Organic-magnesium complex conversion coating on AZ91D magnesium alloy

An organic-magnesium complex conversion (OMCC) coating on AZ91D magnesium alloy was obtained by treating in a solution containing organic compounds. SEM, FESEM and XPS were used to examine the surface morphology, thickness and structure of the conversion coatings. The results show that the continuous and uniform conversion coating is deposited on AZ91D alloy and the main component of the coatings is organic compound containing benzene ring, which forms a chemical bond with magnesium. The polarization measurement and salt spray test show that the corrosion resistance of the conversion coating is much higher than that of traditional chromate conversion coating.     

Barium phosphate conversion coating on die-cast AZ91D magnesium alloy

Poor corrosion resistance limits the application of magnesium alloys.Conversion coating is widely used to protect magnesium alloys because of easy operation and low cost.A novel conversion coating on die-cast AZ91D magnesium alloy containing barium salts was studied.The optimum concentrations of Ba(NO_3)_2,Mn(NO_3)_2 and NH_4H_2PO_4 are 25 g/L,15 mL/L and 20 g/L,respectively,based on orthogonal test results.The treating time,solution temperature and pH value are settled to be 5-30 min, 50-70℃and 2.35-3.0...     

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...     

Improving wear resistance of magnesium alloy AZ91D TiN-CrN multilayer coating by

Applying a novel method of arc-glow plasma depositing, a 2 lain-thick coating with 12 sub-layers of TiN and CrN was deposited alternately on the surface of magnesium alloy AZglD to improve its wear resistance. The wear behavior was investigated by test of ball on disc sliding. The composition and microstructure of the coating were also analyzed by means of X-ray diffraction （XRD） and glow discharge spectrum （GDS）, and the morphology of TiN-CrN film was surveyed through scanning electronic microscopy （SEM） and atom force microscopy （AFM）.The adhesion strength between film and matrix was evaluated by ways of stick-peeling test. The surface micro-hardness of the coating is above HK0.011 433, and the specific wear ratio of specimens coated with TiN-CrN films tested decreases greatly compared to that of the bare metal.     

AZ91D镁合金表面激光重熔Al-Si-Cu涂层的性能

采用等离子喷涂和激光重熔复合工艺在AZ91D镁合金表面制备Al-Si-Cu合金涂层,利用扫描电子显微镜（SEM）、显微硬度计、摩擦磨损试验机等研究了涂层的微观组织、显微硬度与摩擦磨损性能。结果表明,激光重熔后涂层组织致密均匀,涂层与基体呈良好的冶金结合,涂层显微硬度约为基体的2.2倍,由于晶粒细化和硬质相的存在耐磨性较基体明显提高,重熔层的磨损机制主要为磨粒磨损。     

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.     

Microstructure and properties of oxalate conversion coating on AZ91D magnesium alloy

The oxalate coating formed on AZ91D magnesium alloy by chemical conversion treatment methods in oxalate salt solutions was investigated. The surface morphologies and chemical composition of coating were examined using scanning electron microscopy (SEM) equipped with energy dispersive analysis of X-ray (EDX). Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves and salt spray tests were employed to evaluate corrosion protection of the coating to substrate in 5% NaCl solution. The mechanism of coating formations was also considered in details. The results indicate that a compact and dense surface morphology with fine particle clusters of the oxalate coating on magnesium alloy is presented, which mainly consists of oxide or/and organic of Mg, Al and Zn. And the anti-corrosion of the magnesium after oxalate conversion treatment is better than that of the magnesium substrate. The results of salt spray test for oxalate coating is evaluated as Grade 9 according to ASTM B117. The electric resistance of oxalate chemical conversion coating to substrate is below 0.1 Ω.     

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.     

Effect of grit-blasting on substrate roughness and coating adhesion

Statistically designed experiments were performed to compare the surface roughness produced by grit blasting A36/1020 steel using different abrasives. Grit blast media, blast pressure, and working distance were varied using a Box-type statistical design of experiment (SDE) approach. The surface textures produced by four metal grits (HG16, HG18, HG25, and HG40) and three conventional grits (copper slag, coal slag, and chilled iron) were compared. Substrate roughness was measured using surface profilometry and correlated with operating parameters. The HG16 grit produced the highest surface roughness of all the grits tested. Aluminum and zinc-aluminum coatings were deposited on the grit-blasted substrates using the twin-wire electric are (TWEA) process. Bond strength of the coatings was measured with a portable adhesion tester in accordance with ASTM standard D 4541. The coatings on substrates roughened with steel grit exhibit superior bond strength to those prepared with conventional grit. For aluminum coatings sprayed onto surfaces prepared with the HG16 grit, the bond strength was most influenced by current, spray distance, and spray gun pressure (in that order). The highest bond strength for the zinc-aluminum coatings was attained on surfaces prepared using the metal grits.     

