Self-piercing Riveting Of Ultra High Strength Steel And Aluminum Alloy

In order to meet the requirements of automotive lightweight,high-strength,low-density materials are increasingly used in the car body.Traditional spot welding technology is difficult to meet the requirements of the connection of dissimilar metals,The strength of self-piercing riveting joint is about 1.5 times the strength of solder joints,about twice the strength of clinch joints,and the connection process is fast and environmentally friendly,it has a significant advantage,so self-piercing riveting technology become the first choice in the steel and aluminum dissimilar metals connection.The 22MnB5 which is commonly used thermoformed steel plate,can reach the strength of 1300 MPa after forming,it is hard to be deformed at room temperature,traditional spot welding,riveting and other connection technology can’t guarantee the connection strength between the 22MnB5 and aluminum alloy,so that 22MnB5 can’t play the advantages of ultra-high strength steel.This paper presents a new self-pierce riveting method with local heat treatment.This is conducive to forming riveted with using local heat treatment to reduce the steel strength of the riveting area and improve the ductility before the riveting.The temperature of the method is lower than the steel phase transition temperature of the steel,which avoids the destruction of the base metal strength in the heat affected zone.So it can ensure the connection strength between the ultra-high strength steel and aluminum alloy at the same time to achieve riveting of ultra-high strength steel at room temperature.In this paper,the feasibility of the connection method is verified by the finite element simulation,and the strength of the self-punching riveted joint is predicted.In this paper,it is determined to use the high temperature tempering heat treatment that is based on the experimental comparison of several heat treatment methods,then the influence of temperature and time on the properties of 22MnB5 ultra-high strength steel during heat treatment was analyzed and the most reasonable heat treatment parameters were determined: temperature 700 ℃,time 8 min.The constitutive and failure models of 22MnB5,5754 aluminum alloy and 6061 aluminum alloy after heat treatment were established.The Hollomon type hardening formula and MMC failure model were used to describe the material properties,and the failure behavior of steel and aluminum was studied emphatically.The determination method and the changing rule of three failure parameters including failure strain,stress triaxiality and Lode angle parameters are studied.The finite element model of self-pierce riveting between 22MnB5 steel and aluminum alloy after heat treatment was established and the riveting process was simulated.Then the influence rule of the parameters such as the stacking order of the plate member,the size of the rivet,the rivet strength,die diameter,the depth of the die,the die height and other parameters on the joint size were analyzed.The finite element model of tensile-shear and peeling on the joint was established to simulate the tensile-shear and peeling mechanical properties.The strength of the joints between the 22MnB5 and aluminum alloy after local tempering was predicted.And the effects of steel plate order,rivet strength,die depth and die diameter on the joint performance were studied.The results show that the self-riveting with local heat treatment can effectively achieve the connection of the high strength steel and aluminum alloy.In different plate stacking conditions,The performance of the Self-pierce riveting joint between steel and aluminum is quite different.With the increase of the strength of the rivet,the undercutting of the joint increases,but the neck thickness and the bottom thickness decrease.When the depth of the die increases,the joint neck thickness and the bottom thickness are significantly reduced.And when the die diameter increases,the undercutting increases,the neck thickness and the bottom thickness decrease.The effect of the height of the boss on the size of the joint is not so obvious.