Surface Physical Characteristics Of Aeronautical Aluminum Alloy After Milling And Its Corrosion Resistance

Aluminum alloy is widely used as structural parts in aircrafts for its excellent comprehensive properties. During cutting processes, new physical characteristics appear in machined surface, such as the residual stresses, micro cracks, etc, which will affect the corrosion resistance of structural parts in the service environment. Therefore, it is important to the milled surface physical characteristics both in theory and experiments.Firstly, end milling and side milling experiments were conducted with different cutting parameters. Surface residual stress distributions induced in milling was measured with X-ray diffraction technique in different directions. The influence of cutting speed, feed rate on residual stresses was analyzed. The results show that in end milling, mainly compressive residual stresses were generated in surface of workpiece. The variation of cutting speed affect slightly on the value of residual stresses. When feed rate is between2500～2600mm/min, a peak of compressive residual stresses is obtained. In side milling, residual stress status transmit from compressive stress to tensile stress with the increase of cutting speed, while feed rate has lightly effect. The main explanation of such phenomenon is that, the "burnishing effect" holds a leading post in the end milling process, coMPared with the "tensile effect". In side milling, the effect of thermal loading performs increasingly significant as cutting speed increase.Secondly, the milled surface damage was investigated with optical microscope and scanning electron microscope. In end milling, the level of cutting adhesive phenomena and cracks increased with increase of cutting speed. In side milling, few cracks can be observed. Based on above observation, the mechanism of crack initialization was analyzed. From the view of microstructure, milling parameters affect slightly on surface metallographic structure, because cutting temperature is lower than phase transition temperature. Thirdly, corrosion resistances of milled surface were evaluated in salt mist experiment and electrochemistry test. The results show that, uniform corrosion occurred at first in the surface and turn to pitting corrosion later. In the salt mist experiment, the influence of cutting style and parameter is not evident. In electrochemistry test, corrosion potential of end milling surface was general lower than that by side milling. Relative larger negative corrosion potential was achieved at the condition of high cutting speed and feed rate, that is, high cutting speed and feed rate do harm to corrosion resistance.Finally, C-type ring experiments were conducted to reveal the effect of stress on the surface corrosion resistance performance of aluminum alloys. In the compressive stress conditions, the corrosion resistance change gradient is relatively flat. The simulation of stress field, the residual stress generated by different milling parameters and their corrosion resistance prosperities were consistent, that is, low cutting and feeding speed is easy to generate compressive stress, thereby enhancing the corrosion resistance.This paper is supported by National Natural Science Foundation of China (grant number51175306) and Natural Science Foundation of Shandong Province (grant number ZR2010EQ041).