Flow behavior and formation of transverse welding joint of aluminum alloy during billet-to-billet extrusion process were investigated by the 3D finite element method.The results show that

the aluminum alloy exhibits heterogeneous rheo-forming behavior during extrusion process

and a gas gap is formed at the interface top of new billet and old billet.Meanwhile

a transverse welding joint can be observed at interface in role of high pressure and shearing deformation.Factors influencing quality of transverse welding joint were described.The simulated results reveal that the product length with transverse welding joint can be greatly shortened by adjusting length of cone surface of the flat cone die.