The surface, microstructure and corrosion of magnesium alloy AZ31 sheet

This study investigates the effect of some industrial pre-treatments, including heat-treatment, surface grinding and polishing, acid cleaning and sandblasting, on the corrosion performance of Mg alloy AZ31 sheet. It is found that tempering accelerates the corrosion of AZ31. Surface grinding and acid cleaning dramatically improve its corrosion resistance, while sandblasting severely deteriorates its corrosion performance. Surface analysis indicates that the change in corrosion behavior of AZ31 by these pre-treatments can be associated with the alteration of its impurity contamination, surface state, grain size and intermetallic particles. A corrosion model concerning the dissolution and precipitation of tiny Al-Mn-(Fe) particles in grains and grain boundaries is proposed to explain the effect of mechanical deformation and heat-treatment on the corrosion performance of AZ31.     

Novel hybrid sol-gel coatings for corrosion protection of AZ31B magnesium alloy

This work aims to develop and study new anticorrosion films for AZ31B magnesium alloy based on the sol-gel coating approach.Hybrid organic-inorganic sols were synthesized by copolymerization of epoxy-siloxane and titanium or zirconium alkoxides. Tris(trimethylsilyl) phosphate was also used as additive to confer additional corrosion protection to magnesium-based alloy. A sol-gel coating, about 5-μm thick, shows good adhesion to the metal substrate and prevents corrosion attack in 0.005 M NaCl solution for 2 weeks. The sol-gel coating system doped with tris(trimethylsilyl)-phosphate revealed improved corrosion protection of the magnesium alloy due to formation of hydrolytically stable Mg-O-P chemical bonds.The structure and the thickness of the sol-gel film were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The corrosion behaviour of AZ31B substrates pre-treated with the sol-gel derived hybrid coatings was tested by electrochemical impedance spectroscopy (EIS). The chemical composition of the silylphosphate-containing sol-gel film at different depths was investigated by X-ray photoelectron spectroscopy (XPS) with depth profiling.     

AZ31镁合金表面防腐胶粘涂层的研制

胶粘涂层法是有效提高镁合金耐腐蚀性能的表面处理技术之一.以E-44环氧树脂、低分子量650#聚酰胺、云母氧化铁等为主要原料,制备了适用于AZ3l镁合金基体的防腐胶粘涂层.研究了填料含量对涂层外观、施工性和耐蚀性能的影响.结果发现,当填料质量分数为60%、涂层厚度为180～220μm时,防腐胶粘涂层具有良好的外观及施工性,附着力为1级,耐盐雾时间168 h.     

AZ31镁合金稀土转化成膜工艺研究

本文对AZ31镁合金表面稀土转化成膜工艺进行了研究。分析了不同的成膜工艺参数丽土盐溶液组成、转化成膜时间）对稀土转化膜的形貌及耐蚀性能的影响。扫描电镜分析了不同成膜工艺形成的稀土转化膜的表面形貌;极化曲线研究了转化膜的电化学腐蚀行为。结果表明：当转化液中硝酸铈浓度为4．3423g·L^-1和硝酸镧浓度为4．3302g·L^-1时,转化膜的耐蚀性能最好;成膜时间对膜的耐蚀性也有不同程度的影响。     

十二烷基苯磺酸钠对AZ31B镁合金的缓释效果研究

针对镁及其合金由于易腐蚀限制了其广泛使用问题,选用环保型缓蚀剂,利用微弧氧化技术对镁合金进行预处理,采用开路电位、极化曲线、交流阻抗、浸泡腐蚀等方法研究了不同浓度十二烷基苯磺酸钠对微弧氧化预处理镁合金的缓蚀效果,同时用扫描电子显微镜对各样品的腐蚀形貌进行了观察.结果表明,十二烷基苯磺酸钠(SDBS)缓释效率最好,达到6...     

