Study On The Corrosion Behaviors And Protection Of Aluminum Alloy In Coastal Industrial Environment With High Temperature

Aluminum alloys are widely used in high-voltage substation equipments because of their good electrical and thermal conductivity and high specific strength.Substation facilities outdoors are completely exposed to the air.The aluminum alloy equipments in coastal industrial environment are subject to more serious corrosion threats.When used as a contact conductive device,the oxide layer on the surface of the aluminum alloy will cause overheating due to continuous electrical resistance which will cause a high temperature for about 60?80°C.So long-term humidity with high temperature is a severe test for the safe operation of equipment.There is a strong electric field environment in the space around the high-voltage substation.It is of practical significance to investigate the corrosion behavior of aluminum alloys used in coastal industrial with high temperature under electric field conditions.The effect of 0?400k V/m electric field strength on the corrosion behavior of aluminum alloy in corrosive medium of sodium chloride and mixed acidic corrosive media on our self-designed high voltage electric field experimental equipment was analyzed in detail by SEM,EDS,XPS,mechanical properties,SVET and electrochemical test.A cyanide-free system was used to conduct a silver plating process on the surface of the aluminum alloy to reduce the contact resistance.The results show:(1)The self-designed device which can be used in a dry-wet alternate accelerated corrosion in a high-voltage electric field environment consisted of multiple sets of discs to form the upper and lower plates of the electric field.The insulation column was used to adjust the distance between the plates.The voltage equalization ring and water medium protection resistor ensured that the high-voltage test was in a safe and stable condition.The device can operate safely and stably for more than 30 days under the condition of electric field strength of 400k V/m.(2)The corrosion rate of aluminum alloy in the 3.5wt%sodium chloride solution under the action of high voltage electric field of 0?400k V gradually increased with the increase of electric field strength.In the early stage of corrosion,pitting corrosion was the dominant stage,and heterogeneous micro-galvanic corrosion was formed on the surface,and the Al-Fe phase was used as the cathode to promote the dissolution of the aluminum alloy matrix.As the electric field strength increased,the range of micro-galvanic corrosion increased.In the middle and later stages of corrosion,exfoliation corrosion was the main procedure.The alternating wet and dry caused the surface of the aluminum alloy to exhibit alternating corrosion behaviors of"passivation,passivation cracking,micro-galvanic corrosion and shedding".Electrochemical corrosion by the SVET micro-region revealed that in the initial stage of the micro-galvanic corrosion of aluminum oxide and metal aluminum,there was a stable activation region,and the peak current of the activation region first increased and then decreased.(3)The corrosion of aluminum alloys in the industrial environment under the action of a high voltage electric field with 400 k V/m was simulated.As the sulfite ion increased,the corrosion rate gradually decreased and then remained substantially constant.Electrochemical impedance spectroscopy showed that the transfer resistance increased first and then decreased.Under the condition of 0.01mol/L SO₃^2-,the transfer resistance was the largest.Under the condition of low concentration of SO₃^2-,the pitting corrosion was mainly corrosion,and the aluminum oxide and its hydrate were mainly presented on the surface of the aluminum alloy.Under the condition of high concentration of SO₃^2-,exfoliation corrosion was the dominant.There were mainly hydrates of aluminum oxide.(4)A silver layer was prepared on the surface of the aluminum alloy by a cyanide-free chemical deposition method.The roughening treatment,the hydroxylation treatment,the KH580treatment,and the chemical deposition silver plating were sequentially performed.The addition of polyvinylpyrrolidone changed the form of the silver layer.The structure of the silver layer was changed from a granular sheet-like structure to a sheet-staggered structure,which was favor to be a better corrosion resistance.The silver content on the surface can reach to 98.50wt%.The contact resistance was as low as 0.037?·cm.