This study revealed the effect of Mn on the formation of hybrid zirconium-based conversion coatings(HZCC)on low carbon steel.The XPS results indicated that the Mn compounds on the surface of low carbon steel were main...This study revealed the effect of Mn on the formation of hybrid zirconium-based conversion coatings(HZCC)on low carbon steel.The XPS results indicated that the Mn compounds on the surface of low carbon steel were mainly MnO and Mn_(2)SiO_(4).Combined with the electrochemical measurements,the corrosion resistance of HZCC showed an increase followed by a decrease with increasing Mn concentration,which was related to the Mn_(2)SiO_(4) and SiO_(2) on the surface of low carbon steel.The excessive Mn concentration resulted in the loss of SiO_(2) and aggregation of Mn_(2)SiO_(4) on the low carbon steel surface,which caused the aggregation of Zr compounds on the surface and reduced the uniformity of the coating.Meanwhile,a moderate amount of Mn addition would be beneficial to increase the adhesion of organic coatings.展开更多
A V/Ce conversion coating was deposited in the surface of AZ31B magnesium alloy in a solution containing vanadate and cerium nitrate.The coating composition and morphology were examined.The conversion coating appears ...A V/Ce conversion coating was deposited in the surface of AZ31B magnesium alloy in a solution containing vanadate and cerium nitrate.The coating composition and morphology were examined.The conversion coating appears to consist of a thin and cracked coating with a scattering of spherical particles.The corrosion behavior of the substrate and conversion coating was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS).Compared with AZ31B magnesium alloy,the corrosion current density of the conversion coating is decreased by two orders of magnitude.The total impedance of the V/Ce conversion coating rise to 1.6×10^(3)Ω·cm^(2)in contrast with2.2×10^(2)Ω·cm^(2)of the bare AZ31B.In addition,the electrical conductivity of the coating was assessed by conductivity meter and Mott-Schottky measurement.The results reveal a high dependence of the conductivity of the coating on the semiconductor properties of the phase compositions.展开更多
Magnesium(Mg)and its alloys are lightweight as well as biocompatible and possess a high strength-to-weight ratio,making them suitable for many industries,including aerospace,automobile,and medical.The major challenge ...Magnesium(Mg)and its alloys are lightweight as well as biocompatible and possess a high strength-to-weight ratio,making them suitable for many industries,including aerospace,automobile,and medical.The major challenge is their high susceptibility to corrosion,thereby limiting their usability.The considerably lower reduction potential of Mg compared to other metals makes it vulnerable to galvanic coupling.The oxide layer on Mg offers little corrosion resistance because of its high porosity,inhomogeneity,and fragility.Chemical conversion coatings(CCs)belong to a distinct class because of underlying chemical reactions,which are fundamentally different from other types of coating.Typically,a CC acts as an intermediate sandwich layer between the base metal and an aesthetic paint.Although chromate CCs offer superior performance compared to phosphate CCs,yet still they release carcinogenic hexavalent chromium ions(Cr^(6+));therefore,their use is prohibited in most European nations under the Registration,Evaluation,Authorization and Restriction of Chemicals legislation framework.Phosphate-based CCs are a cost-effective and environment-friendly alternative.Accordingly,this review primarily focuses on different types of phosphate-based CCs,such as zinc,calcium,Mg,vanadium,manganese,and permanganate.It discusses their mechanisms,current status,pretreatment practices,and the influence of various parameters-such as pH,temperature,immersion time,and bath composition-on the coating performance.Some challenges associated with phosphate CCs and future research directions are also elaborated.展开更多
The influence of phosphating bath at different temperatures on the formation and corrosion property of calcium-modified zinc phosphate conversion coating (Zn-Ca-P coating) on Mg-Li-Ca alloy was investigated. The mor...The influence of phosphating bath at different temperatures on the formation and corrosion property of calcium-modified zinc phosphate conversion coating (Zn-Ca-P coating) on Mg-Li-Ca alloy was investigated. The morphologies, elemental distribution and chemical structures of the coatings were examined via SEM, EPMA, EDS, XRD and FT-IR. The corrosion resistance was assessed by hydrogen evolution, potentiodynamic polarization and EIS. The results show that the coating is composed of single element Zn and ZnO at below 45 ℃;whereas the coatings are predominantly characterized by Zn3(PO4)2·4H2O and small amount of element zinc and ZnO at above 50 ℃. Mg-Li-Ca alloy with Zn-Ca-P coatings prepared at 55 ℃ has the highest corrosion resistance. However, the hydrogen evolution rates of the coatings obtained at 40-50 ℃ is accelerated due to the galvanic corrosion between the imperfection of the single element Zn coating and the Mg substrate.展开更多
