7075铝合金无铬磷化成膜动力学过程及其性能

直接在7075铝合金表面喷涂油漆,其结合力和防护性能较差。先对7075铝合金作磷化处理再喷涂环氧底漆和聚氨酯面漆。应用X射线衍射仪、Autolab电化学工作站和扫描电子显微镜及加温耐盐水试验对磷化膜的物相组成、成分、表面形貌及其耐蚀性进行了研究;探讨了磷化处理对7075铝合金表面漆膜层结合力及耐腐蚀性能的影响。结果表明:7075铝合金表面磷化动力学过程分为基体阳极溶解、表面形核及膜层增厚3个阶段,主要得到了由Mn Zn2(PO4)2,Zn3(PO4)2,Al PO4等物相组成的多孔磷化膜; 7075铝合金表面的自腐蚀电流由磷化前的40.17μA/cm^2降低到磷化后的7.37μA/cm^2,磷化提高了其耐点蚀性能;磷化处理还极大地提高了漆膜与7075铝合金的附着力和耐腐蚀性。     

Corrosion protection and formation mechanism of anodic coating on SiCp/Al metal matrix composite

The corrosion protection from sulfuric acid anodized coatings on 2024 aluminum and SiC particle reinforced 2024 aluminum metal matrix composite (SiC_p/2024Al MMC) in 3.5 wt.% NaCl aqueous solution was investigated using electrochemical methods. The results show that the anodized coating on 2024Al provides good corrosion protection to 3.5 wt.% NaCl, and the anodized coating on the SiC_p/2024Al MMC provides some corrosion protection, but it is not as effective as for 2024Al because non-uniformity in thickness and cavities present are associated with the SiC particulates. Cavities above SiC particles are the reason that the anodized coating on the MMC cannot be completely sealed by hot water as with anodic Al alloy. SiC particle anodizes at a significantly reduced rate compared with the adjacent Al matrix. This gives rise to alumina film encroachment beneath the particle and occlusion of the partly anodized particle in the coating. It was found that the barrier layer of anodized Al MMC is not continuous, and it is composed primarily of the barrier layer of anodized Al matrix and a barrier-type SiO₂ film on occluded SiC particles in the coating. A new formation mechanism of coating growth during anodizing of a SiC_p/2024Al MMC was proposed.     

Growth and corrosion of aluminum PVD-coating on AZ31 magnesium alloy

Magnetron sputtering was applied to prepare aluminum coating on a mechanically polished AZ31 magnesium alloy. A loose oxide film was spontaneously formed on the surface of AZ31 magnesium alloy during polishing process. The aluminum coating, which was subsequently deposited on this oxide layer, presented a developed columnar microstructure. Attributed to the barrier effect of Al coating, the Al coated AZ31 showed a higher corrosion resistance than bare AZ31 in corrosion tests. Generally, Al coating is cathodically protected by magnesium alloy substrate. But it is interesting in this study that Al coating still suffered from severe corrosion due to the occurrence of the alkalization effect.     

The effect of alkaline etching time on the anticorrosion performance of vanadia film formed on high strength AA2024 in chloride media

Corrosion performance, morphology, and electrochemical characteristics of vanadia-based conversion coatings on high strength aluminum AA2024-T3 alloy were examined as a function of alkaline etching time prior to vanadia treatment. Corrosion resistance and coating performance improved after etching in an alkaline solution for 10 min followed by vanadia treatment at room temperature. Electrochemical impedance spectroscopy and polarization testing correlated to macro- and microscopic surface examination and visual inspection. Proper etching of aluminum AA2024-T3 panels in alkaline solution prior to vanadia coating is a time dependent and considers a critical step for improved coating performance and materials durability. Results showed that the optimum alkaline etching time prior to vanadia treatment was 10 min which offers the best resistance to localized corrosion attack in NaCl solution. Alkaline etching for 10 min has an important role in increasing the number of OH groups on the aluminum surface, contributing to the adhesion of the vanadia-rich aluminum oxide layer by promoting covalent bonding. Based on these results, processes active during alkaline etching are kinetically dependent and strongly influenced by etching time.     

