Taking the susceptibility of the tandem welding joint of 7A52 Al-alloy into account,it is of significance to reveal the effect of the microstructural heterogeneity of the tandem metal inert gas welding joints of 7A52 Al-alloy on the corrosion performance of the micro-arc oxidation (MAO) films prepared on the surface of the weld plate by means of potentiondynamic polarization measurement, OM and SEM with EDS. It follows that the rolling base metal presents a typical fiber-like microstructure. The microstructure of the weld seam is as-cast dendritic structure. Grains in the fusion zone are equiaxed crystallites on the side adjacent to the weld, but are columnar on the other side near the heat-affected zone (HAZ). Recrystallization of grains in the heat affected zone has occurred. The growth rate of the MAO film on the weld seam is slower and Mg can be detected in the film, which may be responsible to the poor compactness and uniformity, and thus the weak passivity of the prepared MAO film, as a result, the protectiveness of the MAO film on the weld seam is worse than that on the HAZ and base metal. In general, for short-term immersion, the difference of the protectiveness of the MAO films on the weld seam, HAZ and base metal is not obvious, however, for long-term immersion, the protectiveness of the MAO film on the weld seam is obviously inferior to that on the HAZ and base metal.

The corrosion morphology and corrosion rate of underwater welding joints, which were prepared via underwater wet welding with E40 steel plate as base material and 359S as special welding rod, in coastal water of Qingdao was assessed by means of corrosion weight loss method. Results indicated that no corrosion was observed on the weld seam, while the base metal and heat affected zone suffered from serious corrosion after immersion in seawater. With the increase of immersion time, corrosion pits on the test samples are increasing, growing and deepening. The micro-morphology of the base metal varied slightly with time. But, the microstructure of the HAZ is more complex and presents a variety of features compared with the base metal. There is a good linear relation between the mass-loss and the corrosion time. The average corrosion rate of the HAZ and base metal is 0.180 mm/a. Temperature has a great influence on the corrosion rate, and the corrosion rate (0.250 mm/a) in the summer and autumn period in Qingdao seawater is much higher than that in the winter and spring, which is 0.118 mm/a.

The corrosion behavior of A710 steel in high S^2- containing 3.5% (mass fraction) NaCl solutions was investigated by means of weight loss measurement, electrochemical measurement, FE-SEM and XRD. Results showed that the addition of S^2- could promote the activation of the steel surface, which in turn leads to the increase of passivation current density. The corrosion product scale formed in the S^2- containing NaCl solutions was loose with pores and cracks, while pitting corrosion occurred beneath the corrosion product scale.

The corrosion behavior of the extra deep drawing cold rolled sheet DC06 was assessed by means of neutral slat spray test, electrochemical impedance (EIS) measurement, macro photography, SEM and XRD. It follows that during the neutral slat spray test, the thickness of the corrosion products had increased significantly with the increasing time, and the color of the corrosion products changed from the original brown red to dark brown, while the surface morphology of the corrosion products also changed from needle-like clumps to cotton-like clumps. The corrosion products composed mainly of Fe₃O₄ plus α-FeOOH and γ-FeOOH. The electrical resistance of the electric double layer is decreasing with the test time. The interface corrosion rate increases and double layer resistance value is small. So that the protective effect of corrosion products is not obvious for the substrate steel.

Ti/IrTaSnSb-G anodes were prepared by thermal decomposition at different sintering temperatures, and then characterized by means of SEM with EDS. The electrochemical performance of the anodes in 1.5% (mass fraction) NaCl solution was assessed and the effect of sintering temperature on the property of the anodes was further studied. Results show that graphene promotes the segregation of IrO₂ with dendritic structure on the surface of anodes at the appropriate sintering temperature, and the secondary crystallization phenomenon was found to produce the nano-needle structure of IrO₂, which increases the active surface areas and improves the electrocatalytic activity of the anodes. However, the much higher sintering temperature will lead to rapid oxidative decomposition of graphene, which results in the decrease of IrO₂ on the anode surface. The study also finds that the electrocatalytic activity of the anodes increases firstly as sintering temperature rises and then the gradually becomes poor . Among others, the anode prepared by sintering at 460 ℃ presents the best performance.

The effect of substrate preheating time at 210 ℃ on the degradation behavior of fusion bonded epoxy powder coating/Q345 steel system was studied by electrochemical impedance spectroscopy (EIS). The corrosion products of the substrate beneath the coating were characterized by means of scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). Results showed that the substrate preheating time had a significant effect on the adhesion of the coating to the substrate, which led to the different corrosion behavior of the metal substrate beneath the coating. The coating exhibited poor bonding performance when the substrate preheating time was less than 2 h, which resulted in the occurrence of premature corrosion of the substrate metal. This might be due to the oxygen enrichment in the interface gap of coating/metal and the cathode reaction was mainly O₂ reduction reaction. In this case, the corrosion of the substrate metal developed rapidly along the depth and the substrate metal was prone to pitting. When the substrate preheating time was 6 and 12 h, the coating showed good bonding performance and the corrosion reaction of the substrate metal beneath the coating happened much later. This could be supposed that the excellent adhesion of the coating made the oxygen deprivation at the interface of coating/metal and iron oxide was reduced in the cathode reaction. The corrosion of the substrate metal developed laterally and the corrosion behavior was closer to be uniform corrosion.

