Galvanic Corrosion Test And Simulation Of Dissimilar Metals In Salt Spray Environment

As the demand for lightweight equipment becomes more and more urgent,the use of dissimilar materials in modern aircraft structures and aviation fields is becoming more and more common.Dissimilar materials are very easy to form galvanic corrosion during service.As a widely existing form of corrosion,galvanic corrosion has a great threat to the safety of aircraft.This thesis studies the metal materials of my country’s aviation connectors 2A12 aluminum alloy,30CrMnSiNi2A steel and The galvanic corrosion behavior between TC4 titanium alloys provides certain theoretical and technical support for aircraft design material selection and corrosion protection.In this thesis,the trimetallic and bimetallic systems were studied by neutral salt spray test and electrochemical method,respectively,and the corrosion behavior of different coupling systems was explored by combining corrosion weight loss and depth measurement,macro-and micro-morphological characterization and corrosion product composition determination.The required boundary conditions are obtained through the self-built electrochemical test platform in the state of thin liquid film,so as to construct the mathematical model and finite element numerical model of each galvanic corrosion system in the salt spray environment,and use the corrosion depth numerical value to compare the simulation results.The results show that:(1)In the four coupling systems,2A12 is the corrosion anode,TC4 is the corrosion cathode,and 30CrMnSiNi2A steel acts as the corrosion cathode in the system with 2A12 aluminum alloy;the types of corrosion products in each system are similar,but the three-metal coupling In the system,AlCl3,α-FeOOH and other representative corrosion products appear earlier in time,which is mainly due to the serious corrosion of the anode metal caused by the increase of the cathode area.The corrosion rates of 2A12 and 30CrMnSiNi2A in this system are 2.55mm/y and 2.06mm/y,respectively.(2)The galvanic effect is affected by the potential difference,the polarization of the metal itself and the area ratio of the cathode and anode.In the bimetallic system,the corrosion of 2A12 and 30CrMnSiNi2Ais mainly controlled by the charge transfer process,and in the trimetallic system,the two are mainly controlled by the mixture of charge transfer and diffusion activities.In terms of the corrosion form of anode metal,the bimetallic system exhibits pitting corrosion characteristics,while the trimetallic system exhibits general corrosion,and the galvanic current on the electrode surface exists|IG-2A12|≈|IG-30Cr|+|IG-TC4| relationship.The corrosion current densities of 2A12 and 30CrMnSiNi2A in the three-metal system are respectively 1.56 × 10-5A · cm-2 and 8.44 ×10-5A·cm-2 It rapidly decreased to 7.77× 10-6A · cm-2,2.13× 10-5A·cm-2.(3)The corrosion simulation results show that the corrosion products are mainly accumulated at the high current density value,and the product porosity of the 2A12/TC4 system decreases from 0.9 to 0.2,which greatly hinders the diffusion and migration of ions.The corrosion depth value comparison shows that the test results are all distributed in the 12%error band of the simulation results.