Self-assembled monolayer and multilayer thin films on aluminum 2024-T3 substrates and their corrosion resistance study

Aluminum alloy 2024-T3 substrates were modified with self-assembled monolayer or multilayer thin films from four different alkylsilane compounds, octadecyltrichlorosilane (C₁₈SiCl₃), octadecyltrimethoxysilane (C₁₈Si(OMe)₃), octyltrimethoxysilane (C₈Si(OMe)₃) and octadecyldimethylchlorosilane (C₁₈SiMe₂Cl). The water contact angle of the aluminum surface increased substantially after modification by the two trimethoxysilane compounds and trichrolosilane C₁₈SiCl₃, but decreased after the modification with monochlorosilane C₁₈SiMe₂Cl. Potentiodynamic polarization test, prohesion exposure, and electrochemical impedance spectroscopic studies revealed that the corrosion resistance of the C₁₈SiCl₃-modified aluminum alloy substrates improved significantly compared to the unmodified and the two trimethoxysilane-modified aluminum alloy samples. The C₁₈SiMe₂Cl-modified substrate also exhibited an improved corrosion resistance compared to the unmodified ones. While extensive corrosion appeared on the unmodified aluminum alloy samples after only 20–30 h of prohesion exposure, early stage corrosion was observed from C₁₈SiCl₃-modified samples after 150–200 h of prohesion exposure and C₁₈SiMe₂Cl-modified samples after 80 h of prohesion exposure. Based on the results obtained so far, it is believed that a mixed monolayer or multilayer thin film with opposite molecular orientations was formed through the self-assembling of alkylsilane molecules on the aluminum 2024-T3 surface.     

Corrosion Behavior and Protection Efficiency of 2024Al and SiCp／2024Al Metal Matrix Composite

The corrosion resistance of 2024 Al and SiC particle reinforced 2024 Al metal matrix composite(SiCp/2024Al MMC) in 3.5% NaCl solution was investigated with electrochemical method and immersion test, and the corrosion protection of sulfuric acid anodized coatings on both materials was evaluated by electrochemical impedance spectroscopy.The results showed that the SiCp/2024AlMMC is more susceptible to corrosion than its matrix alloy in 3.5% NaCl.For 2024Al,the anodized coating provides excellent corrosion resistance to 3.5%NaCl.The anodized coating on the SiCp/2024Al provides satisfactory corrosion protection,but it is not as effective as that for 2024Al because the structure of the anodized layer is affected by the SiC particulates.     

Hydroxyapatite microparticles as feedback-active reservoirs of corrosion inhibitors

This work contributes to the development of new feedback-active anticorrosion systems. Inhibitor-doped hydroxyapatite microparticles (HAP) are used as reservoirs, storing corrosion inhibitor to be released on demand. Release of the entrapped inhibitor is triggered by redox reactions associated with the corrosion process. HAP were used as reservoirs for several inhibiting species: cerium(III), lanthanum(III), salicylaldoxime, and 8-hydroxyquinoline. These species are effective corrosion inhibitors for a 2024 aluminum alloy (AA2024), used here as a model metallic substrate. Dissolution of the microparticles and release of the inhibitor are triggered by local acidification resulting from the anodic half-reaction during corrosion of AA2024. Calculated values and experimentally measured local acidification over the aluminum anode (down to pH = 3.65) are presented. The anticorrosion properties of inhibitor-doped HAP were assessed using electrochemical impedance spectroscopy. The microparticles impregnated with the corrosion inhibitors were introduced into a hybrid silica-zirconia sol-gel film, acting as a thin protective coating for AA2024, an alloy used for aeronautical applications. The protective properties of the sol-gel films were improved by the addition of HAP, proving their applicability as submicrometer-sized reservoirs of corrosion inhibitors for active anticorrosion coatings.     

铝及铝合金零件镀银前化学浸锌的工艺研究

对铝及铝合金电镀工艺的难点进行了分析,通过化学浸锌前处理工艺的试验研究,确定了二次浸锌的较优工艺配方及条件为:400～500 g/L NaOH,50～80 g/L ZnO,适量添加剂,室温,第一次浸锌0.5～1.0 min,第二次浸锌0.5～1.0 min.通过外观、结合力、耐蚀性、电器焊接性能测试表明,经该工艺处理后能获得性能优良的银镀层,满足了生产需求.     

Deposition and corrosion behavior of silicate conversion coatings on aluminum alloy 2024

Potassium silicate was deposited on AA2024 aluminum alloy as environmentally friendly conversion coatings and its corrosion behavior were examined by means of electrochemical impedance spectroscopy, potentiodynamic polarization and surfaces techniques. Potentiodynamic polarization curves show significant decrease in corrosion current density of silicate coated aluminum in NaCl solution. The corrosion resistance was increased with increasing silicate concentration of coating baths. The results indicated that the coating applied from 3 molar silicate baths is more uniform and continuous. The X‐ray diffraction (XRD) and energy discharge spectroscopy (EDS) spectra confirm the existence of silicate film on the AA2024 surface. The coating performance was evaluated in acidic and basic NaCl solution and the results show the stability of silicate conversion coating in these solutions.     

