Robust Optimization of Both Dissolution Time and Heat Affected Zone Over the Friction Stir Welding Process Using SQP Technique

This works deals with the determination of the optimized parameters in friction stir welding (FSW) process; this through the determination of the optimal operating conditions (the welding velocity and power) necessary for welding a typical Aluminum alloy material AA2195-T8. A physical model based on the Lagrangian formulation considering a surfacic heat source that moves during the welding process, was applied. The used model predicts the evolution of the thermal field and the maximum temperature over time. Sequential quadratic programming (SQP) was used to solve the constrained multi-objectives optimization problem, in which the objective functions consist to minimize the dissolution time into heat affected zone (HAZ) and the length heat affected zone. In which, the simulated temperature profiles and the natural aging kinetics have been correlated to predict the hardness profiles in the FSW workpiece. The good agreement between the results of the two approaches would it possible to use the proposed numerical model to predict the thermal field and the maximum value of the temperature. The optimization process has demonstrated its robustness and the main results obtained are: the optimal parameters show a reduction of 13.44% in the temperature value at HAZ compared to the initial case, while a reduction of 46.5% in the dissolution time was recorded. The lower hardness zone in the optimal case retracted to the weld midline, the minimum hardness value at the thermal affected zone increases compared to the initial case.