Microstructure And Corrosion Behaviors Of Friction Stir Welded Joint Of 2297 Aluminum Alloy

As a key aviation material,2297 aluminum alloy has received extensive attention due to its good mechanical properties and corrosion resistance.Friction stir welding（FSW）is widely used in the manufacture of aluminum alloy components with poor weldability due to its many advantages.However,the structural change after welding will change the corrosion resistance of the weld and restrict the application of aluminum alloy in industrial manufacturing.Therefore,in view of the manufacturing process and service behavior of aluminum alloy friction stir welding,in-depth research on the structural properties and corrosion behavior of FSW welds is a key link,which will provide a certain theoretical support for the application of 2297 aluminum alloy.This article first studies the relationship between the microstructure of 2297-T8 aluminum alloy friction stir welding joint and its corresponding mechanical properties and corrosion behavior.The open-circuit potential test and the dynamic potential polarization curve test were used to systematically characterize the electrochemical characteristics of each macro-area of the weld,and the electrochemical characteristics of the weld micro-area were tested using SKP and LEIS,combined with the microstructure characterization results and the immersion test.The observation results of the corrosion morphology,analyze the influence of the difference in the organizational structure between the regions on the corrosion behavior.The results show that the local corrosion occurred in various areas of the 2297-T8 aluminum alloy weld is mainly pitting corrosion induced by the Cucontaining second phase（S phase and AL7Cu2Fe）.The self-corrosion potential of the heat-affected zone in the weld is-0.430 VSCE,which is the lowest compared with other areas and the most prone to corrosion.The self-corrosion potential of the weld nugget is the highest,-0.380 VSCE,and the corrosion resistance is the strongest.Aiming at the macro-galvanic effect formed in each area of the weld and the pitting behavior caused by the typical precipitation phase,COMSOL software was used to model and simulate the corrosion process.The simulation results show that there is a significant macro-galvanic effect between the base metal zone,the heat affected zone and the weld nugget zone.In the galvanic system composed of the heataffected zone,there are differences in the electrochemical characteristics of the weld nugget zone and the base metal zone as the cathode,which causes a difference in the current distribution on the anode heat-affected zone,that is,the junction of the heataffected zone/base metal zone The corrosion current is significantly larger than the heat affected/welded nugget junction.In the pitting system,the S phase and Al₇Cu₂ Fe are different from the anode current provided by the anode in the early stage of corrosion.The pitting corrosion caused by S phase develops fastest in the heataffected zone;the pitting corrosion caused by Al₇Cu₂ Fe develops fastest in the base metal zone.Different second phases have different pitting behaviors in the same area.The macro galvanic effect between the weld areas has a significant effect on the micro-phase corrosion induced by the second phase,and it has a strong influence in the early stage of the development of pitting corrosion;the macro galvanic effect significantly accelerates the development speed of pitting corrosion in the heataffected zone,and suppresses The pitting corrosion in the base metal area and the weld nugget area was achieved.The macro-galvanic current is added to the pitting corrosion and enhancing the micro-galvanic effect is the main reason that the macrogalvanic effect affects the pitting corrosion.