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By using the rigid-visco-plasticity finite element method,the welding process of aluminum porthole die extrusion to form a tube was simulated based on Deform-3D software.The welding chamber height(H),back dimension of die leg(D),process velocity and initial billet temperature were used in FE simulations so as to determine the conditions in which better longitudinal welding quality can be obtained.According to K criterion,the local welding parameters such as welding pressure,effective stress and welding path length on the welding plane are linked to longitudinal welds quality.Simulation ts out that pressure-to-effective stress ratio(p/σ)and welding path length(L)are the key factors affecting the welding quality.Higher welding chamber best and sharper die leg give better welding quality.When H=10 mm and D=0.4 mm,the longitudinal welds have the best quality.Higher process velocity decreases welds quality.The proper velocity is 10 mm/s for this simulation.In a certain range,higher temperature is beneficial to the longitudinal welds.It is found that both 450 and 465℃ can satisfy the requirements of the longitudinal welds.