Zinc calcium phosphate (Zn-Ca-P) coating and cerium-doped zinc calcium phosphate (Zn-Ca-Ce-P) coating were prepared on AZ31 magnesium alloy. The chemical compositions, morphologies and corrosion resistance of coat...Zinc calcium phosphate (Zn-Ca-P) coating and cerium-doped zinc calcium phosphate (Zn-Ca-Ce-P) coating were prepared on AZ31 magnesium alloy. The chemical compositions, morphologies and corrosion resistance of coatings were investigated through energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), electron probe micro-analysis (EPMA) and scanning electron microscopy (SEM) together with hydrogen volumetric and electrochemical tests. The results indicate that both coatings predominately contain crystalline hopeite (Zn3(PO4)2·4H2O), Mg3(PO4)2 and Ca3(PO4)2, and traces of non-crystalline MgF2 and CaF2. The Zn-Ca-Ce-P coating is more compact than the Zn-Ca-P coating due to the formation of CePO4, and displays better corrosion resistance than the Zn-Ca-P coating. Both coatings protect the AZ31 Mg substrate only during an initial immersion period. The micro-galvanic corrosion between the coatings and their substrates leads to an increase of hydrogen evolution rate (HER) with extending the immersion time. The addition of Ce promotes the homogenous distribution of Ca and formation of hopeite. The Zn-Ca-Ce-P coating has the potential for the primer coating on magnesium alloys.展开更多
Ce(SO4)2?H2O2 solution was adopted to prepare a chemical conversion coating on AZ91D magnesium alloy.Additives of Ni(NO3)2 and sodium dodecyl benzene sulfonate were applied to improving the coating formation.SEM,...Ce(SO4)2?H2O2 solution was adopted to prepare a chemical conversion coating on AZ91D magnesium alloy.Additives of Ni(NO3)2 and sodium dodecyl benzene sulfonate were applied to improving the coating formation.SEM,EDS,XRD and GIXD were adopted to study the coating morphology,structure and composition,and the potential change curve in the treating solution was recorded to study the coating growth.Sodium dodecyl benzene sulfonate makes a remarkable improvement in the coating compactness,and shortens the time in the second stage of the coating formation from 5 min to 2 min.Compared to Ni(NO3)2,sodium dodecyl benzene sulfonate makes the more remarkable effect on the corrosion resistance improvement,since it can decrease the current density of corrosion from 7.41×10-5 A/cm2 to 2.20×10-5 A/cm2.The additives of Ni(NO3)2 and sodium dodecyl benzene sulfonate can enhance the Ce content from 18.92% to 22.32% and 25.08% in the coating,respectively.The XRD and GIXD results indicated that all the conversion coating formed in different solutions exhibit amorphous structure.展开更多
Phytic acid (PA) conversion coating on AZ31 magnesium alloy is prepared by a deposition method. pH influences on the formation process, microstructure and properties of the conversion coating are investigated. Elect...Phytic acid (PA) conversion coating on AZ31 magnesium alloy is prepared by a deposition method. pH influences on the formation process, microstructure and properties of the conversion coating are investigated. Electrochemical tests including polarization curve and electrochemical impedance spectroscopy are used to examine the corrosion resistance, and scanning electron microscopy is used to observe the microstructure. The chemical nature of conversion coating is investigated by energy dispersive spectroscopy. And thermodynamic method is used to analyze the optimum pH. The results show that PA conversion coating can improve the corrosion resistance of AZ31 Mg alloy. The maximum efficiency achieves 89.19% when the AZ31 Mg alloy is treated by PA solution with pH=5. It makes the corrosion potential of sample shift positively about 156 mV and corrosion current density is nearly an order of magnitude less than that of the untreated sample. The thermodynamic analysis shows that the corrosion resistance of PA coatings is affected by not only the concentration of PA ion and Mg2+ but also the release rate of hydrogen.展开更多
Magnesium phosphate conversion coating(MPCC)was fabricated on AZ31magnesium alloy for corrosion protection by immersion treatment in a simple MPCC solution containing Mg2+and3PO4?ions.The MPCC on AZ31Mg alloy showed m...Magnesium phosphate conversion coating(MPCC)was fabricated on AZ31magnesium alloy for corrosion protection by immersion treatment in a simple MPCC solution containing Mg2+and3PO4?ions.The MPCC on AZ31Mg alloy showed micro-cracks structure and a uniform thickness with the thickness of about2.5μm after20min of phosphating treatment.The composition analyzed by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy revealed that the coating consisted of magnesium phosphate and magnesium hydroxide/oxide compounds.The MPCC showed a significant protective effect on AZ31Mg alloy.The corrosion current of MPCC was reduced to about3%of that of the uncoated surface and the time for the deterioration process during immersion in0.5mol/L NaCl solution improved from about10min to about24h.展开更多
