Research On Riveting-laser Arc Welding Hybrid Joining Of Aluminum Alloy And High Strength Steel

As an important part of energy saving and emission reduction,automobile lightweight is an important issue for the development of automobile industry.Introducing lightweight materials such as aluminum alloys and high-strength steels on the body can significantly reduce the weight of vehicles.However,the introduction of hybrid body structures inevitably involves the joining of aluminum/steel dissimilar metals.Due to the huge difference in thermophysical properties between aluminum alloy and high-strength steel,it is difficult to achieve an effective joining of them using traditional welding methods,which limits the popularization and application of aluminum/steel hybrid structure components.Aiming at the welding problem of Al alloy and steel,this paper proposed a“riveting-welding hybrid joining”technology that combined laser-arc welding and riveting to join 6061 aluminum alloy and Q460 high-strength steel.Firstly,the lap joints that the aluminum alloy plates were placed on the steel plates were adopted,and then the lap welding experiments were carried out on plates which had been pre-joined by aluminum single-step rivets.Through the above experiments,the preliminary exploration of“riveting-welding hybrid joining”technology was realized.Then,the placement order of plates was changed.The lap joints that the steel plates were placed on aluminum alloy plates were adopted.On the basis of these,the steel single-step rivets were used to achieve the riveting-welding hybrid joining of aluminum alloy and high-strength steel.The mechanical properties and joining mechanism of the hybrid joint were studied.Finally,the structure of rivet was optimized,the multi-step rivets were used to joining Al alloy and high-strength steel,and the mechanism of the action of the multi-step rivet was explored.The results showed that the riveting-laser arc welding hybrid joining technology can successfully achieve the high-quality joining of 6061 aluminum alloy and Q460 high-strength steel.The addition of rivets can transform the joining of aluminum/steel dissimilar materials into the joining of homogeneous materials.The tensile shear load of Al/steel riveting-welding hybrid joints with aluminum rivets could reach 3.36kN,and the fracture mode was a shear fracture.The internal structures of hybrid joints which joined by steel rivets were investigated.The hybrid joint was composed of three loading bear parts under the actions of steel rivet and hybrid welding source,which were respectively the butt joint formed by steel plate and rivet,the Al-steel mixing area formed by steel plate,rivet and Al alloy plate,and the Al-Fe interface formed by rivet sidewalls and Al alloy plate sidewalls.Under the optimal parameters,the joint with single-step rivet had a maximum tensile shear load of 5.3kN and the fracture mode appeared a pull-out fracture;the joint with multi-step rivet had a maximum tensile shear load of 6.2kN and the fracture mode was a pull-out fracture.There was a mechanical interlock between rivet and aluminum alloy plate.Increasing the diameter difference between the rivet cap and the rivet leg could enhance this mechanical interlocking effect.The multi-step structure could change the position of heat source,reduce the melting amount of aluminum alloy,control the type and amount of intermetallic compounds in the hybrid joint,and improve the joining quality of Al-steel mixing area.In the joint with single-step rivet,the intermetallic compounds were composed of FeAl,Fe₂Al₅ and FeAl₃.In the joint with multi-step rivet,the intermetallic compounds were composed of FeAl and Fe₃Al,the transition from Al-rich phase to Fe-rich phase was achieved.