Study On Comprehensive Properties Of 5A06 Aluminum Alloy Friction Stir Welded Joint

5A06 aluminum alloy is a kind of anti-rust aluminum with excellent corrosion resistance,reliable weldability and medium strength.It is widely used in ships,automobiles,aircraft welding parts,subway light rail,transportation equipment and other industries.Friction stir welding is a more advanced solid-phase connection method,which can effectively achieve high-quality connection of aluminum alloy.The current research on the friction stir welding of 5A06 aluminium alloy,the selected welding parameters range is narrow,to explore its impact on the performance of the joint,with limitations,and did not carry out research on the impact of welding parameters on the S line and holes.In this thesis,5A06 aluminum alloy plate（5 mm）is selected.By determining the rotation speed and welding speed range,a large number of experiments are carried out by controlling variable method.The welded joints are tested by universal tensile strength testing machine,microhardness tester,metallographic microscope,electronic scanning microscope（SEM）and electrochemical workstation.The effects of rotation speed and welding speed on the appearance,mechanical properties,corrosion resistance and S line of the joints are studied.In order to obtain excellent welded joints with appearance,mechanical properties and corrosion resistance,it provides guidance for practical application.The primary results of the research are as follows:（1）If the welding speed is kept constant,the tensile strength of the joint first increases and then decreases as the speed increases,whereas if the speed is kept constant,the tensile strength of the joint decreases as the welding speed increases;at a rotation speed of 700 r/min and a welding speed of 75 mm/min,the maximum tensile strength reaches 475 MPa.（2）The microhardness of the joint increases first and then decreases with the increase of rotation speed;with the increase of welding speed,the hardness of the joint decreases first and then increases.（3）As the rotational speed increases,the fracture of the welded joint changes from a brittle fracture to a ductile fracture,with a tendency for the size of the tough nests to become larger;and as the welding speed increases,the number of tough nests increases,with larger second phase particles appearing in the fracture of the joint at700-75.（4）The microstructure and corrosion resistance of different regions have different performances on the friction stir welded joints.With the increase of rotation speed,the corrosion resistance of the thermo-mechanically affected zone is the best,and the corrosion resistance of the joint decreases first and then increases and finally decreases.With the increase of welding speed,the corrosion resistance of the weld nugget zone is the best,and the corrosion resistance of the joint also decreases first,then increases and finally decreases.When the welding parameters areω=700 r/min and v=75 mm/min,the appearance,mechanical properties and corrosion resistance of the joint are excellent.（5）In the FSW welding experiment,the cross section of the joint shows“S”line;when the welding parameters are 400-75,500-75,600-75,obvious hole-type defects appear at the bottom of the weld.The residual particles in the groove formed by corrosion in the central area of the weld may be Al₂O₃particles,which may be due to the oxidation of the base metal by oxygen in the air during the welding process.The oxide is gathered at the“S”curve,which leads to the occurrence of this defect.（6）Welding parameters are the key factors affecting the appearance of welded joints.Correct selection of appropriate parameters can obtain high-quality joints.However,if the heat input is too low,defects such as peeling and holes may appear on the surface of the joint.If the heat input is too high,there may be defects such as flash and rough weld surface;when 5A06 aluminum alloy is welded,sufficient heat input can be obtained when the welding speed is 75～125 mm/min and the rotation speed is600～800 r/min,so as to achieve a joint with no defects and excellent mechanical properties.However,if the heat input is too high or too low,various defects will occur,especially in the weld nugget zone,where the joint will break and the mechanical properties will become very poor.