Study On Fatigue Properties Of 6082 Aluminum Alloy Welded Joint

With the advent of high speed and light weight of vehicle and railway vehicle,aluminum alloy has become a main material to realize high-speed and lightweight railway vehicle due to its small density,high strength and good corrosion resistance.In welded structures,welded joints are the weakest parts of components.Therefore,it is particularly important to study how to improve the fatigue life of welded joints.In this paper,selection the 6082 Aluminum Alloy as the experimental material,the welding joint of 6082 Aluminum Alloy is treated by ultrasonic impact treatment(UIT)and grinded weld residual height technology,respectively,and analysis the effect of UIT and grinding the residual height of the weld joint on the fatigue properties of the welded joint;the fatigue fracture morphology was observed by scanning electron microscope to analyze the fatigue failure mode of the specimen,residual metallographic microscope,microhardness tester and stress analyzer explore the UIT joint surface plastic deformation changes,surface hardness and residual stress of 6082 Aluminum Alloy welding,respectively;transmission electron microscope was used to observe the microstructure of the surface after the UIT and the grain refinement process.From what has been discussed above we can gain the conclusion as followings:(1)In the loading frequency is 10Hz,the stress ratio is 0.1,three groups of test data to plot the S-N curve,the fatigue curve equation of as-welded specimens for Y=-39.72lg(N)+333.84;fatigue curve equation with no residual high welding specimens for Y=-30.41lg(N)+300.85;UIT specimens fatigue curve equation was Y=-41.12lg(N)+352.01;(2)The fatigue strength of no residual high welding specimens and the UIT specimens was obviously improved which compared with the original welded specimen.Three groups of samples in the 2×10~6 fatigue cycles under fatigue strength respectively:fatigue strength of welded specimens is 83.60MPa,no residual high welding specimens fatigue strength is109.27MPa,the fatigue strength of UIT specimen is 92.95MPa,smooth weld reinforcement and UIT relative to the fatigue strength of welded samples was increased 30.71%and 11.18%;(3)Almost all Welded specimens broken in the weld toe.With the influence of weld reinforcement and welding defects it intends to produce large stress concentration;Later the UIT even the weld toe stress concentration has improved the stress concentration still cannot to be removed.The fatigue crack initiation from the source the weld toe that UIT can improve the fatigue life of joints and will not change the mechanism of fatigue failure of welded joints;no residual high welding specimens are broken in the base metal arc transition,the stress concentration was greatly reduced and the base metal arc transition at there is stress concentration,resulting in crack source was born in the adorable;(4)The crack area showed irregular cleavage river pattern,the tear ridge lines,accompanied by cleavage steps and the secondary cracks;fracture zone is mainly manifested in the size of the dimple morphology show that the fatigue fracture of welded joints of 6082Aluminum Alloy was quasi cleavage fracture;(5)After UIT an obvious plastic deformation layer was formed on the surface,there were secondary cracks near the crack source,which could delay the fatigue crack growth and improve the fatigue life;(6)High energy can be input on the surface of 6082 aluminum alloy by UIT,which makes the grain of the near surface produce violent plastic deformation,When the impact parameters are 1.0A/2min,1.0A/5min,1.5A/2min,1.5A/5min,deformed layer thickness is about 35?m,45?m,40?m,and 60?m,respectively;(7)The transverse and longitudinal welding residual stress of the sample plate were63.8MPa and 65.3MPa;the impact of transverse and longitudinal residual stress of the plate are respectively-52.1MPa and-29.6MPa;Cut into small plate warp cutting machine will release some residual stress,performance of welded plate's transverse and longitudinal residual stress were 32.8MPa and 34.6MPa,after the UIT,the longitudinal residual stress were-46.2MPa and-33.4MPa,so UIT can effectively eliminating residual tensile stress at the weld toe and introduced the beneficial residual compressive stress,it can effectively improve the fatigue life of welded joints;(8)From the TEM observation that UIT surface tissue and in four kinds of ultrasonic impact treatment 1.0A/2min,1.0A/5min,1.5A/2min,1.5A/5min,the grains were refined in different degree,the impact parameter is 1.5A/2min,the grain size is about 200nm;(9)After ultrasonic impact,the hardness of the 6082 aluminum alloy surface is obviously improved.The UIT parameters are 1.0A/2min,1.0A/5min,1.5A/2min,1.5A/5min,and the surface hardness is 130HV,143HV,135HV,170HV,respectively.