Showing papers in "Materials protection in 2011"

Preparation of Blue Micro-Arc Oxidation Coating on Magnesium Alloy Surface and Evaluation of Its Corrosion Resistance

Abstract: Blue oxide coating was prepared on the surface of ZM5 magnesium alloy by micro-arc oxidation. The influences of the concentration of major salt Na2SiO3 and coloring agent CoSO4 as well as oxidation time on the composition and corrosion resistance of as-prepared micro-arc oxidation coating were investigated. It was found that compact blue micro-arc oxidation coating with a thickness of 82μm could be obtained by micro-arc oxidation in the electrolyte consisting of 70 g/L Na2SiO3 and 2 g/L CoSO4 at 440 V for 20 min. Resultant micro-arc oxidation coating, mainly consisting of amorphous phases, appeared blue owing to light scattering of cobalt oxides and was able to effectively improve the corrosion resistance of the Mg alloy substrate.

Analysis of Mechanism and Dynamics for Pulse Electrodeposition and Its Verification

Abstract: The mechanism and dynamics principle of pulse electrodeposition were systematically described.According to the feature of pulse electrodeposition,pulse-on time(Ton) was classified into nucleation process and growth process of grains.The two processes were analyzed based on dynamics.Results show that the Ton and pulse-off time(Toff) must be coordinated proportionally in appropriate range.Too long Ton led to concentration polarization and growth of grains;while too long Toff led to extended non-deposition duration and lowered deposition efficiency.Besides,short Ton and Toff were beneficial to the refining of grains.Relevant research results were helpful to theoretical guidance of pulse electrodeposition.

New Technology for Self-Assembled Film Formation on Aluminum Surface

Abstract: Aluminum surface is liable to oxidation,which causes damage to the quality of coatings thereon.Thus self-assembled film was prepared on the surface of Al via one-step route by using organic phosphorus compound,amino triacetic acid and polyepoxysuccinic acid as the major raw materials.The optimized conditions for preparing the film were determined based on orthogonal tests.The morphology and performance of the self-assembled film were compared with those of conventional chromate conversion coating,and the mechanism of self-assembled film formation was explored.It was found that the optimized solution for preparing self-assembled film consisted of 5.0 mL/L organic phosphorus compound,5.0 g/L amino triacetic acid,2.5 mL/L polyepoxysuccinic acid and 10.0 g/L sodium fluoride,and the optimized conditions for self-assembled film formation were suggested as pH = 6,time of 3 min and room temperature.Resultant self-assembled film composed of spherical crystallines was compact and possessed better corrosion resistance,adhesion to substrate and impact resistance than conventional chromate conversion coating.

Influence of Formaldehyde and Emulsifier OP on Semi-Bright Tin Plating of Printed Circuit Board in Acidic Bath

Abstract: Surfactants were introduced into tin electroplating bath to deposit Sn coating on printed circuit boards(PCB)The influence of formaldehyde and emulsifier OP on the coating morphology,current efficiency and cathodic polarization was investigated by making use of a scanning electron microscope,Faraday's law and steady-state polarization techniqueIt was found that both formaldehyde and emulsifier OP were able to significantly refine the grains and change the morphology of the Sn coatingThe Sn coating obtained at a too low concentration of formaldehyde had a cobble-like shape which was transformed to sheet-like and square block-like shapes with increasing concentration of formaldehydeThe Sn coating prepared at a too low concentration of emulsifier OP had cylindrical and square block shapes which were transformed to a sheet-like shape with increasing dosage of emulsifier OPBesides,the current efficiency of tin electrodeposition increased with increasing concentration of formaldehyde and emulsifier OPFormaldehyde contributed to slight increase of the cathodic peak current and increase of the over-potential,while emulsifier OP led to obvious negative shift of the peak potential and great decrease of cathodic peak currentA semi-bright,glossy and even coating was obtained after plating in a bath containing 10 mL/L formaldehyde and 01 mL/L emulsifier OP for 15 min,corresponding throwing power and current efficiency were 9939% and 9780% respectively

