The corrosion behavior of Mg-6Zn-1.2Y-0.8Nd alloy before and after pre-soaking in Hank's solution was comparatively studied. Results revealed that the surface corrosion products formed during pre-shoaking can protect the substrate from corrosion attack to a certain extent. After pre-soaking for 4 h, the product film formed on the surface was relatively uniform and had the best protective effect on the matrix. The corrosion current density was 1.98 μA/cm². As the pre-soaking time was further extended, the corrosion products film formed on sample surfaces became thicker, and tend to be cracked and detached from the substrate, correspondingly the localized corrosion was accelerated, resulting in the decrease in their protective effect. After pre-soaking for 48 h, the corrosion current density of the alloy increased to 3.64 μA/cm².

The application of Ti-alloys is restricted to its low hardness and poor wear resistance. In this paper, a pure Al-fim of 40 μm in thickness was deposited on the surface of TC4 Ti-alloy by multi-arc ion plating, and then micro-arc oxidation (MAO) in constant current mode was carried out to obtain wear-resistant ceramic films. The microstructure, microhardness, wear resistance and bonding strength of MAO films were characterized by mean of SEM, XRD, micro hardness tester etc. The results show that the ceramic film is mainly composed of γ-Al₂O₃, α-Al₂O₃ and a small amount of amorphous SiO₂, and the film is uniform and compact. With the increase of the MAO time, the thickness of alumina ceramic film increases. The hardness of the dense portion of MAO coating is 1261 HV after micro-arc oxidation for 3 h. For the case of micro-arc oxidation for 4 h, the thickness of the generated alumina ceramic film is 60~70 μm, while almost the entire pre-deposited Al-film is oxidized, and the substrate Ti-alloy is slightly oxidized. At the same time, some penetration cracks in the oxide film was found, therefore, the hardness of the film and the bonding strength between the film and substrate all decrease. The friction coefficient of MAO ceramic film is lower than that of Ti-alloy substrate, and the wear rate is also obviously reduced. In sum, the bonding strength of MAO ceramic films with the substrate is higher than 40 MPa, whereas, the maximum bonding strength can reach 68 MPa.

The stress corrosion cracking (SCC) behavior of X70 steel in an artificial sea mud solution containing SRB at different temperatures were studied by slow strain rate tensile tests. The results showed that SRB survived in the range of 20~40 ℃ in the artificial sea mud solution. The temperature has a great influence on the SRB activity. The activity and amount of SRB increased with the increase of temperature. The protectiveness of the biofilm formed on X70 steel surface was closely related with the activity and quantity of SRB. The amount of SRB was the least at 20 ℃, which resulted in the lowest SCC sensitivity of X70 steel in the simulated sea mud solution. At 30 ℃, corrosion galvanic cell with large ratio of cathode area to anode area could formed between the biofilm and the steel substrate, while the fracture of X70 steel was the mixed ductile-brittle fracture due to the action of anodic dissolution and hydrogen-induced cracking. The relatively complete biofilm formed on X70 steel at 40 ℃, in that case however, X70 steel exhibited the highest SCC sensitivity and the cracking mechanism was hydrogen induced cracking.

The effect of static permanent magnetic fields of 28 and 60 mT on the growth rate of marine aerobic bacteria isolated from the East China Sea is studied. The corrosion behavior of pure Cu was also investigated in the artificial seawater with marine aerobic isolated bacteria in the presence of magnetic field by means of electrochemical measurement techniques and surface analysis methods. The formation of biofilm on Cu surface was observed by confocal laser scanning microscopy (CLSM). CLSM images showed that the formation and falling off of the biofilm were accelerated in the presence of magnetic field，while the effect of 60 mT magnetic field was stronger than that of 28 mT. FTIR analysis confirmed that the biofilm structures were changed when magnetic field was introduced to the system, the composition of biofilm changed from lipids, proteins, and carbohydrates to proteins and carbohydrates, while, the amount of protein decreased, but that of the carbohydrate increased. Besides, with the increase of magnetic field intensity, the lipid content decreased. The results of XPS analysis further confirmed that magnetic field affected the nature of corrosion products. The pitting was observed on the Cu surface after removing the formed biofilm using FE-SEM, nevertheless the number and size of pits on the Cu were markedly decreased in the presence of magnetic field. EIS results showed the impedance of pure Cu was significantly increased in the presence of magnetic field. It is concluded that magnetic field could accelerated the formation and falling off of the biofilm by affecting its composition and structure, therewith, inhibit the microbial corrosion process of pure Cu.

