Alternating current (AC) induced corrosion is defined that the electrochemical corrosion process of metals caused by alternating current. Buried metal pipelines are frequently damaged when the alternating current applied. With the increasing cases that high-voltage transmission lines and/or electrical traction system cross over or parallel to buried pipelines, the AC corrosion becomes increasingly serious and the hazard of AC corrosion on buried pipelines can not be ignored. Although the research on AC corrosion has a history over centuries, there are still many difficult problems to be solved. Issue regarding AC corrosion has been intensively and extensively focused on. In this paper, the research progress on the characteristics, mechanism, influencing factors of AC corrosion and the effect of AC corrosion on cathodic protection and microbial corrosion in recent years were reviewed systematically. By discussing the key problems existing in the current research, this paper looks forward to the research prospect and development trend of this field, and provides new ideas for researchers in related fields.

This paper focuses on the present research progress of Micro biologically influence corrosion (MIC) problems of concrete and metal materials and especially the relevant MIC mechanisms, including the biological sulfuric acid corrosion mechanism against concrete materials, and classical corrosion mechanisms and extracellular electron transfer mechanism against metal materials. This paper also introduces research progress of MIC protection methods in building industry, including concrete modification, protective coatings and bactericides. This paper might provide a guidance for further research on MIC mechanisms and protective methods against MIC problems in the building industry.

In order to solve the problems of poor dispersion of graphene oxide (GO) in organic coatings and poor compatibility with resins, m-phenylenediamine, taking as the so called "bridge" material, was grafted on the surface of graphene oxide (GO) via a chemical means to obtain M-GO composite materials. Then the M-GO/epoxy resin E-44 composite anticorrosion coatings were also prepared. The results of FTIR, Raman and TGA showed that amine groups of m-phenylenediamine were successfully bonded with the epoxy group. A few layers of the M-GO composite particulates of lamellar morphology can be observed by transmission electron microscope (TEM), indicating that the dispersibility of GO was improved through m-phenylenediamine-grafting. On the other hand, the cross-sectional morphology of the coating showed that the M-GO composite material also has good compatibility with epoxy resin. In comparison with the epoxy resin coating GO/EP with the inherent graphene oxide GO, the M-GO/EP coating shows far more better anti-corrosion performance, namely, after 1000 h of immersion in 3.5% (mass fraction) NaCl solution, the impedance modulus (|Z^{|_{0.01 Hz}) value of EP/M-GO stayed at 1.0×109 Ω·cm2, and after salt spray test for 12 d, the M-GO/EP coating could still provide effective protection for the metal substrate. The results show that the m-phenylenediamine modified graphene oxide/organic coatings present significantly enhanced anti-corrosion performance.}

Corrosion behavior of domestic galvanized steel in salt water and fresh water was investigated by means of electrochemical impedance spectroscopy and electrochemical noise. The results indicated that corrosion process of galvanized steel can be divided into three different stages both in salt water and fresh water, and distinguished electrochemical characteristic in each stage can be observed. Corrosion rate of the galvanized steel in salt water was obviously higher than that in fresh water. The formed corrosion products are rod-like or lamellar on the surface of galvanized steel after immersion in salt water, but less protectiveness for the substrate. Whereas, the formed corrosion products are compact film composed of sphere-like particulates on the surface of galvanized steel after immersion in fresh water, which can effectively protect the substrate from further corrosion.

Corrosion behavior of domestic galvanized steel in different reverse osmosis waters was investigated by means of open circuit potential measurement, electrochemical impedance spectroscopy and microstructure observation. The galvanized steel showed similar electrochemical characteristics during the failure process in different reverse osmosis waters produced with influent seawaters of different salinity. The corrosion process of galvanized steel was changed with the adjustment of the quality of reverse osmosis water via addition of calcium chloride, sodium chloride and sodium bicarbonate. Corrosion performance of the galvanized steel was related with falling off and adhesion of the formed corrosion products.

The electrochemical behavior of MS X65 pipeline steel in H₂S containing medium by different stress ratios (R) was investigated via electrochemical test techniques such as dynamic potential polarization, linear polarization, and electrochemical impedance. The results indicated that electrochemical kinetic parameters such as free-corrosion current density I_corr, electron transfer resistance R_ct, and linear polarization resistance R_p all increase or decrease first with the increase of the cyclic stress frequency, and then stabilized by a critical cyclic stress frequency. The critical frequency increased from 0.25 Hz for R=0.4 to 1 Hz for R=0.85, which would be related to the interactive influence of different stress ratios and cyclic stress frequencies on the electrochemically active reaction sites on the electrode surface and the diffusion rate of cathode reactants.

The influence of chloride concentration on metastable pitting of 304 stainless steel in a simulated concrete pore solution (pH 12.6) was investigated via potentiodynamic polarization and potentiostatic polarization measurement. The peak current density (I_peak), metastable pit radius (r_pit), pit stability product (I_peak·r_pit), and growth time (t_grow), as well as the repassivation time (t_rep), growth rate (K_grow) and repassivation rate (K_rep) of individual metastable pits were studied by means of the extreme value statistics distribution method. The results revealed that the probability of transition from metastable pitting to stable pitting for 304 stainless steel might increase with the increasing chloride concentration in the simulated concrete pore solution.