Preparation and Performance Evaluation of Water - Based Rust Inhibitor for Iron and Steel

Abstract: Sodium silicate,allyl thiourea,triethanolamine,polymaleic anhydride,sodium benzoate and methyl silanol were used as the main raw materials to develop a kind of water-based rust inhibitor based on formulation optimization via orthogonal test.The rust-inhibition performance of resultant rust inhibitor for iron and steel was comparatively evaluated in relation to commercial rust-proof agent 403 and oil-proof agent 433.It was found that the optimum formulation of as-developed rust inhibitor was 50.0 g/L sodium silicate,12.0 g/L allyl thiourea,24.0 g/L sodium benzoate,10.0 mL/L polymaleic anhydride,40.0 mL/L triethanolamine and 300.0 mL/L methyl ailanol.The optimized processing conditions were suggested as pH value of 10,room temperature and filmformation time of 10 min.As-developed rust inhibitor possessed better performance than similar products in the markets.

Two-Step Elctroless Zinc Plating Process of 1060 Aluminum

Abstract: 1060 Al was pretreated via two-step electroless Zn plating in an alkaline bath,followed by Ni electroplating.The adhesion of the electroless Zn coating to Al substrate was evaluated by measuring corrosion potential-time curve in association with scanning electron microscopic observation,bending test and thermal shock test.The optimized electroless Zn plating bath consisted of 300 g/L NaOH,65 g/L ZnO,50 g/L KNaC4H4O6·4H2O,1 g/L FeCl3 and 2 g/L NaNO3,while the optimized parameters were determined as temperature of 20~30 ℃,time for first electroless Zn plating of 60 s,and time for second electroless Zn plating of 30 s.Resultant electroless Zn coating well met the requirement for follow-up Ni electroplating.

Microwave Absorbing Performance of Electroless Co-Ni-P Alloy Coating on Fly Ash Hollow Microspheres

Abstract: A novel lightweight microwave absorbing powder material with core-shell structure was prepared by conducting electromagnetic modification of fly-ash cenospheres(5 μm scale) via electroless plating of Co-Ni-PThe effects of electroless plating parameters on the morphology,composition and microwave absorbing performance of Co-Ni-P alloy coating were investigated by using a scanning electron microscope,an energy dispersive spectrometer and a microwave vector network analyzerResults show that the coating on the surface of cenosphere particles consists of stacked Co-Ni-P spheres with a size of 05～10 μmThe coating was even in terms of thickness,but its composition was much different from that of the plating bathBesides,the coated hollow microspheres were magnetic loss dielectric media and possessed strong soft ferromagnetic propertiesThe coating obtained from the plating bath with a Co2+/Ni2+ mass ratio of 3∶1 had a Co/Ni mass ratio of 134 and the best microwave absorbing performanceWhen the concentration of hypophosphite in the plating bath was increased to 50 g/L,resultant coating had increased content of amorphous phase and turned into two-phase soft magnetic material,showing enhanced microwave absorbing abilityNamely,it had a lowest reflectivity of-315 dB,and its frequency range corresponding to a reflectivity below-100 dB was as much as 45 GHz(82～127 GHz)

Effect of Phosphating Pretreatment on Properties of Electroless Nickel Coating of Magnesium Alloy

Abstract: AZ31B Mg alloy was pretreated with a phosphating fluid,followed by electroless Ni plating.Resultant phosphating coating and eleotroless Ni coating were evaluated by means of visual method,observation with a scanning electron microscope and measurement of cathodic polarization curves.Results show that desired electroless Ni coating can be obtained on AZ31B magnesium alloy when the substrate is pretreated in phesphating fluid.The corrosion resistance of electroless Ni coating initially rose but declined later with extending time of phos-phating.In the meantime,as compared with directly electroless Ni coating,the one prepared on Mg alloy substrate pretreated in the phosphating fluid for 75 s possessed much better corrosion resistance,having a corrosion potential shifted towards positive side by 650 mV and a corrosion current reduced by three orders of magnitude.

