Study On Microstructure And Corrosion Behavior Of Al-Zn-Mg-X New Type Aluminum Alloy Friction Stir Welded Joints

With the development of science and technology and the needs of national defense,the Al-Zn-Mg-Cu series alloy represented by 7050 alloy has been unable to meet the needs of the current environment.In view of the defects of the Al-Zn-Mg-Cu alloy performance and the poor post-welding performance Good question,a domestic research institute developed three alloys by adding Sc,Ti,Zr and other elements and removing/reducing the content of Cu elements.They are Al-Zn-Mg-Sc-Zr(abbreviated as AS)alloy and Al-Zn-Mg-Sc-Zr-Ti(AST)alloy,Al-Zn-Mg-Sc-Ti-Cu(ASTC)alloy.This paper analyzes the influence of the alloying elements Sc,Zr,Ti,Cu on the structure and properties of the Al-Zn-Mg-X alloy FSW joints by studying the microstructure and properties of the FSW joints of the three alloys,and comprehensively applies the metallographic microscope,SEM-EDS,TEM/STEM systematically characterized the structure of each zone of the three alloy FSW joints;microhardness and tensile tests were used to characterize the hardness,tensile strength and plasticity of the alloy FSW joints;potential dynamics were used Polarization,wire beam electrode,and electrochemical impedance characterize the electrochemical characteristics of three alloy FSW joints,and characterize the macroscopic corrosion behavior of three alloy FSW joints through immersion experiment and intergranular corrosion experiment;based on the above results Above,the influence of alloying elements on the corrosion behavior of Al-Zn-Mg-X alloy FSW joints was systematically analyzed.By comparing the structure of the three alloy FSW joints,it is found that the grain size:AS alloy>AST alloy>ASTC alloy;the degree of continuity of the grain boundary precipitation: ASTC alloy>AST alloy>AS alloy;the coarse second phase type: AS alloy only There is Al3 Fe phase,the coarse second phase in AST alloy and ASTC alloy has Al3(Sc,Zr)/Al3(Sc,Zr,Ti)phase,Al3 Ti phase and Al3 Fe phase;by comparing the hardness and tensile strength of three alloy FSW joints The alloy hardness and strength are obtained from the elongation curve: ASTC alloy>AST alloy>AS alloy;FSW joint plasticity: ASTC alloy>AS alloy>AST alloy;through electrochemical experiments and macroscopic corrosion tests,it is found that the macroscopic galvanic effect is from high to low :ASTC alloy>AST alloy>AS alloy;FSW joint intergranular corrosion sensitivity: ASTC alloy>AST alloy>AS alloy;priority of pitting corrosion: coarse η phase>Al3Fe>Al3(Sc,Zr).In summary,the addition of Ti element can refine the crystal grains and increase the strength of the alloy,but the addition of Ti element reduces the plasticity of the welded joint,and promotes the segregation of elements in each area of the joint,and the coarsening of the precipitated phase and the dispersed phase makes the welded joint The intergranular corrosion sensitivity increases;the addition of Cu increases the hardness,strength and plasticity of the alloy,and the overall potential of the welded joint,but the addition of Cu also increases the macroscopic galvanic effect of the welded joint and promotes the increase of the grain boundary precipitated phase,The susceptibility to intergranular corrosion is increased,and the corrosion resistance of the welded joint is generally reduced;therefore,the overall performance of AS alloy is the best.