硅和镁含量对双镀Zn–23Al镀层的组织结构和耐蚀性的影响第二部分──Zn–23Al–0.5Si–xMg镀层的组织结构和耐蚀性

采用"双镀法"在SPHC钢板表面热浸镀不同镁含量的Zn–23Al–0.5Si–xMg镀层(x=0.5,1.0,2.0,3.0).采用扫描电镜、能谱仪、显微硬度计以及电化学测试、中性盐雾试验等手段研究了浸镀液中镁含量对镀层组织结构、显微硬度和耐蚀性的影响.结果表明:随着浸镀液中镁含量升高,镀层表面块状富锌相逐渐细化,显微硬度增大,耐蚀性先改善后变差.浸镀液中Mg质量分数为2％时,镀层的耐蚀性最佳.     

硅和镁含量对双镀Zn–23Al合金组织结构和耐蚀性的影响第一部分──Zn–23Al–xSi镀层的组织结构和耐蚀性

采用"双镀法"在钢板表面热浸镀不同硅含量的Zn–23Al–xSi合金镀层(x=0.1,0.3,0.5,0.7,1.1).采用扫描电镜、能谱仪、电化学测试和中性盐雾试验研究了浸镀液中硅含量对镀层组织结构和耐蚀性的影响.结果表明,随着浸镀液中硅含量升高,Zn–23Al–xSi合金层厚度先减小后稳定在2μm左右,耐蚀性先改善...     

钢结构件热浸镀阳极性铝合金镀层技术的研究

在热浸镀纯铝的工艺条件下,通过在铝液中加入Zn、In、Sn等合金元素,制备了3种阳极性铝合金镀层:Al–5%Zn–0.02%In、Al–4%Zn–0.06%Sn及Al–5%Zn–0.06%Sn。使用光学显微镜、3.5%Na Cl全浸腐蚀试验及电化学工作站检测了所得铝合金镀层的组织及性能,并与纯铝、纯锌及55%Al–43.4%Zn–1.6%Si镀层进行了对比。结果表明,镀层的最佳组成分别为Al–5%Zn–0.02%In和Al–(4%~5%)Zn–0.06%Sn。在3.5%Na Cl溶液中,其耐蚀性优于55%Al–43.4%Zn–1.6%Si镀层,而腐蚀电位相当;在Cl–浓度为零时未发生铁铝极性逆转,镀层的显微组织与纯铝镀层相同。该热浸铝合金镀层的热浸镀工艺与热浸镀铝完全相同,使用热浸镀铝的设备及工艺即可实现工业生产。     

稀土元素对桥梁缆索用热浸镀Zn-10Al镀层钢丝耐蚀性能的影响

通过双镀法制备Zn-10Al-xRE(x=0.05,0.08,0.11,0.14,0.17)五种热浸镀锌铝镀层,并利用中性加速盐雾试验、电化学实验及扫描电子显微镜（SEM）分析其腐蚀形貌及耐蚀性能。结果表明,五种镀层在中性加速盐雾试验下,可保证基体在120d以内不被腐蚀,而纯锌镀层在30d时已经出现红锈,证明Zn-10Al-xRE的耐蚀性能可达到纯锌镀层4～5倍。Zn-10Al-xRE镀层钢丝的耐蚀性能随稀土含量的上升先升高再降低,添加0.08%RE的Zn-10Al镀层耐蚀性最好。用SEM对120d盐雾试验下的镀层钢丝进行观察,可以看出纯锌镀层的腐蚀产物较为疏松,Zn-10Al-xRE的腐蚀产物较为致密,Zn-10Al-xRE中腐蚀产物大约分为韧窝状、球状及针片状,耐蚀性能最好的Zn-10Al-0.08RE镀层中含有大量韧窝状腐蚀产物。     

湿法超声波机械镀Zn、Zn-5%Al及Al层的形貌与耐蚀性研究

采用湿法超声波机械镀设备制备了Zn、Zn-5%Al及Al层。采用多功能扫描电子显微镜观察了镀层的表面形貌和断面形貌,采用测厚仪测量了镀层的厚度,并采用中性盐雾试验测试了镀层的耐蚀性。结果表明:Zn层及Zn-5%Al层表面均匀平整,Al层表面呈现微观不平整;铝粉的添加使镀层的耐蚀性增强,但厚度降低。     

