镁合金一步酸洗活化前处理工艺

采用失重法、扫描电子显微镜、动电位极化曲线等,对比研究了经四种酸洗活化配方处理后的镁合金的腐蚀行为,并研究了不同酸洗活化配方对后续化学镀Ni-Sn-P镀层的形貌、成分及结合力的影响。结果表明,一步酸洗活化工艺对镁合金的浸蚀效果良好,表面粗糙均匀,无腐蚀产物堆积,与基底的"互锁"效应增强。经一步酸洗活化处理的镁合金基底的耐蚀性最佳。经一步酸洗活化后的镁合金电化学镀层能更有效地保护镁合金基体。     

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。     

AZ31B镁合金在MgSO_4溶液中的电化学交流阻抗谱解析

解析了AZ31B镁合金在MgSO4溶液中的电化学交流阻抗谱,从而得到镁合金在不同极化电位下的腐蚀过程信息。结果表明:在自腐蚀电位下,镁合金溶解,谱图受Mg2+向本体溶液扩散控制;在较自腐蚀电位稍正的范围,镁合金表面开始形成Mg(OH)2沉淀膜;在活化电位附近,镁合金表面又有部分Al(OH)3沉淀的生成,SO2-4离子对合金造成严重的点蚀作用。通过对腐蚀产物进行XRD表征,证实了镁合金中的铝参与了反应。     

镁合金阳极氧化膜在NaCl溶液中的腐蚀行为

利用盐水浸泡实验研究了AZ91D镁合金阳极氧化膜层在3．5％NaCl溶液中的腐蚀行为。结果表明：AZ91D镁合金阳极氧化膜层不论封闭与否,在中性NaCl溶液中浸泡出现第一个腐蚀点后,膜层表面均很少再出现新的腐蚀点,而是原有的腐蚀点向纵、横两个方向扩展形成腐蚀坑,表面呈“树枝”状腐蚀形貌;浸泡溶液的pH值对阳极氧化膜层的耐蚀性影响很大,酸性溶液中的腐蚀速率明显大于中、碱性溶液的;随浸泡溶液温度的升高阳极氧化膜层的腐蚀速率加快。据此,提出了AZ91D镁合金阳极氧化膜层在NaCl溶液中腐蚀过程的模型。     

镁合金表面氟转化层降解过程的电化学阻抗谱

为改善镁合金的生物降解性能,在镁合金AZ31表面制备氟转化层,研究氟转化层的电化学阻抗谱(EIS)在Hank’s仿生溶液中随浸泡时间的变化,并结合浸泡过程中氟转化层表面形貌和成分的变化,探讨氟转化层的形成机理及在仿生溶液中的降解行为。结果表明:氟处理后镁合金表面生成Mg F2转化膜,反应过程中氢气的产生在膜层表面生成不贯穿膜层的孔隙;在Hank’s仿生溶液浸泡过程中,氟转化层电阻随浸泡时间的延长而降低,氟化镁层缓慢溶解并生成氢氧化镁。同时,溶液中的Ca2+、HPO42-和PO43-等离子沉积在表面;由于氟转化层表面存在微孔,浸泡15 min时,小孔腐蚀过程已经开始;浸泡至7 d时,孔核表面区域的膜层溶解穿透,进入腐蚀孔的发展阶段;浸泡至15 d时,发生明显点蚀;氟转化层微孔处溶解速度较大,导致Cl-渗透至基体,镁合金发生点蚀,点蚀产生的腐蚀产物在孔中堆积形成胞状突起。     

镁合金表面磁控溅射-微弧氧化制备Al_2O_3膜层的组织结构及性能

采用磁控溅射-微弧氧化的方法在镁合金表面制备了Al_2O_3膜层,随后采用X射线衍射分析(XRD)、扫描电镜(SEM)、能谱分析(EDX)等方法对微弧氧化膜层的相结构、截面形貌及膜层中的元素分布进行了分析,采用摩擦磨损和电化学腐蚀方法对膜层的耐磨耐腐蚀特性进行了测试。结果表明,通过先进行磁控溅射后进行微弧氧化的方式可以在镁合金表面获得Al_2O_3微弧氧化膜层。通过改变反应终止电压可控制微弧氧化膜层的厚度。当反应终止电压不高于510 V,膜层主要由铝和Al_2O_3组成。而当微弧氧化反应终止电压超过600 V后,铝膜层完全参与反应转变为微弧氧化膜层,膜层主要由Al_2O_3和MgO组成。Al_2O_3微弧氧化膜层的形成有助于提高镁合金表面的耐磨耐腐蚀性能。     

海洋性气候下镁合金与钢件的电偶腐蚀

在高温度、高湿度（81.8%）、多酸雨的盐雾环境中,镁合金表面可以形成一层含Cl^-的电解质膜,这层膜使镁合金与钢件之间构成腐蚀电偶对。根据电化学极化理论、腐蚀热力学和动力学理论,综合分析了钢件对镁合金的腐蚀行为及规律的影响,并探讨了防止镁合金电偶腐蚀的一些方法。     

