Parametric, Mechanical and Metallurgical Characterization of Dissimilar Friction Stir Welded AA2014-AA2219

Abstract

In this study, Friction stir welding (FSW) is carried out on dissimilar aluminium alloys AA2219 and AA2014 using L16 orthogonal array based on Taguchi Mixed Factorial Design (TMFD) under four process variables: traverse speed, rotational speed, tilt angle and tool profile and the effects of FSW parameters on single and multiple responses (Tensile Strength, Yield Strength and Elongation) are analyzed using Response Surface Methodology (RSM) coupled with Augmented Epsilon Constraint Method (AUGMECON). Highest tensile strength and superior percentage elongation are attained at the parameter setting- 1400rpm Rotational Speed, 300mm/min Welding Speed, Tapered Threaded Pin tool profile and 3º Tilt Angle. Maximum yield strength is achieved under the parameter setting 800rpm Rotational Speed, 300mm/min Welding Speed, Tapered Threaded Pin tool and 3º Tilt Angle. A set of 20 optimal Pareto solutions providing a trade-off between the responses was generated. The rotation speed and tool tilt angle determined the trade-off between the extreme Pareto solutions. The microstructural analysis indicates finer grains in the bottom half compared to the top, with improved bonding between AA2219 and AA2014 in the nugget zone. Micro-hardness analysis reveals hardness similar to the parent material in the retreating side and poor hardness in the advancing side, where failures occur. SEM fractography shows a mixed ductile brittle fracture with elongated grains and uniform dispersion of intermetallics. Optimized parameters result in a disk-like planar morphology with a copper-rich GP zone, leading to improved strength and hardness. EDS mapping confirms presence of uniformly dispersed copper particles in the crater region that acts as a binder and resists void formation. XRD analysis further confirms the presence of Al2Cu intermetallic phases.