits was excellent.Discoloration time of concentrated nitric acid test for electroless nickel deposits on magnesium alloys was 445 s,which also indicated excellent corrosion resistance.     

金刚石复合镀层的研究

通过硬度和磨损试验,研究了金刚石含量,粒度,镀覆时间和镀后热处理对金刚石复合镀层耐磨性的影响,并据此筛选了最佳镀覆工艺。试验结果表明,在最佳镀覆条件下,金刚石复合镀层的硬度高达HV1889,为Ni-P化学镀层的2．8倍,耐磨性提高更多,可达Ni-P化学镀层的16倍以上,还探讨了金刚石复合镀层的耐磨机理。     

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.     

络合剂对Ni-P化学镀层在含硫介质中耐蚀性的影响

针对进口原油S含量高腐蚀严重的实际,用电化学和失重法研究方法,结合显微分析和X射线衍射分析手段,研究以柠檬酸和乳酸为络合剂的化学镀Ni-P镀层在Na2S介质中的耐蚀性。结果表明,利用两种络合剂形成的Ni-P镀层均为非晶态,其中以乳酸为络合剂的镀层含P量为10.04%,以柠檬酸为络合剂的镀层含P量为11.93%,在1.0%-2.5%的Na2S介质中,随着Na2S浓度的增加,阳极极化曲线的极化率增大,自腐蚀电位和自腐蚀电流降低。以乳酸为络合剂的镀层耐蚀性更好;两种络合剂形成的镀层在Na2S为1.5mass%时,腐蚀速度出现极大值。     

Influence of Ultrasound on the Properties of Electroless Plated Nickel

Ultrasonic agitation during electroless plating nickel affects the structure and properties of the deposits. In this work, a complete study was made of the action of ultrasound on the plating rate, micro-hardness, phosphorus content and corrosion properties of electroless plated deposits. It was found that in the presence of the ultrasound, the plating rate and micro-hardness of as-deposited were increased by about 30 and 10 percent respectively, whilst the phosphorus content was decreased from 10.49 to 8.39 at%. The changes in these parameters, in turn, affect the corrosion behaviour of the electroless deposits. The deposit formed with ultrasound exhibited active corrosion characteristics, whilst the deposit formed without ultrasound had a passive behaviour in 0.2 M H²SO⁴ solution.     

6063铝合金碱性化学镀镍耐腐蚀性能研究

针对6063铝合金不耐碱腐蚀的问题,对其表面进行了碱性化学镀镍处理以提高其在碱性溶液中的耐腐蚀性能.采用扫描电镜(SEM)、能谱分析仪(EDS)和X射线衍射仪(XRD)分别分析了镀镍层的表面微观形貌、成分和物相结构;采用电化学和全浸蚀腐蚀试验方法测试了铝合金化学镀镍前后在w(NaOH)=4%的NaOH溶液阳极极化曲线和腐蚀失重.研究结果表明,铝合金化学镀镍处理后其表面获得了致密的非晶态高磷镀镍层,化学镀镍后的铝合金阳极极化电位达到析氧过电位时,镀层依然没有破坏,并且该镀层在w(NaOH)=4%的NaOH溶液中基本不发生腐蚀.     

Process Recycling and Environmental Treatment

A useful coating technology for electroless Ni-1.5wt%P has been developed. The bath can work normally for more than 5 turnovers with a plating rate of 20 μm/h. In the as-deposited condition, Ni-1.5wt%P deposit is a supersaturated solid solution of P dissolved in a nanocrystalline Ni matrix with a grain size of several nanometers. The microstructure transformed into a larger grain size Ni matrix with dispersive Ni₃P precipitates with increasing the heat treatment temperature. Ni-1.5wt%P deposit possesses as-deposited hardness and wear resistance superior to Ni-10.5wt%P deposit. The microhardness and wear resistance can be further improved by proper heat treatment. The optimum wear resistance of Ni-1.5wt%P deposit corresponds to its peak hardness (annealing at 375°C for 1 h), whereas for Ni-10.5wt%P deposit the optimum wear resistance is obtained after annealing at 650°C for 1 h. Ni-1.5wt%Ppossesses a corrosion resistance in NaOH solution superior to conventional medium and high phosphorus deposits, which have much better corrosion resistance in NaCl and HCl solution. The rotating fatigue results indicate that electroless nickel deposits cause a decrease in the fatigue strength of 30CrMo steel, and increase the fatigue strength of LY12 alloy. Ni-1.5wt%P deposit demonstrates higher fatigue resistance than Ni-10.5wt%P deposit.     

The Relationship Between Phosphorus Content and Physical Properties of Electroless Nickel Deposits

The physical properties of electroless nickel deposits are intimately related to their composition. The work presented shows the relationship between deposit hardness, both as-plated and heat-treated and phosphorus content.

