Corrosion resistance of Mg-Al-LDH steam coating on AZ80 Mg alloy:Effects of citric acid pretreatment and intermetallic compounds

In this study,the effects of intermetallic compounds(Mg_(17)Al_(12)and Al_(8)Mn_(5))on the Mg-Al layered double hydroxide(LDH)formation mechanism and corrosion behavior of an in-situ LDH/Mg(OH)_(2)steam coatings on AZ80 Mg alloy were investigated.Citric acid(CA)was used to activate the alloy surface during the pretreatment process.The alloy was first pretreated with CA and then subjected to a hydrothermal process using ultrapure water to produce Mg-Al-LDH/Mg(OH)_(2)steam coating.The effect of different time of acid pretreatment on the activation of the intermetallic compounds was investigated.The microstructure and elemental composition of the obtained coatings were analyzed using FE-SEM,EDS,XRD and FT-IR.The corrosion resistance of the coated samples was evaluated using different techniques,i.e.,potentiodynamic polarization(PDP),electrochemical impedance spectrum(EIS)and hydrogen evolution test.The results indicated that the CA pretreatment significantly influenced the activity of the alloy surface by exposing the intermetallic compounds.The surface area fraction of Mg_(17)Al_(12)and Al_(8)Mn_(5)phases on the surface of the alloy was significantly higher after the CA pretreatment,and thus promoted the growth of the subsequent Mg-Al-LDH coatings.The CA pretreatment for 30 s resulted in a denser and thicker LDH coating.Increase in the CA pretreatment time significantly led to the improvement in corrosion resistance of the coated AZ80 alloy.The corrosion current density of the coated alloy was lower by three orders of magnitude as compared to the uncoated alloy.

A novel MgF2/PDA/S-HA coating on the bio-degradable ZE21B alloy for better multi-functions on cardiovascular application

Recently, functional molecules such as Polydopamine(PDA), Hyaluronic Acid(HA) and heparin have been widely studied in the field of surface modification of magnesium(Mg) alloy stents for better degradation behavior and biocompatibility, but their further application is limited by undesirable anticoagulant function, uncontrollable degradation and easy bleeding, respectively.Regarding to this consideration, a magnesium Fluoride/Polydopamine/Sulphonated hyaluronic acid(Mg F2/PDA/S-HA) composite coating was successfully prepared by applying S-HA with sulfur content of 9.71 wt% on the surface of ZE21B alloy in this study. The results showed that the composite coating with a unique mesh structure not only inherited the anticoagulant effect of sulfonic acid group and the excellent cyto-compatibility of S-HA with high sulfur content, but also significantly improved the corrosion performance of ZE21B alloy.These results indicate a great application potential of the composite coating in the field of cardiovascular biomaterials.

Novel PA encapsulated PCL hybrid coating for corrosion inhibition of biodegradable Mg alloys:A triple triggered self-healing response for synergistic multiple protection

Surface coatings have been extensively used to control the degradation rate of Mg alloys for bioimplant applications.However,these coatings only act as passive barriers.In corrosive media,structural damage impairs their barrier properties,resulting in rapid degradation of Mg alloys.The present study incorporates phytic acid(PA)as a healing agent in polycaprolactone(PCL)microcapsules with a unique honeycomb core matrix to obtain a self-healing PA-PCLcaps coating.The contact between simulated body fluid(SBF)and PA-PCLcaps coated ZM21 exhibited Cassie-Baxter interfacial states,resulting in significant hydrophobicity with a contact angle(CA)of 116.3.The corrosion potential(Ecorr)and current density(Icorr)were found to be-0.28 V and 1.1×10^(-9)A/cm^(2),respectively,for PA-PCLcaps coating,resulting in biosafe corrosion rate of 2.5×10^(-4)mm/year.After mechanical scratching,rapid HA mineralization at scratched regions recovered the hydrogen evolution rate(HER,0.36 mL/cm^(2)/day)and pH change(pH 7.10)of scratched PA-PCLcaps coated ZM21 samples to corresponding unscratched samples within one day of immersion.The coating’s self-healing ability could be attributed to PA released from punctured microcapsules,which facilitates HA chelation.The pH-triggered(pH 10)and Mg(II)-triggered(5 mM)conditions enhanced PA release from PA-PCLcaps coating by 2.5 and 3.1 times,respectively.As a result,dense HA mineralization occurred,which protects the coating from structural defects and ensures its durability in stimulating conditions.The findings of present study provide new insight for design of multiple stimuli-feedback based self-healing coatings on biodegradable Mg alloys.