In situ evolution of trivalent chromium process passive film on Al in a corrosive aqueous environment

In situ neutron reflectivity (NR) is used to observe the structure and evolution of a Trivalent Chromium Process (TCP) passive film on Al in a NaCl-D(2)O solution. Using a split liquid reflectivity cell we mimicked the corrosion process on the anodic sites in alloy AA 2024-T3 in a pitting scenario. The split cell separates the anodic and cathodic reactions, allowing NR observation of the corroding anodic surface under potential control. We observed the evolution of the TCP film on the Al anode and compared the degradation of the Al with and without TCP protection. When held at 100 mV above the open-circuit potential (OCP), unprotected aluminum dissolves at a rate of 120 ?/h. By contrast, TCP-coated Al is stable up to the pitting potential (200 mV above OCP). In the passive state D(2)O molecules penetrate the bulk TCP film by partially replacing the hydrate water. In spite of exchange of hydration water, the TCP film is stable and the underlying aluminum is fully protected. The passive character of the TCP film is due to a dense layer at the metal-TCP interface and/or to suppression of ion transport in the bulk film. As the pitting potential is approached the film swells and NaCl-D(2)O solution penetrates the TCP film. At this point, 50 vol % of the TCP film is occupied by bulk NaCl-D(2)O solution. Failure occurs by aluminum dissolution under the swollen TCP film as the imbibed solution contacts the Al metal. Further increase in potential leads to complete stripping of the TCP film.     

2024铝合金阳极氧化膜的结构和耐蚀性能

为促进2024铝合金的进一步应用,用动电位阳极极化和电化学阻抗方法研究了2024 Al合金阳极氧化膜的结构及其在3.5% NaCl水溶液中的耐蚀性.结果表明,经硫酸阳极氧化的2024 Al合金较未处理基体的腐蚀速度降低了2个数量级以上,表现出相当好的保护性能;用光学显微镜、扫描电镜和透射电镜对阳极氧化膜的形貌观察发现,氧化膜表面平整,孔隙分布均匀,每个孔隙周围多含6个孔隙,也有5和7个孔隙结构,其孔隙尺寸细小,大小在10～30 nm之间.     

Influence of LDH conversion coatings on the adhesion and corrosion protection of friction spot-joined AA2024-T3/CF-PPS

Layered double hydroxide(LDH)conversion coatings loaded with corrosion inhibitors were suggested for the surface treatment of the aluminum alloy 2024-T3,prior to friction spot joining with carbon-fiber reinforced polyphenylene sulfide(AA2024-T3/CF-PPS).Vanadate was used as a model corrosion inhibitor.Lap shear testing method revealed an increase of approx.20%of the joint’s adhesion performance when treated with LDH and before exposure to salt spray.The evaluation of the joints after exposure to salt spray demonstrated a significant difference in the corrosion behavior of the joints when the AA2024-T3 is treated with LDH loaded with nitrate and vanadate species.The LDH intercalated with nitrate revealed a clear improvement in the mechanical and corrosion resistance performance of the joints,even after 6 weeks of salt spray.However,the LDH intercalated with vanadate failed in providing protection against corrosion as well as preserving the mechanical properties of the joints.The effect of the galvanic corrosion was further investigated by zero resistance ammeter(ZRA)measurements as well as localized scanning vibrating electrode technique(SVET).     

铝合金环保型钝化及其与漆膜的配套性能

为了进一步提高三价铬钝化膜的耐蚀性及其与漆膜的配套性能,以2024铝合金为基材,筛选出钝化液中的配位剂和缓蚀剂,并确定其工艺条件,开发了一种性能优良的环保型三价铬钝化液。结果表明：经硅溶胶封闭处理后的三价铬钝化膜结构致密,电化学性能优良,耐中性盐雾试验可达168h,其耐蚀性与Alodine1200六价铬钝化工艺相当;与环氧底漆和聚氨酯面漆的配套性好。     

锌合金表面涂装前磷化处理对膜层结合力的影响

锌合金活泼、易腐蚀,在其表面直接喷涂涂层的结合力较差,为了提高锌合金表面与涂层的结合力,对锌合金基材作磷化处理和磷化后封闭处理再喷涂聚氨酯漆膜,探讨了磷化处理及封闭处理对锌合金表面膜层间结合力的影响,并应用扫描电镜(SEM)和X射线衍射仪(XRD)对磷化膜表面形貌、物相组成及成分等进行研究。结果表明:锌合金表面直接喷涂聚氨酯漆膜,漆膜与锌合金基材的结合力差,结合力等级大于5级;而锌合金表面不管是磷化后直接喷漆还是磷化后封闭处理再喷漆均能极大提高涂层与基体的结合力,其结合力等级均小于2级;封闭处理有助于降低磷化膜的孔隙率,磷化膜经封闭处理后孔隙率由13.9%降到3.5%;封闭处理会降低磷化膜与漆膜的结合力。     