It is shown that in both cases maximum hardnesses are obtained with deposits of lower phosphorus content. Care must be taken with low phosphorus deposits to avoid over heat- treatment and recommendations for suitable times and temperatures are made.     

超声化学镀对烧结钕铁硼磁体抗腐蚀性能的影响

采用超声波化学镀方法,研究了在频率为40 kHz超声波条件下化学镀Ni-P合金对烧结NdFeB磁体抗腐蚀性能的影响,测定了超声功率对沉积速度和镀层磷含量的影响,观察了超声场对镀层表面形貌和Ni-P镀层耐腐蚀性的影响.结果表明,随着超声功率的增大,沉积速度增加,而镀层磷含量略有降低.与无超声场下的Ni-P化学镀层相比,超声条件下化学镀Ni-P合金组织更加细小,排列更加紧密,有更加优良的耐腐蚀性,能有效的保护NdFeB磁体.     

非晶态镍磷合金的组织结构与性能

研究了化学沉积非晶态镍磷合金的组织结构与性能。结果表明,随着沉积层中磷含量的增加,合金的非晶化趋势提高,非晶态镍磷合金层的硬度和耐磨性能下降,且明显低于晶态镍磷合金;经过大于６１３Ｋ的时效处理,非晶态镍磷合金晶化且有Ｎｉ３Ｐ生成,沉积层的硬度和耐磨性得以提高并超过晶态合金;非晶态镍磷合金经过时效处理晶化后且组织结构发生变化,耐腐蚀性能下降,硬化性能则提高。     

Electrochemical Measurements of Electroless Nickel Coatings on Zincated Aluminium Substrates

Zincate pre-treatment of aluminium substrates and the effects of deposit thickness on the corrosion resistance of electroless nickel deposits on aluminium have been studied by electrochemical methods. The results show the importance of the controlled zincate pre-treatment step on the induction period for electroless nickel plating. The protective properties of the nickel deposit are evaluated, as a function of thickness, using linear polarisation resistance and zero resistance ammetry techniques. The corrosion resistance of the deposits, which is strongly related to their thickness, is compared to the results of porosity testing on steel substrates. An essentially non-porous deposit is obtained after a thickness of 5–10 microns has been deposited on aluminium substrates under the experimental conditions.     

化学镀镍工艺对镀层耐蚀耐磨性的影响

广义的化学镀镍工艺包括镀前预处理工艺,镀镍工艺和后处理工艺,化学镀镍工艺通过对镀层的成分,组织,孔隙率及表面微马形貌的影响而影响镀层的耐蚀,耐磨性,改进预处理工艺可进一步提高镀层的耐蚀性和镀层与基体的结合力,合适的后处理工艺可提高镀层的耐磨性和抗中性盐雾能力。     

钨含量对Ni-W-P镀层抗垢性能的影响

采用化学镀的方法,调整化学镀工艺参数中钨酸钠的浓度,在低碳钢（1015）表面获得了钨含量不同的Ni-W-P镀层,分别采用扫面电镜、X射线衍射仪以及MH-6表面硬度计研究了钨含量对Ni-W-P镀层表面形貌、结构以及显微硬度的影响。结果表明,镀液浓度对于获得磷和钨含量起到决定性的作用,而磷和钨的含量决定了Ni-W-P镀层的表面形貌和结构。胞状晶的形成是Ni-W-P镀层的共同特征,镀层中钨含量的增加降低了磷的含量,因此改变了纳米晶相的含量。由于钨固溶于镍中诱使镀层产生固溶强化限制了镀层局部塑性变形,从而增加了镀层的硬度。采用差热分析研究相变行为的结果表明,高钨含量的Ni-W-P镀层表现为较高的晶化温度。进一步的污垢沉积试验表明,与低碳钢表面相比,含有不同钨含量的Ni-W-P镀层表面抑制了污垢的黏附。然而,进一步研究表明,污垢沉积速度和Ni-W-P镀层表面粗糙度之间没有必然的联系,与钨的含量有着直接的联系。     

化学镀镍磷表面改性Cu-Zn-Al形状记忆合金的腐蚀行为

采用电化学方法研究了Cu-Zn-Al形状记忆合金(SMA)及其化学镀镍磷表面改性试样在Tyrode's人工体液中的腐蚀行为.结果表明，在Tyrode's人工体液中Cu-Zn-Al SMA发生脱锌腐蚀.化学镀镍磷Cu-Zn-Al SMA随NaCl浓度增加、pH值降低、环境温度升高，阳极活性电流密度增大，电化学溶解敏感性增强.X-射线衍射分析结果表明，Cu-Zn-Al SMA表面化学镀镍磷后，形成了非晶态镀层，其在Tyrode's人工体液中的耐蚀性显著提高；这是由于改性表面形成均匀、稳定的阻碍性镀层，有效地将基体金属和外界腐蚀介质隔绝而达到防护作用. 镀镍磷      

