Effects of electro-discharge machining process on ultra-fined grain copper

Copper alloys, due to their proper ductility, proper thermal conductivity and low electrical resistivity, are very applicable in various industries. Ultra-fined grain materials undergo severe plastic deformation processes, in which the microstructure of the material is drastically changed as well as enhancing the level of the energy stored in the grain boundaries. These processes such as equal channel angular pressing, considerably change the material's properties including strength and hardness. Although some specifications of the ultra-fined grain copper obtained via equal channel angular pressing process is improved, the high level of stored energy makes it thermodynamically unstable and susceptible to microstructural changes during secondary thermo-mechanical processes. In the present paper, the effects of the electro-discharge machining on the ultra-fined grain copper alloy has been studied, and the results have been compared with coarse grain copper. The thickness of the recast layer and heat affected zone of the electro-discharge machined samples was investigated as well as the cracks density and the micro-hardness through optical microscopy, scanning electron microscopy and micro-hardness tester. The results show that the ultra-fined grain samples have thicker recast layer and heat affected zone and higher cracks density, comparing to coarse grain samples. However, the micro-hardness of the electro-discharge machined surface of both groups is approximately identical.