Multi-argument linear stepwise regression were made for the atmospheric corrosion data of steels after sixteen-year exposure at various sites in China to analyze the effects of various factors on the corrosion.First,power function was taken in the regression for the weight loss data.The obtained parameters of the power function were then used as the variants in the stepwise regression.Both chemical compositions of steels and the environment factors were used as the arguments in the stepwise regression.Quantitative relation of the corrosion parameters with both environment factors and chemical compositions of steels was obtained.Apart from sulfur dioxide,marine salt and humidity,the well known three damaging pollution factors,the rainfall and sunshine hours together is a special environment factor,and it has a positive effect on n value but a negative effect on A value.A high rainfall together with a high sunshine hour resulted in a low corrosion rate at the initial stage and a high corrosion rate in later years.About the effect of alloy elements on the corrosion resistance of steels,S is the most damaging element in steel for atmospheric corrosion.P is a full beneficial element.Copper reduces only the n value but has little effect on the A value.The effects of Mn and Si are opposite to that of Cu.They reduce only A value but not n value.Si even increases the n value.Corrosion can be predicted for most carbon and low alloy steels in various environments.

The corrosion behavior of Corten-A weathering steel was investigated by immersion-dry-wet accelerated corrosion test in 0.3% magnesium chloride solution.By using SEM and EDAX technology,the corrosion images as well as the contents of the chloride ion and magnesium under different cycles were provided.It appeared linear relationship between the weight loss and corrosion test cycles.In early stage the main crystal product is β-FeOOH,in late period it is γ-FeOOH with few ε-Fe2O3.The result of the electrochemical tests showed that the cathodic reaction was accelerated due to the reduction of the rust;the large amount of the rust indicated that structure of the rust was loose and the rust did not have protection ability.

The influence of thermal-rate treatment on the corrosion resistance of Mg-7Al-0.4Zn-0.2Mn(AZ70)alloy was studied by observing corrosion morphology,measuring corrosion potential and salt-spray corrosion rate.The results show that the corrosion behavior of AZ70 alloy depends on both its microstructure and iron content.When Ts is 850 ℃,grains are fined and the size of βphase and the distance betweenβphase pasticles are small.The corrosion barrier effect ofβ phase onαphase is enhanced and the iron content does not increase much at this temperature.So the corrosion resistance is improved.The corrosion resistance of AZ70 alloy falls off when Ts is 890 ℃,which attributes to the presence of microporosity,hot cracking and increase of iron content.At the same superheat-temperature,the corrosion resistance is improved with the increase of chilling rate.In comprehensive consideration of microstructure and corrosion resistance of AZ70 alloy,the optimal TRT process is that Ts=850 ℃ and Vc=2.0 ℃/s.In that case,the corrosion potential is 15 mV higher and the salt-spray corrosion rate is 21.9% lower than that of un-TRT treated alloy.

Two layered structure thermal barrier coatings were prepared by electron beam physical vapor deposition.The changes on microstructure and the failure mode of the specimen during thermal cyclic oxidation were analyzed by scanning electron microscopy (SEM) and impedance spectroscopy (IS).It is shown that the spallation of one side coated TBCs occurred mainly in YSZ top coat,instead of in thermally grown oxide (TGO) layer as often observed in double sides coated TBCs.Stress analysis indicates that during thermal cycling,double sides coated TBCs are mainly subjected to the thermal mismatched shear stress parallel to the sample surface,but one side coated TBCs are subjected not only to the shear stress,but also to the stress along the normal direction,and finally crack inside the YSZ.IS method can characterize the initiation and expansion of the transversal crack in the TBCs.

Electrochemical behaviors on the surface of jamesonite in an acidic solution of pH4.0 buffer solution containing diethyl dithiocarbamate were investigated by the methods of cyclic voltammetry and AC impedance.The changes of the reactions,electrochemical adsorption,passivation action,electrochemical impedance and interfacial capacitance on jamesonite were discussed under the different conditions of electrode potentials.In the acidic solution,jamesonite is of a salt characteristics,and its electrode process kinetics is controlled by the electrochemical reactions and the adsorption of their productions.The hydrophobic adsorption film gradually grows and passivates on jamesonite from -78 mV to 42 2 mV.The electrode process of jamesonite at 522 mV is quite controlled by the reaction that is depended on ion diffusion.When the electrode potential is over 622 mV,the hydrophilicity on jamesonite becomes strong due to covering an amount of PbSO4 from the electrochemical reactions.

Surface morphologies,ingredients and structure of electroless plating Ni-P alloy coatings were investigated using field emission scanning electron microscope,X-ray photoelectron spectrometer and X-ray diffraction instrument,the corrosion behavior of Ni-P alloy coatings in Na2S solution was studied by potentiostatic polarization method and the corrosion rate of Ni-P alloy coatings was measured in different concentration of Na2S solutions at different temperatures by gravimetric method.Experiment results indicate that the amorphous Ni-P plating is deposited with cellular structure on the surface.In the same concentration of Na2S solution,the passivation area of the anodic process of corrosion reaction of the Ni-P alloy coatings narrowed gradually with increasing temperature.

Ni-P coatings were prepared on SiCp/Al composite by autocatalytic deposition and their corrosion behaviors in 3.5 % NaCl solution at 25℃ were studied by electrochemical impedance spectroscopy and potentiodynamic techniques.SEM、EDAX and XRD were also employed to examine the coatings so as to understand the corrosion mechanism of the coatings.The plating conditions show great influences on the P content of the coatings and thus the corrosion resistance.The P content of the coatings increases with decreasing the plating temperatures and pH values.The corrosion resistance of the coating can be increased significantly by increasing the P content of the coatings,which is ascribed to that the existence of P can improve significantly self passivation of the coatings in the solution.

