Effect Of A-UIT On Residual Stress And Fatigue Properties Of 7075 Aluminum Alloy Laser Welded Joints

7075 aluminum alloy has the advantages of low density,good corrosion resistance,good toughness and high specific strength,which is widely used in aviation,shipbuilding and other fields.Because 7075 aluminum alloy also has the characteristics of low melting point,high heat transfer coefficient and high thermal expansion rate,it will produce large deformation and residual stress in the welding process,which has a great impact on the fatigue life and bearing stability of components.In addition,the service environment of the component is complex and harsh,and the risk of fatigue fracture is high.Therefore,it is of great significance to take appropriate measures to reduce the influence of welding residual stress on the weld and its heat affected zone,so as to improve the fatigue performance of the component.Thus,the aging + UIT composite treatment(A-UIT)method was proposed.In this paper,ABAQUS is used to establish the thermodynamic model of 7075 aluminum alloy laser welding.Then,the numerical transfer method is used to carry out UIT on the joint,and the coupling model of welding and UIT is established.On this basis,the thermodynamic model of aging treatment is introduced to establish A-UIT model after welding,and the distribution of residual stress after welding under different treatment is analyzed.In order to study the effect of different treatments on the residual stress of 7075 aluminum alloy after welding,on this basis,the fatigue tests were carried out on the welded samples,aging samples,UIT samples and A-UIT samples,and the effects of different treatment processes on the fatigue properties of the samples were studied.The results show that UIT can effectively change the distribution of residual stress and introduce residual compressive stress.Among the parameters of UIT,the impact amplitude,impact frequency and static pressure have little influence on the residual stress;the diameter of impact pin has certain influence on the residual stress after welding and the range of UIT;the moving speed of impact pin,impact mode and impact time have great influence on the residual stress.Both aging temperature and aging time affect the effect of A-UIT on residual stress.In the aging treatment part,the aging temperature should be controlled within 140 ?and the aging time should be selected for 24 h;in the UIT part,the impact needle with diameter of 3 mm,ultrasonic frequency of 20 k Hz and amplitude of 40 ?m are selected,the UIT is carried out with the method of repeated reciprocating impact at the speed of 0.08 m/s with self weight,in the aspect of residual stress,A-UIT treatment effect can be obtained.The tensile test shows that the UIT has little effect on the tensile strength of the sample,while the tensile strength of the sample after aging treatment and A-UIT is significantly improved,with an increase rate of more than 50%.According to the fatigue test,the fatigue strength of the welded sample is 47.48 MPa;the fatigue strength of the aging sample is only31.52 MPa;the fatigue strength of the UIT sample is 68.37 MPa;the fatigue strength of the A-UIT sample is 55.15 MPa,which is less than that of the UIT sample.A-UIT treatment can maintain the good tensile properties after aging treatment,and improve the fatigue strength of the sample to a certain extent,which has the characteristics of aging treatment and UIT.