Study On Formation And Failure Mechanism Of Aluminum Alloy Corrosion Protective Film

As a heat medium,the glycol water based coolant is a key component of cooling systems,which is one of the most commonly used coolants.The acidification of ethylene glycol at high working temperature for a long time results in corrosion of metals in cooling systems.The aluminum alloy has high thermal conductivity,and that it widely is used in cooling systems.Therefore,it is of great significance to study the corrosion mechanism of aluminum alloy in the coolant.In this paper,the high corrosion resistance of eight-type metals(brass,copper,solder,carbon steel,cast iron,cast aluminum,5A02 aluminum and 5A06 aluminum)in a new coolant were evaluated by weight loss test.At the same time,the electrochemical behavior of 5A02 and 5A06 aluminum in the new coolant were investigated by the electrochemical technology,and the effects of chloride ions on the electrochemical behavior were studied.The corroded morphology and chemical structures of corrosion inhibitor film in the new coolant were studied by scanning vibrating electrode technology(SVET)in conjunction with surface testing technology,to explore the formation and failure mechanism of corrosion inhibitor film.The results show that eight kinds of metals corroder different degrees in.Among them,the solder corrode the most seriously.However,the addition of corrosion inhibitors in the ethylene glycol water-based solution resulted in reducing the corrosion rates of the eight-type metals.In this case,the corrosion rate of 5A02 aluminum is 0.025 g·m-2·d-1,and the corrosion rate of 5A06 aluminum is 0.053 g·m-2·d-1,both of them lower than 0.1 g·m-2·d-1.The presence of chloride ions in the new coolant accelerated the corrosion of 5 A02 and 5A06 aluminum.The addition of corrosion inhibitor into the glycol water based solution promoted the passivation process of 5A02 and 5A06 aluminum,reducing the anodic current density.It was indicated that the corrosion inhibitor was an anode-type inhibitor.Once the coolant contained chloride ions,the cathodic and anodic process were promoted,increasing the cathodic and anodic current density.The polarization resistance of 5A02 and 5A06 aluminum decreased with the increasing concentration of chloride ions,indicating that chloride ions promoted the corrosion of 5A02 and 5A06 aluminum in the new coolant.The characteristics of electrochemical impedance spectrum of 5A02 and 5A06 aluminum in the new coolant had two,showing two time constants.The meant the formation process of the corrosion-inhibiting film and the capacitive loop in high frequency meant the corrosion process of aluminum surface.The radius of capacitive loop in low frequency became larger with the immersion time,indicating that the formation of corrosion inhibitor film was occurred,and the corrosion inhibitor played an effective role.When chlorine ions were added,the 5A02 and 5A06 still exhibited two time constants,and the radius of capacitive loop in low frequency became larger,indicating that the chloride ions promote the corrosion of 5A02 and 5A06 aluminum.The film layer gradually thickened with the immersion time.At the same time,the potential of 5 A02 and 5A06 aluminum surface gradually became more uniform.Moreover,the corrosion-inhibiting film mainly contains elements such as C,N,and O,indicating that the active component of the corrosion inhibitor formed a film on the metal surface.However,after adding chlorine ions into the new coolant,the potential of 5A02 and 5A06 aluminum surface gradually became more uneven,indicating that the chlorine ions destroyed the corrosion inhibitor film.