硅烷偶联剂改性氧化石墨烯的制备及表征

通过与不同的硅烷偶联剂反应,得到了三种不同的功能化氧化石墨烯(FGOs)。通过红外光谱、热失重分析、扫描电镜、X-射线衍射等进行表征。结果表明,以硅烷偶联剂为改性剂制备的功能化氧化石墨烯,片层间距有所增加,热稳定性明显提高。     

Localized electrochemical study of corrosion inhibition in microdefects on coated AZ31 magnesium alloy

In the present work corrosion inhibition in microdefects of protective coatings on magnesium alloy was studied by SVET (scanning vibrating electrode technique) and SIET (scanning ion-selective electrode technique) in 0.05 M NaCl. Mg²⁺- and pH-selective microelectrodes were developed to be used by SIET. The microelectrodes were characterized from the standpoint of properties important for corrosion applications, aiming at the reliable functioning during measurements. The combination of SVET and SIET demonstrated to be a useful approach to investigate the inhibition of corrosion processes in microdefects on coated AZ31. In this paper the corrosion inhibiting properties of 1,2,4,-triazole, F⁻ and Ce³⁺ on AZ31 alloy were analyzed. According to the results, 1,2,4-triazole in concentration of 0.01 M showed the highest inhibition efficiency among the studied inhibitors and was able to prevent the increase of pH in the corroding defects, by keeping the corrosion activity on a very low level during the tested immersion period.     

pH对AZ31镁合金表面磷酸钙转化膜性能的影响

采用液相沉积法,以由硝酸钙和磷酸氢二铵组成的转化液在AZ31镁合金表面制备了一层转化膜,考察了转化液pH对膜层性能的影响.使用扫描电镜、能谱仪和X射线衍射仪分析了转化膜的形貌、组成和结构.通过人体仿生液浸泡和动电位极化曲线、电化学阻抗谱测试了转化膜的耐蚀性.结果表明,当转化液pH为5.5时,所制转化膜的主要成分为CaH...     

Corrosion protection behavior of AZ31 magnesium alloy with cathodic electrophoretic coating pretreated by silane

As an alternative process to phosphate and chromate conversion coatings, silane pretreatment was used to improve the performance of cathodic electrophoretic coating (E-coat) on AZ31 Mg alloy in this study. The galvanic corrosion behavior of AZ31 Mg alloy with E-coat coupled with Q235 steel was investigated. Compared to bare Mg alloy and Mg alloy with conventional painting, the corrosion properties of the AZ31 Mg alloy pretreated with silane and subsequently E-coated were studied during salt solution immersion and salt spray testing. The surface morphologies of the Mg alloy were examined in detail after immersion in NaCl solution for different times using digital photography and scanning electron microscopy (SEM). The corrosion current density of the specimens was characterized by DC polarization tests. It was found that silane pretreatment of AZ31 Mg alloy followed by subsequent E-coat led to much better corrosion protection than that without silane treatment. The silane pretreatment and E-coat delayed the galvanic corrosion of Mg alloy coupled with 235 steel bolts.     

环境友好型AZ31B镁合金交流微弧氧化的表征(英文)

研究了一种新的AZ31B镁合金交流电微弧氧化(MAO)工艺,采用了对环境更加友好的含硅酸盐的稀碱溶液作为电解质。结果发现氧化过程分为2个阶段,膜厚与微弧氧化时间呈抛物线关系。形貌观察表明,微弧氧化膜由一个致密层和一个多孔层组成。致密层的厚度约占整个膜厚的40%,膜表面的20%均匀分布着直径1~3μm的孔。动电位极化测量显示,该新型微弧氧化膜的耐蚀性有明显提高,腐蚀电流降低了2个数量级,而自腐蚀电位正移了0.07V。盐雾试验结果同样证实微弧氧化膜的耐蚀性有大幅度提高。     

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.     

