The harsh marine environment makes anti-corrosion a technical problem in marine engineering.In order to improve the service life of marine anticorrosive coatings， the development of intelligent anticorrosive coatings with "active healing" self-repairing function has become a research hotspot.Layered double hydroxides (LDHs) are ideal corrosion inhibitor nanocontainers and chloride ion hardeners due to their unique structure and anion exchange properties.With excellent environmentally responsive self-healing corrosion resistance and mature construction technology， LDHs have been widely used in marine anti-corrosion engineering.In this paper， the structural properties and synthesis methods of LDHs materials and the preparation of LDHs based coatings were reviewed.The applications of LDHs as additive in organic coatings and pre-treatment conversion films in marine environment for metal protection (magnesium alloy， aluminum alloy and steel) and concrete protection in recent years were summarized.In view of the complex problems encountered in the actual service of the coating，the shortcomings and challenges in the research of LDHs materials were put forward， and the future research trend of LDHs materials in the marine environment was forecasted.
Unmanned underwater vehicles are one of the indispensable tools for people to develop， utilize and explore the ocean， and have broad military application prospects.With the continuous progress and development of science and technology， unmanned underwater vehicles continue to break through their own limits of working depth.Due to the particularity and complexity of the marine environment， the requirements for its structural materials are becoming increasingly higher.In this work， based on the latest research progress at home and abroad， a comprehensive analysis was conducted on the corrosion factors of unmanned underwater vehicles structural materials in the marine environment，including seawater temperature， pH value， salinity， chloride ion concentration and dissolved oxygen content.Aiming at the corrosion types of unmanned underwater vehicles structural materials in the marine environment， the causes of corrosion of underwater vehicles structural materials in special working environments were explored.Besides， the anti-corrosion methods of unmanned underwater vehicle structural materials in marine environment were described， and the development of its future anti-corrosion technology was prospected.
Concrete is an important engineering material for national infrastructure construction.However， due to the complexity of the service environment， concrete faces the problem of deterioration caused by microbial corrosion， which brings safety hazards and economic losses to the development of various industries and the safe operation of facilities.Therefore， the protection of concrete is particularly important.In this paper， the application status of concrete materials and the mechanism of microbial corrosion of concrete materials were introduced.According to the ways in which microorganisms corrode concrete， the four main methods of protecting concrete from microbial corrosion were reviewed.Meanwhile， the principles and research progress of microbial inactivation， concrete modification， coatings and biomineralization in preventing microbial corrosion were discussed in detail.Cases of different methods used to resist microbial corrosion were presented， and the advantages and disadvantages of these four methods were summarized.Furthermore， by reviewing the existing concrete protection methods， the future research direction of protection methods for concrete against microbial corrosion was prospected.
In order to improve the prediction accuracy of pitting depth of 316L stainless steel instrument pipe in oily marine atmosphere， a direct discrete grey pitting depth prediction model (SCPSO-DDGM (1，1， λ)) based on improved particle swarm algorithm optimization was established.First， using pitting corrosion data from exposure experiments as an example， the DDGM (1， 1) model was established， and the model was dynamically improved by applying a new information-based variable weight weakening buffer operator and dimension-equivalent gray number supplementation.Then，a nonlinear variation inertia weight and sine-cosine learning factors were used to enhance the optimization ability and convergence speed of the Particle Swarm Optimization (PSO) algorithm， while a Gaussian perturbation strategy was introduced to improve PSO's ability to escape local optima.The SCPSO was then employed to optimize the weight parameter λ in the improved DDGM (1， 1，λ) model.Finally， simulation calculations were performed in MATLAB to analyze and compare the prediction results of the SCPSO-DDGM(1， 1， λ) model with those of the GM (1，1)，DDGM (1，1) and PSO-DDGM (1，1，λ) models.Results showed that during the time period of the study， the predicted depth of the optimized new model was highly consistent with the actual depth， and its performance was better than that of the comparison model.Overall， it was proved that the SCPSO-DDGM (1，1， λ) model can effectively predict the pitting depth of instrument tubes， which provides new ideas and methods for the corrosion research of instrument tubes.
