Studies on electrical discharge machining of AA7075 hybrid composites

Abstract

In this research work, an attempt was made to reinforce an aerospace aluminium alloy AA7075, through liquid stir casting technique. Boron Carbide (B4C) and Silicon Carbide (SiC) particulates of average particle size 5µm was selected as the reinforcement. Particles were preheated to the temperature of 2500C to remove the moisture content in it and K2TiF6 salt was added as the flux to improve the wettability of the composites. The mixture was stirred at the speed of 1000rpm for 10mins and poured into the preheated mould made of die steel. The same procedure was repeated for producing the composites of varying weight percentage and uniform distribution of reinforced materials over the composites were analyzed through Scanning Electron Microscope (SEM) with Energy Dispersive X-ray Spectroscopy (EDS) mapping. The void fraction was computed by comparing theoretical and experimental density and it was found that it lies well below the prescribed limit. Die sink electric discharge machining of the newly fabricated aluminium hybrid composites were conducted by varying current, pulse on time, powder concentration and %reinforcement in used engine oil dielectric medium with an objective of attaining wealth from waste. The experimental runs were designed using Taguchi orthogonal array. The Material Removal Rate (MRR), Tool Wear Rate (TWR), Machined Surface Hardness (MSH) and Surface Roughness (Ra) were recorded as responses. Silicon Carbide (SiC), Boron Carbide (B4C) and Aluminium Oxide (Al2O3) are the distinct foreign particles incorporated in the dielectric fluid to enhance the machining characteristics. The surface topography was studied utilizing SEM. newline