表面活性剂十二烷基磺酸钠对镁合金阳极氧化的影响

在含柠檬酸钠的碱性硅硼体系中对AZ91D镁合金进行电化学阳极氧化成膜处理,通过记录阳极氧化电压随时间的变化以及扫描电镜、能谱仪和电化学测试等方法考察了阴离子型表面活性剂十二烷基磺酸钠(SDS)对镁合金阳极氧化过程和氧化膜性能的影响。结果表明,在阳极氧化过程中,十二烷基磺酸根离子被吸附到镁合金电极表面,增加了表面膜层电阻,提高了阳极氧化电压,使得阳极氧化膜层更致密、厚度分布更均匀,减少了表面微气孔。当SDS含量为0.2~0.4 g/L时,所得阳极氧化膜具有最大的电荷传递电阻和膜电阻,对镁合金具有最好的腐蚀防护性能。     

Hydroxyapatite-carboxymethyl cellulose-graphene composite coating development on AZ31 magnesium alloy: Corrosion behavior and mechanical properties

In this study, hydroxyapatite (HA) coatings containing carboxymethyl cellulose (CMC) and graphene (Gr) were developed on AZ31 magnesium alloy through two-step electrophoretic deposition method. The morphology and chemical bonding of coatings were characterized and also the phase identification was done using scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction, respectively. Moreover, the corrosion behavior of the applied coatings was compared with the bare AZ31 Mg alloy substrate in the simulated body fluid by the means of potentiodynamic polarization test and electrochemical impedance spectroscopy. Obtained results revealed that the novel HA-CMC-Gr coating possesses the highest corrosion resistance compared to the HA, HA-CMC, and HA-Gr coatings due to its uniform and compact structure. To investigate the mechanical properties and to elucidate the effect of CMC on the adhesion of coating-alloy interface, pull-off test was employed, where results demonstrated that the addition of CMC increases the adhesion force from 1.06 MPa to 1.62 MPa. Besides, the modulus of elasticity and the hardness of HA and HA-Gr composite coatings were compared by applying nanoindentation test. Interestingly, it is detected that the presence of Gr has considerably increased the elastic modulus of the coating by approximately 30% in comparison to the pure HA coating.     

AZ31镁合金钙系磷化工艺优化及磷化膜组织结构研究

利用正交试验法优选出适用于AZ31镁合金材料的最佳钙系磷化工艺配方及工艺,即NaH2PO4·2H2O 40 g/L,Ca2+40 g/L,六次甲基四胺1 g/L,有机配体D 15 g/L,pH 3.0,温度30°C。扫描电镜观察发现,镁合金表面钙系磷化膜均匀致密,无明显缺陷,呈花瓣状结晶生长。X射线衍射结果表明,膜层的主要成分为CaHPO4·2H2O。     

AZ31镁合金无氰化学镀镍工艺的研究

研究了在AZ31镁合金表面二次浸锌后直接进行化学镀镍的工艺。分析了pH、温度、镍离子质量浓度和次磷酸钠质量浓度对镀速的影响,并测试了镀层的结合力、表面形貌、成分含量和耐蚀性。结果表明,以二次浸锌法进行预处理,无需氰化镀铜打底;在pH为7,碱式碳酸镍质量浓度25g/L,次磷酸钠质量浓度30g/L时,镀速有最大值;AZ31镁合金化学镀镍后耐蚀性明显提高,腐蚀电位从-1.52V提高到-0.55V;化学镀镍的优化参数为15g/L碱式碳酸镍,25g/L次磷酸钠,pH为6,温度82℃。     

Microstructure and properties of Nb2O5/Mg gradient coating on AZ31 magnesium alloy by magnetron sputtering

A Nb₂O₅/Mg gradient coating was synthesized on AZ31 magnesium alloy through the magnetron sputtering technique. The microstructure and properties of the coating were investigated by SEM, AFM, EDS and XPS, scratch tester, nanoindenter, friction tester, and electrochemical workstation, with a Nb₂O₅ monolayer coating as a control. The results show that all the as-disposed films have an amorphous columnar structure, and can improve the mechanical, anti-wear and anti-corrosion properties of AZ31 magnesium alloy. The Nb₂O₅/Mg gradient coating shows a gradual change in chemical composition through its depth, decreasing the residual stress of the coating/substrate system, thus reducing the risk of film cracking, and increasing compactness of the coating. Compared with a Nb₂O₅ single-layer film of the same thickness, the gradient coating exhibits increased adhesion, H/E and H³/E² increased by about 16 times, 7.8% and 100% respectively, and a wear rate reduced by more than an order of magnitude. In addition, the gradient coating has better corrosion resistance, having a two orders of magnitude lower current density and one order of magnitude higher polarization resistance. This study provides a workable strategy for improving the performance of ceramic coatings on magnesium alloy, for medical applications.     

