There kinds of carbon steels of different grain size with the same chemical composition were prepared by different rolling and heat treatment processes.The relationship between grain size and atmospheric corrosion resistance of carbon steel in industrial environment has been investigated by cyclic immersion corrosion test, micro-analysis of rust and electrochemical test, the polarization curves of different grain size steel in 10% H2SO4 solution were also tested. The results showed that the crack and cavity in the rust after cycle immersion corrosion test were decreased and the atmospheric corrosion resistance was increased by grain refinement of carbon steel from 50 μm to 4μm, but the corrosion rate of carbon steel was increased by grain refinement in 10% H2SO4 solution.The effect of grain sixe on the corrosion current density of local grain boundary was analysed and the mechanics of corrosion was discussed.

The evolution of electrochemical impedance spectroscopy(EIS)and open circuit potential were obtained from dacromet-coating mild steel, which were fully soaked in seawater. The EIS was analyzed by the equivalent circuitRO (RpC) (RDQ). The resistance showed the increasing with immersing time of the polarization resistance Rp, douible layer capacity C,diffusion resistance RD and the value of RD/RP. The conclusion was drawn that Zn dissolved at the beginning of corrosion process of dacromet and its sacrificial anode effects were limited by the accumulation of corrosion products,which thickened the thickness of passivation coating. The physical barrier action was the prominent anticorrosive mean afterqards.Dacromet coating failed to protect the base for pitting afier the cooperation of diffusion and dissolution overtook the barier effects.

AZ91D magnesium alloy was treated by micro-arc oxidation (MAO) in the optimized composite solution of silicate-phosphate system in which Al2O3 powders were added.Morphological characteristic and phase constituent of ceramic coatings were analyzed using the scanning electron microscope (SEM) and the x-ray diffraction (XRD).The results showed that after adding Al2O3 powders pores in ceramic coatings decreased and the loose layer became more compact，new phase of Al2O3 appeared.Electrochemical corrosion experiments in 3.5%NaCl solution showed that corrosion resistance of ceramic coatings after adding Al2O3 powders was also improved greatly.

The relationship between corrosion behaviors and microstructure of thixoformed （TH）AZ91D alloys and permanent mould cast （PMC） AZ91D alloys in 3.5% NaCl aqueous solution was studied by optical microscope，SEM and weight loss method. The result showed that the corrosion resistance of the TH alloy was higher than that of the PMC alloy because their microstructures were significantly different. For the TH alloy， due to the volume fraction of β phase in the substrate was lower than surface layer，the corrosion rate of the former was higher than the latter during the initial stage of corrosion test，but this difference decreased as the corrosion proceeded.The corrosion mainly occurred in the primary α particles and secondary α phase because these two structures were taken as the cathode and β phase as the cathode in galvanic corrosion.The Ecorr between the galvanic couples，the relative distribution of the α and β phases and the area ratio of the α phase to β phase exposured on the speci?鄄men surface were the main factors to determine the corrosion rate.

The corrosion behavior of anodic film on the AZ91D magnesium alloy in 3.5% NaCl aqueous solution was investigated by the saline immersion test.The results show that new corrosion points seldom occur on the surface of the said anodic film over the immersion time in 3.5% NaCl neutral aqueous solution after the first macroscopic corrosion point appeared on the anodic film whether it was sealed or not,while the previous corrosion point extends vertically and horizontally and turns into a corrosion pit which is in form of ＂dendrite＂. The pH value and temperature of the test solution affect substantially on the corrosion resistance of the anodic film. The corrosion rate in acidic solution is obviously faster than that in neutral or alkaline solutions, and the corrosion rate increases with increasing of the immersion solution temperature.A possible model about the corrosion process of the anodic film on the AZ91D magnesium alloy is therefore proposed based on the above experimental results.

Contraposing to the fact that the imported crude oil contains a large content of sulfur and causes serious corrosion, the corrosion resistance of Ni-P electroless deposits using lactic acid and citric acid as complexing agent respectively in sulfur-bearing solution was studied by electrochemical method, gravimetric method, microscopic analysis and X-ray diffraction. The results showed that the two kinds of Ni-P electroless deposits are both amorphous. The phosphorus content in the deposit using lactic acid as complexing agent is 10.04%, and in the deposit using citric acid as complexing agent is 11.93%. As the Na2S content increases, the polarizability increases, and the corrosion current and corrosion potential decrease while the Na2S content is between 1.0%-2.5%. The corrosin resistance of Ni-P electroless deposit using lactic acid as complexing agent is better than that of another kind. The corrosion rates of two kinds of deposits reach the maximum value when the Na2S content is 1.5% and the maximum corrosion rate is 25 mg/(m2·h).

