| The flight process,ice will appear on the surface of the aircraft due to the supercooled cloud region,which has a great impact on the normal flight of the aircraft.At present,the main anti/deicing methods used in aircraft are aerothermal deicing,electrothermal deicing and mechanical vibration deicing.However,these methods not only increase the weight of the aircraft itself,but also complicate the design of the aircraft and increases the manufacturing cost,and ultimately leads to the aircraft can not meet the lightweight and high efficiency fuel requirements of modeen new aircraft.Based on the functional modification technology of material surface,according to the icing condition of aircraft during flight,three conditions are obtained:(1)the surface has high hydrophobic performance;(2)the surface ice delay performance is better;(3)the ice layer adhesion is lower.According to the above three conditions,the special 2A12 cemented aluminum alloy materials for aviation are selected for this study.Different microstructure is constructed on the surface of the alloy,which results in different wetting interface,delay performance of surface water icing and adhesion of ice layer on its surface.The main conclusions of this thesis are presented as follows:(1)Different surface microstructures were constructed by shot peening,hydrothermal treatment and acid etching treatment on the surface of 2A12 aluminum alloy,then fluorinated by FAS-17,the surface wetting angle was all improved.However,combined the specific shot peening(with 0.2mm diameter and 0.4MPa pressure)with hydrothermal treatment(at 95℃ for 5 minutes)can obtain superhydrophobic surface.The maximum wetting angle of the microstructure surface can reach 152.81°,which is 40°higher than that of the substrate.(2)The sample at room temperature was placed at-5℃ environment Then the author observes the freezing time of the droplet on the surface of the sample(the freezing start time is the moment when the sample is put into the confined space to the droplet completely freezing).It is found that under the same conditions,when the shot peening process with 0.2 mm diameter and 0.4 MPa pressure was combined with hydrothermial treatment at 95℃ for 5 minutes,the freezing time of microstructure surface takes the longest,fast 94 min 45.69 s,while the matrix only needs 3 min 36.9 s.By changing the surface morphology,the freezing time of the droplet in the constant temperature evironment is greatly prolonged.The result shows that the extension of icing-time increases with the expension of wetting angle;(3)After the sample was kept at 0℃ for a period of time,and then drop to-15℃.The freezing time of the droplet was observed under the condition of variable temperature.It can be found that,the ice growth rate of the substrate under this condition is 3.5μm/s after shot peening combined with hydrothermal treatment when the surface freezes(micro-nano structure).Under the condition of variable temperature,the rate of ice growth rate on the surface of micro-nano structure is the smallest.(4)In the environment of-15℃,freezing an icicle on the micro surface after different treatment processes(4h),the ice adhesion force on the untreated substrate surface is 41.1N,but the ice adhesion force on the surface with the largest surface wetting angle(152.81°)is only 13.1N.The result shows that the adhesion of ice layer decreases with the expansion of wetting angle.(5)According to the Gibbs free energy theory,a mathematical model is established.The results show that with the increase of wetting angle,the critical nucleation work in the icing process increases,the steady-state nucleation rate and nucleation rate decrease,and the movement rate of solidification interface slows down. |
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