Bactericides are a common method for preventing and controlling microbiologically influenced corrosion (MIC) in the offshore oil and gas extraction industry.However，bactericides may cause changes in the behavior of microbial corrosion，and the presence of petroleum will also have a certain impact on the effectiveness of bactericides.In this work， the effect of tetrakis (hydroxymethyl) phosphonium sulfate(THPS) on the corrosion behavior of biocide sulfate-reducing bacteria (Desulfobaculum bizertense) in the presence of petroleum was studied by cell counting， corrosion weight loss， surface analysis and electrochemical analysis.Results showed that although THPS could inhibit the growth ofD.bizertensis，it aggravated the corrosion ofD.bizertensison X70 pipeline steel.Meantime，the addition of petroleum further increased the corrosion potential， indicating that even with the addition of bactericides， petroleum still promoted the corrosion ofD.bizertensison X70.The above result provided a reference for the rational use of bactericides in marine oily environments.
To study the effect of rare earth Y on the corrosion resistance of low alloy steel， low alloy steel with different rare earth contents was obtained by adding rare earth Y to DH36 low alloy steel.Then， the effect of simulated marine environment on the corrosion resistance of DH36 ship plate steel was investigated using 3.5%NaCl solution as the corrosive medium.The effects of rare earth Y on the corrosion resistance of DH36 steel were investigated using immersion tests， laser confocal microscopy， scanning electron microscopy (SEM)， X-ray diffraction analyzer (XRD)，electrochemical testing and other methods.The residual stress between inclusions unmodified by rare earth and inclusions modified by rare earth and the steel substrate was investigated using electron backscatter diffraction (EBSD)， and the effect of inclusions on the corrosion resistance of low alloy steel was determined.Results showed that rare earths could refine grains， modify inclusions， reduce the peripheral stress of rare earth inclusions， reduce the occurrence of microcracks and micropores， and thus reduce the corrosion sensitivity of low alloy steel in simulated marine environments.The addition of Y could shift the corrosion potential positively， decrease the corrosion current density， and reduce the appearance of pitting pits on the surface of the test steel in the early stage of corrosion，thereby reducing the active area where corrosion occurred.Moreover， the addition of rare earth Y significantly declined the content of γ-FeOOH in the corrosion products， increased the content of Fe3O4and α-FeOOH， and enhanced the stability and compactness of the rust layer.Furthermore， the addition of Y also increased the thickness of the rust layer， more effectively hindering the entry of Cl-.Hence，the addition of rare earth Y could effectively improve the corrosion resistance of low alloy steel.When the mass fraction of rare earth was 0.004 3%，the best corrosion resistance of the test steel was achieved.
In order to study the thermal shock resistance and thermal erosion resistance of Si/Yb2Si2O7coatings at 1 350 ℃， Si/Yb2Si2O7coatings were prepared on SiCf/SiC composites by vacuum plasma spraying technology.Subsequently，the structure and performance of the samples were characterized by metallography， physical phase， SEM， EDS， gas thermal shock equipment and gas thermal flushing equipment.Results showed that the bonding strength between the coating and SiCf/SiC composite material was 25.01 MPa.After 1 350 ℃gas thermal shock for 1 000 times and 1 350 ℃，550 m/s gas thermal scouring for 1 h， the surface phases of the Yb2Si2O7coating were mainly Yb2Si2O7，Yb2SiO5， Yb2O3and SiO2， and the test results of thermal shock resistance and thermal erosion resistance both met the design requirements.Furthermore， the coating had high bonding strength.The composite materials， Si layer and Yb2Si2O7layer were resistant to high temperature and had good thermal matching performance， and the surface layer had strong resistance to gas corrosion， which was the main reason for the good thermal shock and thermal erosion performance of the coating.Besides， the gas combustion time of gas thermal scouring was shorter than the total time of gas thermal shock， and the thermal scouring was a constant temperature continuous scouring without drastic alternation of hot and cold.Therefore， no obvious cracking was observed at the edge of the coating near the tooling after gas scouring，and the black ablation area after continuous scouring was smaller than the area of gas thermal shock.
