【作者】 孙丽萍；

【导师】 江忠浩；

【作者基本信息】 吉林大学 ， 材料学， 2006， 硕士

【摘要】 本文分别以08Al钢板和AZ91D镁合金为基体对光亮纳米锌镍合金涂层进行了研究。08Al钢板是在碱性锌酸盐电镀液中通过电镀方法直接获得纳米锌镍合金涂层,本试验合成了一种添加剂,增大了阴极极化,使阴极上的形核率增加,晶核长大受到抑制,镀层中锌镍共熔体的结晶细化,形成纳米晶粒。通过赫尔槽试验研究了纳米锌镍合金镀层的沉积条件,光亮剂的加入量与镀层区域之间的关系,采用TEM,SEM,XRD等技术对涂层进行了研究,得出了电流密度与晶粒度的关系曲线及电流密度与团簇尺寸的关系曲线。盐雾试验结果表明,该镀层的耐蚀性是纯镀锌层的7～10倍,镀层无氢脆。AZ91D镁合金则先在以硫酸镍为主盐的镀液中通过化学镀方法获得镍磷涂层,然后再电沉积锌镍涂层从而获得镍磷/锌镍复合涂层。通过XRD和SEM技术对AZ91D镁合金上镍磷合金沉积层的形核和机理进行分析。同时对镁基体前处理酸洗时间对化学镀Ni-P涂层的影响也进行了研究。涂层的硬度值达约为660VHN,其不受前处理影响。通过SEM、XRD等技术对AZ91D镁合金表面镍磷/锌镍复合涂层的微观组织形貌和成分进行了研究,也对其结合力及耐蚀性进行了研究,结合力实验结果表明,其结合力很好。盐雾实验结果表明,其耐蚀性也很好。更多还原

【Abstract】 Nanocrystalline zinc–nickel alloy coating on steel obtained from analkaline zincate bath containing a laboratory-made additive and Ni–P/Zn-Nicompound coating on the AZ91D magnesium alloy were investigated in thispaper.We use alkaline bath in order to get uniform nickel content Zn-Nicoating. The effects of the additive content and the cathode current density onthe grain sizes of the coatings were studied.SEM and TEM observations andXRD analysis were performed to examine the microstructure (grain size) andphase composition of the coatings. The experimental results indicated that theaddition of the additive leads to a much brighter and a more uniformnanocrystalline deposition with the grain sizes varying from 14 to 33 nm.The Hull cell test was used to determine the optimum ranges of both thecathode current density and the additive content. Salt spray tests andpolarization measurements indicated that the nanocrystalline zinc–nickelalloy coatings have a better corrosion resistance than the zinc coatingsdeposited from a simple alkaline zincate bath. Direct electroless Ni–P plating on the AZ91D magnesium alloy from aplating bath containing sulfate nickel,then electroplating Zn-Ni coating on theAZ91D magnesium alloy.The nucleation mechanism of Ni–P deposits on theAZ91D magnesium alloy was studied by using XRD and SEM. Theelectroless Ni–P deposits were preferentially nucleated on the β(Mg17Al12)phase and extended to the primary and eutectic α phases of the AZ91Dmagnesium alloy. The effect of the acid pickle treatment time of the AZ91Dmagnesium alloy substrate on the electroless Ni–P plating was alsoinvestigated.With prolonging the acid pickle treatment time, the cluster ofelectroless Ni–P deposition became smaller and the deposits were found to bemore compact. The deposition rate of electroless Ni–P plating wasproportional to the acid pickle treatment time. The hardness values of theNi–P coatings were about 660 VHN and were not influenced by thepretreatments.We investigated micro configuration and component of theNi-P/Zn-Ni compound coatings by SEM and XRD.We also test the adhesionability and anticorrosion property by adhesion test,salt spray test andpolarization curve. The adhesion test result indicate that the adhesion of theNi-P/Zn-Ni compound coatings is finer.The salt spray test result indicate thatthe anticorrosion property of the Ni-P/Zn-Ni compound coatings is excellent.The experiments and theory analysis in this study lead to the followingconclusions:(1) The grain size 14.6~19.8nm nanocrystalline Zinc-Nickel alloycoatings obtained from alkaline zincate bath in the test. The optimum bathcomposition of the bright nanocrystalline Zinc-Nickel alloy coatings was:Zinc oxide 12 g/l, Sodium hydroxide 120 g/l, Nickel ion 1.5 g/l, Heliotropin0.5 g/l, PEAA 30g/l and the additive 8ml/l.(2) The grain size reduces with the increasing of the cathode currentdensity and abruptly at low current density and tends to quite constant after8A dm-2. The grain size of crystals is linear with cathode potentialapproximately. The test results of the grain size of crystals and compositionof phase are same using TEM and XRD. The composition of phase is singleγ-phase (Ni5Zn21). The coating exhibited better corrosion resistance and finergrain size in contrast to Zn–Ni coating reported before. The brightnanocrystalline Zinc-Nickel alloy coatings has shown excellent corrosionresistance and less brittleness and in comparison with the zinc coatings. Theservice life of nanocrystalline Zn-Ni electrodeposits is longer, it provideimproved anticorrosion protection for steel in extremely aggressiveenvironments it is a suitable replacement for zinc. The excellent properties ofan electrodeposited nanocrystalline Zn–Ni coating make it a promisingmaterial for many industrial applications.(3) Direct electroless Ni-P plating on the AZ91D magnesium alloy froma plating bath containing sulfate nickel was first investigated in this paper.The effect of the acid pickle treatment time of the magnesium alloy substrateon the electroless Ni-P plating was also investigated. It was found that withprolonging the acid pickle treatment time, the electroless Ni-P depositsbecame more compact and defect free. The deposition rate of the electrolessNi-P plating was proportional to the acid pickle time. The hardness of theNi-P coating was not influenced by the pretreatments and was about 660VHN.(4) The nucleation mechanism of the electroless Ni-P plating on theAZ91D magnesium alloy was studied by using XRD and SEM. Thedeposition motivation at the initial deposition stage was attributed to theelectrochemically heterogeneous surface of the AZ91D magnesium alloy.From the XRD results and the determinations of the phosphorus contents inthe Ni-P deposits at different plating intervals, it can be seen that theelectroless Ni-P deposits had preferentially nucleated on the β (Mg17Al12)phase and then extended to other phases of the AZ91D magnesium alloy.(5) From the adhesion tests results and the salt spray test results,it can beseen that the adhesion and the corrosion of the Ni-P/Zn-Ni compoundcoatings is excellent.更多还原