The relevance of the corrosion initiation in a chlorine ions containing atmosphere with the surface morphology, peculiarly the texture of metallic materials such as Q235B carbon steel, T91 steel, 7050 Al-alloy and LY12 Al-alloy was studied by means of an atmospheric corrosion chamber and electron backscattering diffraction (EBSD) technique. The results showed that the surface texture of Q235B has no significant influence on the initiation and development of uniform corrosion in the chlorine polluted atmosphere, which may be ascribed to that Q235B steel is activated in the test atmosphere. T91 steel tends to be corroded at grain boundaries, while pitting corrosion is apt to initiate on the grain surface with high surface energy for 7050 Al-alloy and LY12 Al-alloy. Besides, for the metallic materials sensitive to local corrosion, the corrosion of which is likely to occur at sites where the passivation film tends to be destroyed easily, in other words, the passivation film has poor stability at grain boundaries and on spots with high surface energy.

Atmospheric exposure of three types of 300M steel with different surface treatments (bare material, Cd-Ti Plating of low hydrogen embrittlement, high-velocity oxygen-fuel (HVOF) sprayed WC-10Co4Cr coating) were conducted for 2 a in Qingdao marine atmosphere. Then the corroded steels were characterized via surface and cross-section morphology observation and corrosion products analysis. The results of the two-year atmospheric exposure test are as follow: the HVOF sprayed WC-10Co4Cr coating peeled off, while galvanic corrosion and crevice corrosion occurred between the coating and the substrate which acted as anode, and the corrosion rate was the fastest and the corresponding corrosion pits were the deepest. While the corrosion potential of the Cd-Ti plated steel was lower than that of the substrate, and the plating was corroded prior to the substrate. The corrosion rate of the plated steel was the slowest and the corresponding corrosion pits were shallow, which indicated that the protective effect of Cd-Ti plating was the best among the three. The corrosion products on the bare steel as well as the substrate beneath the HVOF coating were mainly composed of α-FeOOH, β-FeOOH, γ-FeOOH and Fe₃O₄, but Cd(OH)₂ and CdO₂ were also appeared on the surface of the steel with Cd-Ti plating. The protective effect of Cd-Ti plating was obvious because of sacrificial anode protection, but the HOVF sprayed WC-10Cr4Cr caused galvanic corrosion and crevice corrosion, which aggravated the corrosion of the substrate.

The effect of synergistic action of Cu and Ni on corrosion rate, morphology and composition of the rust formed on three low alloy steels with different contents of Cu and Ni was studied via indoor spray acceleration tests, aiming to simulate the harsh tropical marine atmosphere. Meanwhile, electrochemical impedance spectroscopy (EIS) and linear polarization tests for the three steels were also carried out in 0.5% (mass fraction) NaCl solution. The results show that with the increase of Cu- and Ni-content, the rust layer formed on the steels subjected to spraying test becomes gradually thinner and denser, and the enrichment of Cu in the rust layer mitigates the invasion of Cl^-. The charge transfers resistance (R_t) and polarization resistance of the metal dissolution reaction were increased to some extent by the synergistic effect of two elements of Cu and Ni, which accelerated the formation and enhanced the protectiveness of the rust layer through inhibiting the anodic electrochemical reaction.

The corrosion behavior of Corten-A weathering steel in two polluted marine atmospheric environments at coastal cities Qingdao and Wanning was simulated by cyclic immersion accelerated test. The corrosion kinetics, corrosion morphology, corrosion products and the correlation between results acquired form the accelerated corrosion test and the outdoors exposure test were studied by weight-loss method, SEM technique, X-ray diffraction analysis, electrochemical measurement techniques and grey correlation analysis. The results showed that the corrosion degree of Corten-A steel increased first and then decreased with the increasing of NaCl concentration in the simulated solution, while the solution with 5% (mass fraction) NaCl presented the greatest corrosion effect on Corten-A steel. It follows that results of the indoor accelerated corrosion tests are well correlated with those of the outdoor exposure in natural marine atmospheric environments. Besides, models suitable to describe the corrosion process of Corten-A weathering steel in the simulated polluted marine atmospheric environments of Qingdao and Wanning were established respectively as: T_QD=251.214 t ^0.718, T_WN=217.498 t ^0.719.

