Influence Of Temperature On Self-piercing Riveting Performance Of TA1 Sheet

With the development of automobile lightweight technology,the application of light metal materials in automobile industry is increasing gradually.Titanium and titanium alloy have attracted the attention of scholars because of their excellent light weight,high strength and corrosion resistance.The hardness of titanium is higher at room temperature.Scholars have realized the self-piercing riveting of titanium by heating the titanium sheet and reducing its hardness.This method of changing the riveting temperature makes the sheet metal which is difficult to be riveted successfully and greatly expands the application scope of self-piercing riveting.In this paper,the influence of temperature on the mechanical properties,forming quality and failure mode of TA1 self-piercing riveting was explored by two ways of preheating before riveting and post heating after riveting.(1)In the range of preheating temperature of 20 ?-150 ?,the same kind of TA1 material was riveted by self-piercing.The static tensile test was carried out on the joint,the load displacement curve and energy absorption value were obtained,the cross section of the joint was cut,the size parameters of the forming section were measured,and the fracture failure mode of the joint was analyzed.The results show that with the increase of preheating temperature,the maximum load and displacement of TA1 joint with the same material decrease,the bottom thickness of formed section has a trend of gradually decreasing,and the pull-out failure of joint changes from the inclined deformation of rivet to the pull-out failure of rivet with less deformation.(2)Three preheating temperatures of 20 ?,100 ? and 150 ? were selected to carry out the self-piercing riveting of TA1 and 5052 dissimilar materials with titanium / aluminum and aluminum / titanium.The static tensile test was carried out on the joint,the load displacement curve and energy absorption value were obtained,the size of the section was observed and measured,and the form of fracture failure was analyzed.The results show that at the same temperature,the maximum load of TA1 + 5052 joint is significantly higher than that of 5052 + TA1,but the maximum displacement difference between TA1 + 5052 and TA1 is not obvious.Two different combinations of self-piercing riveting produce two different forming sections.With the increase of preheating temperature,the maximum load of the two kinds of joints decreases gradually,the maximum displacement changes little,the bottom thickness of the formed section has a trend of decreasing gradually,and the fracture failure form of the joint remains unchanged.(3)The numerical simulations of TA1 sheet metal self-piercing riveting forming at preheating temperature of 20 ?,100 ? and 150 ? were carried out by using simufact software.The equivalent stress nephogram of self-piercing riveting process was obtained,and the joint cross section of numerical simulation and actual experiment was compared.The results show that with the increase of preheating temperature,the equivalent stress of the numerical simulation decreases gradually,and the bottom thickness and inner lock length of the formed section decrease gradually.(4)Three temperatures of 20 ?,600 ? and 850 ? were selected to carry out induction heat treatment experiments after riveting of industrial pure titanium TA1.Tensile tests were carried out on various joints,metallographic tests and SEM analysis were carried out on plates and rivets,and fracture failure of joints was analyzed.The results show that the maximum load and displacement of joints at 600 ? are significantly lower than those at 20 ?,the maximum load of joints at 850 ? is slightly higher,the plasticity of rivets is enhanced after heating,and the failure changes from instantaneous tensile failure to slow deformation failure,and the maximum displacement of failure is significantly increased.(5)The fatigue tests were carried out on three kinds of joints,which were self-piercing riveting at room temperature,preheating before riveting and induction heating after riveting,to analyze the failure mode of fracture,and to analyze the fracture position by ultrasonic C-scan.The results show that under the same load level,the fatigue life of the self-piercing joint under different processes does not change significantly;with the increase of the load level,the fatigue life of the joint decreases gradually.There are three basic forms of fatigue fracture in various processes: rivet fracture,lower sheet crack and upper sheet crack.