For clarifying the influence of fresh acid and residual acid on the corrosion performance of tubing materials and the adaptability of materials in an acid fracturing environment in a certain oil field， the corrosion damage development trend， pitting sensitivity in the whole process of acidizing and corrosion morphology characteristics of P110 and C110 tubing materials under different conditions were analyzed by corrosion weight loss method and three-dimensional stereo optical microscope observation， and the acidizing corrosion inhibitor was optimized.Results showed that as the acidification temperature of fresh acid gradually increased， the degree of material corrosion tends to increased.When the temperature was ≥180 ℃， the average corrosion rate of C110 wasvcorr＝127.7 g/(m2·h)， while the average corrosion rate of P110 wasvcorr＝407.0 g/(m2·h)， which is much higher than the index requirement.When the simulated fresh acid temperature was 100 ℃，pitting nucleation occurred on the material surface.As the temperature increased， the pitting sensitivity gradually increased.In the residual acid environment at ultra-high temperature of 180 ℃， both C110 and P110 materials suffered extremely severe corrosion.Furthermore， the corrosion inhibitor in the acidizing fluid component was obviously ineffective under high temperature conditions， resulting in serious corrosion damage to the pipes in the residual acid flowback environment.The optimized modified manene alkali acidizing corrosion inhibitor significantly slowed down the corrosion rate of the material through the formation of a multilayer adsorption film， and the corrosion inhibition rate was 89.4%in a high temperature fresh acid environment at 180 ℃.
In order to study the corrosion behavior of L360 steel at the pipe wall of water-containing gathering and transportation pipelines under real flow conditions， a self-made cyclic flow corrosion test device was used.The electrochemical impedance spectroscopy and potentiodynamic scanning methods were used to analyze the corrosion electrochemical characteristics of L360 steel.The scanning electron microscope and three-dimensional optical microscope were used to analyze the corrosion micromorphology.Results showed that the average corrosion rate of the test piece increased with the increase of flow rate，and the local corrosion rate presented a trend of first decreasing and then increasing.Properly increasing the flow rate could slow down the local corrosion rate.After the loop was run for 4 h， a relatively complete corrosion product film began to form on the surface of the sample.When the flow rate reached 0.5 m/s， the corrosion product film on the pipe wall began to detach.For clean and smooth samples， the initial stage of corrosion belonged to extremely severe corrosion.
In order to improve the erosion and wear resistance of Cr30 steel surface and its corrosion resistance to sulfuric acid and hydrochloric acid， a nickel-coated WC iron-based alloy coating was prepared on the surface of Cr30 steel by laser cladding technology with using a mixture of ferroalloy powder and nickel-coated WC particles as raw materials.The effects of the mass fraction of nickel-coated WC (10%～30%) in the raw material on the microstructure， phase composition， microhardness， erosion and wear resistance， and sulfuric acid and hydrochloric acid corrosion resistance of the iron-based alloy coating were studied.Results showed that the phases of the iron-based alloy coating without nickelcoated WC were FeCr solid solution and Cr23C6， while the phases of the iron-based alloy coating containing 10%and 20%nickel-coated WC were FeCr solid solution， Cr23C6and Fe3W3C.As the content of nickel-coated WC increased to 30%， new carbides Fe6W6C were precipitated in the iron-based alloy coating， and the phases of the iron-based alloy coating containing 30%nickel-coated WC were FeCr solid solution，Cr23C6， Fe3W3C and Fe6W6C.Meanwhile， with the increase of the content of nickel coated WC， the microhardness， erosion wear resistance and sulfuric acid and hydrochloric acid corrosion resistance of iron-based alloy coating were improved.When the mass fraction of nickel coated WC was 30%， the microstructure of the iron-based alloy coating was dense and the refinement effect was most obvious， and the hardness of the coating was the highest， reaching 786 HV0.5.In general， the iron-based alloy coating with 30%nickel-clad WC possessed the best resistance to erosion wear， sulfuric acid and hydrochloric acid corrosion.
Aiming at the serious corrosion problem of coiled tubing operation in the gas field with high CO2content in Sichuan，a high-temperature and high-pressure autoclave was used to simulate the working conditions of coiled tubing，and the corrosion rate of CT80 and 2205DSS tubing steel in CO2environment was measured by weight loss method.In addition，the surface morphology and element composition of coiled tubing were analyzed by surface analysis techniques such as scanning electron microscopy (SEM)， X-ray diffraction analysis (XRD).Results showed that in the CO2-dominated corrosive environment， with the increase of temperature and pressure， the corrosion rate of CT80 in the gas phase environment gradually increased， the corrosion rate of 2205DSS had little change and was lower than that of CT80.The corrosion rate of CT80 in the liquid phase environment increased with the increase of temperature and pressure and then decreased， and the corrosion rate of 2205DSS was very low and changed little.Moreover， microscopic analysis of corrosion products found that the corrosion products of CT80 liquid-phase corrosion specimens mainly were FeCO3and Fe2O3，and the product films were loose and porous，indicating that the corrosion was more serious.Comparably， the corrosion product of 2205DSS liquid-phase corrosion specimens were mainly Cr2O3，and the product film was denser，indicating that the corrosion was slighter.Overall， 2205DSS coiled tubing had good corrosion resistance and was suitable for use in high CO2gas fields.
