Microstructural characterization of Al-7075-T651 chips and work pieces produced by high-speed machining

High-speed orthogonal machining produced a series of Al-7075-T651 chips and work pieces for microstructural charcterization. The orthogonal machining conditions included two rake angles, three cuttings speeds, and a constant feed rate. The chips and work pieces were characterized using optical metallography, transmission electron microscopy (TEM), and microhardness measurements. TEM observations indicated growth of the η′ precipitates and showed recrystallized equiaxed grains within the shear bands of the chips. Microhardness profiles of the work pieces showed a decrease in hardness at the work surface. The thickness of this deformation layer increased with cutting speed. Microstructural characterizations were correlated with calculated temperature–time profiles to investigate possible mechanisms for the observed microstructure changes.