The galvanic corrosion for weld joints of high strength weathering steel in simulated marine atmosphere was investigated by means of scanning kelvin probe (SKP), electrochemical noise, cyclic wet/dry accelerated corrosion test, and so on. The results indicated that the galvanic corrosion occurred on the welded joint of high strength weathering steel due to the potential difference, while the heat affected zone is the most anode area whereas the base metal is the most cathode area. And the variation of galvanic current on the base metal is differentiated as two stages of decline and stability, the corresponding time of inflexion point synchronizes with the stabilization of the rust layer. There are two stages in the corrosion process of the welded joint: the corrosion rate decreases rapidly at the initial stage of corrosion, and then remains stable in the later stage of corrosion, which may be related to its galvanic corrosion dynamics.

The hydrogen induced cracking (HIC) sensitivity of X100 pipeline steels with different microstructures was evaluated according to the NACE TM 0284-2011 standard. While, the initiation and propagation of HIC, and the aggregation of hydrogen atoms in the steel were characterized via field emission scanning electron microscopy (FE-SEM) and hydrogen microprint technique. The relationship between hydrogen trapping efficiency and HIC sensitivity of X100 pipeline steels with different microstructure was analyzed by using kinetic parameters of hydrogen permeation. The results show that the HIC susceptibility of X100 pipeline steels with different microstructure could be ranked as follows: original specimen with ferrite-bainite microstructure＞furnace-cooling specimen with massive ferrite microstructure＞wind-cooling specimen with acicular ferrite microstructure. The microstructure has higher trapping efficiency, the more susceptible to HIC is. Hydrogen atoms tend to aggregate at the interface between inclusion and matrix, and the HIC could initiate at MnS inclusion, Ca-Al-Si-O composite inclusion and MnO inclusion in the steels.

The variation of free corrosion potential of several metallic materials in natural seawaters off the coast of Qingdao and Zhoushan for 120 d was monitored by means of a home-made multi-channel potential data acquisition device. The variation of corrosion potential versus immersion time and the steady corrosion potential for every test material were peculiarly assessed. Results showed that the free corrosion potential of metallic materials in natural seawater changed quickly in the initial corrosion stage. While different kind of metallic materials presents diversified variations of corrosion potential versus immersion time. The steady corrosion potentials of tested metallic materials in natural seawater can be ranked as a series from low to high as: magnesium anode, aluminum alloys, iron castings, carbon and low alloy steels, copper alloys and stainless steels.

The corrosion behavior of eight typical grounding materials in red soil environment were studied via buried test in real red soil and accelerated corrosion test, as well as weight-loss measurement, corrosion morphology and corrosion product composition analysis. And then the acceleration ratio and interrelation rate between accelerated corrosion test and field corrosion test were calculated. The results showed that different grounding materials had different corrosion acceleration ratios in the same accelerated corrosion test, and the corrosion mechanism of accelerated corrosion test is basically consistent with that of field corrosion test. However, after accelerated corrosion test and field corrosion test, the compositions of the formed corrosion products on Q235 steel and Cu grounding material were all different, because of the differences of microbial activity and CO₂ solubility in soils. Correlation analysis results showed that the Pearson correlation coefficient (P) between accelerated corrosion test and field corrosion test was 0.9663, in other word, the service life of grounding materials buried in the field could be evaluated by the accelerated corrosion test.

