Investigations on deformation and fracture behavior of workpiece material during high speed machining of 7050-T7451 aluminum alloy

Abstract

Research on material deformation and fracture behavior under large strain rate has great practical significance. The dynamic property of 7050-T7451 aluminum alloy under the strain rate ranging from 1.2×105s−1 to 2.0×106s−1 is investigated with high speed orthogonal cutting experiments. The microstructures on fracture surface of serrated and fragmented chips are observed and analyzed. The results indicate that the workpiece material in the primary deformation zone undergoes severe plastic deformation causing the formation of ductile fracture and dimples within the cutting speed ranging from 1000m/min to 5000m/min (i.e. the strain rate is between 1.2×105s−1 and 1.4×106s−1), during which the serrated chips are produced. The fragmented chips are generated due to brittle fracture during the cutting speed ranging from 5000m/min to 7000m/min (i.e. the strain rate ranges from 1.4×106s−1 to 2×106s−1). The Energy Dispersive X-ray Analysis (EDAX) results at different positions in chips show that the content of oxygen element into chip has positive relationship with the cutting temperature raised due to material deformation. Brittle tearing and fragments adhesion can be seen on the finished surface produced under ultra high cutting speed because the fragmented chips are formatted in the mode of brittle fracture. The research shows that material deformation and fracture behavior changes greatly under ultra large strain rate, which then affects the material removal mechanism and finished surface quality during machining process.