The effect of small addition of strontium on the microstructures and electrochemical performances was investigated by optical microscope (OM),X-ray diffractometer(XRD),scanning electron microscope (SEM),energy dispersive spectrometer (EDS)and electrochemical methods.The results show that the crystal grains are diminished with the small addition of Sr and the average grain size decreases from 900 μm to 80 μm when the Sr addition varies from 0 to 0.30%.When the addition of Sr is less than 0.1%,the efficiency is improved,and the open potential shifts negatively.The efficiency and the open potential of the anode will meet the peak values simultaneously with 0.1% Sr additio n which are 54.5% and -1.73VSCE.However,when the Sr addition is more than 0.1%,the efficiency is remarkably decreased,and the open potential shifts notably. The reasons that Sr addition affects the efficiency and the potential are mainly attributed to:(1)when the Sr addition is less than 01%,the microgalvanic cells which are established by the Mg17Sr2 phase(cathode) and theα-Mg matrix(anode),reduce the intergranular corrosion diminishing the particles falling and the efficiency increases.The refined microstructures by small Sr addition increasing the grain boundary areas induce more uniform distribution of the impurities,and the open potential shifts negatively;(2)when the Sr addition is more than 0.1%,more Mg17Sr2 phase pasticles act as the cathode,which increases the corrosion along the grain boundaries and the efficiency drops and the open potential shifts notably.

Magnetron sputtered nanocrystalline Cu-20Zr film was made from as-cast alloy.Potentiodynamic polarization,electrochemical impedance spectroscopy(EIS) techniques，and scanning electron microscopy(SEM) were employed to study the corrosion behaviors of Cu-20Zr in nanocrystalline and the cast alloy in 0.1 mol/L HCl aqueous solution.Results show the grain size of the alloy has a significant influence on the corrosion behavior.Ecorr,icorr and charge transfer resistance of the nanocrystalline film reveal that its corrosion rate generally decreased compared with that of the cast alloy.Namely,the dissolution process of the nanocrystalline Cu20Zr film is greatly restrained.The low electrochemical activity of Zr and the Cu-rich layer formed in the potential range of selective dissolution of Zr atoms，and the corrosion product film,formed in the potential range of dissolution simultaneously of Cu and Zr atoms,were the proper reasons to enhance the corrosion resistance of the nanocrystalline alloy.

A novel silvery gray film was formed on the surface of MB2 magnesium alloy through a new environment-friendly anodizing process.The microhardness,microstructures and phase structures of ceramic coating were studied by means of microhardness instrument,SEM and XRD.The corrosion resistance of the oxide coating was investigated by dynamic potential scanning method.The results showed that the oxide coating was mainly consisted of MgO,MgAl2O4 and Al2O3.The structure of the anodized film was uniform and porous,which included two layers:The outer layer was loose and the inner layer was a compact layer that conjoined strongly to the substrate.The properties of anodized film were dependent on the anodizing current intensity and the concentration of the aluminium ions.The microhardness of the anodized film was 558.4 HV.The new process was more effective to improve corrosion protection of magnesium and its alloys than the film which was obtained by the traditional DOW17 process.And its electrolyte used contained no Cr and P,which was more environment-friendly and economical.

The layer of Fe-B compounds obtaining through boronizing method has very good corrosion resistance.But in boride coatings many physical defects exist,which limits the protective life of the coatings.In order to improve the corrosion resistance of the boride layer,this paper,which directs towards the problem of corrosion in molten zinc urgently to be desiderated in galvanizing industry currently ,studies the effect of the rare- earth element on the corrosion resistance of boroning layer in molten zinc.The boride coatings were investigated in molten zinc at 500℃.Results indicates the anti-corrosion ability of the co-cementation layer is 3 times more than that layer without rare-earth element,the reason is as follows:On one hand,the co-cementation can improve the homogeneous distribution of alloying elements and the surface condition of the layer and reduce the surface defect,as a consequence,the time of the crack nucleation was put off,it is difficult to form the pass of the zinc liquid.On the other hand,addition of rare -earth element can improve the toughness of boride coating,raise resistance of crack and make further improvement on its service life of corrosion resistance in molten zinc.

Cu-Sn-Pb alloy plated layer with appropriate porosity was used as the simulation sample of bronze ware.The effects of corrosion products such as cuprous chloride,copper chloride alkali and copper carbonic acid alkali on the depolarization reaction of oxygen were investigated by corrosion paste experiments and microelectrode method.The simulating corrosion cells were assembled with plated copper-tin-lead alloy electrode and porous oxygen electrode cathode polarization curves testing of porous oxygen electrode were carried out,and the constant current discharge and constant resistance discharge of oxygen electrode with cuprous chloride as active catalytic material were also carried out. The result indicated that cuprous chloride made the corrosion speed of sample higher two orders of magnitude than bivalent copper salts,and it has the highest catalytic activation to the depolarization reaction of oxygen,the discharge performance of oxygen electrode very stabilized and the production procees of copper chloride alkali which has been called the mostly component of “powdery rust” was simulated.The mechanism of porous oxygen electrode to accelerate pitting corrosion of bronze ware has been put forwarded.

There have been widely investigated on the application of semiconductor photoelectrochemical reaction since 1972,particularly TiO2 photocatalysis.In recent years it has been demonstrated that it can apply to the cathodic protection for metal.In this paper the principles of photoelectrochemical approach for metal anticorrosion are briefly presented and it current status are reviewed.