ABSTRACT This study aims to replace traditional chromium‐containing conversion coatings and overcome the drawbacks of polyacrylic acid (PAA) films, including slow formation, high hydrophilicity, and limited stability. A synergistic strategy using epoxy‐functional silane γ‐(2,3‐epoxypropoxy)propyltrimethoxysilane (KH‐560) and zinc ions constructs a ternary PAA/KH‐560/Zn 2+ composite coating on carbon steel. Silane concentration and formation time were evaluated via electrochemical testing, contact angle, SEM, XPS, and FTIR. Optimal performance is achieved at 0.6 vol% KH‐560 with a 10 min formation time. Under these conditions, the low‐frequency impedance modulus reaches 2.25 × 10 4 Ω·cm 2 , the charge‐transfer resistance is increased by more than one order of magnitude relative to bare steel, and a protection efficiency of 95.7% is achieved, and water contact angle is 95°, indicating hydrophobicity. Protection arises from a ternary synergistic mechanism of “coordination–crosslinking–anchoring,” rapidly forming a dense hydrophobic layer. An electrophoretic paint topcoat two‐layer system validates that the optimized pretreatment layer enhances anti‐corrosion performance under industrial‐relevant conditions. This offers new insights for advancing rapid and eco‐friendly metal surface pretreatment.
ABSTRACT An iron specimen embedded in a cement test block was anodically polarized to investigate corrosion and cracking by measuring compressive force with a load cell. The specimen exhibited two stages: unchanged force in Stage I and a linearly increasing compressive force in Stage II . In Stage I , local acidification from water decomposition dissolved the surrounding cement, creating a void that allowed Fe 2+ ions to dissolve, migrate, and precipitate as rust on the cement wall. In Stage II , the void was filled by redeposited iron‐rust‐containing cement, after which continued polarization promoted rust growth on the iron surface. The resulting volume expansion generated tensile force in the cement, leading to cracking. Raman and XRD analyses identified corrosion products, including Fe 3 O 4 , Fe 2 O 3 , α‐FeOOH, and γ‐FeOOH, although some phases may have formed via oxidation upon exposure to air.
Tempering temperature (TT) played a critical role in regulating the microstructure and electrochemical corrosion behavior of laser quenched steels. In this study, laser quenched 40CrNiMoA steel was tempered at 130, 150 degrees C and 170 degrees C, and the effects of TT on the microstructure, oxide-product stability and corrosion behavior of laser quenched 40CrNiMoA steel in 3.5% NaCl solution were systematically investigated. The results show that the tempering promotes the microstructural homogenization while retaining the refined martensitic structure, and the 130 degrees C-tempered sample exhibits the lowest corrosion current density of 5.778 & times; 10-6 A & centerdot;cm-2, the highest polarization resistance of 4572 Omega & centerdot;cm2 and the highest charge-transfer resistance of 1995 Omega & centerdot;cm2 among the three kinds of tempered samples. This improved corrosion performance is attributed to the synergistic effects of microstructural stabilization and suppression of Cl- penetration by the compact oxide-product film, which provides guidance for optimizing the TT of laser-quenched 40CrNiMoA steel for corrosion-resistant applications.
ABSTRACT The growth of Cu 2 S films and the initiation and progression of micro‐galvanic corrosion underneath them were investigated after exposure of Cu to anoxic 0.1 M Cl − solutions containing SH − at concentrations ranging from 10 −5 M to 10 −3 M, for up to 3 years. Post‐exposure surface characterization was performed using scanning electron microscopy (SEM), focused ion beam (FIB) cross‐sectioning, atomic force microscopy (AFM), and surface profilometry. At [SH − ] ≤ 5 × 10 −5 M, a thin and porous Cu 2 S film formed on the Cu surface via general corrosion, favoring surface roughening. Increasing [SH − ] to 5 × 10 −4 or 1 × 10 −3 M resulted in the formation of a compact, crystalline, but non‐uniform Cu 2 S film, under which micro‐galvanic corrosion was observed. A time‐dependent characterization of corrosion damage underlying the Cu 2 S film showed the initiation, propagation, and finally stifling as the film thickened with time. Herein, supported by experimental evidence, a mechanistic pathway for the stifling of the micro‐galvanic corrosion is proposed.
ABSTRACT The growing use of secondary aluminium alloys requires understanding how trace amounts of Cu and Zn interact with heat treatment to affect corrosion. One primary and 3 secondary AA6063 variants were compared before and after T6 heat treatment using polarization, SEM‐EDS and SKPFM, with corrosion assessed in 0.1 M NaCl. Polarization alone did not resolve the localized corrosion responses associated with trace compositional differences. T6 treatment increased the size of Fe‐rich intermetallic particles while maintaining a similar area fraction. It also modified trace‐element partitioning and local electrochemical heterogeneity. In secondary variants, increased particle–matrix Volta potential contrast was associated with earlier trenching. T6 treatment increased the frequency of intergranular corrosion initiation, whereas untreated secondary variants generally developed fewer, larger affected regions during prolonged immersion. Thus, T6 heat treatment shifts the balance between trenching initiation and intergranular corrosion propagation rather than uniformly increasing or decreasing localized corrosion susceptibility.
