AZ91镁合金化学镀镍前处理的工艺

研究了H3PO4+Na2MoO4、H3PO4+KMnO4和H3PO4+Na3PO4三种酸洗工艺以及NH4HF2活化工艺等前处理工艺对AZ91 HP镁合金化学镀的影响.通过金相实验及极化实验,结果表明,AZ91 HP镁合金经H3PO4+ Na3PO4酸洗后再经NH4HF2工艺活化处理后施镀,可获得表面光亮、结合力强和耐蚀性能较好的镍-磷镀层.镁合金酸洗处理后表面的平整程度会影响其化学镀层平整度和光亮度,而活化处理后表面的粗糙程度则影响镀层和基体的结合力.     

A study on the electroless Ni-P deposition on WE43 magnesium alloy

In this paper an attempt has been made to understand the mechanism of the deposition process of an electroless Ni-P (EN) coating on WE43 magnesium alloy. Also a number of properties concerning the deposited coatings have been reviewed. The results show that the starting microstructure of the alloy consists of a primary α phase together with some eutectic β phase at triple points and along with some grain boundaries. Microstructural studies reveal an uneven distribution of alloying elements in the phases and they are predominantly segregated to the eutectic β phase. This phenomenon can result in galvanic coupling between eutectic β and primary α phases. Detailed studies prove that the replacement reaction takes place at the early stages of coating, and is followed by the autocatalytic reaction at the next stages of deposition.The X-ray diffraction patterns of primitive coatings show a broad peak around 2θ of 45°, which is an indication of an amorphous or an extremely fine crystalline structure. Annealing at 400 °C for an hour led the nature of deposits to be changed to crystalline phases of Ni, Ni₃P, and NiP₃. Microhardness values of coatings are considerably higher than those of the bare substrate. These further increase when they are annealed at 400 °C for 1 h. Electrochemical polarization curves and calculated corrosion values reveal higher corrosion potential (E_corr) for the coating than for the bare substrate. This decreases again when the coating is annealed at 400 °C for 1 h.     

高稳定性化学镀镍磷合金工艺研究

采用正交试验法研究了络合剂,促进剂,稳定剂以及温度对镀层和溶液性能的影响,从而得到了一种高稳定性的化学镀镍磷合金工艺。该工艺所得镀层磷含量较高,沉积速度快,镀液使用寿命长,并已在工业生产中加以应用。     

ZL104合金表面化学镀镍磷合金层的研究

在ＺＬ１０４合金表面上进行Ｎｉ－Ｐ与Ｎｉ－Ｃｕ－Ｐ化学镀,以提高ＺＬ１０４合金材料的耐蚀性与耐磨性。结果表明：化学镀可以显著提高ＺＬ１０４合金表面的硬度,并改善其在５％ＮａＣｌ溶液中的耐蚀性;在２００～５２０℃温度下热处理后,镀层的硬度显著提高,但耐蚀性略有降低,这可能与镀层中的析出物Ｎｉ３Ｐ析出有关。     

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.     

AZ91D镁合金的均一化前处理与化学镀Ni-P

采用新型环保的均一化前处理工艺在AZ91D镁合金表面制备了化学镀Ni-P镀层。研究了前处理过程中AZ91D基体微观形貌、镀层沉积过程、成分和相结构。研究结果表明：基体表面的β相在前处理过程中被选择性去除,表面组织得到均一化,从而获得均匀致密的浸Zn层。Ni-P颗粒均匀形核生长,并最终形成致密的镀层。镀层具有优良的耐腐蚀性能。     

Direct electroless Ni-P plating on AZ91D magnesium alloy

An electroless Ni-P plating treatment was applied on AZ91D magnesium alloy to improve its corrosion resistance. Optimum pretreatment conditions and optimum bath of electroless nickel plating for magnesium alloy were found through many experiments. In order to avoid bother of pre-plating medium layer, a set of procedure of direct electroless Ni-P under the acid condition was investigated. The properties of the coating with 10% phosphorus were investigated. The results show that a coating with high hardness, low porosity and good adhesive strength is obtained. X-ray diffraction patterns show that the structure of the coating is an amorphous phase. After annealing at 400 ℃, the amorphous phase of Ni-P is transformed to crystalline phases, and some intermetallics as Ni3P and Ni5P2 are deposited from Ni -P solid solution along with an enhancing hardness from Hv 450 to Hv 910.     

