Optimizing the bake hardening behavior of Al7075 using response surface methodology

In the present work, the bake hardening behavior of Al7075 was investigated using the response surface methodology (RSM). The optimal conditions to attain the maximum bake hardening (BH) amounts and maximum yield stress (FYS) after baking were predicted by RSM. The combination of central composite design (CCD) and response surface methodology (RSM) was also used to predict the maximum bake hardenability of Al7075. This was done by recognizing the most important baking parameters, the significance of baking parameters, and the importance of interactions among process parameters. The bake hardening tests were carried out using the values predicted by the model. The results predicted by the developed model are in a very good agreement with the measured ones. The contour plots are also obtained in order to determine the significance of variables interaction. The correlation coefficient (R2) of the regression models, regarding the bake hardening and final yield stress (FYS), was about 0.99 and 0.976, respectively which confirming the excellent accuracy of the model. The results also showed that the optimum conditions to attain the maximum bake hardenability and final yield stress are met when baking is carried out at 200 °C for 23 min with the pre-straining of 6%. Under these conditions, the BH and FYS amount predicted by the developed model was about 92 and 579 MPa, respectively, whereas the measured BH and FYS was about 90 and 570 MPa, indicating a very good agreement between the predicted and measured values.