Finite element simulation of deformation and heat transfer during friction stir processing of as-cast AZ91 magnesium alloy

Abstract

Friction stir processing of as-cast AZ91 magnesium alloy was simulated by a thermomechanical model using DEFORM 3D finite element commercial package V.11. The model accuracy was verified by comparing predicted temperature history with the experiments, which showed an excellent agreement. The model was developed to calculate the effect of pin shape on different aspects of the process. The tracking of several material points was performed at different intervals of the workpiece's thickness, showing that the conical pin prevents points from accumulating the workpiece's top surface at the advancing side, while the points accumulation occurs by the cylindrical pin. The conical pin increases the material displacement, causing more significant effective strain and a greater increase in the workpiece's temperature than the cylindrical pin. Although the contribution of friction and deformation to the heat generation in the retreating side and the advancing side is not the same, their contribution ratio is such that it leads to the symmetrical distribution of temperature. It was found that pin shape affects the deformation and friction contribution on heat generation at both sides of the tool in the workpiece. For this reason, in the case of the cylindrical pin, the temperature at the retreating side was obtained slightly higher than that at the advancing side, while for the conical pin, it was just the opposite. Moreover, the development of vertical, longitudinal, and lateral tool forces was evaluated in detail by the developed model for conical and cylindrical pins during the plunging and traversing (welding) stages.