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 perform...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.展开更多
The feasibility of forming pollution-free and environmentally benign Ce-based rare earth conversion coatings (short for RECCs) on AZ91 magnesium alloy to enhance corrosion resistance was studied. The effect of optim...The feasibility of forming pollution-free and environmentally benign Ce-based rare earth conversion coatings (short for RECCs) on AZ91 magnesium alloy to enhance corrosion resistance was studied. The effect of optimum processing parameters on corrosion resistance of RECCs, such as density of treating solution, temperature and time of coating formation were discussed. Protective performance of conversion coatings on magnesium alloy was evaluated by moisture/heating test, anodic polarization, etc. The results show that Ce-based RECCs under moisture/heating condition can remain intact, with high coverage and no obvious corrosion phenomenon. Corrosion potential increases and passive phenomenon occurs while current density decreases, therefore Ce-based RECCs can improve corrosion resistance of AZ91 magnesium alloy. The morphology of Ce-based RECCs prepared under optimum process through SEM observation is found to be a few particles coherent to the base coating, and the coating has no cracks and exhibits apparent corrosion resistance during corrosion courses of AZ91 magnesium alloy.展开更多
The morphology change of the magnesium matrix after pre-treatment and the morphology as well as the phase composition of chemical conversion coating formed by phosphate were studied using scanning electron microscope ...The morphology change of the magnesium matrix after pre-treatment and the morphology as well as the phase composition of chemical conversion coating formed by phosphate were studied using scanning electron microscope and X-ray diffraction. The corrosion resistance of the coating was studied by salt spray and damp test, and the corrosion tendency during salt immersion test was analyzed. The results show that the phase composition before and after pre-treatment is almost changeless, and the deep microflaw appears between a andβ phases during acidic pickling. The phosphate conversion coating is mainly composed of Mg, MgO, and some amorphous phase, and it can provide a good protection for the AZ31B alloy. Results from corrosive morphology indicate that the growth and the corrosion resistance of the phosphate conversion coating are related to the forming process of the AZ31B matrix.展开更多
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 HCO...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.展开更多
A novel Mg-Li alloy was treated in a cerium nitrate solution and cerium chemical conversion coating was obtained on the alloy. Then the forming process, structure and corrosion resistance of the coating were investiga...A novel Mg-Li alloy was treated in a cerium nitrate solution and cerium chemical conversion coating was obtained on the alloy. Then the forming process, structure and corrosion resistance of the coating were investigated. The influential factors of cerium conversion coating were discussed through orthogonal experiments, and the optimum processing parameters were confirmed. XPS spectra displayed that the conversion coating consisted of cerium compounds, and the major component of the protective layer was a mixture of Ce (IV) oxide and Ce (IV) hydroxide. In addition, XRD pattern illustrated that there was crystalline CeO2 in the conversion coating. Analysis by SEM showed that the cerium conversion coating was uniform with a fiber-like morphology. The thickness of the conversion coating was 12 μm. The results of electrochemical potentiodynamic polarization and hydrogen evolution measurement indicated that the cerium conversion coating provided effective protection to the novel Mg-Li alloy.展开更多
This paper evaluated the protection effect of the cerium conversion coatings on the SiCp/5A06 Al composite and the 5A06 Al alloy.Electrochemical impedance spectroscopy(EIS) was employed to examine the variation of the...This paper evaluated the protection effect of the cerium conversion coatings on the SiCp/5A06 Al composite and the 5A06 Al alloy.Electrochemical impedance spectroscopy(EIS) was employed to examine the variation of the electrochemical variables of the samples treated and immersed in 3.5% NaCl solution at 35 °C for 1 h,which showed the enhancement of charge transfer resistance(Rt) and coating film resistance(Rc),i.e.,the corrosion resistance of the conversion coated samples was improved.The best protection ef...展开更多
