以硫酸镍为主盐的AZ91D镁合金化学镀镍研究

研究了以硫酸镍为主盐的AZ91D镁合金化学镀镍.采用无铬前处理在AZ91D镁合金表面形成高锰酸盐和磷酸盐化学转化膜,用SEM、EDX、XRD和极化曲线等方法研究化学转化膜和化学镀镍层的形貌、组成及在3.5%的NaCl溶液中的耐腐蚀性能.结果表明,在高锰酸盐转化膜表面形成的化学镀镍层呈胞状,较致密,有微裂纹;在磷酸盐转化膜上形成的化学镀镍层也呈胞状,晶胞大小不均匀,没有微裂纹.镀层厚度均匀,致密,无孔隙.在3.5%的NaCl溶液中的极化曲线表明化学转化膜对镁合金基体的耐腐蚀性能提高不大,经高锰酸盐和磷酸盐前处理的化学镀镍层腐蚀电位分别为-0.48V_(SCE)和-1.12 V_(SCE).以硫酸镍为主盐的经磷酸盐前处理的化学镀镍层较好地提高了镁合金的耐腐蚀性能.     

模拟海洋环境中Ni-Co合金镀层对AZ91D镁合金的腐蚀防护研究

目的提高AZ91D镁合金的腐蚀防护性能。方法采用化学镀前处理在AZ91D镁合金表面制备一种保护性的Ni-Co合金镀层。分别采用环境扫描电镜(ESEM)、X射线衍射(XRD)和能量散射谱(EDS)分析合金镀层的表面形貌、微结构特点和化学成分。采用动电位极化(PC)和电化学阻抗谱(EIS),分析测试在模拟海洋环境(中性3.5%Na Cl溶液)中Ni-Co合金镀层对AZ91D镁合金的腐蚀防护性能。结果镁合金表面化学镀Ni-P镀层均匀覆盖,晶粒生长较致密,表面呈菜花状形貌,Ni-P镀层中P质量分数约为5.6%。Ni-Co合金镀层表面均匀且呈金字塔状形貌,形成了面心固溶体(FCC),镀层中Co质量分数约为31%。Ni-P镀层和Ni-Co合金镀层的厚度分别约为11μm和19μm。在模拟海洋(中性3.5%Na Cl溶液)环境中,镁合金裸基体、化学镀前处理Ni-P镀层、Ni-Co合金镀层的腐蚀电位分别为-1485、-372、-284 m V,其腐蚀电流密度分别是3.4×10-5、1.8×10-6、2.9×10~(-7) A/cm2,所拟合的电荷转移电阻分别为4.72×103、1.70×104、2.06×106?/cm2。结论化学镀前处理Ni-P镀层可为镁合金提供较好的腐蚀防护,Ni-Co合金镀层能够为镁合金提供更显著的腐蚀防护。     

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.     

锡酸盐转化前处理对镁合金化学镀镍镀层的影响

目的利用锡酸盐转化膜中间层避免化学镀镍镀层与金属基体的直接接触,降低其产生原电池腐蚀的趋势,提高镁合金化学镀镍层的耐蚀性及稳定性。方法采用锡酸盐化学转化膜技术在AZ31镁合金表面制备锡酸盐转化膜层,然后通过直接化学镀镍技术在该膜层上沉积Ni-P镀层。利用SEM、EDS、浸泡析氢、电化学测试等手段,研究了复合镀层的显微结构、相组成、耐蚀性。结果锡酸盐转化膜由细小均匀的球形颗粒堆积而成,颗粒之间存在空隙,为直接化学镀镍时镍磷的初始沉积提供了可能。化学转化膜表面沉积的化学镀镍层均匀致密,形成典型的胞状结构。基体-化学转化膜-化学镀Ni-P合金层三者之间的结合良好,保证了复合镀层优良的耐蚀性能。结论化学镀Ni-P层能够在不经过钯活化处理的条件下直接在锡酸盐转化膜上沉积,锡酸盐转化膜中间层避免了Ni-P阴极性镀层与阳极性镁基体的直接接触,降低了Ni-P镀层局部缺陷对整体防护效果的影响,提高了镀层的耐蚀性及耐久性。     

