1镁合金表面处理技术的发展现状 - 王梅

Development Status of magnesium alloy surface treatment technology

Wang Mei, Liu Jianrui, Chenshu Juan, Huang Weidong

(State Key Laboratory of Solidification Technology, Northwestern Polytechnical University, Xi'an 710072, China) Abstract: This paper introduces the principle of several common chemical conversion of magnesium alloy, anodizing, oxidation, organic coatings, metal coatings and other treatment methods, and the resulting characteristicsStructure and corrosion resistance of the film and the like. Analysis of the future direction of the magnesium alloysurfacetreatment technologies.

Keywords: magnesium alloy; surface treatment; corrosion resistance CLC: TG146 .2 +1 Document code: A Article ID: 1000-8365 (2006) 03-0295-04

表面处理技术的发展镁合金王玫，刘建蕊，沉树娟，黄卫东（索尔idification处理国家重点实验室，西北工业大学，西安710072，中国）摘要：回顾上形成PR inciple发，特点，结构和腐蚀镁合金表面薄膜耐性能由几个表面处理达到的方法，如化学转化，阳极氧化，微弧氧化，有机化合物表面处理技术的涂层和金属coating.The发展趋势镁合金进行了展望的未来。 关键词：Magnesiumalloys;表面处理;耐腐蚀

Abstract: A review is made on the formation pr inciple, characteristics, microstructure and corrosion

resistant performance of surface films of magnesium alloys attained by several surface treatment methods, such as chemical conversion, anodic oxidation, micro-arc oxidation, organic compound coating and metal coating.The development tendency of the surface treatment technology for magnesium alloys is also prospected in the future.

Key words: Magnesiumalloys; Surface treatment; Corrosion resistance

Magnesium is one of the lightest metal structural material, density only1 .74g / cm3, a specific strength and specific stiffness are high, and further having a cuttingWorkability and electromagnetic shielding is good, high recovery rate [1], is widely usedIn many areas of automotive, aerospace and electronic products. magnesiumAlloy is becoming the third largest metal construction materials steel, aluminum after,Known as the \material.\the chemical properties of magnesium is very lively, easily with oxygen, nitrogen,Water, CO2, SO2, etc. react to generate induced a lower density coefficientNon-metal film layer, this layer of film can not prevent the further reaction of oxygen and other gases,Metal matrix will not achieve effective protection. Further, the standard of magnesiumElectrode potential is -2 .34eV[2], it is the lowest common metallic structural materialsWhen in contact with other metals, prone to galvanic corrosion accelerated dissolutionCorrosion, these have become key issues that limit the application of magnesium alloy. in order toFurther improve the performance of magnesium alloy, magnesium alloy expanded range of applicationsWai, in addition to the development of new high-purity magnesium or magnesium alloy addition, proper tableSurface treated to improve its corrosion resistance is also an effective method. CurrentlyAction using mainly chemical conversion treatment, anodic oxidation treatment,Oxidation, organic coatings, metal coatings.

1.A chemical conversion treatment

Chemical conversion treatment is by chemical or electrochemical reaction,The matrix metal ions and anions in solution or atom, fromIn the metal surface to form a thin film protects the base material forUse [3]. Chemical conversion treatment method for forming a film of a uniform, simple process,Especially suitable for complex shape parts. At present magnesium alloy chemical conversionProcessing technology research more chrome treatment and phosphate treatment.Chrome treatment with chromate or dichromate aqueous chemistryConversion, is more mature, the most widely used surface treatment sidelaw. During film formation process of chromium, magnesium atoms in the surface of the first metalIt is dissolved in an aqueous solution to form a divalent magnesium ions and magnesium ions in solutionChromate ion reacts in a thin layer of metal deposited on the surface of hexavalentAnd a mixture of trivalent chromate colloidal metal compound and the base, the mainComposition Cr2O3 · nC rO3 · mH2O, Mg (C rO2) 2, MgO,Al2O3, MnO [4], its main reaction equation is as follows:Mg ※ Mg 2 + + 2eMg2 + + 2CrO -2 ※ Mg (CrO2) 2(1)This gum layer between the substrate and the environmental barrier layer is formed, serveProtective effects. And chromate conversion coating with self-healing capabilities, without lossHygroscopic can go when crystal water, when it is damaged, will be expanding waterExpansion, the purpose to protect the substrate [5].Chromate-treated film obtained capacity than natural oxidation corrosionFilm, but the thin film layer (0 .5 ~ 3 .0 μm), and there was a large number ofTemporary protection microcracks [6], generally used only for decoration, shipping, storage timeAnd coating the bottom.Although chromate conversion coating technology is relatively mature, but the process.