Characterization of 2024-T3: An aerospace aluminum alloy

The 2024-T3 aerospace aluminum alloy, reported in this investigation, was acquired from a local aerospace industry: Royal Malaysian Air Force (RMAF). The heat treatable 2024-T3 aluminum alloy has been characterized by use of modern metallographic and material characterization techniques (e.g. EPMA, SEM). The microstructural characterization of the metallographic specimen involved use of an optical microscope linked with a computerized imaging system using MSQ software. The use of EPMA and electron microprobe elemental maps enabled us to detect three types of inclusions: Al–Cu, Al–Cu–Fe–Mn, and Al–Cu–Fe–Si–Mn enriched regions. In particular, the presence of Al₂CuMg (S-phase) and the CuAl₂ (θ′) phases indicated precipitation strengthening in the aluminum alloy.     

2024铝合金微弧氧化涂层的耐磨性能

为了提高2024铝合金的耐磨性,对其进行微弧氧化。利用扫描电镜(SEM)和X射线衍射仪(XRD)分析了涂层的微观组织结构和物相组成;采用高速往复摩擦磨损试验机对2024铝合金微弧氧化涂层在不同载荷下的磨损性能进行了研究,并采用白光三维形貌仪进行磨损形貌分析及磨损体积计算。结果表明:2024铝合金微弧氧化涂层是一种微孔结构,涂层相主要成分为α-Al_2O_3、γ-Al_2O_3,且Al_2O_3具有高硬度、耐磨损的优良特性,有利于提高铝合金的耐磨损性能;微弧氧化涂层的摩擦系数随着载荷的增加而减小,而磨损量随载荷的增加而增加,磨损机理为磨粒磨损。     

Fatigue behavior of AA7075-T6 aluminum alloy coated with ZrN by PVD

The present investigation has been conducted in order to study the effect of the deposition of a ZrN coating, of 3 μm in thickness, on the static mechanical properties and fatigue behavior of a 7075-T6 aluminum alloy substrate. It has been determined that the coating deposition process gives rise to a significant decrease in such properties, which is not fully compensated for the presence of the film. When fatigue tests were carried out in a 3 wt.% NaCl solution at low alternating stresses, the ZrN film partially compensated for the decrease in fatigue properties of the coated substrate. Extensive delamination of the coating from the substrate was observed under the action of cyclic stresses greater than approximately 220 MPa. Below this stress and in the presence of NaCl, the behavior of the coated material approached that of the uncoated alloy, which highlighted the good corrosion resistance of the ZrN coating and its ability to protect the substrate when it remained adhered to the latter.     

改性纳米氧化锆与水性聚氨酯复合涂层的防腐蚀性能

为了改进纳米氧化锆(ZrO_2)在涂料中的分散性,以丙酮为介质,用3-氨基丙基三甲氧基硅烷(APS)对纳米ZrO_2进行了改性,并在镀锡板表面制备了改性纳米ZrO_2/水性聚氨酯(WPU)复合涂层。通过扫描电镜、原子力显微镜、红外光谱、电化学测试、盐雾腐蚀、附着力测试等技术,研究了WPU与不同含量改性纳米ZrO_2复合涂层的防腐蚀性能。结果表明:改性纳米ZrO_2的含量为0.2%(质量分数)时,在WPU中的团聚现象消失,分散性良好,该复合涂层具有优良的耐蚀性和较大的附着力。     

Surface effects in chromate conversion coatings on 2024-T3 aluminum alloy

Chromate conversion coatings formed on samples of 2024-T3 aluminum alloy, which had been given different pre-treatments, were examined by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and corrosion tests. Two pre-treatments were considered, namely a simple mechanical polish, and polishing followed by an etch in a HF-H₂SO₄ solution. The latter treatment leads to significant Cu enrichment at the oxide-alloy interface, and this in turn can lead to a deleterious effect on the corrosion protection afforded by a subsequently applied chromate coating. Discussions are given of the behaviour of Cu in the coating formed on the sample that received an acid etch in the pre-treatment. This involves both migration through the coating and a non-uniform redeposition of Cu on to the coating surface. By contrast, the sample that initially was given just the mechanical polish in the pre-treatment does not show a Cu enrichment in the surface region, and the subsequently applied coating appeared stable after a 24 h immersion in a NaCl test solution.     

定量研究2024-T351铝合金搅拌摩擦焊过程中的时效相行为

采用差示扫描量热法研究了2024-T351铝合金搅拌摩擦焊接过程中时效相回溶或粗化的相对值,给出了一种定量研究搅拌摩擦焊接过程中时效相行为的方法.结果表明:相对于母材,焊缝不同区域时效相的回溶或粗化值可通过公式f=Sx/SBM-1来计算;当搅拌摩擦焊搅拌头转速为700r·min-1,焊接速度为200mm·min-1时,...