Chaofang Dong

Effects of Applied Magnetic Field on Corrosion of Beryllium Copper in NaCl Solution

The effects of an applied magnetic field on the corrosion process of beryllium copper in NaCl solution have been investigated by electrochemical measurements, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that a horizontal magnetic field with 0.4 T barely shifted the open circuit potentials ( E corr ) of beryllium copper in NaCl solution with different concentrations. However, the horizontal magnetic field increased the limiting current density of beryllium copper in NaCl solution with low concentration, while decreased the limiting current density of beryllium copper in NaCl solution with high concentration. It was found that magnetic field accelerated the diffusion of CuCl 2− away from the electrode surface and delayed the formation of Cu 2 O. The results of SEM and EDS showed that the influence of magnetic field over the elements distribution of the corrosion products differed from the different concentration of the immersion solution.

Failure analysis of AZ31 magnesium alloy sheets based on the extended GTN damage model

Based on the Gurson-Tvergaard-Needleman (GTN) model and Hill’s quadratic anisotropic yield criterion, a combined experimental-numerical study on fracture initiation in the process of thermal stamping of Mg alloy AZ31 sheets was carried out. The aim is to predict the formability of thermal stamping of the Mg alloy sheets at different temperatures. The presented theoretical framework was implemented into a VUMAT subroutine for ABAQUS/EXPLICIT. Internal damage evolution due to void growth and coalescence developed at different temperatures in the Mg alloy sheets was observed by scanning electron microscopy (SEM). Moreover, the thermal effects on the void growth, coalescence, and fracture behavior of the Mg alloy sheets were analyzed by the extended GTN model and forming limit diagrams (FLD). Parameters employed in the GTN model were determined from tensile tests and numerical iterative computation. The distribution of major and minor principal strains in the specimens was determined from the numerical results. Therefore, the corresponding forming limit diagrams at different stress levels and temperatures were drawn. The comparison between the predicted forming limits and the experimental data shows a good agreement.

Anodic dissolution of a crack tip at AA2024-T351 in 3.5wt% NaCl solution

The anodic dissolution process of a crack tip at 2024-T351 aluminium alloy (AA2024-T351) was determined by means of scanning Kelvin probe (SKP). Wedge-open loading (WOL) specimens were immersed in a 3.5wt% NaCl solution. After various durations of immersion, the Volta potential distributions around the crack were measured by SKP and the surface morphologies were observed by scanning electron microscopy (SEM). It is found that there is a nonuniform distribution of Volta potential around the crack. Before immersion, the Volta potential at crack tip is more negative than that in other regions. However, after immersion, a converse result occurs with the most positive Volta potential measured at the crack tip. SEM observations demonstrate that the noticeable positive shift of Volta potential results from the formation of corrosion products which deposit around the crack tip. Energy-dispersive spectrometry (EDS) analysis shows that the corrosion products are mainly Al oxide and Cu-rich particles. These observations implicate that the applied stress contributes to the preferential anodic dissolution of the crack tip and the redistribution of Cu.

Insights into SO2 and H2O co-adsorption on Cu (100) surface with calculations of density functional theory

Abstract The co-adsorption behaviors of SO2 and H2O on face-centered cubic Cu (100) ideal surface were studied using the GGA-rPBE method of density functional theory (DFT) with slab models. The optimized structures of single H2O and SO2 on Cu (100) surface were calculated at the coverage of 0.25 ML (molecular layer) and 0.5 ML. The results show that there was no obvious chemical adsorption of them on Cu (100) surface. The adsorbed structures, adsorption energy and electronic properties including difference charge density, valence charge density, Bader charge analysis and partial density of states (PDOS) of co-adsorbed structures of H2O and SO2 were investigated to illustrate the interaction between adsorbates and surface. H2O and SO2 can adsorb on surface of Cu atoms chemically via molecule form at the coverage of 0.25 ML, while H2O dissociated into OH adsorbed on surface and H bonded with SO2 which keeps away from surface at the coverage of 0.5 ML.

Localized electrochemical impedance spectroscopy study on the corrosion behavior of Fe-Cr alloy in the solution with Cl− and SO42−

The corrosion behaviors of Fe-Cr alloy under three different pH values solutions with Cl− and SO42− were investigated by localized electrochemical impedance spectroscopy (LEIS) measurements and the corrosion products were analyzed by laser Raman spectrometry. The results show that the high corrosion resistance of Fe-Cr Alloy is attributed to a passive film which is formed more easily when the alloy contains a large quantity of Cr element. However, its corrosion resistance varies in the solutions with different pH values, especially in the initial corrosion. The average impedance values in neutral and alkaline solution are much higher than that in acidic solution because the passive film is more likely to dissolve in the acidic condition. Moreover, the destructive effect of Cl− and SO42+ ions on the passive film is also demonstrated in corrosion process through the change of the impedance value with the steeping time.

Corrosion of Carbon Steel under Epoxy-varnish Coating Studied by Scanning Kelvin Probe

The corrosion behavior of partly coated carbon steel was investigated by salt spray test and scanning Kelvin probe (SKP) in order to understand the long-term corrosion behavior of coated carbon steel in marine atmosphere environment. The localized corrosion was accurately characterized by SKP in both coated and uncoated regions. The SKP results showed that Volta potential varied with the test time, and the more the corrosion products, the more positive the potential. The borderline between coated and uncoated regions of partly coated steel shifted towards the coated side with the increasing of test time. The coating disbonding rate could be determined according to the shift of potential borderline measured by SKP. The corrosion mechanism of partly coated steel in NaCl salt spray was discussed according to the potential maps and corrosion morphologies.

Initial formation of corrosion products on pure zinc in saline solution

Corrosion product formed on zinc sample during 2 weeks immersion in saline solution has been investigated. The corrosion layer morphology as well as its chemical composition, was analyzed using scanning electron microscopy (SEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Electrochemical measurement was used to analyze the corrosion behavior. Zinc oxide, zinc hydroxide and zinc hydroxide chloride were formed on zinc surface in saline solution. The thickness of corrosion layer increased with the time increased. The pure Zn has an estimated corrosion rate of 0.063u202fmmu202fy−1 after immersion for 336u202fh. Probable mechanisms of zinc corrosion products formation are presented.