Surface Integrity And Corrosion Resistance In High Speed Milling Aluminum Alloy 7050-T7451

High speed cutting is a technology of high cutting speed, feed rate, machining accuracy. It meets the requirements of workpiece quality, manufacturing efficiency, production cost and environmental impact in modern manufacturing industry. It has been studied extensively by many researchers with different materials. Aluminum alloy is one of those materials applied with high-speed cutting technology. It is widely used in manufacturing aircraft, automobile, ship and chemical industry, because of its favorable property of high strength, light weight, low cost and feasible processability characteristics. Aluminum alloy milled at the cutting speed lower than 3000m/min have been investigated by many researchers, while the surface quality at higher cutting speed was little-referenced. Based on the facts above, the surface quality and corrosion resistance of milled aluminum alloy 7050-T7451 at the cutting speed of 3000-5000 m/min is investigated in both theoretical and experimental ways in this paper. The microstructure change induced by cutting process is introduced to interpret the phenomenonn generated. The results provide theoretical basis and experimental validation for application of aluminum alloy 7050-T4751 milled at 3000-5000m/min cutting speed.Compared with the uncut surface,the second phase precipitation phenomenon on 7050-T7451 workpiece surface at 3000-5000m/min cutting speed are analyzed. The deformation statics in machining and mechanism of chip formation was studied.The results show that phase transition exists in the high speed cutting aluminum alloy 7050-T7451. According to the results, strain and strain rate of the machining process increase with cutting speed. The strain rate reaches 107s-1 at the cutting speed of 5000m/min.The cutting force and cutting temperature under different cutting parameters was studied to analysis the microstructure change of milled surface. The experimental results show that the main cutting force and average temperature of shear plane increased with the cutting speed before the cutting speed reach 4500m/min. The results of 5000 m/min is also greater than those at the cutting speed of 3000 m/min.Based on the microstructure change and deformation mechanism investigated above, study of 7050-T7451 workpiece surface quality was carried out. the change of workpiece surface roughness and surface morphology was analyzed under different cutting parameters. The formation mechanism of micro defects, and the layer distribution of residual stress and work hardening was investigeted. Results show that the surface roughness of workpiece increase with the cutting speed, with an inflection point appeared at the cutting speed of 4250 m/min. Surface roughness values decrease to minimum at 5000 m/min, but the surface texture on workpiece is more apparent compraed with other results of speed. The residual compressive stress on surface increases with the cutting speed when it is parallel to the feed direction, while the surface residual compressive stress perpendicular to feed direction changes little. In the feed direction, the peak value of residual compressive stress in workpiece surface layer decreases with the increase of cutting speed, while peak value of residual compressive stress value perpendicular to feed direction changes little. The depth of working-hardening peak value increases with cutting speed initially, and then decreases at the cutting speed of 4000m/min.In the study of micro defects, two kinds of defects generated in the cutting process was analyzed:white bands and micro-cracks in different phases. Three layers were divided by analyzing the surface layer. They are cutting edge extrusion deformation layer, mechanical stress deformation layer and process deformation layer. The depth of each layer increased with the cutting speed.In order to evaluate the quality of the workpiece surface, the neutral salt-spray corrosion experiment was carried out to research the surface corrosion resistance. Analyzed with the salt fog corrosion mechanism on aluminum alloy 7050-T7451 workpiece surface, surface corrosion characteristics of different phases in salt fog corrosion was determined, and the phases was investigated with micro defects to find it whether worked in salt-spray corrosion experiment. The experiment was also taken with different parameters. Compared with the surface of 1500m/min cutting speed, the workpiece surface corrosion resistance of high speed cutting is improved.Based on the results of the study, the technology of milling 7050-T7451 aluminum alloy at 3000-5000m/min can be applied with appropriate cutting parameters.