Understanding the material flow pattern in the hot extrusion of aluminium alloys is useful for a better control of the process. The material flow pattern is greatly affected by the friction between the tool and billet interface. In this communication, an inverse analysis method is firstly adopted to match the calculated extrusion force with the measured force by treating the friction law and the friction coefficient as free parameters. Three widely accepted friction laws are investigated: Tresca friction, Coulomb friction and viscoplastic friction. The use of Tresca friction is shown to yield more accurate results and explanations than the other models. The influence of the constitutive laws on the material flow pattern is emphasized. It is found-that the use of the clasto-plastic model gives a much better prediction than the use of the visco-plastic model. It is also found that the quasi-static deformation is not fully established until a short time after the peak load has occurred.