Q235carbon steel and Q450 weathering steel were exposed to the hot and dry environment of Turpan,China for three years.The corrosion rates of both steels were calculated and compared.The morphologies of the rust layer products were observed by optical microscopy and scanning electron microscopy.Analyses of the rust layers were performed by X-ray photoelectron spectroscopy,X-ray powder diffraction,and Raman spectroscopy,and analysis results indicate that the compositions of rust are main iron rich oxide such as FeOOH,Fe_3O_4,and Fe_2O_3.The iron oxide layer content proportion was calculated through a semi-quantitative algorithm.The resistance elements(Cr,Ni,and Cu)enhanced the resistance properties of the Q450 weathering steel matrix.Moreover,the resistance elements increased the proportion of goethite crystals in the corroded rust layer.
Qiang YUChao-fang DONGYue-hua FANGKui XIAOChun-yun GUOGang HEXiao-gang LI
The corrosion behavior of expandable tubular materials was investigated in simulated downhole formation water environments using a series of electrochemical techniques. The corrosion morphologies in the real downhole environment after three months of application were also observed by stereology microscopy and scanning electron microscopy(SEM). The results show that, compared with the unexpanded sample, the area of ferrite increases dramatically after a 7.09% expansion. The expanded material shows a higher corrosion current in the polarization curve and a lower corrosion resistance in the electrochemical impedance spectroscopy(EIS) plot at every studied temperature. The determined critical pitting temperatures(CPT) before and after expansion are 87.5°C and 79.2°C, respectively. SEM observations demonstrate stress corrosion cracks, and CO2 corrosion and H2 S corrosion also occur in the downhole environment. Due to additional defects generated during the plastic deformation, the corrosion performance of the expanded tubing deteriorates.
Shu-jun GaoChao-fang DongAn-qing FuKui XiaoXiao-gang Li
A chitosan(CS)-based low-p H-sensitive intelligent corrosion inhibitor was prepared by loading a p H-sensitive hydrogel with benzotriazole(BTA); the p H-sensitive hydrogel was synthetized by crosslinking CS with glutaraldehyde(GTA). Analysis by Fourier-transform infrared(FT–IR) spectroscopy showed that Schiff reactions occurred between amino and aldehyde groups. The swelling ability of the hydrogel was investigated using a mass method, and it was observed to swell more in an acidic environment than in an alkaline environment. The hydrogel's loading capacity of BTA was approximately 0.377 g·g-1, and its release speed was faster in an acidic environment than in an alkaline environment because of its swelling behavior. The corrosion inhibition ability of the intelligent inhibitor was tested by immersion and electrochemical methods. The results showed that after 4 h of immersion, the polarization resistance(Rp) value of copper with the intelligent inhibitor was approximately twice of that of copper with BTA, indicating that the intelligent inhibitor could effectively prevent copper from corroding.
Yu-ning WangChao-fang DongDa-wei ZhangPan-pan RenLi LiXiao-gang Li
A composite conversion coating was prepared on magnesmm alloy by the only one-step immersion treatment.The characteristics of the conversion coating were investigated by scanning electron microscopy(SEM)and X-ray photoelectron spectroscopy(XPS).The results indicate that the composite conversion coating consists of magnesmm hydroxide,magnesmm phosphate and manganese phosphate.The electrochemical behavior of the conversion coating was investigated systematically by electrochemical impedance spectroscopy(EIS) and potentiodynamic polarization measurement in different NaCl solutions.Polarization measurements and EIS results reveal that the magnesium alloy with the conversion coating have better corrosion resistance compared to the bare magnesium alloy in these conditions.And the corrosion rate of the magnesium alloy with conversion coating increases consistently with the chloride ion concentration.In alkaline conditions,the magnesium alloy with conversion coating has superior corrosion resistance by the synergistic effects between Mg(OH)_2 film and conversion coating.Moreover,the electrochemical corrosion mechanism of the magnesium alloy was analyzed with respect to the conversion coating in a Cl^- containing environment.
The influence of oxide scales on the corrosion behaviors of B510 L hot-rolled steel strips was investigated in this study. Focused ion beams and scanning electron microscopy were used to observe the morphologies of oxide scales on the surface and cross sections of the hot-rolled steel. Raman spectroscopy and X-ray diffraction were used for the phase analysis of the oxide scales and corrosion products. The corrosion potential and impedance were measured by anodic polarization and electrochemical impedance spectroscopy. According to the results, oxide scales on the hot-rolled strips mainly comprise iron and iron oxides. The correlation between mass gain and test time follows a power exponential rule in the damp-heat test. The corrosion products are found to be mainly composed of γ-Fe OOH, Fe3O4, ?-Fe OOH, and γ-Fe2O3. The contents of the corrosion products are different on the surfaces of the steels with and without oxide scales. The steel with oxide scales is found to show a higher corrosion resistance and lower corrosion rate.
Accelerated corrosion tests of the 7005-T4 aluminum alloy were conducted to determine a suitable service life prediction method by using alternating wet–dry cycles in three kinds of solutions. The morphology and composition analysis of the corrosion product revealed that slight corrosion occurred on the surfaces of the samples immersed in a 0.25 wt% Na_2S_2O_8 solution. However, pitting corrosion occurred on the surfaces of the samples immersed in a 3.5 wt% NaCl solution, whereas exfoliation corrosion occurred on the surfaces of the samples immersed in a mixture of 0.25 wt% Na_2S_2O_8 and 3.5 wt% NaCl solutions. A power exponent relationship was observed between the mass loss and exposure time of the 7005-T4 aluminum alloy immersed in the three kinds of solutions. In the mixture of 0.25 wt% Na_2S_2O_8 and 3.5 wt% NaCl solutions, the mass loss of the aluminum alloy yielded the maximum value. Based on the calculation of the correlation coefficients, the alternating wet–dry procedure in a 3.5 wt% NaCl solution could be used to predict the corrosion behavior of 7005-T4 aluminum alloy exposed in the atmosphere of Qingdao, China. The prediction model is as follows: T = 104.28×t^(0.91), where T is the equivalent time and t is the exposure time.
Xiao-guang SunPeng LinCheng ManJian CuiHai-bo WangChao-fang DongXiao-gang Li
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.