Preparation of Environmentally Acceptable Water-Based Rust Inhibitor

Abstract: A kind of environmentally acceptable water-based anti-rust agent containing silicate as the major component was prepared by complexing with various anti-rust auxiliaries.The performance of resultant rust inhibitor was evaluated based on observation of appearance,immersion test in NaCl solution,humid test,measurement of Tafel polarization curve and observation of scanning electron microscopy,and the auxiliaries possessing synergistic anti-rust function with silicate were selected.Orthogonal tests were carried out to determine the optimized composition of the anti-rust agent,and the effects of various factors on the anti-rust performance of the anti-rust agent were investigated.It was found that the rust inhibitor obtained by introducing 50 mL H2O,0.1 mL triethanolamine,0.05 g boric acid,0.08 g ethylene diamine tetraacetic acid and 0.40 g sodium tungstate into 600 g/L silicate solution possessed the best anti-rust performance.Resultant rust inhibitor with a low cost was able to generate uniform and compact anti-rust coating and hence significantly decreased the corrosion rate of iron and steel,showing promising application prospects.

Influence of Gelatin and Benzaldehyde on Semi-Bright Tin Coating Electrodeposited in Acidic Bath

Abstract: A scanning electron microscope and a steady-state polarization curve measurement instrument were performed to investigate the influences of gelatin and benzaldehyde on the cathodic polarization process and morphology of semi-bright tin coating electrodeposited in acidic bath.It was found that both gelatin and benzaldehyde had significant effects on the morphology,grain size and compactness of tin coating.In the absence of gelatin and benzaldehyde or at low dosage of gelatin and benzaldehyde,Sn coating tended to grow into layers of coarse grains.With the increase of the dosage of gelatin and benzaldehyde,Sn coating tended to grow into blocks of significantly refined grains.At excessive dosage of gelatin and benzaldehyde,spine-like precipitates were formed in Sn coating.The current efficiency of tin electrodeposition increased firstly and then decreased with increasing concentration of gelatin and benzaldehyde.When no gelatin or benzaldehyde was added,the electrodeposition reaction of Sn occurred around-0.43 V,and the peak current density was 115 mA/cm2.Both gelatin and benzaldehyde contributed to increased over-potential and decreased peak current as well as inhibition of hydrogen evolution reaction.A semi-bright,glossy and uniform Sn coating could be obtained by electroplating under appropriate conditions for 15 min.Resultant Sn coating was dominated by preferential orientation along(101) and(112) planes and could be applied to printed circuit boards.

Galvanic Corrosion Behavior of B10/H62 Couple in Seawater of Different Flowing Rate

Abstract: Galvanic corrosion behavior of brass(H62) and Cu-Ni alloy(B10)in seawater of different flowing rate(0,1,3,5m/s) was studied.The effects of seawater flowing rate on the galvanic corrosion tendency,rule and micro-morphology were investigated based on natural corrosion monitoring,galvanic corrosion test and three-dimensional video microscopy.It was found that in seawater of different flowing rate,H62 and B10 were liable to galvanic corrosion.H62 as the anode experienced accelerated corrosion,while B10 as the cathode was protected.In the meantime,with increasing flowing rate of seawater,galvanic corrosion effect was initially reduced but later increased,and the minimum galvanic corrosion effect was obtained in seawater with a flowing rate of 3m/s.Besides,the flowing rate sensitive factor of galvanic corrosion tended to increase with increasing seawater flowing rate,and the corroded surface of H62 was dominated by more prominent erosion.

