Corrosion Mechanism And Life Prediction Of Cold Spray Coating Of Friction Stir Welding Joint Of High Strength Aluminum Alloy

Since the high-strength aluminum alloy widely used in aviation and aerospace fields is welded by Friction and Stir Welding(FSW),this method can make up for the defects of welding hot crack and pores caused by traditional welding methods,however,in the process of service,as the welded structure is affected by the corrosive environment,the service life of the structural parts will be shortened and the safety risks will be increased.In order to improve the corrosion resistant properties of FSW joint,in this paper,cold spraying technology was used to protect 2219 aluminum alloy FSW joint from corrosion to improve its corrosion resistance,the FSW joint cold spraying layer under the condition of different electrolytes of electrochemical corrosion behavior,salt fog corrosion behavior and mechanism are studied,and a finite element model is established to predict the corrosion life of the joint.By testing the open circuit potential and polarization curve of the cold spray layer of FSW joints and the cold spray layer,the test is under different Cl~-concentration and PH,the electrochemical behavior and mechanism of were studied.The results of electrochemical test show that the corrosion tendency of open circuit potential,corrosion potential and current density of the cold spray layer is significantly lower than that of the FSW joint area and the base material area in a variety of corrosion media with different Cl~-concentration and PH.For example,in the Na Cl corrosion solution with a PH of 3.5 and a concentration of 3.5%,the open circuit potential of the base material,the joint and the cold coating area were-0.859V,-0.814V and-0.735V,and The corrosion current densities were 19.77?A/cm~2,14.60?A/cm~2,and 8.96?A/cm~2,respectively.The electrochemical difference between each area of FSW joint is mainly caused by the different structure and the distribution of the second phase particles,and the cold spraying technology enables the joint to obtain uniform coating protection.The salt spray corrosion behavior and mechanism of cold spray coating of FSW joint were studied by orthogonal salt spray test.The corrosion behavior of salt spray in different areas of base metal,welded and cold spray coating under different Cl~-concentration,PH and corrosion time was studied.The results showed that Cl~-concentration and PH had great influence on the corrosion development of each region.By weight-loss experiment analyzed the corrosion kinetics of various regions,cold spray coating area with the extension of time,low corrosion rate can be divided into three phases,the first phase of the corrosion rate in the initial stage to reduce the rate of corrosion is larger,with the accumulation of corrosion products,the corrosion rate in the second and the third stage to reduce the rate of becoming more slowly.Matlab software was used to fit the corrosion rates of each region,and the results showed that PH value and cl-concentration had a greater impact on the corrosion rate,and PH had a greater impact,and there was a synergistic effect between PH and corrosion time,cl-concentration and corrosion time,and Cl~-concentration and PH on the corrosion rate.Through the analysis of the corrosion mechanism of salt spray in the cold spray coating area,it is shown that the corrosion in the cold spray coating area starts from pitting and gradually develops to depth,and finally develops to serious peeling corrosion.Based on Comsol multi-physical field simulation software,the corrosion behavior of FSW joint of 2219 aluminum alloy and friction stir welding joint protected by cold spray coating was numerically simulated by building finite element model.Early results showed that the corrosion,the coupling model and cold spraying protective layer of the solution of joint model are maintaining high potential in the base area,and the higher with the weld area,the greater the potential of distance,near the center of the welding of the cathode electrode current density is the largest,the cold spraying layer of low voltage range than the weld area of the welded joint.With the development of corrosion reaction,the electric potential in the solution increased,and the difference of corrosion current density between the electrodes increased.In addition,the corrosion depth of the joint in the finite element model and the corrosion depth of the cold spraying layer are in good agreement with the test data,which proves the cold spraying layer improves the corrosion resistance of joint.Conclusively,the study shows that the cold spray coating plays an effective corrosion protection role in the friction stir welding joint,which can be promoted as an important corrosion protection method of the joint.The finite element simulation method can be extended to the study of corrosion resistance of the joint and provide a theoretical basis for the study of corrosion life of the coating.