AZ91D镁合金电镀前处理工艺研究

为了得到适用于AZ91D镁合金的电镀前处理工艺,提高镀层与镁合金基体的结合力及镁合金的耐蚀性,采用正交试验方法研究了酸洗液中不同组分用量和酸洗时间对试样表面状态的影响,利用场发射扫描电子显微镜和X射线能谱仪分析了活化时间和浸锌时间对镁合金浸锌后表面形貌及微观成分,采用称重法考察了浸锌不同时段镁合金的质量变化,通过热震试...     

Corrosion resistance and chemical stability of super-hydrophobic film deposited on magnesium alloy AZ31 by microwave plasma-enhanced chemical vapor deposition

A super-hydrophobic film was successfully deposited on magnesium alloy AZ31 by the microwave plasma-enhanced chemical vapor deposition (MPECVD) process. The film surface showed a static water contact angle of more than 150°. The hydrophobicity and root mean square roughness of the film surface increased with an increase in deposition time. The anticorrosion resistance of the deposited film was estimated by electrochemical impedance spectroscopy (EIS) measurements. The EIS measurements and appropriate equivalent circuit models revealed that the super-hydrophobic film considerably improved the anticorrosion resistant performance of magnesium alloy AZ31. The anticorrosion mechanism of the super-hydrophobic film was also considered. Moreover, the chemical stability of the super-hydrophobic film in acidic, neutral, and alkaline aqueous solutions was investigated. The super-hydrophobic film showed high chemical stability in acidic and neutral aqueous solutions.     

Development of HA-CNTs composite coating on AZ31 magnesium alloy by cathodic electrodeposition. Part 1: Microstructural and mechanical characterization

Magnesium alloys are considered as a new class of biodegradable alloys having many favorable properties to overcome the problems of currently used biomedical materials. Hydroxyapatite (HA) containing carbon nano-tubes (CNTs), with concentration ranging from 0 to 1.5?wt.%, coated on AZ31 magnesium alloy by direct and pulse cathodic electrodeposition methods. The coating properties including phase analysis, chemical bonding, morphology, and thickness were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and field emission scanning electron microscopy (FESEM), respectively. Nano-indentation, micro-hardness and adhesion tests were also used to evaluate the mechanical properties of the coatings. The results showed that a dense and fine coating structure was obtained by pulse deposition method. Moreover, the presence of carbon nanotubes in composite coating increased crystallization, presumably due to the increase in nucleation sites affecting the growth direction of hydroxyapatite crystals. The optimum condition having high crystallinity (71.2%) along with an uniform structure was the pulse deposited hydroxyapatite coating containing 1?wt.% CNTs. The elastic modulus and hardness of this sample increased by approximately 42% and 130% compared to the pure HA coating, respectively. Furthermore, the fracture toughness of pulse deposited HA–1wt % CNTs on AZ31 alloy reaches 1.96 ± 0.72MPa/m^0.5 which is in the range of compact bone.     

六次甲基四胺对AZ91D镁合金阳极氧化的影响

向主要成分为氢氧化钠、硅酸钠与对苯二甲酸的基础电解液中添加六次甲基四胺(HMTA),在AZ91D镁合金表面制备阳极氧化膜。采用扫描电镜(SEM)、光学显微镜、X射线衍射仪(XRD)及极化曲线测量,分析了六次甲基四胺对镁合金阳极氧化过程以及阳极氧化膜的形貌、相组成和耐腐蚀性能的影响。结果表明:在镁合金恒电流阳极氧化过程中,六次甲基四胺能够提升氧化电压,抑制弧光放电,令膜层中SiO-₂相增多,膜层微孔数减少,致密度和厚度都得到提升,进而提高膜层的耐腐蚀性能。