Statistical Modeling and Optimization of Two-Layer Aluminum–Copper Pipe Fabrication by Friction Stir Welding

In this research, the process and geometric parameters in the fabrication of copper–aluminum double-layer pipe using friction stir welding have been optimized by Box–Behnken design of response surface methodology. This research aims to optimize the rotational and traverse speed of the tool as well as the diameter and thickness of the pipe to achieve the maximum tensile strength of the double-layer copper–aluminum pipe. In order to establish the relationship between input variables and joint strength, a quadratic model was used. The coefficients for the quadratic terms for the tool rotation speed and pipe thickness were considered to be very important, which shows that these parameters have a much greater effect on the joint strength. However, the effect of traverse speed and pipe diameter on joint strength is negligible in terms of linear and nonlinear effects. The composite desirability of the parameters is D = 0.9168. This desirability in the parameters of rotational speed, traverse speed, pipe diameter, and pipe thickness, which are 660 rpm, 80 mm/min, 24 mm, and 1.4 mm, respectively, has shown the joint strength of 341.86 MPa. Also, the average tensile strength measured from the experiments is 347.33 MPa, which is very close to the models’ estimated value. The R2 value after modifying the model indicates the 88% predictability of the model.