Process produces harmful hexavalent chromium ions, is not easy to deal with waste on the environment madeTo pollution. Therefore, people are working on the development of chromium-free conversion treatment workart. Phosphate - potassium permanganate method is commonly used as a new chrome-freeChemical conversion treatment [7], and its formation mechanism is similar to chromate treatment,The difference is that potassium permanganate is a strong oxidant, can be formed when dissolved reductionCheap low degree of hydrolysis of manganese oxide into the film. With the extension of timeLong, the manganese content in the film is gradually increased, gradually add color filmDeep, this may be because the film due to the formation of manganese dioxide. formPhosphate coating [7, 8] The main component of the manganese oxide and magnesium fluorideMaterial, thickness of 4 ~ 6 μm. This film layer is a porous structure, and the substrate junctionCombined firm, has a good adsorption, corrosion resistance and chromium film quite,It can be used as a substrate of magnesium alloy processing step between short-term corrosion or painted beforeLayer, but due to the treatment liquid drains faster, and pre-treatment used in high concentrationOf phosphoric acid increases the cost, making the application of phosphate coatings is limited [7].In addition to the above two conversion coating, the researchers also developed a molybdateConversion coatings [5], tungstate conversion coating [5], organic conversion coatings [5], stannatesConversion film [7], fluorozirconate conversion film [7], the rare earth conversion film [9] as well as forChemical conversion coating Mg-Li alloys [10] and other low-cost, non-polluting, dedicatedType chemical conversion treatment of new technology, they have certain application.

2 anodizing treatment

Anodic oxidation process at the appropriate electrolyte solution toThe metal to be treated as an anode, stainless steel, iron, chromium, nickel or electrolytic conductivityPool itself is a cathode, at a certain voltage and current conditions, the anode surfaceOxidation, thereby obtaining anodic oxide film layer on the metal surface.Anodized oxide film thickness in the formation of a magnesium alloy surfaceLike the 10 ~ 40 μm, and has a double structure, the inner layer is thinner denseLayer, the outer layer is thicker, porous layer [7]. Studies have shown that [11], anodizingThe complex composition of the film, composed mainly of magnesium oxide, the atomic groupAnd phase into the matrix alloy, anodizing electrical parameters by an electrolyte solutionControl and influence the composition and concentration, solution temperature and other factors, as the electrolysisChanges in fluid and voltage, current density and other parameters, to form an oxide film groupCombined into force, uniformity, roughness, corrosion resistance, abrasion resistance, and the matrixSuch as different levels of change will occur. Corrosion protection of anodized filmWith the film thickness, generally thicker the film, the better the performance of its protection.Film thickness, strength, corrosion resistance, good abrasion resistance than chemical treatment,Therefore, as a moderately corrosive atmosphere in the protective layer. However, due to the filmLarge gaps, uneven, generally as a coating pre-treatment, still needIt is filled with other post-processing [10].Factors affecting the anodizing film effect of electrolyte components andConcentration, electrical parameters (voltage, current) type and magnitude of its control,Solution temperature, pH value and the processing time, wherein the power mode and electrolyticLiquid component is a decisive factor in magnesium anodized greatly affectedThe magnesium anode oxide film formation and film properties. So far, magnesiumAlloy anode oxidation process according to the composition oxidizing solution into the acidic oxygenOf the alkaline solution and the oxidizing solution types. Acidic solution DOW17 oxygenAs the representative of the fluid, mainly composed of phosphoric acid, the process temperature is about 80 ℃, intoFilm better, but containing Cr6 + compounds, pollution of the environment; alkaline solutionIn HAE liquid oxidizing solution represented mainly composed of KOH andAl (OH) 3, which processing temperature is about 30 ℃, acidic liquid due to overcomeHigh temperatures and unstable shortcomings of the current anodic oxidation under alkaline conditions