Preparation and property evaluation of electroless Ni-P coatings on AZ91D magnesium alloy

Taking a bath with basic nickel carbonate as the source of nickel, sodium hypophosphite as the reducing agent and citric acid as the complexing agent, the N i-P coatings on AZ91D magnesium alloy were prepared. The influence of pH value of the bath on the content of phosphorus, microhardness and corrosion resistance of the deposits was examined. The XRD analysis results show that the Ni-P coatings plated under all conditions have a mixed microstructure of amorphous and nanocrystalline and undergo a phase transformation to crystalline nickel and nickel phosphide upon heat-treatment. The microhardness of the Ni-P coatings increases with the increase ofpH value of the bath and has a maximum at pH=6. The potentiodynamic polarization test in 3.5%（mass fraction） NaCl solution reveals that the Ni-P coatings exhibit a very good corrosion resistance to protecting AZ91D magnesium alloy.     

AZ91D镁合金无铬铈盐转化膜的正交试验研究

为了代替剧毒Cr^6＋化学转化膜处理工艺,采用硝酸铈以及高锰酸钾为无铬化学转化处理液的主要成膜成分,通过正交试验优化了以Ce（NO3）3,为主盐的镁合金铈盐化学转化膜工艺,并对成膜规律进行了研究。试验表明,本工艺所获得的铈盐化学转化膜具有优良的外观和良好的耐腐蚀性。此外,借助扫描电镜分析手段对转化膜的微观形貌进行了分析,还对氧化膜成膜机制进行了探讨。     

AZ91D镁合金等离子喷涂Ni-Al/陶瓷涂层的组织和性能

以Ni-Al为粘结层,在AZ91D镁合金基体上等离子喷涂Ni-Al/Al2O3、Ni-Al/Al2O3-13%TiO2(Ni-Al/AT13)、Ni-Al/Al2O3-20%TiO2(Ni-Al/AT20)复合涂层及Ni-Al/Al2O3/Al2O3-13%TiO2/Al2O3-20%TiO2(Ni-Al/Al2O3/AT13/AT20)梯度涂层,利用SEM、EDS和XRD分析涂层的微观组织特征,通过硬度、拉伸和热震实验研究涂层硬度、结合强度和抗热震性能,并与直接喷涂Al2O3、AT20的涂层进行比较。结果表明:Ni-Al粘结层因"自粘结"效应与基体形成较为致密并具有冶金结合的界面,且与Al2O3、AT13和AT20陶瓷层互有渗透、交叉和啮合,涂层致密性及结合力大为提高,表现出优良的抗热震性能。Al2O3涂层主要由亚稳态γ-Al2O3组成,AT20涂层以Al2O3和Al2TiO5为主。镁合金表面喷涂Al2O3陶瓷层后硬度大幅提高,由于加入TiO2,AT13和AT20涂层的硬度略低于Al2O3涂层的。Ni-Al/Al2O3-TiO2复合陶瓷的涂层结合强度高于Ni-Al/Al2O3单一陶瓷涂层的,而Ni-Al/Al2O3/AT13/AT20梯度涂层的结合强度比Ni-Al/AT20涂层的更高。     

AZ91D镁合金化学复合镀Ni-P-ZrO2的工艺与性能

对镁合金传统化学镀工艺进行了改进,避免了使用氢氟酸和六价铬等有毒物质。采用化学镀与化学复合镀相结合方法,在AZ91D镁合金上获得了Ni-P-ZrO2纳米化学复合镀层,并研究了新工艺化学镀前处理和镍沉积机理及复合镀层的结构和性能。结果表明:新工艺方法获得的Ni-P镀层更均匀、致密,耐蚀性优于传统工艺化学镀层;Ni-P-ZrO2复合镀层与AZ91D合金基体在3.5%NaCl溶液中的动电位极化曲线对比表明,该复合镀层对镁合金可以起到明显的保护作用;从磨损实验结果可见,Ni-P镀层的磨损质量损失率几乎为Ni-P-ZrO2镀层的3倍,说明ZrO2纳米粉的加入能改善镀层的耐磨性。     