The corrosion properties of SPV50Q steel were performed in H2S-containing sour environment by potentiodynamic polarization measurement and electrochemical impedance spectroscopy (EIS). The results show that the presence of H2S considerably influences the corrosion process of SPV50Q steel and its corrosion tate increases with increasing H2S cotent. With decreasing pH and increasing in temperature of the testing solutio, the corrosion of this steel is also enhanced. Although the semicircular diameter of capacitive loop increases with immersion time, its variation amplitude is not obviously great and begins to diminish after certain periodic time, suggesting that the sulfide film formed on the surface can not effectively prevent SPV50Q steel for avoiding the further corrosion.

The corrosive behavior of X70 steel in acid solution at various pH and saturated with N2 or saturated with CO2 was studied by means of Potentiondynamic polarization measurements and EIS.The result showed that the concentration of H+ in solution increase ,at the same time the reduction of H2CO3 and HCO3- could be the additive cathodic reaction,which accelerated the reaction of X70 steel.The adsorption intermediate product was Fe(OH)ads in process of the corrosion reaction of X70 steel in HAc-NaAc solution.

Electrochemical measurement techniques are applied to investigate the effect of applied stress on free corrosion potential，breakdown potential and protection potential of LY12CZ in 3% NaCl.Meanwhile pit propaga－tion rate(PPR)-potential curve technique and potential scanning techniques and micro measurement technique are applied to study the influence of applied stress on the real pit propagation rate of LY12CZ under preselected po－tential.The results show that when stressed， free corrosion potential，breakdown potential and protection potential of LY12CZ all move negatively，the movement extent depend on the stress.the pitting current density also increase with the increment of stress.The results show that mechanochemical effect can greatly enhance the pitting sensi－tivity of LY12CZ aluminum alloy.

The initial pitting of 1Cr18Ni9Ti stainless steel in 3.5% NaCl solution was studied by electrochemical noise(ECN) and electrochemical impedance spectroscopy(EIS). The results indicated that, the initial immersion stage (to 48 hours), the fluctuation amplitude of potential and current noise were small, the slope of the power spectral density of potential(PSDV)plots changed hardly,and an inductive component was observed on impedance plane, which means the formation of the metastable pitting and continuous reparation of the passive film on the surface of the 1Cr18Ni9Ti stainless steel.When immersed to the stage of 48 hours to 60 hours,noise pulse emerged in the plots of electrochemical noise,the slope of the power spectral density (PSD) plots changed suddenly, on the impedance plane inductive component disappeared, which means the transition from metastable to stable pitting. SEM image showed pitting emerged in the surface after immersion for 60 hours.

The effects of different amounts of titanium powder （200 mesh）， used as additive， on the resistivity of the coating of coal tar epoxy resin cured with polyamine in distilled aqueous 3.5%（mass%） sodium chloride so－lution has been studied by electrochemical impedance spectroscopy （EIS）. The influencing factors of the resis－tivity were discussed， and the variation of the resistivity was also studied by calculating permittivity for the coat－ings herewith. Analysis of the electrochemical impedance spectra of the coating as a function of titanium content and immersion time showed that for short immersion times （half an hour） the resistivity was increased when the titanium content was decreased and that for long immersion times （192 hours） the reverse was the case.

TiC matrix Fe40Al intermetallic composites were made by spontaneous infiltration. The oxidation ki?鄄netics of Fe40Al/80vol%-88vol%TiC composites were investigated by means of conducting the oxidation experi?鄄ments in air at temperature of 700 ℃ ~ 1100 ℃ for up to 65 hours， and measuring the variations of the weight gains of the composites with the oxidation times. The microstructure evolution of the composites during the oxida?鄄tion processing was studied by using SEM/EDS and XRD. The effect of the surface roughness of the composites on the oxidation behavior was also studied. The results show that， the weight gain data were fitted a power type law with the oxidation time with power coefficients ranging 0.63 ~ 0.75， the oxidation rate decreased with in?鄄creasing the oxidation time. The oxidation layer was mainly composed of dense crystalline TiO2， the crystalline size of TiO2 was effected by the oxidation temperature and the surface roughness of the composites.

Corrosion and scale deposit reasons of tubes were discussed, through the in-situ investigation, pro?鄄duced water composition analysis, XRD analysis of scaling samples of single well in Western oilfield, combining scaling prediction and corrosion rate monitor. The results show that scaling types are mainly CaCO3?CaSO4 and iron rust, scaling in connection with corrosion. Predominating factors affecting corrosion and scaling of tubing are abundant in Ca2+?HCO3-?Cl- containing in produced water and CO2 exiting in accompanying gas with crude oil. Severe corrosion and scaling of tubes were found in this oilfield.

The development of volatile corrosion inhibitors on metal corrosion was reviewed. The principle and the application of volatile corrosion inhibitor were analyzed. The evaluation method and the relation between the inhibition mechanism and the grouping of molecule were discussed. The development trend of volatile corrosion inhibitors has been prospected.