Study On MAO/BTESPT Composite Treatment Of TC4 Alloy Surface And Its Coupled Corrosion Behavior With Steel

Titanium alloy has the characteristics of high specific strength and excellent corrosion resistance,and is often used as bolts to connect steel structures in ships and Marine equipment.However,due to the high electrode potential of titanium alloy,it is easy to cause serious galvanic corrosion and failure of steel when it is connected with steel,resulting in dangerous accidents and huge economic losses.In this paper,the surface of TC4 titanium alloy was combined with micro-arc oxidation（MAO）and silanization（BTESPT）,the galvanic corrosion behavior of TC4 alloy connected to AH36 steel was studied,and a simulation model was established by COMSOL Multiphysics finite element analysis to predict the long-term galvanic corrosion change rule.SEM,XRD and White Light Interferometry were used to detect and analyze the morphology and phase composition of the film layer and corrosion products,and study on the corrosion mechanism.The depth of corrosion pit was measured by Super Depth of Field 3D Microscope System.Electrochemical workstation was used to study the corrosion tendency of electric pair.The galvanometer was used to monitor the corrosion current,and the effect of galvanic corrosion rate was studied by weight loss test.The influence on tensile properties had also been studied.The main research results were as follows:（1）Study on the growth mechanism of micro-arc oxide film on the surface of TC4 titanium alloy and its galvanic corrosion behavior after connecting with AH36 steel.The results showed that the pore diameter of the coating increased to 5μm and the porosity increased from 1.35%to15%.The phase composition of the micro-arc oxidation coating was Anatase Ti O₂ and Rutile Ti O₂.After silanization,the micro-arc oxidation coating porosity decreased greatly.The immersion experiments showed that the average galvanic current density of AH36 steel was reduced by 96%and 98%after the combined the silanization,compared with that without protection when TC4 is connected with AH36 steel by micro-arc oxidation.The average galvanic corrosion rate（K_c）decreased by 55%,and decreased by 87.5%after silanization.The galvanic corrosion grade was raised from unprotected D grade to A grade.The main corrosion products on the surface of AH36 steel were Fe O（OH）,Fe₂O₃ and Fe（OH）₃ after immersion experiment.（2）When the electrode distance was between 10-40 mm,the average galvanic current density and galvanic corrosion rate increased first and then decreased with the increase of corrosion time.When the electrode distance was 40 mm,the minimum galvanic current was 0.023μA,the minimum corrosion rate was 9.21 mm/a,and the minimum corrosion pit depth was 1.78μm.The main corrosion products were Fe O（OH）and Fe₂O₃.（3）When the area ratio of the anode and cathode was 1:0.5,1:1,1:2 and 1:3,respectively,the average galvanic current density and galvanic corrosion rate first increased and then decreased with the increase of corrosion time.When the area ratio was 1:3,the minimum average galvanic current was 0.012μA,the minimum galvanic corrosion rate was 6.93 mm/a,and the minimum corrosion pit depth was 2.63μm.With the increased of area ratio,the corrosion products Fe O（OH）and Fe₂O₃ on AH36 steel surface increased gradually.（4）The composite treatment of micro-arc oxidation/silanization on the surface of TC4titanium alloy was carried out,and the electrode distance and area ratio of AH36 steel and TC4titanium alloy were changed to study the galvanic corrosion.When the micro-arc oxidation time was 8 mins,the galvanic corrosion sensitivity of AH36/TC4 pair was significantly reduced.When the electrode distance of electric pair was 40 mm and the area ratio was 1:3,the corrosion degree of electric couple was the lowest.（5）COMSOL software was used to simulate the coupling corrosion process of titanium alloy matrix,titanium alloy after micro-arc oxidation and titanium alloy after micro-arc oxidation/silanization composite treatment,respectively,to predict the long-term extension of galvanic corrosion depth.The results showed that the error between the simulated corrosion depth and the experimental results was less than 10%,so the model was reliable.The error between the corrosion rate obtained by linear fitting with the simulation results of more time nodes and the experimental results was less than 10%,so it can be used to predict the long-term galvanic corrosion depth of actual structures.