Effects of ultrasonic dispersion on structure of electrodeposited Ni coating on AZ91D magnesium alloy

To obtain the refined electrodeposited nickel layer on AZ91D magnesium alloy, ultrasonic technology was applied in the processes of pre-treatment and electrodeposition. The phases of pre-treatment layer and the nickel coating were analyzed by X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS), and the microstructure was observed by scanning electron microscopy (SEM). Then, the effects of ultrasonic dispersion on the microstructure of pre-treatment layer and the grain refinement of electrodeposited nickel layer were discussed. The results showed that the pre-treatment electrodeposited Cu-Sn layer with compact microstructure could be synthesized in alkaline copper-tin liquid with ultrasonic agitation, as a result, smooth and refined nickel coating formed on AZ91D magnesium alloy. On the other hand, preferred orientation in the coating decreased because of the refined grains.     

Study of the formation and growth of tannic acid based conversion coating on AZ91D magnesium alloy

A tannic acid based conversion coating was formed on AZ91D magnesium alloy through a solution containing C₇₆H₅₂O₄₆ (tannic acid), NH₄VO₃, K₂ZrF₆ and H₃PO₄. The growth process and corrosion resistance of the conversion coating were investigated by SEM, FESEM, XPS, IR, potentiodynamic polarization and EIS test. The results showed that the main components of the coatings were penta-hydroxy benzamide–magnesium complex, Al₂O₃ and MgF₂. Zr(HPO₄)₂·H₂O(α-ZrP) was first formed in the time interval of 70 s–120 s, which acted as catalyst to activate the main reaction of gallic acid being oxidized into the penta-hydroxy benzamide–magnesium complex, as well as the formation of MgF₂ and Al₂O₃, which took place in the time interval of 120 s to 600 s. The thickness of coating treated for 300 s and 600 s was 1.1 μm and 1.6 μm, respectively. Polarization measurement and EIS test in 3 wt.% NaCl solution indicated that the conversion coating treated for about 300–600 s shows good corrosion resistance while an excess time treatment (720 s) induces the coating surface coarse and uneven, leading to the reduction of corrosion resistance of the conversion coating.     

AZ91D镁合金微弧氧化膜在不同浓度NaCl溶液中的腐蚀行为(英文)

采用微弧氧化技术(MAO)在镁合金 AZ91D 表面制备微弧氧化陶瓷膜。利用电化学技术和浸泡实验研究该镁合金试样在不同浓度(0.1%,0.5%,1.0%,3.5%和 5.0%,质量分数) NaCl 溶液中的腐蚀行为。结果表明,试样的腐蚀速率随着氯离子浓度的升高而增大。在较高浓度(1.0%,3.5%和 5.0%)的 NaCl 溶液中的主要腐蚀形式是点蚀,而在较低浓度(0.1%和 0.5%)中是全面腐蚀。腐蚀过程可以分为两个阶段:亚稳态蚀点的出现和蚀点的生长。根据腐蚀过程中阻抗谱的特点,对镁合金微弧氧化膜试样在不同浓度 NaCl 溶液中浸泡 120 h 提出了不同的等效电路来模拟其腐蚀行为。     

2-Hydroxy-4-methoxy-acetophenone as an environment-friendly corrosion inhibitor for AZ91D magnesium alloy

The inhibition behavior of 2-hydroxy-4-methoxy-acetophenone (paeonol) as an environment-friendly corrosion inhibitor for AZ91D magnesium alloy was investigated in 0.05 wt.% NaCl solution by means of polarization curve, AC impedance, weight loss measurement, scanning electron microscopy, Fourier transformation infrared spectroscopy, ultraviolet analysis, and computer molecular simulation. The results show that paeonol can inhibit the corrosion of AZ91D. The maximum inhibition efficiency is achieved when paeonol concentration is 50 ppm by weight in this study. It is proposed that paeonol chelates with Mg to form a paeonol-Mg complex mixing with the original Mg(OH)₂ film on the surface to inhibit the anodic dissolution of AZ91D.