A promoting nitric oxide-releasing coating containing copper ion on ZE21B alloy for potential vascular stent application

Magnesium-based biodegradable metals as cardiovascular stents have shown a lot of excellent performance, which have been used to treat coronary artery diseases. However, the excessive degradation rate, imperfect biocompatibility and delayed re-endothelialization still lead to a considerable challenge for its application. In this work, to overcome these shortcomings, a compound of catalyzing nitric oxide(NO) generation containing copper ions(Cu^(2+)) and hyaluronic acid(HA), an important component of the extracellular matrix, were covalently immobilized on a hydrofluoric acid(HF)-pretreated ZE21B alloy via amination layer for improving its corrosion resistance and endothelialization. Specifically,the Cu^(2+) chelated firmly with a cyclen 1,4,7,10-tetraazacyclododecane-N’, N’’, N’’’, N-tetraacetic acid(DOTA) could form a stability of hybrid coating, avoiding the explosion of Cu^(2+). The chelated Cu^(2+) enabled the catalytic generation of NO and promoted the adhesion and proliferation of endothelial cells(ECs) in vascular micro-environment. In this case, the synergistic effect of NO-generation and endothelial glycocalyx molecules of HA lead to efficient ECs promotion and smooth muscle cells(SMCs) inhibition. Meanwhile, the blood compatibility also had achieved a marked improvement. Moreover, the standard electrochemical measurements indicated that the functionalized ZE21B alloy had better anti-corrosion ability. In a conclusion, the dual-functional coating displays a great potential in the field of biodegradable magnesium-based implantable cardiovascular stents.

CORROSION BEHAVIOR OF A ZIRCONIUM-TITANIUM BASED PHOSPHONIC ACID CONVERSION COATING ON AA6061 ALUMINIUM ALLOY

The conversion coating was formed by dipping AA6061 in a fluorotitanate/zirconate acid and amino trimethylene phosphonic acid （ATMP） solution at room temperature. The formation process and the anti-corrosion performance of the conversion coating were investigated using electrochemical test and salt spray test （SST）, respectively. The electrochemical test shows that the Zr/Ti and ATMP coating improves the corrosion resistance of AA6061 as good as the chromate （VI） coating. But the results of SST show that the corrosion resistance of Zr/Ti and ATMP coating is not as good as the chromate （VI） coating. The corrosion area is less than 2% after 72 h.

Applications of carbonic acid solution for developing conversion coatings on Mg alloy

Works on exploring an environmentally clean method for producing an Mg,Al-hydrotalcite(Mg6Al2(OH) 16CO3·4H2O) layer and/or calcium carbonate(CaCO3) layer on Mg alloy in a carbonic acid solution system(aqueous HCO3-/CO3 2-or Ca 2+ /HCO3-) at 50℃ were reviewed.Conversion treatment for the Mg,Al-hydrotalcite conversion coating was as follows.Mg alloy was treated first in acidic HCO3-/CO3 2-aqueous for precursor layer formation on Mg alloy surface and then in alkaline HCO3-/CO3 2-aqueous to form a crystallized Mg,Al-hydrotalcite coating.Duration of an Mg,Al-hydrotalcite coating on Mg alloy surface was reduced from 12 h to 4 h by the conversion treatment.On the other hand,for reducing the formation time of CaCO3 coating on Mg alloy,the aqueous Ca 2+ /HCO3-with a saturated Ca 2+ content was employed for developing a CaCO3 coating on Mg alloy.A dense CaCO3 coating could yield on Mg alloy surface in 2 h.Corrosion rate(corrosion current density,Jcorr) of the Mg,Al-hydrotalcite-coated sample and CaCO3-coated AZ91D sample was 7-10μA/cm 2,roughly two orders less than the Jcorr of the as-diecast sample(about 200μA/cm 2) . No corrosion spot on the Mg,Al-hydrotalcite-coated sample and CaCO3-coated sample was observed after 72 h and 192 h salt spray test,respectively.

Corrosion protection of AZ91D magnesium alloy by a cerium-molybdenum coating-The effect of citric acid as an additive

In order to improve the corrosion resistance of AZ91D magnesium alloy,a coating was formed by a potentiostatic technique from a solutions containing Ce(NO_(3))_(3),Na_(2)MoO_(4)and citric acid(H_(3)Cit).The degree of corrosion protection achieved was evaluated in simulated physiological solution by monitoring the open circuit potential,polarization techniques and electrochemical impedance spectroscopy(EIS).Surface analysis techniques(SEM,EDS,X-ray diffraction and X-ray photoelectron spectroscopy(XPS))were used for coating characterization.The film is mainly composed by cerium and molybdenum oxides and magnesium oxides and hydroxides.The obtained results show that the corrosion resistance of the coated electrodes has been increased significantly.This improvement in the anticorrosive performance is in part due to the corrosion inhibition properties of H_(3)Cit.