Cracking and low thickness are major obstacles to the high corrosion performance of conversion coating on magnesium alloy.In this work,the ratio of total acidity to p H(TA/p H)was applied as an indicator,and new princ...Cracking and low thickness are major obstacles to the high corrosion performance of conversion coating on magnesium alloy.In this work,the ratio of total acidity to p H(TA/p H)was applied as an indicator,and new principles regarding the design of conversion bath were proposed.The treatment bath should be composed of species that can be categorized into two groups:the first group of species that react with Mg substrate to increase the local p H at the interface;the second group that precipitate and contributes to the growth of coating.The species belong to second group exists in a supersaturated state and its precipitation process is almost independent on the reactions of the species in first group.By this way,a thick and crack-free two-layered conversion coating is obtained.Moreover,the nature of the adjustment of TA/p H and the roles of the oxidizing agent and catalyst were discussed.展开更多
In this study, Mg–6.0Zn–3.0Sn–0.5Mn(ZTM630) magnesium alloy was pre-activated by colloidal Ti, oxalic acid, and phosphoric acid,and a phosphate conversion coating(PCC) was prepared on the alloy surface. The morphol...In this study, Mg–6.0Zn–3.0Sn–0.5Mn(ZTM630) magnesium alloy was pre-activated by colloidal Ti, oxalic acid, and phosphoric acid,and a phosphate conversion coating(PCC) was prepared on the alloy surface. The morphology and corrosion resistance of the prepared PCCs were investigated. Surface morphology studies showed that the phosphate crystals that formed the coating were the smallest for the sample pre-activated by phosphoric acid. The coating on the colloidal Ti and the phosphoric acid samples had the largest and the smallest thickness and surface roughness, respectively. The reason for the discrepancy was analyzed by comparing the surface morphologies of alloy samples immediately after the pre-activation treatment and various phosphating treatments. X-ray diffraction analysis revealed that all three PCCs contained the same compounds. The corrosion resistance time from the copper sulfate drop test and the electrochemical data from the potentiodynamic polarization curves showed that the coating pre-activated by phosphoric acid had the best corrosion resistance. Finally, the 1500 h neutral salt spray corrosion test confirmed that the phosphating treated magnesium alloy, which was pre-activated by phosphoric acid,exhibited excellent corrosion resistance and behavior.展开更多
A no pollution organic acid based conversion coating solution MIS. No.1 has been examined as to its suitability as possible replacement for chromate containing formulations on magnesium alloys. Investigations have c...A no pollution organic acid based conversion coating solution MIS. No.1 has been examined as to its suitability as possible replacement for chromate containing formulations on magnesium alloys. Investigations have concentrated on the formation of passive film from simple MIS. No.1 solution using immersion. The morphology of passivated surfaces was examined using scanning electron microscopy (SEM). The corrosion resistance of the passivated surfaces and the painted surface was assessed using electrochemical techniques as well as humidity and salt fog tests. It was concluded that the surface treatment magnesium alloy by MIS.No.1 solution is more effective than that by chromate coating treatment, and the MIS.No.1 coating is also suitable for painting's pretreatment.展开更多
A method of concentration analysis based on X-ray photoelectron spectroscopy (XPS) results was introduced. The concentration of Ce-rich conversion coating on the anodized Al based metal matrix composites AI6061/SiCp w...A method of concentration analysis based on X-ray photoelectron spectroscopy (XPS) results was introduced. The concentration of Ce-rich conversion coating on the anodized Al based metal matrix composites AI6061/SiCp was then studied according to this method. The results revealed that the Ce conversion coating on the anodized AI6061/SiCp consisted of Al oxide, Ce oxide and Ce hydroxide. The state of Ce element exhibited the mixture of Ce3+ and Ce4+. Some of Cell I was oxidized to be CelV in the outer layer coating.展开更多
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 co...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.展开更多
A Cu/Al galvanic couple was established to study the influence of the oxidantKMnO_4 on the film-forming process of rare earth metal (REM) conversion coating on LY12 aluminumalloy. It is found that the galvanic couple ...A Cu/Al galvanic couple was established to study the influence of the oxidantKMnO_4 on the film-forming process of rare earth metal (REM) conversion coating on LY12 aluminumalloy. It is found that the galvanic couple simulative experiment accords with the actual immersion,and it can be substantially used to simulate the behavior of LY12 aluminum alloy in thefilm-forming process. It is showed that the formation of the coating is quickened in CeCl_3 solutioncontaining KMnO_4 compared with that not containing KMnO_4. XPS results reveal that the coatingformed on cathode is composed of oxide or hydroxide of Ce and Mn, so the mechanism of formation ofREM conversion coating changes when KMnO4 is added.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51974069)the National Key R&D Program of China(No.2019YFE0123900)the Special Fund for Basic Scientific Research of Central Colleges(N2125035).