More research [10, 12].Anodic oxidation process is essentially a process of electrochemical reaction, by the

The entire process is affected by many factors, so that different parts of a metal surfaceGrowth bit uneven film is always carried out, leading to the metal surface film thickness

Uneven distribution of degree. Therefore, from the start of the treatment process factors,Anodized to develop a suitable electrolyte, stable power supply in the form of other conditions

Processing method, to form a uniform, effective protection of the metal surfaceFilm is anodized magnesium alloy processing a development direction for the future.

3 micro-arc oxidation treatment

Micro-arc oxidation technology known as micro-plasma oxidation or anodic spark ShenProduct,

anodic oxidation is essentially a high-pressure, and is a new type of metalSurface treatment technology [3]. The process is at an appropriate electrical pulse parameters andHydrolyzate under conditions in which the anode surface micro plasma arc discharge current

Like, on the anode native oxide melts instantly, while the electrolyte by coldBut the role, and then grown in situ on the surface of metal oxide film on a ceramicprocess. Compared with ordinary anodizing film, the porosity of the membrane is substantiallyReduced,so that the corrosion and wear resistance have been greatly improved. Currently, microArc oxidation technology is mainly used Al, Mg, Ti and other non-ferrous metal or a combination

Surface treatment of gold.Magnesium oxide film alloy micro arc oxidation formed mainly byMgO and MgAl2O4 spinel phase, with a total thickness of up to 100 μmAbove [13], with a clear three-layer structure: the outer layer of loose, intermediateThe dense layer and the inner layer bonding. The final total thickness of the dense layer90% of micro-metallurgical bond with the substrate is formed. There are many loose layerHoles and other defects [15], its physical and chemical characteristics of the micro-arc oxidationWhen processing the electrical parameters of the choice of the electrolyte formulations and sample their specialAbout sex. Compared with the conventional anodic film, micro-arc oxidation film is emptyThe gap is small, low porosity, matrix-bound tightly, and in corrosion resistance, wear resistanceOther aspects of the greatly improved [14].Micro-arc oxidation film generated good overall performance, and the matrixCombined with a solid and simple process, environmental pollution, currently its growthLaw, growth mechanism and influencing factors [13] and so have more in-depthResearch in the industry to a certain application, is a kind of latent developmentMagnesium alloy surface treatment technology force.

4 organic coating

After most of magnesium alloy surface treatment, needs paintedA layer of organic matter to enhance the protection, play a role in shielding, passivating corrosion inhibitionAnd electrochemical protection. About the salt spray test showed [15], untreatedChromium and magnesium alloys, respectively, after treatment, the anodized coatingAfter the resin protective film corrosion resistance has been greatly improved, corrosion-resistantEtching time can reach several thousand hours.There are various types of organic coatings [16], the magnesium alloy may be used epoxy resinGrease, polyurethane and rubber and other organic coating materials to obtain a protective film can also beThrough the oil, grease, paint, wax and asphalt is coated on the surface to obtainA certain degree of protection. Wherein the epoxy resin coating due to the strong adhesion,No water infiltration, high strength and a relatively broad application.Organic coating method [15] with a liquid paint brushing, spraying, dipElectrophoresis stain or paint and powder coatings, the fluidized bed method, spray method.MagnesiumAlloy is more powder coating method. Australia HilustMagnesium alloy surface re Co atings Pty Ltd developed epoxy resinCoating process [18] is by electrostatic spraying the epoxy powder coatedMagnesium alloy surface and then subjected to solid at a temperature in the range of 150 ~175 ℃, The formation of an effective protective layer. It can also be sprayed on the surface of the epoxy resinAfter spray a layer of acrylic resin, in order to further improve the surfaceCorrosion resistance and abrasion resistance.