镁合金黑色微弧氧化膜在NaCl溶液中腐蚀电化学演变

目的 评价镁合金黑色微弧氧化热控膜层在氯离子作用下的腐蚀演变行为.方法 在电解液中添加不同浓度的添加剂制备微弧氧化膜层,分析不同微弧氧化膜试样在0.1 mol/L NaCl溶液中的电化学演变过程.采用电化学极化、电化学交流阻抗表征和拟合,结合扫描电镜等方法,对膜层演变规律及机理进行了探讨.结果 未经微弧氧化的镁合金自腐蚀电流密度为17.7 μA/cm2,自腐蚀电位为-1.464 V;经微弧氧化后,试样自腐蚀电流密度减小至0.09 μA/cm2,自腐蚀电位下降至-1.628 V.添加剂加入后制备的微弧氧化膜相比于镁合金基体,其耐蚀性能提高,且随着添加剂浓度的增加,耐蚀效果呈现先增加、后减弱的趋势,添加剂质量浓度在10 g/L时制备的膜层具有最好的防腐效果.镁合金微弧氧化热控膜层在NaCl溶液中腐蚀过程分为三个阶段:一是腐蚀性离子进入多孔膜层,引起界面熔融层变化;二是MgO与水分子反应造成内层膜更加致密,阻抗有所增加;三是腐蚀溶液接触到部分镁合金基底,发生电化学腐蚀,形成楔形效应,引发裂纹,最终导致局部腐蚀失效.结论 微弧氧化提高了膜层的耐蚀性能,其在0.1 mol/L NaCl溶液中的腐蚀过程可分为介质进入孔内、水合反应和局部腐蚀三个阶段.     

镁合金磷酸盐 /氮化硅双层复合膜结构及耐蚀性能研究

目的针对传统镁合金化学转化膜裂纹尺寸大、耐腐蚀性差等问题,制备一种镁合金磷酸盐/氮化硅双层结构的抗腐蚀复合膜。方法先对镁合金进行传统磷酸盐转化处理,再运用等离子体增强化学气相沉积技术沉积氮化硅膜层,分析复合膜的形貌、元素分布、表面电位及极化曲线,并与磷酸盐转化膜进行对比。结果氮化硅膜层能在磷酸盐转化膜裂纹处选择性优先沉积,从而在相当程度上填补转化膜层的裂纹,形成致密的复合膜结构。具有复合膜结构的镁合金表面电位和腐蚀电位明显高于传统磷酸盐转化处理的镁合金。结论镁合金表面制备磷酸盐/氮化硅双层复合膜后,抗腐蚀能力明显高于传统磷酸盐转化处理的镁合金。     

AZ31镁合金表面磁控溅射沉积铝膜研究

在AZ31镁合金表面采用直流磁控溅射技术沉积铝膜,通过能谱分析仪、原子力扫描显微镜和LK9805电化学分析仪分别研究了铝层的成分分布、形貌和耐蚀性能。结果表明:在镁合金表面沉积形成晶粒细小且均匀分布的致密铝镀层;铝层和基体之间存在混溶的过渡层,且与基体镁合金结合良好,表现出一定的耐蚀性能。铝镀膜有利于镁合金表面防护层的形成,减小其腐蚀倾向。     

Properties of fluoride film and its effect on electroless nickel deposition on magnesium alloys

The physical characteristics and microstructure of the fluoride film formed during activation were investigated using SEM,XPS and SAM,and its stability in electroless nickel(EN) bath was analyzed.The effects of the fluoride film on EN deposition were studied additionally.The results show that the fluoride film on magnesium alloys is a kind of porous film composed of MgF2 with thickness of 1.6-3.2 μm.The composition of the activation bath and pretreatment of EN processing have influence on the composition of the fluoride film.The fluoride is stable and dissolves little in EN bath;as a result,the fluoride film can protect magnesium substrate from the corrosion of EN bath.The composition of fluoride determines the initial deposition of EN and part of the fluoride film finally exists as inclusion in EN coating.     

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.     

Effect of the Substrate Surface Morphology on the Porosity of Electroless Nickel Coatings

Electroless nickel (EN) plating is an autocatalytic chemical reduction process, the EN deposition developing in three dimensions during the plating. The substrate surface morphology determined by basis metal conditions and pretreatment process can significantly affect the porosity of the EN deposit. Models of EN deposition on different substrate surfaces were postulated based on the results of investigations by Scanning Electron Microscopy (SEM) and stylus 3D surface measurements. The postulated models indicate “morphology conflict” during EN plating. Examples of EN plating are given to confirm the postulated EN deposition models. The methods to reduce the porosity of EN and make high quality (pore-free) EN coating are discussed.     