文摘This study revealed the effect of Mn on the formation of hybrid zirconium-based conversion coatings(HZCC)on low carbon steel.The XPS results indicated that the Mn compounds on the surface of low carbon steel were mainly MnO and Mn_(2)SiO_(4).Combined with the electrochemical measurements,the corrosion resistance of HZCC showed an increase followed by a decrease with increasing Mn concentration,which was related to the Mn_(2)SiO_(4) and SiO_(2) on the surface of low carbon steel.The excessive Mn concentration resulted in the loss of SiO_(2) and aggregation of Mn_(2)SiO_(4) on the low carbon steel surface,which caused the aggregation of Zr compounds on the surface and reduced the uniformity of the coating.Meanwhile,a moderate amount of Mn addition would be beneficial to increase the adhesion of organic coatings.
基金financially supported by the National Key Research and Development Program of China (Nos. 2016YFB0301105 and 2017YFB0702100)。
文摘A V/Ce conversion coating was deposited in the surface of AZ31B magnesium alloy in a solution containing vanadate and cerium nitrate.The coating composition and morphology were examined.The conversion coating appears to consist of a thin and cracked coating with a scattering of spherical particles.The corrosion behavior of the substrate and conversion coating was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS).Compared with AZ31B magnesium alloy,the corrosion current density of the conversion coating is decreased by two orders of magnitude.The total impedance of the V/Ce conversion coating rise to 1.6×10^(3)Ω·cm^(2)in contrast with2.2×10^(2)Ω·cm^(2)of the bare AZ31B.In addition,the electrical conductivity of the coating was assessed by conductivity meter and Mott-Schottky measurement.The results reveal a high dependence of the conductivity of the coating on the semiconductor properties of the phase compositions.
基金Uchchatar Avishkar Yojna(UAY)(Phase II)project(codeIITBBS_004)Prime M inister’s Research Fellows(PMRF)。
文摘Magnesium(Mg)and its alloys are lightweight as well as biocompatible and possess a high strength-to-weight ratio,making them suitable for many industries,including aerospace,automobile,and medical.The major challenge is their high susceptibility to corrosion,thereby limiting their usability.The considerably lower reduction potential of Mg compared to other metals makes it vulnerable to galvanic coupling.The oxide layer on Mg offers little corrosion resistance because of its high porosity,inhomogeneity,and fragility.Chemical conversion coatings(CCs)belong to a distinct class because of underlying chemical reactions,which are fundamentally different from other types of coating.Typically,a CC acts as an intermediate sandwich layer between the base metal and an aesthetic paint.Although chromate CCs offer superior performance compared to phosphate CCs,yet still they release carcinogenic hexavalent chromium ions(Cr^(6+));therefore,their use is prohibited in most European nations under the Registration,Evaluation,Authorization and Restriction of Chemicals legislation framework.Phosphate-based CCs are a cost-effective and environment-friendly alternative.Accordingly,this review primarily focuses on different types of phosphate-based CCs,such as zinc,calcium,Mg,vanadium,manganese,and permanganate.It discusses their mechanisms,current status,pretreatment practices,and the influence of various parameters-such as pH,temperature,immersion time,and bath composition-on the coating performance.Some challenges associated with phosphate CCs and future research directions are also elaborated.