Influence of deposition temperature and heat treatment on the performance of electroless Ni-B films

Electroless nickel-boron (Ni-B) was synthesized on mild steel or copper surface. The deposition of thin electroless Ni-B films using an acidic bath having nickel chloride as a source of nickel and dimethylamine borane (DMAB) as a reducing agent and operated at low temperature has been investigated in this paper. The effect of the plating time and temperature on the quality of Ni-B coatings was estimated. The results revealed that the plating rate decreases with increasing plating time and increases with increasing plating temperatures. The boron (B) content of the electroless Ni-B layer increased with increasing temperature. The resulting surfaces were examined and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). XRD analysis was performed to investigate structural modifications. Microhardness, corrosion and oxidation resistance of electroless as-plated and heat-treated Ni-B coatings, were evaluated. The effect of heat treatment temperature on the phase structure and microhardness of Ni-B coated at different temperatures was discussed. XRD patterns reveal that electroless Ni-B coatings deposited at 60 and 80 °C are amorphous in as-plated condition and undergo phase transformation to crystalline nickel and nickel borides upon heat-treatment. Heat treatment achieved significant improvement in the microhardness and corrosion resistance due to the formation of the Ni-B compound phases (Ni₃B).     

Ni/AlN Composite Coating for Corrosion and Elements Interdiffusion Resistance in Molten Fluoride Salts System

The Ni/AlN composite coating was prepared for increasing corrosion and elements interdiffusion resistance of GH3535 alloy in molten fluoride salts,and the effect of mechanical interlocking on adhesion strength between AlN layer and nickel coating was also studied.Results indicated that the adhesion strength between AlN layer and nickel coating could be signifi-cantly enhanced through mechanical interlocking effect,which effectively prevented the nickel coating from flaking off at elevated temperature.Through an etching pre-treatment of AlN layer,the corrosion resistance of the Ni/AlN coated GH3535 alloy in molten FLiNaK salt was further improved,and elements interdiffusion between the substrate and nickel coating was completely suppressed.AlN layer as a diffusion barrier remained compact and continuous in Ni/GH3535 system after high-temperature molten salt corrosion.Moreover,a Ni-P layer consisting of Ni3P and Ni phases formed in the Ni coating after corrosion.     

添加剂对AZ91D镁合金化学镀镍磷耐蚀性的影响研究

采用常温碱性超声波清洗、酸洗和活化的前处理工艺在AZ91D镁合金表面化学镀镍,研究了辅助络合剂氨基乙酸和加速剂巯基乙酸对镀层耐蚀性的影响。结果表明:镀层表面由Ni-P固溶体组成,呈现尖锐的晶态峰,磷原子与镍原子形成置换固溶体,表面平整致密,无明显缺陷。氨基乙酸含量对镀层耐蚀性和腐蚀速率影响不大,随着巯基乙酸含量的增加,镀层腐蚀电位先升高后降低,腐蚀速率整体比镁合金基体慢,镀层总体呈现钝化趋势,在4 g/L时腐蚀电位最高。     

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...     

Electroless deposition of Ni-P composite coatings containing kaolin nanoparticles

Abstract

The ability to codeposit particulate matter in a matrix of electroless nickel has led to a new generation of composite coatings with unique properties, such as high hardness wear, abrasion, corrosion and high temperature oxidation resistance. In this paper, the authors report on the development of electroless Ni–P–kaolin composite coating, and the characteristic properties of the selected deposits were evaluated by scanning electron microscopy, energy dispersive X-ray and X-ray diffraction techniques. A good rate of deposition of 12 μm h^?1 was observed for the optimised concentration of 6 g L^?1 of kaolin in the bath. For the optimised bath composition and operating conditions, the composite deposit was found to contain 81·7%Ni, 9·8%P and 10·5%kaolin. Heat treatment at 400°C for 1 h results in an increase in the hardness and wear resistance of the composite coating. The corrosion resistance is also highly enhanced by the incorporation of kaolin in the nickel–phosphorus matrix. The crystallite size of the composite coating is 20 nm, and the codeposition of kaolin follows the Langmuir adsorption isotherm.     

Corrosion characteristics of electroless Ni–P coating in sulfur‐bearing solution

The corrosion behaviors of electroless Ni–P coatings deposited on carbon steel in sulfur‐bearing solutions were investigated by weight gain test and scanning electron microscopy. The results indicate that the corrosion rate of electroless Ni–P coating was directly related to the sulfur content, immersion time, and test temperature. The corrosion rate increased with the prolonged immersion time. Increasing the temperature can markedly increase the corrosion rate of electroless Ni–P coating. The electroless Ni–P coating had a better corrosion resistance than 316L stainless steel against Cl^? corrosion in sulfur‐bearing solution.