Corrosion issues limit the development of sub / supercritical water oxidation technology.In particular， phosphates will form lowmelting-point mixed molten salts in a supercritical water environment，creating a more severe corrosion environment，and how to solve the problems of corrosion and salt deposition has become the focus of current research.In this work， the corrosion behavior of Alloy625 in subcritical/supercritical water-phosphate environment was studied by weight loss method， X-ray diffraction (XRD)， energy dispersive spectrum (EDS)and scanning electron microscopy (SEM)， and the evolution characteristics of surface morphology and corrosion products was characterized in detail.Results showed that in addition to metal phosphates， the corrosion products were mainly Cr2O3， NiO， FeO and NiCr2O4under subcritical conditions.In contrast， the inner layer of the corrosion product film under supercritical conditions was composed of dense flaky Ni2O3，Cr2O3and NiCr2O4spinel， and the outer layer was composed of loose needle-shaped Fe2O3and FePO4.Moreover， phosphates could cause severe peeling of the oxide film， thereby exacerbating corrosion.The corrosion weight loss law under subcritical conditions at 350 ℃followed a parabolic curve.In the 450 ℃supercritical condition， the corrosion weight loss was influenced by the evolution process of the corrosion product film (generation-detachment-regeneration)， and the change in corrosion quality was much higher than that under subcritical conditions.
To investigate the effects of anodic polarization on the corrosion behavior and re-passivation behavior of martensitic stainless steel in a chloride ion environment， electrochemical testing methods including cyclic polarization， constant potential polarization， and electrochemical impedance spectroscopy (EIS) were employed.Additionally， the influence of anodic polarization potential on the corrosion resistance of 1Cr12Ni3Mo2VN stainless steel was studied using confocal laser scanning microscope (CLSM)， scanning electron microscope (SEM)， energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS).The study analyzed the behavior processes of pitting and re-passivation of the material， as well as the relationship between corrosion resistance and the composition of the passivation film.Results showed that no pitting corrosion was observed on the surface after polarization at a low potential in the passivation zone.The content of Cr2O3and Fe2O3in the passivation film was found to increase， while the content of hydroxides decreased， which enhanced the stability of the passivation film and improved the material's corrosion resistance.When the passivation area was polarized at a high potential， an inductive arc appeared in the lowfrequency region of the electrochemical impedance spectrum， and a stable pitting corrosion was formed on the material's surface.The pitting holes were semi-ellipsoidal， and the content of Cr and Mo in the surface layer of the pitting holes increased，while the content of Fe and Ni decreased.After the mixed potential dropped to the protection potential， re-passivation occurred.The repaired passivation film was thinner， the impedance value decreased， and the pitting sensitivity increased.
Reinforced concrete structures often fail prematurely due to rebar corrosion.Adding corrosion inhibitors can effectively mitigate rebar corrosion and enhance the durability of reinforced concrete structures.Lignosulfonate， as a green and efficient component， exhibits good corrosion-inhibiting properties.However， its water-reducing effect is bad， and it cannot independently meet the technological demands of modern concrete technology for high fluidity and strength.In this study， sodium lignosulfonate was modified by grafting hydroxyl and carboxyl groups to synthesize sodium lignosulfonate derivatives.These derivatives were then incorporated into simulated pore solutions and cement mortar to investigate their corrosion-inhibiting effects on rebar.Results showed that， in both simulated alkaline chloride environments and mortar accelerated corrosion environments，the sodium lignosulfonate derivatives increased the charge transfer resistance and reduced the corrosion current density，demonstrating significant corrosion inhibition.When the water-cement ratio was 0.35，the flowability of the cement paste with the addition of sodium lignosulfonate derivatives reached 350 mm， with a water-reducing effect comparable to that of polycarboxylate， thus meeting the requirements for concrete flowability and strength.
