Analysis of solid-phase temperature regulation mechanism of friction stir welding by simulation comparison between analytical heat source and ALE methods

In view of the inherent property of friction stir welding, which maintains the solid phase temperature range independently of the process conditions, an analytical heat source model and mechanical thermal coupling model were used to simulate the interface friction heat generation process between the stirring head and aluminum welds, respectively. It aims to analyze the influence of welding thermal physical quantities and process parameters on the thermal cycle curve and reveal the solid phase temperature regulation mechanism inherent in friction stir welding behavior. Therefore, the simulation model of a Gaussian surface and double ellipsoid complex moving heat source and an arbitrary Lagrange-Eulerian (ALE) adaptive mesh was established according to the equivalent thermal load of the spot welding process. The transient temperature field was simulated according to the welding thermal boundary conditions, and the temperature distribution measured at multiple points using thermocouples was utilized to verify the validity of the field prediction. The results show that the numerical simulation accuracy of the ALE method is 6.3% higher than that of the analytical method. The central peak temperature fluctuates from 477 ℃ to 589 ℃ due to the parameter limit changes of the spindle speed and shoulder size, and the pre-peak temperature rise rate decreases continuously. This is mainly due to the rheological yield stress of the alloy, which is highly negatively related to the temperature change. The softening behavior at high temperature reduces the deformation resistance and interfacial friction coefficient of the material, thus limiting the heat production rate to rise through negative feedback regulation.