Mathematical modeling and optimization of friction stir welding process parameters for armor-grade aluminium alloy

The properties of lightweight, high strength, better corrosion resistance, high electrical conductivity, etc. made aluminium alloys one of the favorite materials for industrial purposes. The aerospace, marine, automobile and railway industries use these alloys very commonly. But the lower melting temperature, high thermal conductivity and unusual grain growth make it difficult to weld material. So solid-state welding process named friction stir welding (FSW) is used for higher welding joint efficiencies for these alloys. The performance of FSWed joints directly depends upon the levels of input parameters used for the welding process. The present study is an attempt to optimize the process parameters for FSW of armor-grade aluminium alloys AA5083. Tool design parameters (Shoulder Diameter, Shoulder Flatness and Pin Profile) along with machine parameters (welding speed) are used for variation to analyze their effects on the quality of the joints. The experiments were designed by the response surface methodology and the significance of these parameters was analyzed by ANOVA. Where all four considered parameters were found significantly affect the responses i.e. ultimate tensile strength, yield tensile strength and elongation. An optimized set of parameters was revealed by Desirability a multi-objective optimization approach. “Desirability” suggests 18.5 mm shoulder diameter, 2.0 mm shoulder flatness, square pin profile and 48.9 mm/min welding speed as a set of optimized parameters. The 77.9% joint efficiency can be achieved at the mentioned optimized parameters. To analyze the relationships between variation in responses with the variation in process parameters and the microstructure of the welded joints the microstructure analysis has been conducted. The microstructural analysis revealed that high heat input causes an unwanted grain growth in the heat-affected zone and the lower heat input causes an insufficient temperature for the softening of the material in the nugget zone.