The effect of the charging time and current density of the electrochemical hydrogen charging process, as well as the crystallographic structure of the steel on the hydrogen embrittlement sensitivity of stainless steels were assessed via slow strain rate tensile test. The results showed that for ferritic stainless steel, with the increase of hydrogen charging time and current density, the plasticity decreases significantly, and the sensitivity of hydrogen embrittlement increases greatly. The SEM observation results of the fracture morphology show that the fracture type changed from ductile fracture to brittle fracture. As a contrast, under the same conditions, the sensitivity of hydrogen embrittlement of austenitic stainless steel was lower, and the resistance of hydrogen embrittlement was higher. It was found that there was a large amount of hydrogen on the surface of the tested steel after hydrogen charging, and the hydrogen content gradually decreased with the depth of the sample. As hydrogen traps, grain boundaries may affect the hydrogen embrittlement sensitivity of steels.

Failure behavior of epoxy coating used for fresh water tank, namely epoxy coating/Q235 carbon steel, in different media including three different fresh water and one kind of salt water was investigated by means of adhesion test, water absorption test and electrochemical impedance spectroscopy. Failure of the epoxy coating in fresh water was earlier than that in salt water owing to the faster penetration rate. The failure process of the epoxy coating in fresh waters, including reverse osmosis water, conditioning water and drinking water was similar, and can be differentiated as the following three stages: the quick penetration of water, corrosion of the substrate at the interface of coating/steel and the corrosion inhibition of pigments in the coating.

Mg-3Zn-1Y-xZr (x=0, 0.2, 0.4, 0.6) alloys are prepared by traditional gravity casting. The influence of Zr amount on the microstructure and corrosion behavior of Mg-3Zn-1Y alloys is systematically investigated via optical microscope (OM), scanning electron microscope (SEM), mass loss testing and electrochemical testing. Results show that the Mg-3Zn-1Y alloy is mainly composed of α-Mg matrix and Mg₃YZn₆ (I) phase. The addition of Zr does not change the type of the second phase, while can remarkably refine the grains by increasing nucleation rate, optimize the structure and improve the corrosion resistance of Mg-3Zn-1Y alloys. Meanwhile, the addition of Zr can increase the corrosion potential of alloy substrate, reduce the corrosion current density, thereby decreasing the tendency of corrosion and inhibiting the corrosion. The mass loss results indicate that the Mg-3Zn-1Y-0.6Zr alloy has the best corrosion resistance with corrosion rate of (0.325±0.042) mm/a.

The corrosion behavior of E690 steel in 3.5% (mass fraction) NaCl solution by applied elastic alternating stresses of different frequencies (0.1, 0.5, 1.0, 1.3, 1.8 and 2.0 Hz) was studied by electrochemical test and surface characterization. Results show that there is a critical loading frequency for the applied alternating stress that divides the corrosion electrochemical behavior into two different regions. When loading frequency is below the critical frequency, the maximum strain rate of E690 steel and the number of active sites on steel surface increases with the increasing loading frequency. The corrosion process is mainly controlled by activation. The corrosion rate and the portion of localized corrosion area increase with the increase of the loading frequency. When loading frequency is higher than the critical frequency, the corrosion process is mainly controlled by diffusion. Hence, the loading frequency has little impact on the corrosion rate and localized corrosion area.

The corrosion behaviour of X70 pipeline steel in an artificial CO₂-containing formation water at various temperatures was studied in a high-temperature, high-pressure reaction kettle via mass loss measurements, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometer, and electrochemical methods. Thermodynamic and kinetic factors related to the CO₂ corrosion mechanism of X70 steel were assessed. The results show that the temperature influenced the corrosion rate of X70 steel by affecting the supersaturation, nucleation rate, and grain growth rate of FeCO₃. The corrosion product scale could not form on the surface of X70 steel at 30 ℃ because of the lower FeCO₃ supersaturation. A dense FeCO₃ scale formed at 60 and 90 ℃, resulting in a decrease in the corrosion rate. When the temperature was higher than 120 ℃, the nucleation rate of FeCO₃ was less than its growth rate, consequently, a complete protective FeCO₃ scale could not form on the X70 steel surface, while the stress accumulation inside the scale led to the rupture of the scale, which may be the cause leading to the formation of a galvanic cell consisting of the FeCO₃ film and matrix metal, which resulted in local corrosion.

