Study Of Corrosion Performance Of Aluminium Alloy In Seawater

Aluminum alloys are commonly used in marine application with excellent corrosion resistance. Since seawater is recognized to be very corrosive for metals, the oxide film breaks down at specific points leading to the formation of pits on the aluminum surface. It is necessary to study the corrosion and its protection of aluminum alloy in deep-sea and-corrosion rate of aluminum alloys in different kinds of seawater is an important corrosion parameter which is widely used in marine engineering. In this paper, potentiodynamic scanning, electrochemical impedance spectroscopy(EIS) electrochemical techniques and scanning electron microscopy(SEM),3D screen materials research tools were used to study the corrosion behaviors of aluminum alloys 1060 and 5083 in different kinds of seawater. The research results of this paper are as follows:1. The effect of temperature and dissolved oxygen on the corrosion behavior of aluminum alloy 5083 in seawater and the change of average monthly corrosion rate of aluminum alloys 1060 and 5083 in real sea were studied. When the dissolved oxygen was 6.5mg/L with decrease of the temperature, the corrosion potential of aluminum alloy 5083 and pitting potential shifted positively, passive current density decreased; when the dissolved oxygen was 2mg/L with decreased of the temperature, the corrosion potential of aluminum alloy 5083 shifted negatively, the pitting potential shifted positively, and passive current density increased. With decreasing temperature, capacitance arc diameter increased, so the impedance modulus increased. Impedance spectroscopy showed a capacitance arc in low temperature, low-frequency Warburg impedance appeared in high temperature. The morphology of the alloy 5083 showed that the alloy 5083 suffered obvious pitting corrosion in seawater at low temperature and low content of dissolved oxygen, while the oxide films were prone to form on the alloy 5083 at high temperature and dissoved oxygen. Temperature was the main factor affecting corrosion rate of aluminum alloy 1060 and 5083 in real sea, corrosion rate of the two aluminum alloys had similar a law, but the corrosion rate of aluminum alloy 5083 was higher than that of aluminum alloy 1060.2. The effect of pH on the corrosion behavior of aluminum alloy 5083 in seawater at low temperature and dissolved oxygen was studied. The corrosion potential of aluminum alloy 5083 shifted negatively, passive current density increased and the passivation region broadened, but the pitting potential changed little with the increase of pH value. The result obtained from AC impedance test indicated that capacitance arc diameter decreased, the impedance modulus decreased with the he increase of pH value, showing the fastest corrosion rate of aluminum alloy 5083 in alkaline seawater. When the pH value was 7.2,7.7,8.2, Warburg impedance appeared at low frequency, and the cathode process was controlled by diffusion. The lower the pH value, the more easily occurred pitting corrosion, with the pH value increased, aluminum alloy 5083 mainly occurred uniform corrosion.3. The pitting process of aluminum alloy 5083 in seawater at low temperature and dissolved oxygen was studied. We found the corrosion potential and the pitting potential of aluminum alloy 5083 shifted positively with the immersion time prolonging, the passivation-region-broadened,but passive current density decreased firstly, and then became stably, the impedance modulus increased firstly, and then decreased. We also found when the aluminum alloy 5083 was immersed 0-12h, the oxide film was complete, this period was at pitting initiation. After being immersed 12-48h, a large number of pits generated, this period was at pitting development. After 48-96h, the number of pits decreased, this period was at corrosion middle stage. After 96h, the sample surface generated oxide film, the aluminum alloy 5083 mainly occurred uniform corrosion, this period was at corrosion later stage.