Electrochemical Noise Of AZ91D Magnesium Alloy

This paper summarizes the research status, background and the development of electrochemical noise. Then, the corrosion process of AZ91D magnesium alloys has been investigated by using the electrochemical measurement system for collecting the effective noise data. And the datas are analyzed using time-domain analysis and frequency-domain analysis, which evolve the characteristic parameters of electrochemical noise. Finally, the relationship between the corrosion process of AZ91D alloys and electrochemical noise is established. Meanwhile, the morphology of AZ91D magnesium alloys is observed by scanning electronic Microscopy (SEM) when the fluctations of noise appear on the electrode surface. At last, the effect of Cl^- on electrochemical noise is discussed when pitting corrosion occurs on AZ91D alloys. The results show that there are different phenomenons of electrochemical noise for AZ91D alloy in NaCl solutions. The results of time domain analysis show that the parameters of standard deviation, pitting index and noise resistance are increasing with the concetration of Cl^-, and corrosion rate also increases.The result of frequency domain analysis show that the slopes of high frequency linear part are greater than -20dB·dec-1. It is indicated that pitting corrosion takes place on AZ91D magnesium alloys surface. The value of white noise level W can reach the maximum in 0.10mol·L-1 NaCl solution. It is found that electrochemical noise characteristic varies with materials in different concentration of Cl^- solutions. It is easily for metals to take place electrochemical noise in the erosive solutions. Otherwisee, the greater the concentration of Cl^-, the more likely the stable pitting corrosion formed.The corrosion behaviors of N80 steel are also studied in this paper. This part summarizes development and mechanism of CO₂ corrosion and linear polarization technique.Corrosion rate of N80 steel is studied in a high–temperature and high-pressure with different CO₂ partial pressures by weight-loss method for simulation of the corrosion occurred at oil fields. The results show that with the CO₂ partial pressure increase, corrosion rate of N80 steel increases. The Rp of N80 steel is determined with linear polarization method, thus corrosion rate can also be calculated.The results show that corrosion rate of N80 steel is smaller in the lower concentration of medium solutions. Under different temperature, there is serious corrosion in the middle temperature areas. At different concentration of NaCl solutions, the corrosion of N80 steel is slightest when the concentration of Cl^-is 3%.