基金Project(51241001)supported by the National Natural Science Foundation of ChinaProject(ZR2011EMM004)supported by the Natural Science Foundation of Shandong Province,China+1 种基金Project(SKLCP21012KF03)supported by the Open Foundation of State Key Laboratory for Corrosion and Protection,ChinaProject(TS20110828)supported by Taishan Scholarship Project of Shandong Province,China
文摘The influence of phosphating bath at different temperatures on the formation and corrosion property of calcium-modified zinc phosphate conversion coating (Zn-Ca-P coating) on Mg-Li-Ca alloy was investigated. The morphologies, elemental distribution and chemical structures of the coatings were examined via SEM, EPMA, EDS, XRD and FT-IR. The corrosion resistance was assessed by hydrogen evolution, potentiodynamic polarization and EIS. The results show that the coating is composed of single element Zn and ZnO at below 45 ℃;whereas the coatings are predominantly characterized by Zn3(PO4)2·4H2O and small amount of element zinc and ZnO at above 50 ℃. Mg-Li-Ca alloy with Zn-Ca-P coatings prepared at 55 ℃ has the highest corrosion resistance. However, the hydrogen evolution rates of the coatings obtained at 40-50 ℃ is accelerated due to the galvanic corrosion between the imperfection of the single element Zn coating and the Mg substrate.
基金Project(51571134)supported by the National Natural Science Foundation of ChinaProject(2014TDJH104)supported by the SDUST Research Fund+1 种基金the Joint Innovative Centre for Safe and Effective Mining Technology and Equipment of Coal Resources,Shandong Province,ChinaProject(cstc2012jj A50034)supported by the Natural Science Foundation of Chongqing,China
文摘Zinc calcium phosphate (Zn-Ca-P) coating and cerium-doped zinc calcium phosphate (Zn-Ca-Ce-P) coating were prepared on AZ31 magnesium alloy. The chemical compositions, morphologies and corrosion resistance of coatings were investigated through energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), electron probe micro-analysis (EPMA) and scanning electron microscopy (SEM) together with hydrogen volumetric and electrochemical tests. The results indicate that both coatings predominately contain crystalline hopeite (Zn3(PO4)2·4H2O), Mg3(PO4)2 and Ca3(PO4)2, and traces of non-crystalline MgF2 and CaF2. The Zn-Ca-Ce-P coating is more compact than the Zn-Ca-P coating due to the formation of CePO4, and displays better corrosion resistance than the Zn-Ca-P coating. Both coatings protect the AZ31 Mg substrate only during an initial immersion period. The micro-galvanic corrosion between the coatings and their substrates leads to an increase of hydrogen evolution rate (HER) with extending the immersion time. The addition of Ce promotes the homogenous distribution of Ca and formation of hopeite. The Zn-Ca-Ce-P coating has the potential for the primer coating on magnesium alloys.
基金Project (20070420772) supported by Postdoctoral Science Foundation of ChinaProject (7010404) supported by the Natural Science Foundation of Guangdong Province,China
文摘Ce(SO4)2?H2O2 solution was adopted to prepare a chemical conversion coating on AZ91D magnesium alloy.Additives of Ni(NO3)2 and sodium dodecyl benzene sulfonate were applied to improving the coating formation.SEM,EDS,XRD and GIXD were adopted to study the coating morphology,structure and composition,and the potential change curve in the treating solution was recorded to study the coating growth.Sodium dodecyl benzene sulfonate makes a remarkable improvement in the coating compactness,and shortens the time in the second stage of the coating formation from 5 min to 2 min.Compared to Ni(NO3)2,sodium dodecyl benzene sulfonate makes the more remarkable effect on the corrosion resistance improvement,since it can decrease the current density of corrosion from 7.41×10-5 A/cm2 to 2.20×10-5 A/cm2.The additives of Ni(NO3)2 and sodium dodecyl benzene sulfonate can enhance the Ce content from 18.92% to 22.32% and 25.08% in the coating,respectively.The XRD and GIXD results indicated that all the conversion coating formed in different solutions exhibit amorphous structure.
文摘Phytic acid (PA) conversion coating on AZ31 magnesium alloy is prepared by a deposition method. pH influences on the formation process, microstructure and properties of the conversion coating are investigated. Electrochemical tests including polarization curve and electrochemical impedance spectroscopy are used to examine the corrosion resistance, and scanning electron microscopy is used to observe the microstructure. The chemical nature of conversion coating is investigated by energy dispersive spectroscopy. And thermodynamic method is used to analyze the optimum pH. The results show that PA conversion coating can improve the corrosion resistance of AZ31 Mg alloy. The maximum efficiency achieves 89.19% when the AZ31 Mg alloy is treated by PA solution with pH=5. It makes the corrosion potential of sample shift positively about 156 mV and corrosion current density is nearly an order of magnitude less than that of the untreated sample. The thermodynamic analysis shows that the corrosion resistance of PA coatings is affected by not only the concentration of PA ion and Mg2+ but also the release rate of hydrogen.
