Study On Interface Evolution Behavior Of Resistance Riveted Joint Of Aluminum Alloy/Steel

With the rapid development of industry,the coordinated development of low-carbon,environment-friendly society construction has become the inevitable choice of automobile lightweight.The main ways of automobile lightweight are replacing ordinary steel plate with high-strength steel plate,replacing steel plate with light metal materials such as aluminum alloy,and replacing steel plate with composite material.At this stage,considering the economic cost and lightweight effect comprehensively,advocating"suitable materials are used in the right place,multi material lightweight structure"is considered as the mainstream development direction in the future.Due to the wide and cross application of light materials such as aluminum alloy and steel,it is inevitable to connect aluminum/steel dissimilar metals.Therefore,it is of great theoretical significance and practical value to carry out the research of aluminum/steel dissimilar metal connection.In this paper,the composite method of self-piercing riveting and resistance spot welding is used to connect the 2 mm thick A6061 aluminum alloy and Q235B low carbon steel,in which 1 mm thick steel process gasket is added to the upper plate.This paper studies and compares the RRW composite connection method with RSW and SPR single point connection method,analyzes the influence of the main process parameters riveting load on the shear and tensile strength of SRR joint,the influence of spot welding current and time on the interface metal compound of RSW joint and RRW joint,and obtains the best combination parameters.The fracture mode of the joint under different welding parameters was observed,and the failure reason of the joint was analyzed and discussed.The macro morphology of the welded joint was analyzed by optical microscope,and it was found that the three connection methods made the aluminum alloy and low carbon steel form a close connection.The structure of the joint was analyzed by SEM.The rivets in the SPR joint penetrated through the process gasket and aluminum alloy,and locked in the low carbon steel.The mechanical connection was very firm.In RSW joint,aluminum alloy and low carbon steel form a close metallurgical bond.A layer of IMC(intermetallic compound)with uniform thickness is formed at the interface.RRW composite joint has both mechanical connection and metallurgical connection.Gasket and rivet are the same material to form mechanical combination;Both the outer side and the inner side of the rivet leg form a good bonding interface with different contact surfaces,and the metallurgical bonding effect between the outer side of the rivet leg and the interface is significantly lower than that between the inner side of the rivet leg and the different interface.The IMC formed on the interface between low carbon steel and rivet on the outside of rivet leg is mainly Zn O and Fe Al.The main IMC formed on the joint surface of aluminum alloy and low carbon steel inside the rivet leg is Fe Al2,Fe Al3 and Fe₂Al₅,and the IMC near the aluminum alloy is Fe Al₃;The IMC of steel side is Fe₂Al₅;The IMC of the middle layer is Fe Al₂.It is this double connection that makes the joint have good mechanical properties.With the increase of riveting load,the tensile force and shear force of the joint increase first and then decrease.When the riveting pressure is 24k N,the maximum tensile strength and shear resistance of the joint are 3.87k N and 6.19k N.When the current of spot welding is 16k A and the time of spot welding is 20 cycles,the maximum tensile force and shear force of the joint are 1.34k N and 4.12k N.When the current of spot welding is 6k A and the time of spot welding is 400ms,the maximum tensile force and shear force of the joint are 4.48k N and 7.72k N.When the aluminum alloy/low carbon steel is welded by the composite connection method,the properties of the joint are improved significantly.The performance of RRW joint is better than that of RSW and SPR joint,The tensile strength of RRW joint is 15.7%higher than that of SPR joint,and the shear strength is 24.7%.Compared with RSW joint,the tensile strength and shear strength of RRW joint are increased by about 234%and87.3%respectively.