Ceria/stannate multilayer coatings on AZ91D Mg alloy

In this work, CeO₂/stannate multilayer coatings on AZ91D magnesium alloy were successfully obtained by chemical conversion and sol–gel dip coating. The stannate conversion coatings were prepared from a stannate aqueous bath containing Na₂SnO₃, CH₃COONa, Na₃PO₄ and NaOH at different temperatures and immersion times. Ceria films were produced on stannate/AZ91D starting from Ce(III) nitrate solutions in H₂O. In some cases, the PVA was added as chelating agent. Ceria top coatings were fired at 200 °C for 1 h. Coating microstructure was examined by FE-SEM. Finally, the corrosion resistance features of the coatings were tested by the electrochemical impedance spectroscopy (EIS) in 3 wt.% NaCl solution. The effect of PVA addition was evaluated in terms of microstructure and corrosion resistance features. CeO₂/stannate multilayer films, 3 μm thick, uniform, well adherent and nearly crack free were obtained. The formation of CeO₂ phase was confirmed by XRD and XPS analyses. The XPS depth profiles showed a limited diffusion of Mg towards the ceramic film. The EIS tests showed a significant improvement of corrosion resistance of the multilayer coatings (~ 16.6 kΩ after 48 h in NaCl solution) with respect to the blank alloy (~ 2.4 kΩ after 48 h in NaCl solution).     

Electrodeposition of zinc on AZ91D magnesium alloy pre‐treated by stannate conversion coatings

A stannate chemical conversion process followed by an activation procedure was employed as the pre‐treatment process for AZ91D magnesium alloy substrate. Zn was electroplated onto the pre‐treated AZ91D magnesium alloy surface from pyrophosphate bath to improve the corrosion resistance and the solderability. The surface morphologies of conversion coating and zinc coating were examined with scanning electron microscope (SEM). The phase composition of conversion coating was investigated by X‐ray diffraction (XRD). The electrochemical corrosion behavior of the coatings in the corrosive solution was investigated by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). The experimental results showed that the activated stannate chemical conversion coating provided a suitable interface between zinc coating and the AZ91D magnesium alloy substrate. The corrosion resistance of the AZ91D substrate was improved by the zinc coating.     

新型三元复合络合剂体系对AZ91D镁合金表面酸性化学镀Ni-P的影响

利用含新型三元复合络合剂的酸性化学镀镍液体系,在AZ91D镁合金表面通过化学镀制备Ni-P防护镀层。结果表明,镀层沉积速率随着镀液中三元复合络合剂浓度的变化而改变。利用X射线衍射（XRD）、扫描电子显微镜（SEM）和差热分析（DSC）对镀层结构、形貌以及热稳定性进行表征和分析。通过交流阻抗（EIS）和动电位扫描极化曲线对Ni-P镀层在3.5%NaCl溶液中的耐蚀性能进行评价。镀液中三元复合络合剂的浓度对Ni-P镀层的结构与形貌有显著影响。Ni-P镀层的热稳定性随着三元复合络合剂浓度的增加而降低。当镀液中三元复合络合剂浓度为0.035 mol/L时,所制备的Ni-P镀层致密、均一,在3.5%NaCl溶液中表现出良好的耐蚀性能。     

Direct electroless nickel–boron plating on AZ91D magnesium alloy

A Ni–B coating was electroless-deposited directly on acetic acid pickled AZ91D. The plating rate was found to be influenced by pH, temperature, and bath composition. The electroless Ni–B plating exhibits a uniform surface and an amorphous structure. Polarization curve and electrochemical impedance spectroscopy measurements in 3.5 wt.% sodium chloride aqueous solution suggest that the plating can protect the magnesium alloy substrate from corrosion attack. It is proposed that different deposition reactions dominate in different stages of the plating process.     