镁合金化学镀镍层的结合机理

镁合金在直接化学镀前的活化处理时，表面生成一层氟化物保护膜，溶解度计算及XPS分析表明，氟化物膜在镀液中可稳定存在，用SEM，XPS，SAM考察了初始沉积Ni，镀层横截面以及开裂后的断面形貌与成分，发现在镀层与基体之间存在着氟化物，镀液成分与Ni的混杂层，这一混杂层是镀层与基体结合的最薄弱环节，镀层开裂通常首先发生在此混杂层内。     

镁合金无铬无氟前处理直接化学镀镍研究

采用磷酸为主要成分的溶液取代传统的铬酸加氢氟酸对镁合金进行活化处理,然后直接化学镀镍;用SEM/EDAX考察了无铬无氟前处理转化膜和化学镀镍沉积层的形貌、成分.结果表明,无铬无氟转化膜主要由磷酸镁组成,化学镀镍层表面较均匀、致密、无明显缺陷.经热处理后,镀层和基体的结合强度超过23 MPa.动电位极化测试结果表明,镀层体系的自腐蚀电位约为-0.36 V(SCE),有明显的钝化区间,对基体镁合金起到较好的防护作用.     

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.     

One-step pickling-activation before magnesium alloy plating

A one-step pickling-activation process was proposed as an environmental friendly pretreatment method in phosphate-permanganate solution before electroplating on magnesium alloys. The effects of pickling-activation on qualities of coating were assessed by adhesion and porosity testing of copper plating. The interfacial reactions between specimen and solution were analyzed with SEM, EDX and XRD. The results show that the developed process of pickling-activation can equalize the potentials on substrate surface. The compacted zinc film can be obtained by zinc immersion after treating magnesium alloy in the pH 4-6 phosphate-permanganate solution for 3-5 min. The adhesion and corrosion resistance of copper plating are enhanced. The one-step pickling-activation can replace the existing two-step process of acid pickling and activation which contains a great deal of chromium and fluorine. The procedure of surface pretreatment is simplified and the production environment is improved.     

镁合金表面化学镀镍前处理工艺的研究进展

镁合金作为最轻的金属结构材料,具有密度低、比强度高、弹性模量大等优势,在航天航空、汽车工业、电子通讯等领域广泛应用,但其化学性质非常活泼,在常温下很容易发生腐蚀,严重限制了其进一步推广应用。化学镀镍具有镀层致密、环境友好等优点,可有效提高镁合金的耐蚀性和耐磨性,但与普通基体相比,镁合金属于难镀金属,化学镀镍前既要去除基体表面原有的疏松多孔的氧化膜,又要生成具有保护和催化作用的新膜层,因此前处理工艺是影响镀层质量及镁合金防腐性能提高的关键因素。以化学镀镍前处理工艺为研究内容,介绍了镁合金化学镀镍前处理工艺的国内外研究现状,从除油、酸洗、活化、浸锌法、预镀层和化学转化膜等方面进行了文献综述和分析,指出相应工艺的优缺点,并探讨了研发方向。根据前处理技术的机理和不同牌号镁合金的特点,研发工艺简单、镀层性能优良、可控性强、环境友好、通用性强的低成本工艺,将是镁合金化学镀镍前处理的研究方向和发展趋势。     

Optimizing parameters affecting electroless Ni-P coatings on AZ91D magnesium alloy as corrosion protection barriers

Magnesium alloys are materials difficult to plate due to their high reactivity. The surface passive layer formed in air or water must be first removed prior the plating process. Generally, it was shown that electroless Ni–P coatings on AZ91D alloy are directly related to its surface pretreatment parameters and the various plating conditions. Micro-image morphology and chemical composition of the different coats were characterized by SEM, EDX, XRF and XRD techniques. Electrochemical polarization, porosity and adhesion tests were also performed to study the corrosion resistance of the samples. The plating step was accomplished either after a zincating treatment or directly after the fluoride activation treatment using basic nickel plating bath. Successful direct EN coatings obtained are good corrosion barriers for AZ91D alloy in aggressive environments.     

一种无铬低氟的镁合金化学镀镍前处理工艺

为了获得一种更加环保的镁合金化学镀镍前处理工艺,通过多种方法和手段对比研究了3种不同的酸洗活化工艺对镁合金化学镀镍的影响。通过开路电势-时间(OCP-t)曲线解释了不同前处理方法导致不同沉积速度的原因。采用SEM、EDX和XRD分析发现,3种工艺所得镀层均为高磷合金镀层(P含量约为11%),镀层的表面形貌和结构比较接近。动电位极化曲线表明,采用H_3PO_4+HNO_3酸洗,K_4P_2O_7和NH_4HF_2分别活化的前处理工艺所得镀层耐蚀能力略优于传统工艺镀层。新工艺酸洗液对镁合金存在横向的刻蚀,可增强镀层与基底间的机械咬合作用,使得镀层的结合力更强。