Improving surface integrity of electrical discharge machined ultra-fined grain Al-2017 by applying RC-type generator

Abstract

Ultra-fined grain materials are thermodynamically unstable and they are prone to microstructural changes by small external energy. Electrical discharge machining is a thermo-electrical process that erodes the surface of the workpiece by melting and vaporizing the surface layers. During electrical discharge machining of the ultra-fined grain materials, recast layer, and heat-affected zone are formed on the surface layers of the workpiece, having several adverse effects, such as microstructural changes, grains growth, alternation of hardness, micro-cracks and changing the compositions. These effects result in losing the unique properties of the ultra-fined grain materials. Using an RC-type generator in the electrical discharge machining process, decreases the discharge duration, and therefore, instead of melting and vaporization, electrostatic forces remove the material properly. Eventually, the thickness of the recast layer and the heat-affected zone is decreased considerably. In this study, the effects of using an RC-type generator in the electrical discharge machining process on the ultra-fined grain aluminum samples are investigated and the results in roughing mode and finishing mode are compared with normal electrical discharge machining. The results show that by applying an RC-type generator, the thickness of the recast layer and heat-affected zone, the cracks density, the micro-hardness changes, and the surface roughness are tangibly decreased, and the surface quality is improved