A homogenisation pre-treatment for adherent and corrosion-resistant Ni electroplated coatings on Mg-alloy AZ91D

Multi-step Ni electroplatings were applied to AZ91D following the development of a homogenisation pre-treatment. The Ni coating was well adhered, as verified by thermal shock testing, and provided corrosion protection in 3.5 wt.% NaCl for 74 h at a coating thickness of ∼15 μm. Being a cathodic coating, further protection in the presence of defects was not demonstrated herein, however realisation of quality Ni coatings on Mg is technologically important. To this end, achieving microstructural homogeneity on AZ91D is critical prior to plating or coating (such as electroless plating and chemical conversion coating) multi phase Mg-alloys.     

镁合金化学转化膜上化学镀镍的研究

将化学转化和化学镀镍结合在一起,先对AZ91D镁合金进行化学转化处理,然后在转化膜上进行化学镀镍.并用扫描电镜(SEM)、X射线衍射技术(XRD)研究了镀层表面形貌和组织结构及处理后镁合金的耐蚀性能.结果表明:两种工艺结合得到的镀层使腐蚀电位正移0.83 V,腐蚀电流降低,有效的提高了镁合金耐腐蚀性能.     

Electroless Ni-Sn-P coating on AZ91D magnesium alloy and its corrosion resistance

An electroless Ni-Sn-P coating was deposited on AZ91D magnesium alloy in an alkaline-citrate-based bath where nickel sulphate and sodium stannate were used as metal ion sources and sodium hypophosphite was used as a reducing agent. The phase structure of the coating was amorphous. SEM and attached EDS observation revealed the presence of dense and uniform nodules in the ternary coating and the content of tin was 2.48wt.%. Both the electrochemical analysis and the immersion test in 10% HCl solution proved that the ternary Ni-Sn-P coating exhibited better corrosion resistance than the Ni-P coating in protecting the magnesium alloy substrate.     

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...     

AZ31镁合金表面碱性化学镀镍工艺研究

试验研究了AZ31镁合金表面碱性化学镀镍工艺。采用扫描电镜(SEM)、能谱成分分析(EDS)和X射线衍射(XRD)等方法对镀镍层的表面形貌、镀层成分及物相结构进行了分析,并测定了AZ31镁合金及镀层在w(NaCl)=3.5%的水溶液中的腐蚀电位和极化曲线,以此评价镀层的耐腐蚀性能。结果表明,预镀镍层为晶格畸变的晶态低磷镀层,二次镀镍层为非晶态高磷镀层,镁合金表面腐蚀电位在化学镀镍后明显升高,二次镀镍后钝化电位范围明显扩大,其耐腐蚀性能明显优于预镀镍层的。     

Formation of an aluminum-alloyed coating on AZ91D magnesium alloy in molten salts at lower temperature

An aluminum-alloyed coating was formed on an AZ91D magnesium alloy in molten salts containing AlCl₃ at a lower temperature of 380 °C. The microstructure and phase constitution of the alloyed layer were investigated by optical microscopy, scanning electron microscopy, energy dispersive spectrum and X-ray diffraction. The nano-hardness of the coating was studied by nanoindentation associated with scanning probe microscopy. The corrosion resistance of the coated specimen was evaluated in a 3.5 wt.% NaCl solution by electrochemical impedance spectroscopy and cyclic potentiodynamic polarization. The results show that the aluminum-alloyed coating consists of Mg₂Al₃ and Mg₁₇Al₁₂ intermetallic layers. The formation of the coating is dictated by the negative standard free energy of the reaction: 2AlCl₃ + 3 Mg = 3MgCl₂ + 2Al. This process is associated with a displacement reaction mechanism and diffusion process that takes place during the molten salt treatment. High activity of Al elements in molten salts contributes to the lower temperature formation of the Al-alloyed coating. The alloyed coating markedly improves the hardness as well as the corrosion resistance of the alloy in comparison with the untreated AZ91D magnesium alloy, which is attributed to the formation of the intermetallic compounds.     