基金supported by a research grant from Korea Institute of Materials Science (PNK4652)
文摘Magnesium phosphate conversion coating(MPCC)was fabricated on AZ31magnesium alloy for corrosion protection by immersion treatment in a simple MPCC solution containing Mg2+and3PO4?ions.The MPCC on AZ31Mg alloy showed micro-cracks structure and a uniform thickness with the thickness of about2.5μm after20min of phosphating treatment.The composition analyzed by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy revealed that the coating consisted of magnesium phosphate and magnesium hydroxide/oxide compounds.The MPCC showed a significant protective effect on AZ31Mg alloy.The corrosion current of MPCC was reduced to about3%of that of the uncoated surface and the time for the deterioration process during immersion in0.5mol/L NaCl solution improved from about10min to about24h.
基金supported by the Science and Technology Plan Project of Liaoning Province,China(No.2006221011).
文摘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.
文摘The feasibility of forming pollution-free and environmentally benign Ce-based rare earth conversion coatings (short for RECCs) on AZ91 magnesium alloy to enhance corrosion resistance was studied. The effect of optimum processing parameters on corrosion resistance of RECCs, such as density of treating solution, temperature and time of coating formation were discussed. Protective performance of conversion coatings on magnesium alloy was evaluated by moisture/heating test, anodic polarization, etc. The results show that Ce-based RECCs under moisture/heating condition can remain intact, with high coverage and no obvious corrosion phenomenon. Corrosion potential increases and passive phenomenon occurs while current density decreases, therefore Ce-based RECCs can improve corrosion resistance of AZ91 magnesium alloy. The morphology of Ce-based RECCs prepared under optimum process through SEM observation is found to be a few particles coherent to the base coating, and the coating has no cracks and exhibits apparent corrosion resistance during corrosion courses of AZ91 magnesium alloy.
基金supported by the National Natural Science Foundation of China(No.50474007)Science and Technology Project of Jiangxi Provincial Departmentof Education (No.[2006]1)
文摘The morphology change of the magnesium matrix after pre-treatment and the morphology as well as the phase composition of chemical conversion coating formed by phosphate were studied using scanning electron microscope and X-ray diffraction. The corrosion resistance of the coating was studied by salt spray and damp test, and the corrosion tendency during salt immersion test was analyzed. The results show that the phase composition before and after pre-treatment is almost changeless, and the deep microflaw appears between a andβ phases during acidic pickling. The phosphate conversion coating is mainly composed of Mg, MgO, and some amorphous phase, and it can provide a good protection for the AZ31B alloy. Results from corrosive morphology indicate that the growth and the corrosion resistance of the phosphate conversion coating are related to the forming process of the AZ31B matrix.
基金Project supported by the Ministry of Education Under the ATU Plan
文摘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.
基金Funded by the National Natural Science Foundation of China (No.50603003)
文摘A novel Mg-Li alloy was treated in a cerium nitrate solution and cerium chemical conversion coating was obtained on the alloy. Then the forming process, structure and corrosion resistance of the coating were investigated. The influential factors of cerium conversion coating were discussed through orthogonal experiments, and the optimum processing parameters were confirmed. XPS spectra displayed that the conversion coating consisted of cerium compounds, and the major component of the protective layer was a mixture of Ce (IV) oxide and Ce (IV) hydroxide. In addition, XRD pattern illustrated that there was crystalline CeO2 in the conversion coating. Analysis by SEM showed that the cerium conversion coating was uniform with a fiber-like morphology. The thickness of the conversion coating was 12 μm. The results of electrochemical potentiodynamic polarization and hydrogen evolution measurement indicated that the cerium conversion coating provided effective protection to the novel Mg-Li alloy.
基金supported by Higher Education Commission of Pakistan
文摘This paper evaluated the protection effect of the cerium conversion coatings on the SiCp/5A06 Al composite and the 5A06 Al alloy.Electrochemical impedance spectroscopy(EIS) was employed to examine the variation of the electrochemical variables of the samples treated and immersed in 3.5% NaCl solution at 35 °C for 1 h,which showed the enhancement of charge transfer resistance(Rt) and coating film resistance(Rc),i.e.,the corrosion resistance of the conversion coated samples was improved.The best protection ef...