镁合金化学镀中预处理氟化镁膜的特征与作用

对镁合金的表面前处理工艺进行研究,探讨氟化镁在化学镀层中的存在形式及作用。结果表明：酸浸使镁合金表面形成一层氧化物膜;活化过程生成的氟化镁不具备反应活性,对镁合金基体有保护作用,使之免于受镀液的过度腐蚀;对化学镀层断口进行SEM元素分布分析显示氟化镁层集中存在于镁合金基体与Ni-P镀层之间;但过度活化会导致化学镀层孔隙率升高,以3.5%NaCl溶液为介质的动电位极化测试表明,过度活化会导致化学镀层耐蚀性下降。     

pH值对镁合金化学镀Ni-P合金的影响

为进一步确定pH值对镁合金化学镀Ni-P合金的影响,利用扫描电镜(SEM),能谱仪(XPS),显微硬度仪以及极化曲线等方法分析镀层的形貌和性能.结果表明:pH值对镀层的性能影响较大,pH值很低时难于施镀 ,形貌在pH值为8时最好,镀层的含磷量随着pH值的升高而降低;在一定范围内,硬度随着pH值的升高而降低;在pH值为4时,其镀层的自腐蚀电位最高达到-0.92V,耐腐蚀性能最好.     

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.     

Electroplating zinc transition layer for electroless nickel plating on AM60 magnesium alloys

Electroplating zinc coating as transition layer of electroless nickel plating on AM60 magnesium alloys was investigated. The zinc film can be deposited in a pyrophosphate bath at 50-60 ℃ under current density of 0.5-1.5 A/dm^2. A new fore treatment technology was applied by acid cleaning with a solution containing molybdate and phosphorous acid, by alkaline cleaning in a bath containing molybdate and sodium hydroxide. The subsequent electroless plating was carried out in nickel sulfate bath. The SEM observation shows that the deposition is uniform and compact. The polarization curve measurements show that the corrosion potential of the zinc plating in 3.5% NaCl is about -1.3 V（vs SCE） which is noble than that of magnesium substrate. The zinc eleetroplating can be applied as the pretreatment process for electroless nickel plating on magnesium alloys.     

镁合金AZ51直接化学镀镍研究

采用沉积速率计算、镀镍形貌观察和腐蚀性能测试，研究了镀镍时间对镁合金AZ51直接化学镀镍的影响。结果表明，镁合金AZ51表面可通过直接化学镀镍形成镍磷合金镀层。随着镀镍时间的增加，沉积速率先增加后降低并在镀镍时间为0．5h时取得最大值，而腐蚀速率逐渐降低，腐蚀性能逐渐增强。     

微过滤及超过滤技术在化学镀镍工艺中的应用研究

实验表明在以工业级药品为原料的化学镀镍工艺中应用微过滤或超过滤技术,可显著地改善镀层的耐蚀性,其效果可与以试剂级药品为原料的化学镀镍层媲美。     

镁合金在镀液中的腐蚀行为

摘要：通过腐蚀实验和阳极极化曲线研究了硫酸镍主盐配制的化学镀镍液成分和温度对AZ91D镁合金的腐蚀行为的影响，比较了碱式碳酸镍主盐和硫酸镍主盐两种镀镍液的腐蚀性以及施镀后的镀层质量。结果表明：硫酸镍镀液的腐蚀性比碱式碳酸镍镀液大，在低温下，镁合金在硫酸镍镀液中表面的氟化镁膜不致密，镀液对基材的腐蚀性高；而在高温下，Mg^2 与F^-的反应性增强，氟化反应完全，形成的氟化镁钝化膜致密性高，可保护镁合金基体免遭镀液的腐蚀。在施镀温度下，镀液中F^-的缓蚀作用，可使SO4^2-离子对镁合金的腐蚀速率大大降低。     