Corrosion behavior of Cr/Cu-coated Mg alloy (AZ91D) in 0.1 M H2SO4 with different concentrations of NaCl

An electroplating process was proposed for obtaining a protective Cr/Cu deposit on the two-phase Mg alloy AZ91D. The corrosion behavior of Cu-covered and Cr/Cu-covered AZ91D specimens was studied electrochemically in 0.1 M H₂SO₄ with different NaCl concentrations. Experimental results showed that the corrosion resistance of an AZ91D specimen improved significantly after Cr/Cu electrodeposition. The corrosion resistance of Cr/Cu-covered AZ91D decreased with increasing NaCl concentration in 0.1 M H₂SO₄ solution. After immersion in a 0.1 M H₂SO₄ with a NaCl-content above 3.5 wt.%, the surface of Cr/Cu-covered AZ91D suffered a few blisters. Cracks through the Cr deposit provided active pathways for corrosion of the Cu and the AZ91D substrate. Formation of blisters on the Cr/Cu-covered AZ91D surface was confirmed based on the results of an open-circuit potential test, which detected an obvious potential drop from noble to active potentials.     

Corrosion resistance of WE43 and AZ91D magnesium alloys with phosphate PEO coatings

The corrosion performance of WE43-T6 and AZ91D magnesium alloys with and without treatment by plasma electrolytic oxidation (PEO) was investigated by electrochemical measurements in 3.5 wt.% NaCl solution. For untreated WE43-T6 alloy, formation of a uniform corrosion layer (Mg(OH)₂) was accompanied by initial pits around magnesium-rare earth intermetallic compounds. The AZ91D alloy disclosed increased corrosion susceptibility, with localized corrosion around the β-phase, though the β-phase network phase acted as a barrier for corrosion progression. PEO treatment in alkaline phosphate electrolyte improved the corrosion resistance of WE43-T6 alloy only at the initial stages of immersion in the test solution. However, PEO-treated AZ91D alloy revealed a relatively high corrosion resistance for much increased immersion times, contrary to the relative corrosion resistances of the untreated alloys. The improved performance of the PEO-treated AZ91D alloy appears to be related to the formation of a more compact coating.     

AZ31镁合金轧态薄板化学镀Ni-P合金的工艺研究

为了改善AZ31镁合金轧态薄板的耐腐蚀性能,通过正交试验优化了化学镀Ni-P的配方及工艺,并对Ni-P镀层的形貌、镀层厚度、镀层中P元素的含量以及镀层在3．5％NaCI溶液中的极化曲线进行了测试和表征。结果表明,AZ31镁合金化学镀Ni—P的最优方案为：碱式碳酸镍10g／L,次亚磷酸钠25g/L,温度80％,pH值=8。所得的Ni—P镀层均匀,无明显缺陷,厚度约为18～23μm,P元素的质量分数为9．68％。试样经化学镀Ni—P后的自腐蚀电位大幅度提高,出现了约600mV的钝化区间,其耐蚀性能明显提高。     

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。     

环保型 AZ91D 镁合金直接化学镀镍工艺研究

目的开发一种无铬、低氟、稳定的镁合金直接化学镀镍工艺。方法通过SEM,EDX及浸泡实验、动电位极化曲线、划格试验等方法 ,以稳定系数和镀速等参数为对象,对比新工艺和传统工艺对镀层或镀液性能的影响。结果在以硫酸镍为主盐的基础液中,添加质量浓度为0.5 mg/L的硫脲,镀液的稳定性可得到明显的提高。在使用硝酸+磷酸酸洗后的镁合金试样表面,获得了良好的腐蚀形貌结构,这种结构有利于增强镀层与基底间的机械咬合作用。新工艺获得的镀层属高P镀层(P的质量分数约为11%),在Na Cl溶液中的自腐蚀电位由-1.5 V正移至-0.5 V,腐蚀电流密度降低了约3个数量级。结论以硫酸镍主盐镀液获得的镀层耐蚀性优于碱式碳酸镍主盐镀液获得的镀层,镀液的最佳p H=5,化学镀镍温度为82℃。     

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.