To investigate the corrosion mechanisms of low-lying areas in the gathering and transportation pipelines of the Daniudi Gas Field，the distribution of accumulated liquid along the pipeline was simulated.A low-lying section of the pipeline located 1 207 m from the starting point was identified as the primary monitoring point.Excavation of pipeline sections and installation of coupons were conducted on-site.Weight loss testing was used to calculate the corrosion rates of the coupons， and the microscopic structure and composition of the corrosion products were characterized using scanning electron microscopy (SEM)， energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD).Results showed that the uniform corrosion rate of the coupons at the gas tree was 0.003 5 mm/a， the corrosion degree was slight， and no obvious local corrosion tendency was observed.The uniform corrosion rate of the low-lying coupon was 0.059 9 mm/a， the local corrosion rate was 0.138 0 mm/a， the pitting corrosion coefficient was 2.3， and the degree of localized corrosion was severe.The structure of the corrosion products on the surface of the low-lying pipe samples was loose，and the corrosion products were mainly composed of FeCO3，FeS and Fe2O3.It was speculated that the corrosion was mainly caused by the corrosive gases CO2and H2S， with Cl-in the effluent playing an accelerating role.
Although the development of laser surface strengthening and surface micro-nano structure manufacturing technologies in China began relatively late， it has progressed rapidly in recent years.Significant advancements have been made in areas such as the fundamental theories of laser-material transient interactions， laser shock peening ， laser surface melting， laser surface cladding， laser direct writing and laser-induced surface microstructures.However， compared to countries with earlier research in laser technology， China still faces challenges such as a lack of pioneering process technologies and weak fundamental research in laser-material transient interactions.Additionally，there are gaps in industrial technology applications and equipment development.In this paper， the research progress in laser surface strengthening and micro-nano manufacturing technology was reviewed.With the continuous advancement of micro-nano structure manufacturing industry， the increasing application demand for new alloys and new materials，and heightened environmental requirements，laser surface strengthening and laser surface micro-nano structure manufacturing technologies are expected to continue progressing towards higher efficiency，precision and performance，with further developments in practical applications.
Powder bed fusion titanium alloys， as an important metallic material， are widely used in aerospace， medical devices and automotive industries.However， due to their unique material properties and processing methods， surface quality and performance remainone of key issues that constrain their application.In this paper， the research progress on surface polishing techniques for powder bed fusion titanium alloys was reviewed.The advancements in chemical polishing， electrochemical polishing， plasma electrolytic polishing， laser polishing and mechanical polishing were introduced.These techniques have provided options for achieving surface quality and performance that meet various application needs for powder bed fusion titanium alloys.Additionally， the development of composite polishing technologies and related advancements were also prospected.
Metal chromium coating has been widely used as decorative and functional coatings in the metallurgical and chemical industries due to its high hardness， excellent corrosion resistance and aesthetic appearance.The traditional chromium electroplating process uses hexavalent chromium electroplating.However， hexavalent chromium electrolytes are highly toxic and strong carcinogens， which harm human health and seriously pollute the environment.Trivalent chromium electroplating is considered one of the most important and effective processes to replace hexavalent chromium electroplating.However， due to the limitations of aqueous solutions， trivalent chromium electroplating exhibits shortcomings such as hydrogen evolution， difficulty in thickening the coating and low current efficiency， which restrict its development.Seeking a new electrolyte system that can replace aqueous solutions has become one of the research directions for trivalent chromium electroplating.As a new type of green solvent， deep eutectic solvents (DESs) show great promise in the electrodeposition of metals due to their advantages， including ease of synthesis， high electrical conductivity， wide electrochemical window and good solubility.They overcome the shortcomings of the high volatility of organic solvents， the complex preparation process of ionic liquids and high costs.In this paper， the physicochemical properties of deep eutectic solvents used for chromium electrodeposition and the forms in which metal ions exist within them were introduced.The research progress on chromium and its alloys electrodeposition in DESs was reviewed.The effects of additives on chromium electrodeposition in DESs were discussed.Issues related to chromium electrodeposition in DESs were analyzed， and directions for further research were explored.
