Enhancing the properties of friction stir welded stainless steel joints via multi-criteria optimization

An attempt is made to establish empirical relationships to predict the properties of friction stir welded stainless steel joints. The process parameters namely, rotational speed, welding speed and shoulder diameter and the properties such as tensile strength, notch tensile strength, impact toughness and degree of sensitization are considered. The investigated properties are correlated with the macrostructure and microstructural characteristics of different zones of FSW joints to understand the influence of process parameters. Multi-criteria optimization is used to obtain optimum welding conditions that can yield enhanced properties of FSW joints. The optimized results indicated that, the properties can be enhanced with the use of rotational speed of 441 rpm, welding speed of 118 mm/min, and shoulder diameter of 17.5 mm. This is mainly due to very fine stir zone grain structure in the order of 5.5 μm and the presence of thin layer of banded structure at the advancing side of fabricated joints under optimum parameters.