铈元素对热浸锌–铝–镁合金镀层显微组织及耐蚀性的影响

在Zn–Al–Mg镀液中添加不同量的稀土Ce以提高热浸镀Zn–Al–Mg合金层性能。通过分析合金镀层的表面形貌和截面形貌以及中性盐雾试验,系统地研究了镀液中Ce添加量对合金镀层显微组织结构和耐蚀性的影响。当铈的添加量≤0.05%(质量分数)时,随铈添加量增大,热浸镀Zn–Al–Mg合金层的晶粒逐渐细化,尺寸逐渐均匀;δ相层的厚度变化不大,而ζ相层略微减薄。当铈添加量0.05%时,随铈添加量增大,镀层合金相厚度骤减。中性盐雾试验表明,镀液中添加Ce有利于提高Zn–Al–Mg合金镀层的耐蚀性,但其添加量不宜超过0.05%。     

钒含量对热浸Zn–0.05%Ni–V合金镀层组织与性能的影响

向Zn-0.05%Ni热浸镀浴中添加微量的钒,在硅含量为0.09%的钢上获得了Zn-0.05%Ni-V合金镀层,研究了V含量对镀层组织的影响.通过电化学阻抗谱、极化曲线和高温氧化实验,研究了纯Zn、Zn-0.05%Ni及Zn-0.05%Ni-V镀层的耐蚀性和抗氧化性.结果表明:在Zn-0.05%Ni镀浴中添加质量分数大于0.03%的钒可以有效抑制铁锌反应,控制ζ相层的超厚生长.与纯Zn和Zn-0.05%Ni合金镀层相比,Zn-0.05%Ni-V合金镀层在质量分数为5%的NaCI溶液中的电化学阻抗增大,自腐蚀电位更正,极化电阻增大,腐蚀电流密度减小,耐蚀性提高.Zn-0.05%Ni-V合金镀层的高温抗氧化性能优于纯Zn和Zn-0.05%Ni镀层.当钒含量为0.05%时,其表面形成了更为致密的氧化产物,具有最优的高温抗氧化性能.     

钒含量对热浸Zn-0.05%Ni-V合金镀层组织与性能的影响

向Zn-0.05%Ni热浸镀浴中添加微量的钒,在硅含量为0.09%的钢上获得了Zn-0.05%Ni-V合金镀层,研究了V含量对镀层组织的影响.通过电化学阻抗谱、极化曲线和高温氧化实验,研究了纯Zn、Zn-0.05%Ni及Zn-0.05%Ni-V镀层的耐蚀性和抗氧化性.结果表明:在Zn-0.05%Ni镀浴中添加质量分数大于0.03%的钒可以有效抑制铁锌反应,控制ζ相层的超厚生长.与纯Zn和Zn-0.05%Ni合金镀层相比,Zn-0.05%Ni-V合金镀层在质量分数为5%的NaCI溶液中的电化学阻抗增大,自腐蚀电位更正,极化电阻增大,腐蚀电流密度减小,耐蚀性提高.Zn-0.05%Ni-V合金镀层的高温抗氧化性能优于纯Zn和Zn-0.05%Ni镀层.当钒含量为0.05%时,其表面形成了更为致密的氧化产物,具有最优的高温抗氧化性能.     

热浸镀锌铝合金的研究

通过热浸镀的方法制得含铝为6.5%（质量分数）的锌铝合金镀层,研究了助镀剂、热镀温度和热镀时间对镀层质量和镀液寿命的影响,中性盐雾试验和二氧化硫加速腐蚀试验结果表明,热浸镀锌铝合金（wAl=6.5%）层的耐蚀性优于镀锌层。     

镀液温度对脉冲电镀Zn-Ni-Mn合金镀层的影响

采用脉冲电镀法在Q235钢表面制备了Zn-Ni-Mn合金镀层。研究了镀液温度(25~40℃)对合金镀层成分、沉积速率、表面形貌和耐蚀性的影响。结果表明,随镀液温度升高,Zn-Ni-Mn合金镀层中锰的质量分数降低,锌和镍的质量分数升高;沉积速率增大;镀液θ为30℃时制备的Zn-Ni-Mn合金镀层晶粒大小均匀,表面平整致密,耐蚀性最好。     

钛和铈对热浸锌镀层组织与耐蚀性能的影响

为了获得厚度适中、耐蚀性能好的热浸镀锌层,在锌浴中添加微量的Ti和Ce,分别在Zn-0.04%Ti、Zn-0.02%Ce和Zn-0.04%Ti-0.02%Ce镀浴中制得热浸锌合金镀层.采用金相显微分析以及电化学阻抗谱、电化学极化测试、中性盐雾试验,研究了Ti和Ce对镀层组织和耐蚀性能的影响.结果表明:在锌浴中添加0.0...     