基金financial support from the National Natural Science Foundation of China(51531007 and 51771050)China Postdoctoral Science Foundation(2019M651128)+1 种基金the National Program for Young Top-notch Professionalsthe Fundamental Research Funds for the Central Universities(N170205002)
文摘Cracking and low thickness are major obstacles to the high corrosion performance of conversion coating on magnesium alloy.In this work,the ratio of total acidity to p H(TA/p H)was applied as an indicator,and new principles regarding the design of conversion bath were proposed.The treatment bath should be composed of species that can be categorized into two groups:the first group of species that react with Mg substrate to increase the local p H at the interface;the second group that precipitate and contributes to the growth of coating.The species belong to second group exists in a supersaturated state and its precipitation process is almost independent on the reactions of the species in first group.By this way,a thick and crack-free two-layered conversion coating is obtained.Moreover,the nature of the adjustment of TA/p H and the roles of the oxidizing agent and catalyst were discussed.
基金financially supported by National Key Research and Development Program of China (Nos. 2017YFB0103904, 2016YFB0301105)National Natural Science Foundation of China (No. 51804190)+2 种基金Youth Science Funds of Shandong Academy of Sciences (No. 2020QN0022)Youth Innovation and Technology Support Program of Shandong Provincial Colleges and Universities (No. 2020KJA002)Jinan Science & Technology Bureau (No. 2019GXRC030)。
文摘In this study, Mg–6.0Zn–3.0Sn–0.5Mn(ZTM630) magnesium alloy was pre-activated by colloidal Ti, oxalic acid, and phosphoric acid,and a phosphate conversion coating(PCC) was prepared on the alloy surface. The morphology and corrosion resistance of the prepared PCCs were investigated. Surface morphology studies showed that the phosphate crystals that formed the coating were the smallest for the sample pre-activated by phosphoric acid. The coating on the colloidal Ti and the phosphoric acid samples had the largest and the smallest thickness and surface roughness, respectively. The reason for the discrepancy was analyzed by comparing the surface morphologies of alloy samples immediately after the pre-activation treatment and various phosphating treatments. X-ray diffraction analysis revealed that all three PCCs contained the same compounds. The corrosion resistance time from the copper sulfate drop test and the electrochemical data from the potentiodynamic polarization curves showed that the coating pre-activated by phosphoric acid had the best corrosion resistance. Finally, the 1500 h neutral salt spray corrosion test confirmed that the phosphating treated magnesium alloy, which was pre-activated by phosphoric acid,exhibited excellent corrosion resistance and behavior.
文摘A no pollution organic acid based conversion coating solution MIS. No.1 has been examined as to its suitability as possible replacement for chromate containing formulations on magnesium alloys. Investigations have concentrated on the formation of passive film from simple MIS. No.1 solution using immersion. The morphology of passivated surfaces was examined using scanning electron microscopy (SEM). The corrosion resistance of the passivated surfaces and the painted surface was assessed using electrochemical techniques as well as humidity and salt fog tests. It was concluded that the surface treatment magnesium alloy by MIS.No.1 solution is more effective than that by chromate coating treatment, and the MIS.No.1 coating is also suitable for painting's pretreatment.
基金This work has been carried out with the support of The Chinese Postdoctoral Science Fund and The Special Funds for the Major State Basic Research Projects G19990650.
文摘A method of concentration analysis based on X-ray photoelectron spectroscopy (XPS) results was introduced. The concentration of Ce-rich conversion coating on the anodized Al based metal matrix composites AI6061/SiCp was then studied according to this method. The results revealed that the Ce conversion coating on the anodized AI6061/SiCp consisted of Al oxide, Ce oxide and Ce hydroxide. The state of Ce element exhibited the mixture of Ce3+ and Ce4+. Some of Cell I was oxidized to be CelV in the outer layer coating.
基金Funded by the Key Laboratory of Superlight Materials and Surface Technology,Ministry of Education
文摘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.
基金[This work was financially supported by the National Natural Science Fund of China (No.59771067).]
文摘A Cu/Al galvanic couple was established to study the influence of the oxidantKMnO_4 on the film-forming process of rare earth metal (REM) conversion coating on LY12 aluminumalloy. It is found that the galvanic couple simulative experiment accords with the actual immersion,and it can be substantially used to simulate the behavior of LY12 aluminum alloy in thefilm-forming process. It is showed that the formation of the coating is quickened in CeCl_3 solutioncontaining KMnO_4 compared with that not containing KMnO_4. XPS results reveal that the coatingformed on cathode is composed of oxide or hydroxide of Ce and Mn, so the mechanism of formation ofREM conversion coating changes when KMnO4 is added.