Fabrication and Optimization of Process Parameters for Friction Stir Welding AA7075+10%wt.SiC Composite by Taugchi Method

Abstract

Aluminium alloy 7075 as matrix and silicon carbide (SiC) as reinforcement has been widely used in aircrafts and space industries because of high strength to weight ratio. Fusion welding of this Aluminium Metal Matrix Composite (MMC) will lead to many problems such as porosity, micro-fissuring and hot cracking. However, friction stir welding (FSW) can be used to weld this MMC without above mentioned defects. Objective of this investigation are fabrication of AA7075-10%wt.SiC Aluminium Metal Matrix Composite and determine the optimal process parameters of Friction Stir Welded AA7075-10%wt.SiC Composites. Composites were prepared   by the mechanical stir casting process. Experiments were performed with four process parameters such as tool rotational speed, weld speed, axial force and tool geometry considering three levels of each. The quality characteristics considered are tensile strength (TS) and percentage of tensile elongation (TE). The Welding experiments were conducted using L₂₇ orthogonal array. A combination of orthogonal array and design of experiments was used to give best possible welding parameters that give optimal T.S and P.E results. Tensile strength of joints were evaluated and correlated with percentage of tensile elongation. The fabricated welded joints using rotational speed of 1500rpm, welding speed (1.3mm/sec), axial force(7k/n) of and tool geometry(Square) gives best possible results. Experimental result reveals that the tool rotation speed, welding speed and axial force  are the significant process parameters affecting the welding performance. The  predicted optimal value of percentage elongation are 4.34. The confirmation tests also have been done for verifying the results. The impact of responses were also be investigated by Scanning Electron Microscopic (SEM) analysis.