In order to investigate the effect of porosity on the comprehensive performance of bioactive coatings， a TiO2coating was prepared on the surface of TA2 pure titanium using micro-arc oxidation.By varying the concentrations of Na2B4O7and NaOH in the electrolyte， the effects of electrolyte composition on the phase composition， microstructure， hardness， thickness and hydrophilicity of the micro-arc oxidation coating were examined under constant current mode.Results showed that the coating phase was primarily rutile TiO2.The phase composition， morphology， thickness， hardness and wear resistance of the coating were significantly affected by the concentrations of sodium hydroxide and sodium tetraborate.Moderate addition of NaOH can enhance the thickness， porosity， hardness， wear resistance and corrosion resistance of the coating.However， when the concentration of sodium hydroxide was too high， porosity decreased and coating performance was reduced.When the electrolyte formula was 0.15 mol/L NaOH and 0.10 mol/L Na2B4O7， a porous coating with a "trabecular bone-like" structure was prepared， exhibiting high porosity and good comprehensive performance.
In order to prolong the service life of magnesium alloys， superhydrophobic coatings were prepared on the surface of ME20M rare earth magnesium alloy through cathodic deposition and superhydrophobic modification.A stearic acid ethanol solution was used for chemical modification of the cathodically deposited Mg(OH)2films on the magnesium alloy.Single-factor experiments were conducted to investigate the effects of stearic acid concentration，solution temperature and immersion time on surface wettability，in order to determine the optimal modification process.The corrosion resistance of typical samples was evaluated using drop tests，full immersion corrosion tests and modern electrochemical testing techniques.The adhesion strength of the film to the substrate was assessed by the cross-cut method， and the surface microstructure and composition of the samples were analyzed using scanning electron microscopy (SEM)， fourier transform infrared spectrometer (FT-IR)and X-ray diffraction analyzer(XRD).Results showed that the cathode deposited Mg(OH)2film could be rendered superhydrophobic by brief immersion in a low-concentration stearic acid solution， achieving a static contact angle (SCA) of up to 151.5° with distilled water and a rolling angle (SA) as low as 1.0°， exhibiting low viscosity.The combined treatment of cathodic deposition and hydrophobic modification could significantly improve the corrosion resistance of magnesium alloys.Compared with the blank sample， the discoloration time of the droplet on the composite treated sample was extended by nearly 25 times， the self-corrosion current densityJcorrin 3.5%NaCl solution was reduced by nearly 3 orders of magnitude， and the characteristic impedance modulus ｜Z｜0.1Hzwas increased by nearly 4 orders of magnitude.The surface micromorphology of cathodic deposition Mg(OH)2thin film with hydrophobic treatment showed a sword-like structure at the micro/nano scale.There were obvious absorption peaks of -CH3and -CH2- in the infrared spectrum of the sample.
In order to clarify the relationship between the corrosion resistance of zirconium films and the surface flatness of sheets from amechanism perspective，chemical polishing was used to alter the surface flatness of cold-rolled steel sheets and aluminum alloy sheets.These modified surfaces were compared with untreated cold-rolled and aluminum sheets.Zirconium films were prepared on the sample surfaces，and their micro morphology were observed using scanning electron microscopy (SEM).Electrochemical methods were employed to test the corrosion resistance of the passivation films.The corrosion resistance of the films and the adhesion of paint film was evaluated using salt spray test chamber， cyclic alternation tester and paint adhesion testing equipment.Results showed that the polished cold-rolled steel sheets and aluminum alloy sheets exhibited smooth and even appearances.The zirconium films prepared on these polished surfaces displayed a uniform and dense particle distribution， with significantly reduced roughness.The corrosion current of the zirconium films was lower，and the impedance radius was larger.In contrast， the unpolished cold-rolled and aluminum alloy sheets appeared rough and uneven， and the zirconium films prepared on these surfaces had irregular particle sizes and arrangements.After impact， cup tests and cross-cut adhesion tests， the adhesion of the zirconium films on both cold-rolled and aluminum alloy sheets met the requirements.After 1 000 h of salt spray testing， the maximum single-sided expansion width of the cold-rolled plate paint film on the polished flat surface was approximately 1.9 mm， with no bubbling on the paint surface.For the unpolished cold-rolled sheets， the maximum single-sided expansion width of paint film was about 2.3 mm， also with no bubbling.For the polished aluminum alloy sheets，the paint film exhibited a single-sided expansion width of corrosion of 2.0 mm after 30 cycles of alternating testing，with no bubbling on the paint surface.Conversely， the unpolished aluminum alloy sheets showed a single-sided expansion width of corrosion of 2.6 mm after the same number of cycles， with no bubbling.
