Corrosion Behavior Of Cu-Al Clad Plates In Different Corrosive Medium

As a new type of composite material,Cu/Al clad plates meet the requirements of modern industry for the combination of low cost and high performance,and they have been widely used in various fields.However,the performance evaluation of Cu/Al clad plates is not enough,especially the performance stability of materials in use and life prediction are need to be further studied,which limits the application in important engineering fields or key components.Corrosion plays an important role in affecting the performance stability and life span of Cu/Al clad plates.Especially,the corrosion mechanism of Cu/Al clad plates is quite different in the corrosive environment containing complex medium,and it is difficult to determine the change of the service performance and life span of materials,so the systematic research is undoubtly needed.Therefore,this article systematically studies the chemical and electrochemical corrosion mechanism of Cu/Al clad plates based on the corrosion behavior in different corrosive medium,finally a life prediction method is put forward based on the corrosion failure analysis.The electrochemical corrosion characteristics,the corrosion dynamics and the corrosion weight loss of Cu/Al clad plates were studied through accelerated salt spray corrosion experiments,and the corrosion mechanism was analyzed.The results show that the galvanic corrosion accelerated the corrosion rate of Cu/Al clad plates.With the extention of corrosion time,the corrosion rate firstly increased,then decreased and finally increased,which was attributed to the forming and peeling of corrosion products.In addition,the corrosion resistance is inversely proportional to the concentration of chloride ions.With the increase of temperature,the corrosion resistance firstly decreased and then increased.As the temperature rose,the activation energy of ions and the reaction rate increased.However,when the temperature rose to a certain level,the content of dissolved oxygen in the solution decreased,which inhibited the reduction reaction of cathodes,further reduced the reaction rate.The influence of different corrosive ions on the corrosion behavior of Cu/Al clad plates was studied through immersion corrosion in the simulated acid rain solution by observing the morphology of corrosion products,calculating corrosion weight loss and electrochemical tests.The result shows that there were two types of corrosion:chemical corrosion and electrochemical corrosion.With the increase of p H values,the corrosion rate decreased.The copper reacted with H⁺to produce copper ions,which adsorbed on the aluminum matrix and were replaced as the elemental copper.Electrochemical corrosion between the aluminum matrix and the elemental copper accelerated the corrosion of aluminum.The corrosion resistance of Cu/Al in the acid solution containing three kinds of anions was as follows:NO₃^-<SO₄^2-<Cl^-.Cl^-caused pitting corrosion on materials.NO₃^-and SO₄^2-had strong oxidation in the presence of H+in the solution which accelerated the corrosion rate of the Cu/Al clad plate.In the alkaline solution containing a large amount of OH^-,the competitive adsorption between OH^-and various corrosive ions on the surface of materials made the corrosion behavior greatly different from that in the acid solution.The three-dimensional corrosion morphology of Cu/Al clad plates were observed by the confocal laser scanning microscope.The coverage of the corrosion product film was analyzed by the electrochemical test,finally the corrosion weight loss was calculated.The result shows that the corrosion only occurred on the aluminum in the alkaline solution.The large amount of OH^-in the solution was involved in both the formation and the dissolution of corrosion products.When p H≤10,the Cu/Al showed the local corrosion.When p H>10,severe denudation occurred on the aluminum matrix.The higher the concentration of Cl^-,the lower the pitting potential and the severer corrosion was.The Cu/Al clad plate was passivated,and the passivation film had a good protection for the material and the corrosion rate of Cu/Al clad plates was reduced in the alkaline solution containing SO₄^2-and NO₃^-.The corrosion resistance of Cu/Al plates in the alkaline solution containing three kinds of anions was as follows:Cl^-<SO₄^2-<NO₃^-.The failure model of Cu/Al clad plates was established based on the corrosion dynamics model.The salt spray accelerated corrosion test was conducted from 0h to 1968h.The relationship between the corrosion weight loss and interfacial bonding strength was established through conducting the peeling test on Cu/Al clad plates.The results show that with the decrease of the bonding area between the aluminum plate and the copper plate,the peeling strength of Cu/Al clad plates decreased.Combined with the relationship between the peeling strength and corrosion weight loss,the failure model among corrosion time,the concentration of Cl^-and the interfacial peel strength was established based on the corrosion kinetics model after salt spray corrosion with different concentration of Cl^-is shown as follows:P=-4.8×10^-3×(0.00172C^3.13928·t^{-0.18327C+1.98459})+12.6.The life was predicted according to the national standard of Cu/Al clad plates.According to the failure model,it was calculated that the service life of Cu/Al clad plates was more than 40 years in the coastal area containing0.0107wt.%Cl^-in the air.When the aluminum matrix appeared generally denudation,the weight loss was 125 g/m² and the average depth of corrosion pits at the interface was greater than 0.787mm,the plate was identified as failure.