Formation of a cerium conversion coating on magnesium alloy using ascorbic acid as additive.Characterisation and anticorrosive properties of the formed films

Cerium-based conversion coatings were formed on AZ91D magnesium alloy by immersion of the substrate in solutions containing Ce(NO_(3))_(3),H_(2)O_(2) and ascorbic acid(HAsc).The characterisation of the films was performed by electrochemical and surface analysis techniques such as SEM,EDS,X-ray diffraction and X-ray photoelectron spectroscopy(XPS).The degree of corrosion protection achieved was evaluated in simulated physiological solution by the open circuit potential monitoring,polarisation techniques and electrochemical impedance spectroscopy(EIS).The presence of HAsc in the conversion solution causes changes in the morphology,adherence and anticorrosive performance of the films.The improvement in the corrosion resistance is closely associated with the corrosion inhibition properties of HAsc.

Comparison of Properties between Phytic Acid and RE-phytic Conversion Coatings of Mg-Li Alloy

The properties among of phytic acid conversion coatings,RE-phytic conversion coatings,rare earth conversion coatings and chromate conversion coatings were compared.The surface micrograph and the corrosion morphology of matrix and various coatings were observed,and the polarization curve,amount of hydrogen evolution and coating binding force were tested.The infrared spectra of phytic acid solution,phytic acid conversion coatings and RE-phytic conversion coatings were compared.The results indicated that the phytic acid coating and RE-phytic acid coating have better corrosion resistance and the RE-phytic acid coating is much better.The infrared spectra indicated that the characteristic peak of phytic acid conversion coatings shift left compared to that of phytic acid.The characteristic peak of RE-phytic conversion coating is similar with that of the phytic acid conversion coating.The di-hydrogen phosphate group of phytic acid reacted with metal matrix or rare earth conversion coating to generate hydrophosphate or phosphate.Phytic acid conversion coating consists of magnesium salt,aluminum salt,zinc salt and ferrous salt.The RE-phytic coating contains cerium salt besides those salts.

Study on Phytic Acid Conversion Coating on Mg-Li Alloy

The impact of phytic acid concentration,immersion time and soaking temperature on phytic acid conversion coating of the Mg-Li alloy are studied.The surface morphology and the corrosion of the phytic acid conversion coating are tested by using scanning electron microscopy and the electrochemical analyzer.The results show that phytic acid concentration and immersion time,soaking temperature affects the microstructure and corrosion resistance of the phytic acid conversion coating.There is a passivation interval with a smaller capacitor and larger resistor in the phytic acid conversion coating.The phytic acid conversion coating is made up of white particle and flake film.

Influence of intermetallic Al-Mn particles on in-situ steam Mg-Al-LDH coating on AZ31 magnesium alloy

The influence of intermetallic Al-Mn particles on the corrosion behavior of in-situ formed Mg-Al layered double hydroxide(Mg-Al-CO32--LDH)steam coating on AZ31 Mg alloy was investigated.The alloy was pretreated with H3PO4,HCl,HNO3or citric acid(CA),followed by hydrothermal treatment,for the fabrication of Mg-Al-LDH coating.The microstructure,composition and corrosion resistance of the coated samples were investigated.The results showed that the surface area fraction of Al-Mn phase exposed on the surface of the alloy was significantly increased after CA pretreatment,which promotes the growth of the Mg-Al-LDH steam coating.Further,the LDH-coated alloy pretreated with CA possessed the most compact surface and the maximum coating thickness among all the coatings.The corrosion current density of the coated alloy was decreased by three orders of magnitude as compared to that of the bare alloy.

Structural investigation of the zirconium-titanium based amino trimethylene phosphonate hybrid coating on aluminum alloy

A zirconium-titanium based amino trimethylene phosphonate hybrid coating on AA6061 aluminum alloys was formed by dipping in a fluorotitanate/zirconate acid and amino trimethylene phosphonic acid （ATMP） solution for improving the lacquer adhesion and corrosion resistance as a substitute of chromate coatings. The morphology and structure of the hybrid coating were studied by means of scanning electron microscopy （SEM） and atomic force microscopy （AFM）. The surface composition and structure characteristics were also investigated by means of X-ray photoelectron spectroscopy （XPS） and Fourier transformation infra-red spectroscopy （FTIR）. The results of SEM and AFM show that the hybrid coating present piece particle distribution which is much denser than that of the zirconium-titanium coating. The results of XPS and FTIR indicate that the hybrid coating is a hybrid composite structure composed of both the zirconium-titanium and amino trimethylene phosphonate coatings.

