Continuous and ultra-fine grained chip production with large strain machining

• We applied large strain machining on aluminum 6061-O samples.
• Temperature effect on microstructure evolution was considered.
• Inverse relation between hardness and strain versus cutting velocity was observed.
• Contact length parameter significantly influences the final microstructure.
• Production of continuous ultra-fine grain chip even in high velocities.

In this study, orthogonal cutting technique as a severe plastic deformation (SPD) method for producing chips with an ultra-fine grained microstructure and fair mechanical properties is investigated; further, it has been suggested that by controlling the cutting velocity and contact length between tool and material, it is possible to produce a severely deformed and continuous chip with unrestored microstructure even at high cutting velocities. Solution treated Al-6061 samples in plane strain condition were severely deformed through applying various cutting velocities (from 50 to 2230 mm/s) for three different rake angles (−5°, −10° and −20°) in fixed cutting parameters. Chip thickness, contact length, shear strain, and Vickers microhardness variations were examined for different samples and chip formation mechanism was discussed for different processing conditions. In addition, the microstructure of especial produced chips was studied using transmission electron microscopy (TEM). The results showed that during the dominance of seizure mechanism at the contact surface, microhardness and shear strain (as well as contact length) have inverse dependency upon the variation of the cutting velocity. The results are discussed by considering the heat-time effect contribution in the final microstructure and mechanical properties.