Surface and subsurface modifications of AA7075-T6 induced by dry and cryogenic high speed machining

The high speed machining process is considered as one of the manufacturing technologies more prone to increase the productivity. The increasing interest in this manufacturing process is also due to the good surface quality (e.g. low roughness) as well as the significant alteration of the subsurface (improved hardness and microstructure refinement) of the machined parts. This paper describes the metallurgical phenomena occurring during high speed turning performed under dry and cryogenic conditions on aluminium alloy AA7075 T6 and investigates their effects on the surface integrity. Two cutting parameters, namely cutting speed and feed rate, were varied to induce surface and subsurface changes, such as microstructure and surface topography variation as well as mechanical properties modifications. The surface integrity was analysed through optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray diffraction (XRD), surface roughness and micro-hardness measurements.