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Xue J.,Nanjing University | Su P.,Shanghai Aerospace Equipment Manufacturer | Dong W.,Nanjing University | Jiang X.,Nanjing University | And 2 more authors.
Applied Surface Science | Year: 2015

In this study, a series of anodic aluminum oxide (AAO) ordered nanoporous matrix layers were prepared, and hydrophobic (perfluoroalkyltriethoxysilanes, PFO) and hydrophilic (3-Aminopropyltrimethoxysilane, APTS) materials were modified on these surfaces. The static contact angle of these specimens was in the range of 30-153°. By using the f values in the theory equation and comparing with the experiment value, the wetting state of the surface was determined. Under impact pressure, the wetting states of the porous surface with the hydrophobic PFO-modified material were more stable, and the contact angle on these surfaces under external pressure remains constant. However, the hydrophobicity of the surface modified with APTS was metastable, and the surface hydrophobicity decreased as the impact pressure increased. Under sufficient hydraulic pressure, the liquid would wet a rough structure, and the hydrophobic state would be lost and not automatically restored. In addition, the change in the wettability of the APTS-modified surface occurs spontaneously due to the immersion conditions. Finally, the critical pressure of the PFO-modified surfaces was investigated. Although the critical pressure of the surface is on the micrometer level, which is similar to the static energy barrier (ΔP), our experimental data are smaller and on the nanometer scale, which is discussed in this study. © 2015 Elsevier B.V. All rights reserved. Source

Yu X.,Chongqing University | Shen S.,Shanghai Aerospace Equipment Manufacturer | Jiang B.,Chongqing University | Jiang B.,Chongqing Academy of Science and Technology | And 5 more authors.
Applied Surface Science | Year: 2016

This paper studies the effect of the existing state of Y element on the high temperature oxidation resistance of magnesium alloys. Different levels of Al element were added into Mg-2.5Y alloy to obtain different existing state of Y. The oxidation rate of Mg-2.5Y-2.5Al alloy is the highest among Mg-2.5Y, Mg-2.5Y-2.5Al and Mg-2.5Y-4.2Al alloys at 500 °C. An effective and protective Y2O3/MgO composite oxide film was formed on the surface of Mg-2.5Y alloy after oxidized at 500 °C for 360 min. The results show that the dissolved Y element in the matrix was beneficial to improve the oxidation resistance of magnesium alloys. Once Y element transformed to the high temperature stable Al2Y compound, its ability in preventing oxidation would disappear. The formation of Al2Y compound severely deteriorated the oxidation resistance of Mg-2.5Y alloy. In addition, the dissolved Al can also cause the rise of oxidation resistance at a certain extent. © 2016 Elsevier B.V. All rights reserved. Source

Zhao W.,Nanjing University of Aeronautics and Astronautics | Chen C.,Nanjing University of Aeronautics and Astronautics | He N.,Nanjing University of Aeronautics and Astronautics | Li L.,Nanjing University of Aeronautics and Astronautics | And 2 more authors.
Nanjing Hangkong Hangtian Daxue Xuebao/Journal of Nanjing University of Aeronautics and Astronautics | Year: 2015

Minimum quantity lubrication (MQL) has been accepted as a successful semi-dry application because of its satisfactory performance in practical machining operations. However, the oil mist generated from MQL machining process has a direct impact on the ambient air quality, and then does harm to those who permanently work in this environment. Using the weighing method, the oil mist concentration in machining workshop is measured. The effect of milling speed on the oil mist concentration under different MQL system parameters such as oil flow rate, air pressure, spray distance to target and jet temperature, is analyzed. The research results show that, the oil mist concentration PM10 and PM2.5 in machining workshop will increase with the increase of milling speed due to the secondary atomization, which results from the fierce collision between oil mist particles generated from MQL system and cutting tool with high rotation speeds. But the varying patterns of oil mist concentration PM10 and PM2.5 are changing with the increase of milling speed at different MQL system parameters. © 2015, Editorial Department of Journal NUAA. All right reserved. Source

Qiao F.,Shanghai Aerospace Equipment Manufacturer | Cheng K.,Brunel University | Wang L.,Shanghai Aerospace Equipment Manufacturer | Wang L.,Tongji University | And 2 more authors.
Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture | Year: 2016

This article presents an industrial feasible approach to robustly joining dissimilar materials of AA6061-T6 and 1Cr18Ni9Ti using refill friction stir spot welding processes and the associated joints assessment. The microstructure and shear strength property tests are taken on the dissimilar joints of 2-mm-thick plates. The results indicate that the microstructure change of the joints can be categorized in stir zone, heat-affected zone, thermomechanically affected zone and base material. The 1Cr18Ni9Ti material is squeezed toward the 6061-T6 material and forms the hook tissue, which enhances the mechanical properties of the refill friction stir spot welding-enabled joints of two dissimilar materials. The shear strength of the joints increases at first and then decreases with increase in the tool rotational speed, the indentation depth, the axial force and welding time. When the welding process is carried out at the tool rotational speed of 1800 r/min, indentation depth of 2.3 mm, the axial force of 15.65kN and the welding time in 7.5 s, the maximum shear strength of the joints can be achieved as being able to take the loading of 8650N as experimentally tested. © 2015 IMechE. Source

Zhang D.,Shanghai Aerospace Equipment Manufacturer | Chen W.-H.,Nanjing University of Aeronautics and Astronautics | Sun Y.-H.,Shanghai Aerospace Equipment Manufacturer | Dong F.-B.,Shanghai Aerospace Equipment Manufacturer
Hangkong Cailiao Xuebao/Journal of Aeronautical Materials | Year: 2013

Electron beam welds, Friction stir welding and gas tungsten arc welds of aluminum alloy 2219 were made and their mechanical properties were compared by tensile testing and micro-hardness. The reasons for the difference of mechanical properties were researched by scanning electron microscopy and optical microscope. It is shown that the tensile strength of EBW joints is about 79% of base metal and hardness of the joints reaches 97HV. The tensile strength of FSW joints is about 74% of base metal and hardness of the joints reaches 97.6HV. But the tensile strength of TIG joints is only about 53% of base metal and hardness of the joints reaches 72HV. The EBW joints and the FSW joints had better performances than the TIG joints. According to the microstructures, fracture and section morphology analysis, fine equiaxed grains, distribution more evenly of copper elements and less defects that the EBW joints and the FSW joints have are the main reasons for superior mechanical properties. Source

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