Microstructure And Corrosion Behaviors Of Friction Stir Welded Joints Of Al Alloy

Friction stir welding(FSW)has unparalleled advantages,It has been widely used in the aluminum alloy welding.However,there are significant differences in the microstructural structure between the stress state and the heat input of the welds during the welding process.The difference in the micro structure of the welds can significantly affect the mechanical properties and corrosion resistance of the weld,and affecting the overall service performance of the components.Therefore,the study of corrosion behavior of FSW weld of aluminum alloy has become an indispensable content in aluminum alloy FSW research.The micro structure and corrosion behaviors of friction stir welded joints of 2219 and 5083 aluminium alloys were studied.The microstructure in ifferent regions of the joints were characterized by scanning electron microscopy(SEM),electron backscattered diffraction(EBSD)and Microhardness test.The corrosion behavior of the joints and joints of each partition were studied by electrochemical test and corrosion morphology observation.The results show that:There are significant differences in the microstructure between the base material area,the heat affected zone and the shoulder affected zone of the FSW joints in the 2219 aluminum alloy.The microstructural differences lead to a "W" shape of the microhardness of the joint surface.Compared with the base material zone,the hardness of the heat affected zone and the shoulder area is significantly reduced.The differences in micro structure of the joints also change the corrosion behavior of the weld area.The corrosion resistance of the heat affected zone and theshoulder area is improved compared to the base zone.The interface between the different regions of the organization can form galvanic corrosion,in which the base material area as the anode,heat affected zone and shoulder area as the cathode.In the galvanic corrosion process,as the cathode of the base zone and the shoulder area still exists in the self-dissolved metal.The type of corrosion is mainly pitting,and the phase of the second phase of the high phase is the origin of pitting,and there is also the phenomenon of uniform dissolution of the matrix.The cathode/anode area ratio,Cl-concentration and temperature have a significant effect on the galvanic corrosion behavior of welds.The base material zone,the heat affected zone and the shoulder area are all sensitive to intergranular corrosion.The intergranular corrosion of the heat affected zone is the most serious,the base metal area is the second,and the shoulder area is the lightest.But when the formation of galvanic corrosion between the three organizations,the heat affected zone and the shoulder area of the weld to become insensitive to intergranular corrosion.There are significant differences in the microstructure between the base material area,the heat affected zone and the shoulder affected zone of the FS W joints in the 5083 aluminum alloy.The difference in microstructure leads to a large fluctuation in the microhardness of the joint surface.Compared with the hardness of the base material area,the hardness of the heat affected zone is slightly lower,while the hardness of the shoulder area is significantly increased.The differences in microstructure of the joints also change the corrosion behavior of the weld area.Compared with the base material zone,the corrosion resistance of the heat affected zone is reduced and the corrosion resistance of the shoulder affected zone is increased.The base material area is sensitive to intergranular corrosion,and the heat affected zone and the shoulder affected zone are insensitive to intergranular corrosion.The weld can form macroscopic galvanic corrosion,in which the heat affected zone is used as the anode,the base material zone and the shoulder affected zone as the cathode.Tthe galvanic corrosion between the regions of the weld does not change the original intergranular corrosion susceptibility.