Anodic Coating Characteristics of Different Aluminum Alloys for Spacecraft Materials Applications

Anodic oxide coatings on aluminum alloys are used for space environment applications. These provide specific thermo-optical properties to spacecraft surface. Fragments of these coatings lead to generate the contamination in satellites and affect the mission lifetime. The current work concerns studying of the anodic processes applied on aluminum and different groups of aluminum alloys as Al7075, Al2024 and Al6061. Experimental procedures are performed using sulfuric acid at different values of current density (1 - 2 A/dm2). The influence of the parameters of anodic film formation on the coating characteristics and layer thickness of aluminum alloys has been investigated. Reflectance and optical properties of the anodized aluminum alloy coatings are determined and found to be dependent on the alloying elements. Changes in anodic coating weight and film thickness of aluminium alloys with the process parameters as current density, temperature, time duration, acid concentration, and sealing system have been studied. Moreover, morphology and surface structure of the considered samples are carried out in attempt to understand the physical characteristics. The obtained results are compared and briefly outlined.

<i>In Vitro</i>Corrosion and Bioactivity Study of Surface Phytic Acid Modified AZ31 Magnesium Alloy

The purpose of the present work was to examine in vitro corrosion and bioactivity of surface phytic acid treatment AZ31 magnesium alloys. Untreated AZ31 magnesium alloys were used as control. The surface morphologies of magnesium alloys were observed by SEM. EDS was used to analyze the surface chemical elemental compositions and elemental concentration distribution. Corrosion properties were evaluated by electrochemical tests. Human osteosarcoma MG-63 cells were used to examine cell viability and proliferation. The results showed that surface phytic acid treatment resulted in a surface coating formation, which did not significantly improve the corrosion resistance of the alloys. The corrosion potential of AZ31 magnesium alloy positive shifted only about 0.04 V (from -1.50 V to -1.46 V);and the corrosion current decreased only 0.354 mA/cm2 (from 2.547 × 10-3 mA/cm2 to 2.193 × 10-3 mA/cm2). However, the cell analysis showed that this coating induced obviously higher MG-63 cell viability and proliferation, and displayed good surface bioactivity.

草酸预处理AM50镁合金表面快速原位制备 蒸汽Mg−Al LDH涂层的耐蚀性

通过暴露合金表面的金属间化合物(β-Mg17Al12和AlMn),研究草酸(OA)酸洗对AM50镁合金表面原位蒸汽Mg−Al层状双氢氧化物(LDH)涂层成膜机制和耐蚀性的影响。结果表明,OA预处理使镁合金表面金属间化合物比例显著增加,Mg−Al LDH在Al−Mn相周围成核并生长。当酸洗时间为45 s时,所得LDH涂层的厚度最大、耐蚀性最佳,与基体相比,其腐蚀电流密度降低3个数量级。最后,提出了AM50镁合金表面Mg−Al LDH涂层的成膜机制。

植酸化氧化石墨烯的制备及硅溶胶复合涂层的防腐蚀性能

[目的]为了实现对高化学活性的镁锂(Mg-Li)合金的腐蚀防护,需采用性能温和的涂层,在阻止腐蚀介质侵入的同时,不对Mg-Li合金产生不良影响。[方法]以植酸为改性剂,采用水热法,通过磷酸酯化对氧化石墨烯(GO)进行改性,制备了植酸化氧化石墨烯(PGO),通过傅里叶变换红外光谱(FTIR)、X射线光电子能谱(XPS)、X射线衍射(XRD)、扫描电镜(SEM)等手段表征了GO和PGO的结构和形貌。将1%的GO和PGO分别作为功能填料添加到硅溶胶中,在Mg-Li合金表面制备了GO-硅溶胶复合涂层和PGO-硅溶胶复合涂层,探讨了GO和PGO对涂层防腐蚀性能的影响。[结果]相比于纯硅溶胶和GO-硅溶胶涂层,PGO-硅溶胶复合涂层的耐蚀性最佳。[结论]经植酸改性的PGO具有磷酸酯结构和疏松褶皱形貌,能赋予硅溶胶涂层更好的防腐蚀性能。

