| Aluminum and 2024 aluminum alloys are widely used in marine engineering and aerospace due to their excellent properties.Aluminum and 2024 aluminum alloys can form a passivation film in the environment to prevent pitting corrosion,but C l~-can break the oxide film and cause pitting corrosion.In the presence of Cl~-,aluminum will pitting and anodic hydrogen evolution.At the same time,the negative difference effect(NDE)in the process of anodic hydrogen evolution will accelerate the corrosion of aluminum and reduce its service efficiency.Although there have been a lot of researches on the corrosion behavior and corrosion protection of aluminum and aluminum alloys at home and abroad,most of the research is often explained relative to the electrochemical data.The morphology and relative position of the direct reaction process for pitting corrosion of aluminum and 2024 aluminum alloys are limited.In addition,there are few studies on the hydrogen evolution reaction associated with pitting corrosion of aluminum and 2024 aluminum alloy,and the research and explanation of the mechanism of hydrogen evolution increase(negative difference effect)is also controversial.These correlative factors may restrict the further application of aluminum and 2024 aluminum al oy in ocean engineering and aerospace field.In this paper designed and assembled an electrochemical real-time monitoring device,which can not only monitor the change of pitting potential and current of aluminum and 2024aluminum alloy,but also obtain the intuitive position and pictures of surface hydrogen evolution and corresponding electrochemical data in the process of polarization simultaneously and in real time.In this thesis,the effects of different surface pretreatment methods on pitting and hydrogen evolution of aluminum and 2024 aluminum alloy were studied by electrochemical real-time monitoring device combined with potentiodynamic polarization,cyclic voltammetry and scanning electron microscopy.On this basis,the pitting and hydrogen evolution behaviors of aluminum and 2024 aluminum alloy in Na Cl solution were studied,and the relationship between pitting and hydrogen evolution of aluminum and2024 aluminum alloy in the presence of C l~-was revealed,as well as the characteristics of the mechanisms related to the pitting and anode hydrogen evolution of C l~-.The conclusions of this experiment are expected to provide useful information for studying the pitting mechanism and hydrogen evolution behavior of aluminum and aluminum alloys.The experimental results are as follows:(1)Different surface pretreatment methods have effects on pitting corrosion and anodic hydrogen evolution behavior of aluminum and 2024 aluminum alloy,but 2024 aluminum alloy reduces the influence of different pretreatment methods on pitting corrosion and anodic hydrogen evolution due to its alloying effect.Both aluminum and 2024 a luminum alloy under S3(boiling water sealing)show good corrosion resistance during polarization and anodic hydrogen evolution is also weak relative to other states.The other three states of aluminum and 2024 aluminum alloy exhibit different pitting and anodic hydrogen evolution characteristics;different surface pretreatment methods have less influence on the cathodic polarization hydrogen evolution potential of aluminum and 2024 aluminum alloy,and aluminum in four states.The hydrogen evolution potential of the cathode of 2024 aluminum alloy is about-1.5V and-1.2V,which indicates that the cathode hydrogen evolution potential during cathodic polarization is only related to the characteristics of aluminum and 2024aluminum alloy itself.Therefore,for exploring the mechanisms of pitting and hydrogen evolution in aluminum and 2024 aluminum alloys,the relevant differences in different pretreatment methods should not be ignored.(2)Alloying can improve the performance of 2024 aluminum alloy,so that the 2024aluminum alloy has better pitting resistance in the solution containing C l~-.However,after pitting occurs,2024 aluminum alloy will accelerate the corrosion rate,and the surface corrosion is more serious than aluminum,which will cause greater corrosion damage to 2024aluminum al oy.(3)In the absence of Cl~-,aluminum and 2024 aluminum alloys did not show pitting and hydrogen evolution during anodic polarization.The C l~-present in the solution ruptures the oxide film on the surface of aluminum and 2024 aluminum alloy,causing pitting and hydrogen evolution during the anodic polarization of the surface of aluminum and 2024aluminum alloy.The high concentration of C l~-increases the corrosion tendency of aluminum and 2024 aluminum alloy,the corrosion potential decreases,the corrosion current density increases,and the anodic hydrogen evolution reaction is intensified.(4)The passivation film of aluminum and 2024 aluminum alloy is continuously ruptured and recombined in Na C l solution,and it is in a state of dynamic equilibrium.At the same time,the formation of pitting may be the result of the characteristic(penetration or adsorption)of Cl~-such that the surface film at the local position is not present or poorly protected.Through experimental analysis,it can be found that the alloying can improve pitting corrosion resistance and reduce the negative difference effect. |
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