Optimization and numerical analysis of friction stir welding parameters of AA7075-T651 and AA 1200-H19 using tapered tool

The response surface technique approach was used in this study to determine the best processing parameters for the three responses. For the friction stir welded dissimilar AA7075-T651 and AA1200- H19 aluminium alloys, the rotating and the welding speed, as well as the tool tilt angle, were used as input variables. Mechanical tests were performed on the weldment and the average hardness ranges from 64.26 to 99.72 HV, while the Ultimate Tensile Strength (UTS) ranges from 111.51 to 152.48 MPa. The impact energy was found to varry between 2.9 and 21.4 J. The results from the Signal to Noise (S/N) ratio revealed optimal welding parameters for hardness, UTS and impact energy as 1500 rpm speed of tool rotation, 30 mm/min transverse speed, and 2° tool tilt angle, while for UTS, it is a rotational speed of 1500 rpm, 90 mm/min transverse speed, tool tilt angle of 2° and finally for impact energy as 1500 rpm rotational speed, 30 mm/min transverse speed and 2° tool tilt angle. The results from the grey relational analysis gave optimal process parameters of 1500 rpm rotational speed, 60 mm/min transverse speed and 2° tool tilt angle. The results from the ANOVA revealed that tool rotational speed has the highest significant contribution of 41.79% to the hardness of the weldment followed by the rotational speed (34.46%) and then the transverse speed (19.44%). For UTS, tool rotational speed has the highest significant contribution (35.03%) followed by tool tilt angle (33.72%) and then transverse speed (30. 23%). Also, tool rotational speed has the highest significant effect on the impact energy of the weldment (37.45%) followed by transverse speed (32.00%) and then a tool tilt angle of (27.02%). Empirical models were developed using the Minitab 17 software with the central composite design (CCD) from which the UTS of 150.99 MPa, hardness of 99.102 HV and impact energy of 20.039 were obtained and were found to be close to the experimental values obtained. This study is significant as it gives insight into the optimum processing parameters of joining AA7075-T651 and AA1200- H19 aluminium alloys using the FSW and can be recommended for producing high quality welds with good joint integrity.