镁合金表面微弧氧化/氧化石墨烯/硬脂酸复合超疏水涂层在不同盐雾条件下的腐蚀过程

[目的]研究镁合金表面超疏水复合涂层在标准中性盐雾(35℃)、45℃的中性盐雾和模拟海水盐雾3种试验条件下的腐蚀过程。[方法]在AZ91D镁合金表面先后采用微弧氧化、电沉积和自组装技术制备了微弧氧化/氧化石墨烯/硬脂酸(MAO/GO/SA)超疏水复合涂层。[结果]在3种盐雾试验条件中,复合涂层出现腐蚀坑前都能维持超疏水状态,水接触角保持在150°左右。出现腐蚀坑后,标准中性盐雾条件下涂层的水接触角比其他两种盐雾条件下降得更慢。极化曲线测试结果表明,复合涂层的腐蚀电流密度比镁合金基体降低了3个数量级。3种盐雾条件下试验192 h后,复合涂层的腐蚀电流密度仍比镁合金基体低,但标准模拟海水盐雾试验后试样的腐蚀电流密度增速最快,涂层最先被腐蚀。[结论]MAO/GO/SA超疏水复合涂层具有优异的耐蚀性,能够有效阻止介质对镁合金基体的腐蚀,令镁合金基体的腐蚀速率降低。

镁合金表面二氧化铈/硬脂酸超疏水涂层的制备及其耐蚀性

镁和镁合金的高化学活性以及氧化膜的疏松多孔导致镁合金的耐腐蚀性能较差。以AZ31B镁合金为基体,采用水热法在镁合金表面制备出二氧化铈/硬脂酸超疏水涂层,重点研究了水热反应温度和时间对涂层形貌及耐腐蚀性能的影响。通过X射线衍射(XRD)、扫描电子显微镜(SEM)和能谱(EDS)对镁合金表面涂层的相组成、微观形貌及元素组成进行测试,通过电化学测试来表征二氧化铈/硬脂酸超疏水涂层的耐腐蚀性能,利用超疏水测试检验涂层的疏水性。结果表明:当水热反应温度为120℃,反应时间为6h时,可以在镁合金表面制备出均匀的涂层,该涂层由大量细小球形颗粒紧密连接而成,涂层致密完整,厚度约为13μm,涂层主要组成相为CeO_(2)。电化学测试结果表明:与空白镁合金基体相比,二氧化铈/硬脂酸复合涂层的腐蚀电流密度为5.36×10^(-6)A·cm^(-2),降低了一个数量级,且其电化学容抗弧直径明显增大,说明该涂层可以显著提高镁合金基体的耐腐蚀性能。同时,该涂层还具有较好的超疏水性,水滴静态接触角达161°。

Cr30钢表面镍包WC增强铁基合金涂层的微观组织和耐磨耐蚀性能研究

为改善Cr30钢表面的耐冲蚀磨损性能以及耐硫酸、盐酸腐蚀性能,以铁合金粉和镍包WC颗粒的混合物为原料,采用激光熔覆技术在Cr30钢表面制备含镍包WC铁基合金涂层,研究了原料中镍包WC质量分数(10%~30%)对铁基合金涂层的显微组织、物相组成、显微硬度、耐冲蚀磨损性能、耐硫酸和盐酸腐蚀性能的影响。结果表明:不含镍包WC的铁基合金涂层物相为FeCr固溶体和Cr_(23)C_(6);含10%和20%镍包WC的铁基合金涂层物相为FeCr固溶体、Cr_(23)C_(6)和Fe3W3C;随着镍包WC含量增至30%,铁基合金涂层中析出了新的碳化物Fe_(6)W_(6)C,含30%镍包WC的铁基合金涂层物相为FeCr固溶体、Cr_(23)C_(6)、F_(e)3W_(3)C和Fe_(6)W_(6)C。随着镍包WC含量的增加,铁基合金涂层的显微硬度、耐冲蚀磨损和耐硫酸、盐酸腐蚀性能提高,当镍包WC质量分数为30%时,铁基合金涂层的组织致密、细化效果最明显,涂层的硬度最高,达到786 HV_(0.5);30%镍包WC的铁基合金涂层的耐冲蚀磨损、耐硫酸和盐酸腐蚀性能最佳。

Corrosion resistance of an amino acid-bioinspired calcium phosphate coating on magnesium alloy AZ31

An L-cysteine-bioinspired calcium phosphate(Ca-P)coating is prepared upon magnesium alloy AZ31 in a water bath at 60℃.FE–SEM,FTIR,XRD,electrochemical characterization,hydrogen evolution tests and XPS were used to evaluate the microstructure,chemistry and corrosion performance of the samples.Results indicate that L-cysteine promotes the nucleation process of the coating and significantly increases its thickness.This can be attributed to the complexation of the carboxyl group and mercapto group of L-cysteine with calcium ions.Indeed,the obtained Ca-P coating possesses higher corrosion resistance than that prepared in L-cysteine-free bath.