镁合金锡酸盐化学转化表面处理工艺研究

研究了AZ91D镁合金的锡酸盐化学转化表面处理工艺,利用中性盐雾试验和极化曲线法测试了转化膜的耐蚀性,使用划格法测试了转化膜对有机涂层的附着力,采用扫描电镜、能谱仪、射线衍射仪分析了转化膜的微观形貌、成分和结构并讨论了成膜机理.结果表明,最佳工艺条件下的锡酸盐转化膜为致密的MgSnO3·3H2O晶粒所构成,盐雾腐蚀评级达到了8级,自腐蚀电位降低了40 mV,对铁红漆的附着力达到了3B级.     

AZ91D镁合金表面钼酸盐(Na_2MoO_4)转化膜的研究

为了提高AZ91D镁合金的耐蚀性能,对镁合金表面进行转化处理。采用不同配比的Na2MoO4-NaF钼酸盐溶液对AZ91D镁合金表面进行化学转化,测试了转化膜在3.5%NaCl溶液中的腐蚀率。经金相组织、SEM、EDS检测,结果分析表明:转化膜均匀,致密,由MgF2、MoO2,MoO3组成;在20%Na2MoO4-6%NaF溶液转化后的AZ91D镁合金的腐蚀率为1.79mm/a,仅为未经转化的AZ91D合金11.61mm/a腐蚀率的15.4%。     

AZ31镁合金钼酸盐转化膜

利用钼酸盐溶液在AZ31镁合金表面获得棕黄色的转化膜。用扫描电镜（SEM）和X射线光电子能谱（XPS）对膜层的形貌和组分进行研究,采用动电位极化曲线测试对膜层的耐蚀性进行研究。结果表明：膜的微观形态由球形颗粒构成,膜层厚度约12 μm,对镁合金的覆盖作用良好;转化膜表层中Mo元素主要以MoO3形式存在,在膜的内部钼主要以MoO2和MoO（OH）2存在,并含有部分MoO3;钼酸盐转化膜在阳极极化过程中发生明显的钝化,腐蚀电位正移683 mV,腐蚀电流密度降低2个数量级,明显提高AZ31镁合金的耐蚀性能。同时对镁合金表面钼酸盐转化膜的成膜机理进行初步探讨。     

AZ91D镁合金表面锰酸盐化学转化膜的研究

在AZ91D镁合金表面利用无铬的KMn04-Mn(H2PO4)2-pH值调整剂转化液进行化学转化。分析了转化膜的形成机理。经XRD分析结果显示,转化膜为非晶态结构,SEM观察发现,转化膜表面均匀,存在有利于增强涂装层附着力的网状裂纹。转化膜经EDS和XPS分析表明,主要元素为Mg、Al、Mn、O,由MgO、Mg(OH)2、MgAl2O4、MnO2组成。转化后的AZ91D镁合金在3.5%的NaCl溶液中全浸试验结果表明:其腐蚀速率低于其他化学转化膜;其表面采用有机涂料防护,涂层与基底的结合强度优于涂层与Q235钢的结合强度。     

AZ91D镁合金表面化学转化处理及镀镍

通过扫描电镜、盐雾实验、显微硬度测量等实验方法,分析AZ91D经化学转化处理及镀镍后的表面形貌、防腐能力以及镀层硬度.实验结果表明:转化膜与基体结合良好;化学转化膜的存在可避免镀镍层失效后发生强烈的电偶腐蚀,增加镀层的耐腐蚀性能;转化膜上沉积的镀镍层具有较高的显微硬度,可以对镁合金基体起到良好的防护作用.     

AZ91D镁合金表面无铬化学转化膜的研究

在AZ91D镁合金表面利用无铬的KMnO4-Mn(H2PO4)2-pH值调整剂转化液进行化学转化,分析了转化膜的形成机理.经XRD分析结果显示,转化膜为非晶态结构,SEM观察发现,转化膜表面均匀,存在有利于增强涂装层附着力的网状裂纹.转化膜经EDS和XPS分析表明,主要元素为Mg、Al、Mn、O,由MgO、Mg(OH)2、MgAl2O4、Al2O3、Al(OH)3、MnO2组成.转化后的AZ91D镁合金在3.5%的NaCl溶液中全浸试验结果表明,其腐蚀速率低于其他化学转化膜.     