Effect of pretreatment of rust Q235 carbon steel with phytic acid solution on the corrosion resistance of epoxy coating was studied by means of electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and adhesion test. The results showed that this pretreatment process could enhanced the adhesion of the rust scale to the matrix, thereby enhance the adhesive strength and corrosion protectiveness on property of the epoxy coating obviously. Which might be attributed to that the phytic acid conversion film consisted of a dense inner layer and a loose outer layer rich in PO₄^3- and OH^- functional groups. This could improve the adhesion between the phytic acid conversion film and epoxy coating, therewith enhance the adhesion and corrosion protectiveness of the entired composite coating.

High corrosion resistant organic coatings are widely used for various industrial applications. These coatings normally have service life as long as tens of years. It is of great scientific interest and engineering significance to rapidly evaluate and compare the corrosion resistance of different long-life organic coatings. Different from the negative DC voltage used in the published AC/DC/AC (alternating current/direct current/alternating current) cyclic method to cathodically polarize an organic coating system before AC electrochemical impedance spectrum (EIS) in each cycle, a positive voltage was employed in this paper for the DC polarization in the AC/DC/AC cycling. The modified AC/DC/AC technique proved to be able to accelerate the damage of an alkyd varnish coating on carbon steel and thus quickly evaluate the coating corrosion resistance. Based on the measured impedance spectra and the recorded surface morphologic changes, the acceleration processes involved in the coating corrosion damage were analyzed, and a physical model for the accelerated failure of the coating/metal system was proposed. Based on the experiment results of electrochemical impedance spectroscopy and corrosion morphology from the immersion test, AC/cathodic DC/AC cyclic accelerated test, and AC/anodic DC/AC cyclic accelerated test, it shows that the evaluation method with the combination of cathodic and anodic polarization will be one of the effective and reasonable methods to evaluate the performance of organic coatings.

The effect of pulse current on micro-arc oxidation (MAO) process for 1050 Al-alloy was investigated. The thickness and roughness, surface morphology and corrosion performance of the prepared MAO coatings were assessed by means of eddy current thickness gauge and roughness tester, scanning electron microscope (SEM) and potentiodynamic polarization measurement respectively. The energy consumption of MAO process was calculated based on voltage versus time curves. Results indicate that with the increasing pulse current from 100 to 800 A, the arcing time shorten from 360 s to 15 s, while the arcing voltage rose from 341 V to 887 V. The diameter of micropores of the coatings was enlarged but the quantity reduced. While thicker and coarser ceramic coatings were obtained on the Al-alloy but with degraded corrosion resistance. The energy consumption of arcing process decreased at first then raised, and which presented the minimum value of 18.3 kJ for a pulse current of 200 A. The energy consumption of MAO coating process presented approximately a linear growth with the increasing pulse current density.

TiO₂ film surface normally presents micro porous after annealing treatment, which is one of the key factors on restraining the application of photogenerated cathodic protection of it. This study has prepared DMF modified TiO₂ film by sol-gel and dip-coating method on the substrate of FTO glass. The influence of DMF on the corresponding film composition, microstructure and surface wettability are explored by XRD, Raman spectroscopy and SEM. The property of photo response and cathodic protection behavior of the film coupled with 316 stainless steel are studied under UV illumination. The results indicated that the addition of DMF has essentially improved the compact continuity of the TiO₂ film, which supplies effective inhibition on the corrosive ions migration to the substrate. And the modified film presents comparable photogenerated cathodic protection property to that of pure TiO₂ film.

The initial formation process of oxide scale on 2205 duplex stainless steel at 1050 ℃ was studied in static atmospheric air within a closed container of 304 type stainless steel. The morphology, structure and composition of the formed oxide scale was analyzed by means of metallographic microscope, scanning electron microscope, Raman spectroscopy and glow discharge spectrometer. Results show that at the beginning of oxidation (less than 3 min), the oxidation degree and type of oxides formed on ferrite and austenite phases are obviously different, namely, which on the surface of ferrite phase composed mainly of Cr-rich oxides, while on the austenite phase composed mainly Fe-rich oxides. The oxidation resistance of ferrite phase seems better than that of the austenite phase. With the increase of the oxidation time (more than 5 min), the oxidation rate of the ferrite phase increased while Fe-rich oxides scale thickened on their surface. On the contrary, the Cr-rich oxide scale grew thicker on austenite phases, while their oxidation rate became gradually gentle. With the progress of oxidation, Cr diffused and migrated from sub-surface to the surface, leading to the formation of Cr-rich oxide on the whole surface of the duplex stainless steel. In this confined environment, the surface of the duplex stainless steel is easy to form granular compounds containing nitrogen and oxygen preferably on the ferrite phase, and afterwards these compounds also formed on the austenite. The number of the granular compounds is increasing with oxidation time and finally would cover entirely the steel sample.

On the basis of previous studies on bio-based furan inhibitors, the corrosion behavior of Q235 carbon steel in different concentration of hydrochloric acid solutions with FGE was studied by means of corrosion weight-loss measurement, Tafel polarization curve measurement and electrochemical impedance spectroscopy (EIS). Results show that when the concentration of FGE is 4.92×10^-4 molL^-1, the inhibition effect for Q235 carbon steel achieves the optimum with the inhibition efficiency of more than 94.0% and the corrosion rate of 0.076 mgcm^-2h^-1. In addition, it is proved that the adsorption process of FGE on Q235 carbon steel is in accord with the Langmuir adsorption model, which is the result of the interaction of physical adsorption and chemical adsorption.