Effect of Ceramic Shot-Peening on Fatigue Behavior of Aluminum Alloy

Abstract: Ceramic shot was adopted for shot-peening of 2124 Al alloy so as to improve the fatigue behavior.The morphology,residue stress distribution and average residue stress of the alloy after shot-peening with ceramic shot,cast-steel shot and glass shot as well as double shot-peening were investigated,and the effect of shot-peening on the fatigue behavior of Al alloy was explored.Results show that the surface compressive residue stress of Al alloy after shot-peening with ceramic shot is the largest,and the surface morphology of the alloy varies slightly.Cracks were initiated beneath the strengthened layer after ceramic shot-peening,and shot-peening with ceramic shot helped to extend the anti-fatigue life of Al alloy most effectively.The Al alloy surface after shot-peening with steel shot had the lowest residue stress,and deep crevices were formed on the surface leading to strong stress concentration.Steel shot-peening had slight effect on the fatigue behavior of the Al alloy.Besides,shot-peening with glass shot and double shot-peening lay in between in terms of the ability to improve the fatigue behavior of the Al alloy.

Corrosion Behavior of 304 Stainless Steel in Saline Lake Brine

Abstract: The corrosion behavior and electrochemical feature of 304 stainless steel in saline lake brine were studied by using outdoor exposure tests(up to 2 a of exposure) and indoor electrochemical test.It was found that the stainless steel exposed to field saline lake brine for 2 a had a corrosion rate of 0.000 3 mm/a.In this case,the corrosion process was dominated by pitting corrosion and deep pitting holes were formed at the side area with machined defects of the sample.After 768 h of indoor immersion in the same brine,the passivation film on the surface of the stainless steel was partly destructed leading to pitting holes.

Quantitative Analysis of Phase Structure of Hot Galvanized Alloying Coatings

Abstract: The phase structure of hot galvanized coatings obtained at different galvanizing durations was comparatively analyzed by combining scanning electron microscopic observation with electrolytic stripping test.Results show that electrolytic stripping technique can be applied to realize step-by-step dissolution of various phase species in the galvanized coatings under the condition that the potential scanning rate is low enough.It was feasible to quantitatively determine the phase structure of the galvanized coatings via polarization curves and initial dissolution potential of each phase.

Application of Molybdenum Disilicide in High Temperature Oxidation Resistant Coatings

Abstract: A review was given about the antioxidation mechanism and physical properties of MoSi2.The application of MoSi2 in high temperature oxidation resistant coatings of refractory metals and C/C composites was briefed,and the methods to preparing MoSi2 were summarized.Moreover,worthful topics in future were also suggested.

Effect of Metal Impurity Ions in Trivalent Chromium Plating Bath on Coating Quality and Treatment Efficacy for Them

Abstract: The endurance of TCR-3000 trivalent Cr plating bath to metal impurity ions and the effect of the impurity ions on the appearance of electroplated Cr coating were investigated using Hell cell tests.A selective cation exchange resin was adopted to treat the metal impurity ions in the plating bath.It was found that the plating bath could not work well when Cu2+,Ni2+ and Zn2+ concentrations were up to 10,50,60 mg/L respectively.It was feasible to greatly decrease the concentration of impurity ions by making use of selective cation exchange resin,and resultant treated plating bath was reusable.

Effect of Saccharin on Microstructure and Properties of Pulse Electrodeposited Nickel Coating

Abstract: Fine crystalline nickel coating was prepared by pulse electrodeposition.The influence of saccharin on the grain size,surface morphology,crystal orientation and microhardness of the Ni coating was investigated.It was found that nanocrystalline Ni coating with a grain size of below 30 nm could be prepared by introducing saccharin into the plating bath.The introduction of saccharin caused transformation of crystal preferred orientation from a(200) texture to a strong(111) texture and increased the corrosion resistance of the Ni coating.The microhardness of the Ni coating was related with grain size.When the grain size was large,the microhardness of the coating was consistent with Hall-Petch law(HPL);when the grain size was ultrafine,"nano-effect" occurred and the microhardness of the coating was against HPL.

