Study Of Galvanic Corrosion Behavior And The Protection Of 6016 Aluminum Alloy/DC01 Steel Used In Vehicle

Energy conservation and environmental protection are the main melody of global manufacturing development.Energy conservation and emission reduction in the automobile industry can not be separated from the vehicle lightweight.Currently,the application of lightweight materials is the main measure to reduce vehicle weight,but a single material cannot meet the performance requirements of vehicle,and the body materials tend to be mixed with multiple materials.However,the mixed use of multiple materials in the realization of lightweight vehicles will make the problem of galvanic corrosion prominent,accelerating the corrosion damage of components and affecting the safety of long-term driving.As the two main metal materials for lightweight body,the problem of galvanic corrosion between steel and aluminum alloy is inevitable.6016 aluminium alloy and DC01cold-rolled steel of automotive used were selected in this paper,and the electrochemical performance of both were investigated by conventional electrochemical testing methods.The macroscopic and microscopic signals of 6016/DC01 galvanic corrosion were real-time monitored by electrochemical noise technique and scanning vibrating electrode technique.The corrosion behaviour and evolution of the electrocouple were analysed by time domain and frequency domain wavelet analysis,combined with electron microscopy to reveal the corrosion mechanism of 6016/DC01 electrocouple.The results show that the potential of6016 is lower.After coupling with DC01,6016 acts as the anode with the corrosion rate being accelerated,increasing by an order of magnitude compared with self-corrosion,and the aluminum alloy shows uniform corrosion after 24h.Different from the dominant characteristic of pitting corrosion presented by self-corrosion,the aluminum alloy after coupling has both matrix crystalline corrosion and pitting corrosion.The noise signal and morphological analysis show that the corrosion evolution of 6016/DC01 coupling over 24h can be divided into four stages.The first stage is the initiation of crystalline corrosion.The second stage,which is still dominated by crystalline corrosion,contains the initiation of pitting corrosion.The third stage is the initiation and expansion of pitting corrosion and crystalline corrosion.The fourth stage includes pitting corrosion initiation and growth,and the continuing growth of the existent crystalline corrosion.Further,the effectiveness of aluminium alloy titanium-zirconium conversion treatment,steel galvanisation and combined protection against galvanic corrosion is investigated on the basis of the industry's more promising anti-corrosion surface treatment methods.The results show that the titanium-zirconium conversion treatment of aluminium alloys alone cannot achieve effective protection.Corrosion grade is E grade.The galvanizing of cold-rolled steel alone results in a significant reduction of the galvanic current and a reversal of polarity,with the galvanised steel acting as a cathodic protection for the aluminium alloy.Combined protection further reduces the current density and the susceptibility to galvanic corrosion to class A.Combined protection can effectively inhibit galvanic corrosion.COMSOL finite element software is used to simulate the galvanic corrosion process in order to quickly determine the macroscopic current density distribution and provide a quick guide for galvanic corrosion protection.Based on the polarisation curves of 6016 and DC01as boundary conditions,the diffusion of solution ions,anodic dissolution and the hindering effect of Al(OH)₃ corrosion products on subsequent corrosion were taken into account.The results show that the model used is in good agreement with the experimental results for the simulation of 6016/DC01 coupling pair before and after combined surface protection,and the model has a certain degree of reliability.