Surface morphology and microcrack formation for 7050-T7451 aluminum alloy in high speed milling

The study in this paper focuses on surface morphology and crack formation of 7050-T7451 aluminum alloy in high-speed milling, from 3000 to 5000 m/min. The surface roughness of machined workpiece was investigated with optical profiler; minimum R (a) and R (q) value were obtained at the cutting speed of 5000 m/min. Defects such as smeared material, metal debris, and feed marks on workpiece surface were observed with scanning electron microscope. One kind of edge-oxidized feed mark was found on surface. Width of it was measured and two hypotheses were introduced to interpret this phenomenon. Based on the hypothesis, the workpiece surface was determined to be formed at cut-off process. Two kinds of microcracks were observed on Al7Cu2Fe and Mg2Si phase. Those cracks showed different orientations, and this was helpful for interpreting the formation of microcracks in high-speed machining. The heat imposed to surface was connected with cracks on different phases. The results provided a complete view of surface morphology generation and microcrack-formation mechanism in high-speed cutting process. The two aspects of this research were helpful for controlling the integrity of surface and prolong service life of workpiece.