Effect of Rare Earth,Aluminum and Magnesium on Corrosion Resistance of Hot-Dipped Galvanizing Coatings

Abstract: Seven kinds of hot-dipped Zn-alloy coatings were prepared by introducing Re,Al and Mg into Al-Zn and Zn-Mg plating baths.The influence of alloying elements Re,Al and Mg on the corrosion resistance of hot-dipped galvanized coatings was investigated by conducting immersion tests,salt-spray tests and electrochemical tests(Tafel,EIS),and the anticorrosion mechanism of the coatings was primarily explored.Results show that Re,Al and Mg can all increase the corrosion resistance of hot-dipped galvanizing coatings.Zn-1%Al-2%Mg-0.1%Re alloy coating had the best corrosion resistance,and its corrosion resistance was about twice as good as that of pure Zn coating.Hopefully,the established galvanizing technology can be applied in industry.

Electrochemical Performance and Formation Mechanism of Zirconia Conversion Coatings on Iron and Steel

Abstract: Zirconia conversion coatings with the corrosion resistance were prepared on 45 steel by immersion process.Polarization curves were measured to investigate the effects of Zr4+ concentration and pH value of the conversion fluid on the corrosion resis-tance of the conversion coatings.Potential-time curves were mea-sured,and the effect of NO-3 concentration on the formation of the conversion coatings was explored.The morphology and elemental composition of the conversion coatings were analyzed by means of scanning electron microscopy and energy dispersive X-ray spectrometry.Moreover,open circuit potential and electrochemical impedance spectra were measured to investigate the formation process of the conversion coatings.It was found that the optimized Zr4+ concentration was 0.16 g/L,and the pH value was 4.As-prepared conversion coatings were amorphous and composed of Zr,Fe and O elements.The concentration of NO-3 only had slight effect on the formation of the conversion coatings.Moreover,the formation of the conversion coatings was similar to the local alkalization at cathode and could be divided into five stages,including activation of the substrate by acid etching as well as rapid growth,slow growth,dynamic stability and dissolution of the conversion coatings.The conversion coatings had the best corrosion resistance when the conversion time was 300 s.

Preparation of Coating Containing Tantalum on Titanium Substrate via Thermal Decomposition Route

Abstract: Thermal decomposition process of TaCl5-butanol solution in N2 atmosphere(≥99.99%) was studied.Coating containing tantalum was then prepared on titanium substrate by thermal decomposition of coated TaCl5butanol precursor in Ar atmosphere(≥99.99%).The effects of themal decomposition temperature and coating cycle on the morphology,phase composition and adhesion to substrate were investigated.It was found that TaCl5-butanol solution was nearly completely decomposed around 300℃,and the final products consisted of Ta,O and a small amount of residual Cl.The oxidation of Ta was retarded in highly pure inert atmosphere.Besides,the Ta coating on Ti substrate had crack-like appearance,and its phase composition was dependent on sintering temperature and cycles of coating,mainly consisting of Ta,Ta2O or Ta,Ta2 O,Ta2 O5.Moreover,thermal decomposition temperature had significant effect on the adhesion of coating,but the thickness of coating had relatively minor effect on the adhesion.

Corrosion Resistance of Micro-Arc Oxidation/Air Sprayed Composite Coatings on Magnesium Alloy

Abstract: Micro-arc oxidation(MAO) coating was prepared on the surface of AZ31B Mg alloy from a sodium silicate(Na2SiO3) electrolyte system using a direct current pulse power supply,followed by deposition of air sprayed(AP) nanostructured ceramic coating.The corrosion resistance,composition and microstructure of the MAO/AP composite coating were evaluated by means of salt spray test,scanning electron microscopy and X-ray diffraction.Results indicate that because the pores in the MAO coating are well sealed by the AP coating,the MAO/AP composite coating is smooth and possesses much better corrosion resistance than the MAO coating.The as-obtained MAO coating consisted of MgO and Mg2SiO4,and the introduction of the air sprayed ceramic coating had no effect on the phase composition of the MAO coating.