Aiming at the problem of early fatigue cracks in plasma nitrided H13 steel precision hot forging dies， plasma nitriding process tests were conducted under a nitriding temperature of 520 ℃， a pressure of 250 Pa and different nitrogen to hydrogen ratio conditions to reveal the effect of nitrogen hydrogen ratio in a nitriding atmosphere on the microstructure and wear properties of coating.The phase structures， microstructure， microhardness and wear properties of the nitrided coatings with different nitrogen hydrogen ratios were examined and analyzed using X-ray diffraction (XRD)， confocal microscopy， scanning electron microscopy (SEM)， microhardness tester and a friction and wear test machine.Results showed that the nitrided coatings with N ∶H ＝1 ∶3，1 ∶4 and 1 ∶5 after 3 h mainly consisted of ε-Fe2-3N， γ′-Fe4N and αN-Fe(N) phases， respectively， while nitrided coatings with N ∶H＝1 ∶8 mainly consisted of γ′ and αN.The depth and hardness of the nitrided layers decreased with the reduction of N concentration in the nitriding atmosphere.The depth of the nitrided layer with N ∶H ＝1 ∶8 increased with nitriding time， and the hardness reached 800～900 HV0.1at a depth of 60 μm.The wear mechanisms were mainly fatigue wear for the nitrided coatings with N ∶H＝1 ∶3，1 ∶4， and abrasive wear for the coatings with N ∶H＝1 ∶5，1 ∶8.When ion nitriding H13 steel with a nitrogen to hydrogen ratio of 1 ∶8 was carried out， there was no compound layer or vein like structure in the nitriding layer， and the nitriding layer could obtain moderate hardness and better toughness， with good wear resistance.
To further enhance the mechanical properties and service temperature of silicone resin coatings， the effects of the silane coupling agent KH-560 and low melting point glass powder on the thermal protection performance of silicone resin coatings were investigated.The elastic modulus， bonding strength， thermal expansion coefficient， ablation， thermal insulation and thermal shock properties of the coating were tested using a high-temperature solid material dynamic elastic property tester， a universal electronic tensile machine， an expansion meter and a gas thermal shock experimental system； The composition， surface micromorphology and elemental content of the coating were analyzed using infrared spectroscopy， emission scanning electron microscopy， and its attached energy spectrum analysis.Results showed that with increasing KH-560 content (0～3%)， the elastic modulus and adhesion strength of the silicone resin coatings were initially increased and then decreased.When 2.0%KH-560 was added，the maximum values for the elastic modulus and adhesion strength of the coatings were achieved at room temperature， reaching 24.10 GPa and 4.40 MPa， respectively.This was mainly attributed to the enhancement of bonding between the silicone resin and the metal substrate， as well as between the filler and the silicone resin facilitated by KH-560.The addition of 110%glass powder was found to effectively improve the thermal stability and thermal shock resistance of the silicone resin coatings at 800 ℃， due to the melting of glass powder，which filled the voids generated by the decomposition of silicone resin， thereby preventing further oxidation decomposition of the silicone resin.Additionally， silicone resin coatings with a glass powder content of 110%were observed to exhibit good thermal insulation and ablative properties.
In order to assess the potential for implementing the 1-hydroxyethylidene-1，1-diphosphonic acid (HEDP) copper plating process in engineering applications， copper coatings were prepared on the surfaces of A3 steel substrates using HEDP plating method and cyanide plating method.The macroscopic and microscopic morphologies， deposition rates， dispersion abilities， and deep plating capabilities of the copper coatings produced by the two processes were compared.Additionally， the coating adhesion and hydrogen embrittlement performance of the HEDP copper plating layer were characterized.Results showed that the HEDP copper plating layer exhibited fine crystallization with a dense distribution of grain grooves and undulations.The cyanide copper plating layer， on the other hand， displayed a granular structure with grains of varying sizes.At a current density of 1.0 A/dm2， the deposition rate of the HEDP copper coating reached 0.19 μm/min， which was 35.7%higher than the 0.14 μm/min deposition rate observed in the cyanide copper plating process.The dispersion and deep plating capabilities of both the HEDP and cyanide copper plating processes were found to be comparable.Additionally， the HEDP copper plating layer demonstrated good adhesion to the steel substrate and qualified hydrogen embrittlement performance.
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