The corrosion behavior of Cu-Al laminated boards was investigated by means of indoor neutral salt spray test, aiming to simulate the atmospheric environment induced corrosion, and electrochemical workstation, as well as scanning electron microscopy (SEM) with energy spectrometer (EDS), and X-ray diffractometer (XRD). The results show that Cu- and Al-laminates act as corrosion galvanic couple in salt spray environment, where the Cu plays as cathode, while Al as anode. The greater the area ratio of cathode to anode, the greater the corrosion rate. As the corrosion continued, the corrosion mainly occurred on the Al plate , and the corrosion was the most serious near the interface of the Cu-Al plates, serious denudation corrosion may appear on the Al-plate for long-term corrosion, while the Cu plate has almost no change. The corrosion products composed mainly of Al₂O₃, Al(OH)₃ and AlO(OH). The electrochemical results show that during the corrosion process, the corrosion rate of Cu-Al composite laminated board increased firstly, then decreased and finally increased again.

To provide theoretical reference for the corrosion protection engineering of metallic facilities in the water treatment process of shale gas fracturing produced water, the corrosion behavior of L245 steel induced by iron bacteria (FB) in shale gas fracturing produced water was studied by means of immersion test with mass loss measurement, electrochemical test and SEM characterization. Results showed that both of the shale gas fracturing produced waters with and without iron bacteria could all cause corrosion of L245 steel, but mass loss analysis and polarization curve analysis proved that the presence of FB promotes the corrosion of L245 steel. Further, the electrochemical impedance fitting results showed that in the shale gas fracturing produced water without FB, the corrosion rate of L245 steel increased slowly in the first 5 d, and then rapidly decreased. Whereas, in the shale gas fracturing produced water containing FB, the corrosion rate of L245 steel first decreased untill 8 d and then increased rapidly. SEM analysis results showed that the formed corrosion product films are quite different in the shale gas fracturing produced waters with and without iron bacteria.

Extruded bi-metal rods composed of AZ31 Mg-alloy core of 30 mm in diameter and 2A12 Al-alloy cladding of 4 mm in thickness were made by isothermal indirect extrusion process. The microstructure and corrosion behavior in 3.5%NaCl solution of the cladding surface, the core AZ31 Mg-alloy and the intermediate layer of AZ31/2A12 were comparatively examined by means of optical microscopy and scanning electron microscopy, as well as mass loss method in accordance with GB10124-88, polarization curve measurement and electrochemical impedance spectroscopy. The results showed that recrystallization was happened during the indirect extrusion process for the profiles with precipitated phases of β (Al₃Mg₂) and γ (Mg₁₇Al₁₂) at the interface area of cladding 2A12/core AZ31, while only γ (Mg₁₇Al₁₂) phases were precipitated along the grain boundaries for the core AZ31 Mg-alloy without cladding. It follows that a passivation film was formed on the surface of the extruded profile with the 2A12 Al-alloy cladding during corrosion process, so that the extruded profiles could be prevented from further corrosion by the passivation film. Therefore, the research shows that the indirect co-extrusion technology is beneficial to improve the corrosion resistance of the AZ31 Mg-alloy clad with 2A12 Al-alloy.

Artificial particulates of calcium magnesium aluminum silicate (CMAS) induced hot-corrosion of Gd₂(Zr_1-xCe_x)₂O₇ (x=0, 0.1, 0.2, 0.3) ceramics at 1250 ℃ for 5, 10 and 20 h in lab atmosphere. Was assessed by means of XRD, SEM and EDS. The results show that the reaction of CMAS and Gd₂(Zr_1-xCe_x)₂O₇ (x=0, 0.1, 0.2, 0.3) ceramics will generate the corrosion products composed mainly of fluorite Ca_0.2(Zr_xCe_1-x) _0.8O_1.8 and apatite Ca₂(Gd_xCe_1-x)₈(SiO₄)₆O_6-4x. The more Ce⁴⁺ doping content, the thinner the reaction layer, and GZ7C3 has the thinnest reaction layer thickness for any corrosion time period, thereby, its resistance to CMAS induced hot-corrosion is the best. The doping of Ce⁴⁺ accelerates the reaction rate between CMAS and ceramics, thereby quickly forming a dense reaction layer to prevent the CMAS from inward corrosion and increase the strain tolerance of the ceramic.

The effect of applied stress and medium flow on the corrosion behavior of 20# steel and L245NS steel in H₂S/CO₂ co-existence environment was studied by mass loss method using high-temperature and high-pressure corrosion test kettle with magnetic drive shaft. Then, the surface morphology and composition of corrosion products of the four-point bending specimens after immersion corrosion were characterized by means of SEM and XRD. Results show that the average corrosion rate of 20# steel is higher than that of L245NS steel in H₂S/CO₂ containing medium. When a stress is applied on the test piece and/or the medium flows, the corrosion rate of both materials increases. The effect of stress on corrosion rate is more significant. The corrosion mechanism is speculated as follows: H₂S plays a leading role in the corrosion process and produces a protective FeS corrosion product film. The stress will lead to the formation of a large number of microscopic channels in the corrosion product film, which promotes the corrosion process. Fluid flow speeds up the dissolution of metals and the diffusion of corrosive substances, resulting in enhanced corrosion rates.