The corrosion behavior of 20G steel, L245 steel, 5Cr steel, 16Mn steel and 316L stainless steel in CO₂ containing fluids at different temperatures and pressures was assessed by weight loss method via an autoclave, which aims to simulate the operating situation of the field. Then the morphology and composition of corrosion products were characterized by scanning electron microscopy (SEM), electronic energy spectrum (EDS) and X-ray diffraction (XRD). The results show that the average corrosion rate of 20G steel, L245 steel, 5Cr steel, 16Mn steel and 316L stainless steel increases first and then decreases with the increase of CO₂ partial pressure at a given temperature, and with the increase of temperature by a given CO₂ partial pressure respectively. The maximum average corrosion rate of the five materials emerged at 80 ℃ and 0.5 MPa of CO₂ partial pressure. 20G steel, L245 steel, 5Cr steel and 16Mn steel were suffered from non-uniformly general corrosion with corrosion products composed mainly of FeCO₃. Whilst 316L stainless steel was passivated with slight pitting corrosion in the corrosive medium.

Nano-composite coatings composed of nano-silica materials and Zn-rich epoxy coating were prepared, and their corrosion resistance was comparatively assessed with two zinc-rich epoxy coatings without addition of nano-silica by means of pull-off test for adhesion, immersion test, salt spray test and electrochemical impedance spectroscopy, as well as Zn content measurement. The results show that nanocomposite coatings have good performance in adhesion and cohesion, and they can act as good organic barrier to inward migration of corrosive species in the early corrosion stage, then present a moderate cathodic protection effect for a long term in the middle stage and finally the corrosion product of Zn can provide good barrier effect in the later stage, in the contrast, the two zinc-rich epoxy coatings without addition of nano-silica may prematurly break down due to blistering and rusting.

The failure process of the epoxy coating subjected to test of alternating immersion in artificial seawater and dry in air was studied by means of electrochemical impedance technique (EIS), Fourier transform infrared spectrometry (FT-IR), scanning electronic microscope (SEM), adhesion test and water absorption measurement. The results showed that, in the earlier test period, the epoxy coating subjected to wed-dry cycle test presents higher protectiveness than that subjected to merely immersion test. At the last test period, the former coating failed faster than the later one. The failure mechanism of the epoxy coating during wet-dry cycle testing may be proposed as that the coating matrix underwent alternate absorption and loss of water during the test, correspondingly, the relevant swelling and shrinking may generate more porosity within the coating, as a result, mechanical damages, such as cracks may develop from the interior to the surface of the coating, leads to lower adhesion and blisters of the coating eventually.

Aiming at the problem that the conventional Ag/AgCl marine electric field electrode is susceptible to Br^-, I^- corrosion in seawater, this paper proposes a novel replacement, which composed of PVC+NaCl as the solid electrolyte layer and Nafion film as the protective layer. Compared with the conventional Ag/AgCl electrode, the new electrode presents not only the same grade of responsiveness to the electric field, but also higher stability and corrosion resistance. The electrode can accurately respond to electric field signals at frequencies of 1, 0.1 and 0.01 Hz, correspondingly the linearity is 2.163%, 4.356% and 6.720%, respectively, while the intrinsic noise of the new electrode can be as low as 14.037 \mathrm{n}\mathrm{V}\text{/}\sqrt[]{\mathrm{H}\mathrm{z}}.

Ti6Al4V alloy was selectively laser melted (SLM) to produce the deposited alloy and which was subsequently heat treated at 800 ℃ to optimize its microstructure. The electrochemical corrosion behavior of the as deposited and post-heat treated Ti6Al4V alloys was investigated in 3.5% (mass fraction) NaCl solution. The results show that the as deposited alloy composes of dominantly acicular α'-martensite and some prior β-grains. After heat treatment, the microstructure transforms to a combination of lath-like α-phase and residual β-phase. Both alloys exhibit spontaneous passivation in 3.5%NaCl solution. Based on the polarization behavior, it is evident that the influence of heat treatment on the cathodic process is insignificant. However, the anodic reaction rate is greatly reduced, which results in the significant decrease of corrosion rate and ennoblement of open circuit potential and corrosion potential. In both cases, a protective film on the alloy surface is confirmed. However, the passive film formed on the heat-treated alloy is much thicker and compact. The polarization resistance of Ti6Al4V alloy after heat treatment is 3.8 times higher than that of the as deposited ones. Our results suggest that the as deposited Ti6Al4V alloy produced by SLM should undergo suitable heat treatment in order to prolong its service life in corrosive circumstances.