Ni2+对铝合金磷化膜结构和耐蚀性的影响

通过表面分析和电化学测试等研究了Ni2+对LY12铝合金表面锌系磷化膜结构和耐蚀性的作用.结果表明,LY12铝合金表面锌系磷化膜的主要成分是Zn3( PO4)2·4H2O,而Ni2+的细化晶粒作用使锌系磷化膜的结构变得更加完整致密,其加入不影响锌系磷化膜的化学组成和相组成;与不含Ni2+的磷化液处理相比,经含有Ni2+的磷化液处理后的铝合金在3.5％的NaCl溶液中的腐蚀电流密度明显下降,在100 mHz频率下的阻抗值明显增大,表现出良好的防护性.     

氯离子对6063铝合金铈-锰转化膜耐蚀性的影响

在Ce-Mn稀土钝化液中添加Cl-作为促进剂,以6063铝合金为基体制备了Ce-Mn转化膜。分别采用扫描电镜(SEM)和能谱仪(EDS)研究了转化膜的表面形貌及元素组成,并采用硫酸铜点滴腐蚀实验、动电位极化曲线以及电化学阻抗谱(EIS)研究了Ce-Mn转化膜的耐蚀性。结果表明,Ce-Mn转化膜主要由Ce、Mn、O等元素组成,往稀土钝化液中添加Cl-可使膜层更平整、致密,转化膜的平均耐点滴时间从50s提高至100s,在NaCl质量分数为3.5%的腐蚀介质中的腐蚀电流密度明显降低,转化膜极化电阻增大,铝合金的耐蚀性显著提高。     

Nanocrystalline Ni–Co alloy coatings: electrodeposition using horizontal electrodes and corrosion resistance

Nanocrystalline Ni–Co alloy coatings containing 0–45 wt% Co were electrodeposited using horizontal electrodes in a modified Watts bath. Different techniques including scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, microindentation, and potentiodynamic polarization were used to characterize the alloy coatings. Properties of the alloy coatings were investigated as a function of the cobalt ion concentration (Co²⁺) in the bath. It was observed that the alloy codeposition exhibits anomalous behavior. Co content in the alloy coatings increases with increasing Co²⁺ in the bath and with electrolyte agitation. Morphology and grain size of alloy coatings are greatly affected by Co content. By increasing Co content, surface morphology of the alloy coatings changes from pyramidal to spherical. Microhardness of the alloy coatings increases with increasing Co content mainly due to decreasing grain size that follows the Hall–Petch relation. In addition, Ni–17 wt% Co alloy exhibits better corrosion resistance compared to pure Ni and other Ni–Co alloy coatings. The higher corrosion resistance of Ni–17 wt% Co coating is discussed based on its phase structure, grain size, and preferred orientation.     

Al diffusion coating on Mg alloy by a surface nanocrystallization enhanced CVD process

Surface nanocrystallization by mechanical attrition was used to enhance the chemical vapor deposition process. An aluminum (Al) diffusion coating was produced on AZ91 Mg alloy surface. This process was conducted at a relatively low temperature (400°C) for a short time of 120 min. The results indicated that a continuous and dense Mg₁₇Al₁₂ intermetallic coating with a thickness of ～8 μm formed on the Mg alloy substrate. Almost no corrosion was observed after the coated samples were immersed in 3 wt % NaCl solution for 6 h, reflecting a relatively good corrosion resistance. The formation mechanism of the Al diffusion coating is discussed based on the experimental results.     

Corrosion behaviors of Zn/Al-Mn alloy composite coatings deposited on magnesium alloy AZ31B (Mg-Al-Zn)

After being pre-plated a zinc layer, an amorphous Al-Mn alloy coating was applied onto the surface of AZ31B magnesium alloy with a bath of molten salts. Then the corrosion performance of the coated magnesium alloy was examined in 3.5% NaCl solution by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results showed that the single Zn layer was active in the test solution with a high corrosion rate while the Al-Mn alloy coating could effectively protect AZ31B magnesium alloy from corrosion in the solution. The high corrosion resistance of Al-Mn alloy coating was ascribed to an intact and stable passive film formed on the coating. The performances of the passive film on Al-Mn alloy were further investigated by Mott-Schottky curve and X-ray photoelectron spectroscopy (XPS) analysis. It was confirmed that the passive film exhibited n-type semiconducting behavior in 3.5% NaCl solution with a carrier density two orders of magnitude less than that formed on pure aluminum electrode. The XPS analysis indicated that the passive film was mainly composed of AlO(OH) after immersion for long time and the content of Mn was negligible in the outer part of the passive film. Based on the EIS measurement, electronic structure and composition analysis of the passive film, a double-layer structure, with a compact inner oxide and a porous outer layer, of the film was proposed for understanding the corrosion process of passive film, with which the experimental observations might be satisfactorily interpreted.     

