Rationalizing Tool and Machine Parameters for Micro Friction Stir Welding of Dissimilar Aluminium Alloys AA2024 & AA6061 Using RSM

Abstract

Friction Stir Welding is a welding technique invented in last part of twentieth century in which a high speed rotating tool traverses through the two base materials to be welded in solid state below melting temperature. Heat input for FSW is considerably less than conventional welding techniques like TIG, MIG. Micro FSW was performed in this research work on Aluminium alloys AA 6061-T6 and AA 2024-T3 with thickness of 1mm. Process parameters and tool end features were varied to optimize the mechanical and microstructure properties. Three types of tool with varying tool shoulder end features was used for the process and results analyzed. RSM was used for Design of Experiments and Design Expert-12 was utilized to apply RSM and evaluate results. Microstructural analysis was carried out to analyze the microstructure. Four distinct zones were formed, namely base material, stir zone, heat affected zone & thermo-mechanically affected zone. UTS was found through tensile test while micro-hardness test was carried out to find hardness of different zones formed. Results of the experiments show that traverse rate was the most influential parameter while tool end features improved the weld strength as well as the microstructure of the welded samples. Optimal parameters found were tool speed 1750 rpm, traverse rate 40 mm/min and tool with most number of holes at its shoulder base. The results highlight the fact that optimized heat input is the key to successful welds. Insufficient heat input reduces strength and lead to improper material mixing while heat input more than required causes damage to base material and leads to defects like weld flash etc.