以锡酸钠为主盐的AZ91D镁合金化学转化处理工艺

利用扫描电镜(SEM)、X射线光电子能谱(XRD)和全浸蚀试验等手段,研究了AZ91D镁合金锡酸盐化学转化膜的形貌特征及耐腐蚀性。溶液主要成分包含Na2SnO3、NaOH、乙酸钠和适量添加剂。结果表明,转化膜主要由镁的α相、β相和MgSnO3.3H2O组成;该环保型化学转化新工艺可获得银白色膜层,表面由近球状颗粒构成,孔隙分布均匀,膜层厚度在微观尺寸上较均匀。该膜层可以对AZ91D镁合金提供有效的保护。     

AZ91D镁合金表面处理过程中的前处理工艺研究

研究AZ91D镁合金表面前处理的除油、酸蚀工艺,对不同除油、酸蚀工艺配方进行了失重、外观性能指标的对比分析,提出了最佳工艺配方;在酸蚀溶液中添加硫脲、六次甲基四胺缓蚀剂减少镁合金溶解量,提高光泽度;采用自腐蚀电位跟踪法研究了镁合金在不同前处理溶液中的电位变化情况;采用光学金相显微镜研究了前处理后镁合金表面形貌;在添加1 g/L缓蚀剂的乙酸溶液中可以获得表面光泽度好、微观缺陷少的镁合金基材。     

AZ31镁合金表面锡酸盐化学转化膜的研究

对AZ31镁合金表面采取锡酸盐化学转化处理,采用对比试验测定了转化膜在质量分数3.5%NaCl溶液中的腐蚀率,利用扫描电镜(SEM)及能谱(EDS)观察分析了转化膜的形貌和元素含量.结果表明:经锡酸盐转化后的AZ31镁合金的腐蚀率为2.65mm/a,未经转化的AZ31镁合金的腐蚀率为30.36mm/a,耐蚀性有明显提高;锡酸盐转化液pH值在3.5～12范围时对AZ31镁合金均形成了转化膜保护层.     

镁合金化学转化膜

综述了镁合金化学转化膜技术的现状，主要涉及化学转化处理工艺及在多种不同处理液中所得到的转化膜的特性，最后还展望了今后镁合金化学转化膜的发展趋势。     

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...     

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。     

Corrosion of AZ91D magnesium alloy with a chemical conversion coating and electroless nickel layer

A chemical conversion treatment and an electroless nickel plating were applied to AZ91D alloy to improve its corrosion resistance. By conversion treatment in alkaline stannate solution, the corrosion resistance of the alloy was improved to some extent as verified by immersion test and potentiodynamic polarization test in 3.5 wt.% NaCl solution at pH 7.0. X-ray diffraction patterns of the stannate treated AZ91D alloy showed the presence of MgSnO₃ · H₂O, and SEM images indicated a porous structure, which provided advantage for the adsorption during sensitisation treatment prior to electroless nickel plating. A nickel coating with high phosphorus content was successfully deposited on the chemical conversion coating pre-applied to AZ91D alloy. The presence of the conversion coating between the nickel coating and the substrate reduced the potential difference between them and enhanced the corrosion resistance of the alloy. An obvious passivation occurred for the nickel coating during anodic polarization in 3.5 wt.% NaCl solution.     

Rheo-diecasting of AZ91D magnesium alloy

A rheo-diecasting process (RDC) was investigated for semisolid processing of an AZ91D magnesium alloy. The results of the RDC samples in as-cast state indicate that the microstructure of primary α-Mg particles has a fine size, nearly spherical morphology, and uniform distribution throughout the components. Due to the advanced microstructure and reduced level of defects, the RDC AZ91D Mg alloy exhibits an apparent improvement in mechanical properties. The quantitative metallographic investigations reveal that increasing the intensity of forced convection during the slurry preparation results in a promoted nucleation and reduced volume fraction of the primary phase solidified in the slurry maker.     

Crystallization of a chemical conversion layer that forms on AZ91D magnesium alloy in carbonic acid

This investigation studied the crystallization of a chemical conversion layer that formed on AZ91D Mg alloy in carbonic acid. The layer was an amorphous precursor to a crystalline Mg–Al layered double hydrotalcite, which improved the corrosion resistance of the alloy. The precursor must be treated with a strongly alkaline solution, causing the leaching out of amphoteric Al³⁺. The leaching step evidently caused crystallization from an amorphous precursor layer to a crystalline coating. Nuclear magnetic resonance analysis indicated that Al³⁺, which was originally randomly coordinated with surrounding OH⁻ in the precursor, coordinated octahedrally with OH⁻ groups in the crystalline conversion coating.     

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.     

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。