AZ31镁合金“两步法”化学镀Ni -P合金组织及性能研究

研究了AZ31镁合金表面的“两步法”化学镀Ni -P工艺(TSENP).结果表明:在AZ31镁合金表面直接中性化学键8min后可以实现以硫酸镍为主盐的第二步化学镀Ni -P合金,镀层的表面光亮、均匀、致密、无明显缺陷,含磷质量分数为11.42％,表面硬度比AZ31镁合金基体有了很大的提高,与基底的结合力好,并具有优良的耐蚀性能.     

镁合金表面化学镀Ni-P合金研究

镁是一种极活泼的金属,其合金具有优异的性能,是得到广泛应用的重要原因.然而,镁合金在各介质中的不耐蚀,其应用受到了制约.据文献报道,已有多种方法被应用到镁合金上,但效果都不很理想;而化学镀镍技术是近年来发展较快的一种表面处理方法.进一步探讨了在AZ91D表面上进行化学镀镍的研究过程:通过多次试验确定了镁合金的前处理方案,研究了在酸性条件下镁合金表面直接化学镀镍的一套工艺路线,配置简单,操作方便,避免了预镀中间层的麻烦.并且测定了镀层的厚度、显微硬度,观察了镀态的金相组织;热震实验和划痕实验的结果表明镀层与衬底具有良好的结合力.     

Corrosion and wear properties of electroless Ni-P plating layer on AZ91D magnesium alloy

A direct electroless Ni-P plating treatment was applied to AZ91D magnesium alloy for improving its corrosion resistance and wear resistance. Corrosion resistance of the Ni-P coatings was evaluated by potentiodynamic polarization and immersing experiments in 3.5% NaCl solution. The wear resistance of the coatings was investigated by the wear track and the mass change after ball-on-disk experiment. The results show that corrosion resistance and wear resistance of the AZ91D alloy are greatly improved after direct electroless Ni-P plating. No discoloration is noticed until 4 d of immersion in 3.5% NaC1 solution. Potentiodynamic polarization experiments show that the free corrosion potential of magnesium alloy is shifted from -1 500 mV to -250 mV and passivation occurs at 1 350 mV after direct electroless plating. The friction coefficients and wear rates of Ni-P coating and Ni-P coating after tempering are 0.10-0.351, 9.038×10^-3 mm^3/m and 0.13-0.177, 3.056×10^-4 mm^3/m, respectively, at a load of 1.5 N with dry sliding. Although minor hurt on corrosion resistance was caused, significant improvement of wear resistance was obtained after tempering treatment of the coating.     

Electroless Ni-P coating of different magnesium alloys

Coating of AZ31B, AE 42 and ZRE1 wrought magnesium alloys was carried out using electroless Ni plating technique in a solution of nickel sulphate, sodium hypophosphite, ammonium hydrogen fluoride and glycine with a zinc immersion pre-treatment.The results of SEM/EDX investigations and X-ray diffraction indicate that the coat exhibit a typical surface morphology with compact nodules with good adherence to the substrate. The coat was composed of amorphous structure, which transformed to a mixture of crystalline Ni and Ni₃P precipitates after heat treatment at 673°K for 1 h. The phosphorous (P) content increased gradually from the substrate towards the surface reaching a maximum of 10 wt.% to 18 wt.% on the surface depending on the substrate alloy and the thickness of deposit. The hardness of the coat was found to increase with the P content and also after heat treatment. The electrochemical corrosion test in NaCl solution indicated a great improvement in the corrosion resistance of the Mg substrates and that a noble behaviour of Ni-P was obtained regardless of the heat treatment process. The forming ability test indicates that hot rolling of the coated substrate does not succeed to keep a continuous coat due to cracking of the coat in both as-coated and heat treated specimens.