Influence of rare earths addition on the corrosion behaviour of Zn-5%Al (Galfan) alloy in neutral aerated sodium sulphate solution

The effect of rare earth metal (Ce, Er, Y) additions on the corrosion behaviour of Zn-5Al Galfan alloy has been investigated. The corrosion resistance of Zn-5Al-1Ce, Zn-5Al-1Er and Zn-5Al-1Y alloys has been assessed by various electrochemical tests, such as corrosion potential measurements, polarization curves and electrochemical impedance spectroscopy. They have been performed in a 0.1 M Na₂SO₄ solution, at approximately neutral pH, without stirring and in contact with the air. For comparison, the electrochemical tests have also been carried out on the Zn-5Al alloy. Moreover, the surface morphology and nature of the corrosion products have been investigated. The results indicated that rare earths’ addition improves the corrosion behaviour of Galfan, the effect being more pronounced for the Er- and Y-containing alloys. The mechanism by which the corrosion resistance of Zn-5Al alloy is enhanced in presence of the rare earths is discussed.     

Effect of nitrogen pressure on the microstructure,mechanical and electrochemical properties of CrAlN coatings deposited by filter cathode vacuum arc

CrAlN coatings were prepared on Al–Si alloys using filter cathode vacuum arc deposition technique with nitrogen as the reactive gas and Cr₂₅Al₇₅ alloy target as the arc source. The effect of nitrogen pressure on the microstructure, mechanical properties and electrochemical properties of the coatings had been systematically studied. The results showed that the composition, structure and performance of the CrAlN coating depended on the nitrogen pressure. As the nitrogen pressure increased, the Al and Cr content decreased while the N content increased slowly in the coating. Meanwhile, the phase structure gradually changed from AlN phase to CrN phase. The hardness of the CrAlN coating increased significantly with the increase of nitrogen pressure from 0.04 to 0.06 Pa due to the formation of CrN phase and grain refinement. However, further increasing the nitrogen pressure to 0.07 Pa, the hardness was reduced owing to the deterioration of the surface quality caused by target poisoning. Moreover, the adhesion strength of the coating gradually decreases, and the corrosion resistance of the CrAlN coating first increased and then decreased with increasing the nitrogen pressure. The CrAlN coating deposited at a nitrogen pressure of 0.05 Pa had the best corrosion resistance, with the highest polarization resistance, charge transfer resistance and pore resistance, which was related to the combined effect of great compactness and AlN-dominant phase structure in the coating.     

Effect of Al on the galvanic ability of Zn-Al coating under thin layer of electrolyte

The effect of Al on the galvanic ability of Zn-Al coating has been studied under thin electrolyte layers by measuring surface potential and surface pH. The changes of surface potential and surface pH over Zn-Al/steel galvanic couple corroding in artificial sea water (ASW) were measured at 60% and 90% RH at 298 K. In the initial stage of corrosion, Zn-55Al coating has shown better galvanic protection ability than Zn-5Al coating in both 60% and 90% RH. However, Zn-5Al coating was better in long term corrosion. The better galvanic ability of Zn-55Al coating in the initial stage of corrosion was related to the observation of pH as low as low as 2 on its surface. The low pH value was due to hydrolysis of Zn²⁺ and Al³⁺ ions. The low pH value was further confirmed by observing evolution of gas due to H⁺ reduction on the Zn-55Al coating. With the progress of corrosion, the low pH region of coating layer extended towards the base steel. This helped expand the deposition of zinc corrosion products on the steel surface. The enhanced dissolution of zinc in Zn-55Al coating led to the formation of a barrier layer which limited the galvanic protection of remaining steel. This was not the case in Zn and Zn-5Al coating. The X-ray analyses of the corroded samples have shown the deposition of zinc corrosion products on the steel surface, which greatly depended on the RH value. The part of the steel surface covered with zinc corrosion products has shown relatively less noble potential than other part indicating that zinc corrosion products took a role to protect the base steel against corrosion. The results from surface potential and surface pH measurements were substantiated by the surface observation of the corroded sample during and after the corrosion test.     

Microstructure and corrosion behavior of electroless Ni�CP coatings on 6061 aluminum alloys

The microstructure and corrosion behavior of electroless Ni–P alloy plating on 6061 aluminum alloys substrate in an alkaline plating bath with sodium hypophosphite as reducing agent were investigated. The effects of bath temperature on the plating rate, compositions, and microstructure of the electroless Ni–P deposits were studied. The results showed that the deposition rate and the P content of the electroless Ni–P deposits increased with the rise of the bath temperature. Scanning electron microscopy (SEM) of the deposits showed nodular structure for binary deposits. X-ray diffraction patterns of all the deposits revealed a single and broad peak which indicated the amorphous structure of the deposits. Corrosion resistance of the Ni–P coatings was evaluated by potentiodynamic polarization. The results indicated that electroless Ni–P plating could obviously improve the corrosion resistance of 6061 aluminum alloy.