Organic coating types, wide adaptability, simple process. However, the resultingThe film is thin (less than 1 μm), have poor porosity, mechanical performance, strong corrosionPitting media,

erosion, impact, high temperature easy to fall off, usually as a magnesium alloyAn auxiliary means of protection [17]. Therefore, the development of high corrosion resistanceThe coating materials and the corresponding coating process, so closely integrated with thesubstrateCombined organic coating process is also an important research content.

5 metal coating

Magnesium alloys can also be used to protect metal coating, usually by chemicalPlating methodon the surface of the metal plating. Plating solution is goldMetal cations revert to the ground state of metal is deposited on the surface to form a protective coatingLayer, the reaction provided the desired electronic directly from the matrix metal. PlatingThe biggest advantage is that it can in the shape of complex samples, especially in the holeAnd deep pockets can get a uniform coating thickness [18]. It has been appliedChemical plating magnesium alloy mainly Cu / Ni / C r, Ni / A u, chemicalNickel and other [19].Electroless nickel plating is widely used in recent years, a chemical plating method,However, due to the lower electrode potential of magnesium, high chemical activity, process largeThe amount of hydrogen evolution, coating and the substrate adhesion is poor, difficult to directly electroless plating.Daichang Song et al. [20] After several tests, the use of added immersed in the process

Zinc pretreatment method, to obtain a uniform thickness, good corrosion resistance, chemical Nickel plating. A .K .Sharma fluoride is used as activator, the use ofLearn nickel plating, passivation and heat treatment method enables a direct chemical on magnesiumNickel plating process, the resulting coating has good mechanical properties, corrosion resistance andWeldability, and can drill holes into the interior of the device, for spacecraftMember of the stringent requirements [8].Magnesium alloy after nickel plating, and then on the resistant plating on the surface as needed

The method of etching the metal has entered the stage of practical application, but there is often Acid bath will corrode the magnesium matrix used and magnesium bath maleIons react reduces the life of the bath. In the large-scale workIndustry production, chemical nickel plating solution stability is not high, difficult process conditionsControl, corrosion resistant metal plating bath last used usually contain harmfulCyanide. Therefore, the development of a non-acidic, high stability, longevityLong life, non-polluting chemical plating magnesium alloy surface treatment technologyAn important direction of development [18].In addition, laser surface modification technology [21] of the matrix of small heat-affected, appropriate

Material more widely, it can refine the surface of the grain, improving strength,It is also animportant surface treatment method. Nitrided layer surface treatment [21] throughThrough nitriding or ALUMINIZING, greatly improve the strength of the alloy, this method is the mostThe big advantage is that the environmental pollution caused by small, it has a very importantResearch significance. Physical vapor deposition [22] a cooling speed (can be superOver 106K / s), Gas fast curing, etc., using the high-energy beam assistedPVD method, may be deposited in a specific component magnesium alloy surface as neededAlloy layer, but also one of the development of magnesium alloy surface treatment technology.In recent years, through the use of ion implantation, laser annealing, rapid solidificationProcessing technology, surface protective coating can be obtained nanostructure film, mention

High corrosion resistance of magnesium alloy. With the development of nanotechnology, makeMagnesium alloy surface coating of nano-structure will also be a surface treatment

processImportant direction of development.

6 Conclusion

As a new structural material, magnesium alloy will get increasingly

The more widely used, and the corresponding surface treatment method will also be fastSpeeddevelopment. Chromium treatment of environmental pollution and the production of magnesium alloy harm peopleHealthy body, many researchers are looking for new ways to replace the existingTreatment process, phosphate processing magnesium alloy chromium-free treatment are more development beforeWay approach, substituted chrome treatment trend. Micro-arc oxidation technology.Technique has simple process, materials wide adaptability and other characteristics of theresulting film areUniform, hard, will be the development direction of a magnesium alloy anode oxidation. organic

The coating may play a protective role in the long term, but the coating and the substrate junction.Not too close together, which is also an important factor restricting its development, development.The new coating materials and coating process is to improve the performance of organic coatings

A good way.Therefore, to enhance the development of magnesium alloy surface treatment technology, in-depth studyMechanism of protective film is formed, and further improve the performance of surface protection film toTo improve the corrosion resistance of magnesium alloy, magnesium alloy material for promotingthe application hasGreat practical significance and economic benefits.

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