Friction stir welding (FSW) is a solid-state welding process, which has a significant
role in solid-state welding processes for nonferrous alloys. Conventional arc welding processes
for aluminum alloys such as metal inert gas (MIG) and tungsten inert gas (TIG) are replaced by
FSW. The effect of FSW parameters such as rotational and traverse speeds, tool geometry,
plunge depth, tilt angle, etc., on weld quality were considered in several optimization studies.
Hence, the effect of fixture position is included in this study. Multi-criteria decision-making
(MDCM) techniques such as grey relational analysis (GRA) were used to determine the
optimal condition among experimental runs designed by response surface methodology (RSM).
The Taguchi method was widely applied with MCDM techniques. Therefore, the experiments
were conducted according to response surface methodology. Input parameters were (14, 16 and
18) mm for shoulder diameter (SD), (0.0, 0.2 and 0.4) mm for plunge depth (PD), and (30, 60
and 90) mm for fixture position (FP), which is the distance between fixture bolts used to fix the
welded plate. The results obtained by GRA were similar to the ANOVA optimizer, and the
optimum process conditions are shoulder diameter of 14 mm, plunge depth of 0.2 mm, and
fixture position of 60 mm.