FAILURE ANALYSIS AND PROCESS PARAMETER INFLUENCE ON MECHANICAL AND METALLURGICAL BEHAVIOR OF FRICTION STIR WELDED AA2219-T87 JOINTS

Abstract

Friction Stir Welding (FSW) was carried out on AA2219-T87 alloy plates with various process parameters. Multiparametric optimization was carried out using Taguchi-Grey Relational Analysis (T-GRA) to determine the most influencing factors on the responses like Ultimate Tensile Strength (UTS) and Yield strength (YS) of AA2219-T87 butt joints. In this work, defect-free welding parameters were selected from the wide range of trial and L18 Taguchi Mixed factorial design was fit to further optimize the parameters by T-GRA techniques. Parameters like tool rotational speed, welding speed and tool profile were varied, tool tilt angle and thrust force were kept constant. The macro and microstructures were examined to correlate with tensile, yield and hardness property to analyze the predominant factor that would improve joint efficiency. Finer grains were found in nuggets when compared to other zones and the grain size was found to decrease from top to bottom due to centrifugal action. Scanning Electron Microscopy (SEM) studies were carried out on fracture tensile specimen to determine the mode of fracture in the different regions. EDS elemental mapping was done in fracture region of the tensile specimen and it was encountered that crack initiation is along the copper-enriched region. Tensile strength was reported to be 73% of the parent metal and optimized parameter combination was observed for tool with taper threaded pin profile that enhances metal flow.