Deep-Sea Corrosion Behavior And Coating Protection Of Corrosion-Resistant Aluminum Alloys

Deep sea technology has become the frontier of the whole marine science.The corrosion behavior of engineering materials commonly used in deep sea must be understood and mastered as soon as possible.The actual corrosion environment of different sea areas and different depths in the same sea area is very different,so the real sea experiment is very important and one of the main methods in this paper.However,because the real sea test is expensive,time consuming and the recovery rate is low,and the interface mechanism information is not provided,so the simulated deep sea corrosion test is still a useful supplement for the study of the corrosion of deep-sea metal materials.Therefore,the corrosion rate,morphology and composition of corrosion products and electrochemical kinetic parameters of 5A06 aluminum alloy exposed to 500,800,1200 and 2000 m in a sea area for 1year are studied.The corrosion behavior of 5A06 aluminum alloy is analyzed by indoor simulation acceleration experiment.The corrosion behavior of 5A06 aluminum alloy is analyzed by dissolved oxygen,hydrostatic pressure and temperature,and the electrochemical mechanism of corrosion is discussed.The results of real sea show that the corrosion of the sample is the most serious at the depth of 500 m,the main corrosion form is pitting corrosion,and the corrosion degree is the least at the depth of 2000 m.The results of weight loss corrosion and electrochemical test are consistent.The results of grey correlation analysis show that the concentration of dissolved oxygen is the primary environmental factor affecting the corrosion of 5A06 aluminum alloy in deep sea environment,followed by pressure and temperature.Under the simulated deep-sea accelerated corrosion test conditions,the electrochemical test results show that the lower the dissolved oxygen content is,the faster the corrosion rate is in the range of 2 mg / L to 7 mg / L,which can be attributed to the high dissolved oxygen environment providing the oxygen needed in the process of passive film damage repair.When the hydrostatic pressure of corrosion environment increases,the corrosion rate first increases and then decreases,and the pressure will promote the halogen ions to enter the passive film and damage the passive film The corrosion rate of aluminum alloy decreases when the pressure is higher than 20.0 MPa,which may be due to the change of density and form of passive film on the metal surface under high pressure,so the corrosion rate is lower than that at 20.0 MPa.In the seawater environment of 4.0 ℃,the corrosion rate first increased and then decreased with the prolongation of immersion time.The electrochemical test results showed that at the beginning of immersion,the impedance fluctuated,the immersion time prolonged,and the impedance gradually stabilized.When the temperature of the corrosive medium solution increases to 20.0℃,the corrosion rate of the sample accelerates,the electrochemical impedance spectrum shows obvious Warburg impedance,and the film gap appears.When the temperature rises to 35.0℃,the corrosion rate begins to decrease.This may be because the transfer rate of halogen ions increases with the increase of electrolyte solution temperature.However,when the temperature rises to a certain extent,the properties of passive film on the surface may change,resulting in the decrease of corrosion rate.According to the corrosion rate of different factors,a power function accelerated model of corrosion loss thickness is established.When other factors remain unchanged,the influence of a certain factor on the corrosion rate can be evaluated,such as the corrosion behavior of samples in the same depth,the same temperature but different dissolved oxygen environments.According to the above research results,the protective performance of 5A06 aluminum alloy deep-sea coating was explored.The epoxy coating and modified thick paste epoxy coating were placed in the pressure environment of 20.0 MPa and 30.0 MPa.The comparison showed that the higher the pressure of the corrosion environment,the faster the corrosion rate,and the shorter the time of coating failure.When the epoxy coating is immersed in 20.0 MPa hydrostatic pressure for 4 cycles,it shows a widened time constant with little change in impedance.However,the impedance of the modified thick paste epoxy coating sample decreases significantly in the third cycle,and two obvious time constants appear in the fourth cycle.Under the hydrostatic pressure of 30.0 MPa,the impedance of the epoxy coating sample decreases obviously when it is immersed in the third cycle,and there are two obvious time constants when it is immersed in the fourth cycle,while there are two time constants when the modified thick paste epoxy coating is immersed in the third cycle.In contrast,epoxy coating is more suitable for surface protection of deep-sea 5A06 aluminum alloy,which may be due to the formation of oxide film on the surface of aluminum alloy,and the adhesion of modified thick paste epoxy coating on its surface is not as good as that of epoxy coating.