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Fabrication of Super-hydrophobic Films on Magnesium Alloys and Their Relevant Properties

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Tutor: XuBingShe
School: Taiyuan University of Technology
Course: Non-ferrous metallurgy
Keywords: AZ31magnesium alloy,wet chemical method,super-hydrophobic film,corrosion resista
CLC: TG174.4
Type: Master's thesis
Year:  2013
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Abstract:
Magnesium alloys, as the lightest structural alloys, have many advantages such as high specific strength, high specific stiffness, good cushioning, electromagnetic shielding, high radiation tolerance and free-cutting, etc. Therefore magnesium alloys have become ideal candidate materials for their application in automotive, aerospace and other fields to lose weight. However, two remaining challenges, poor plastic deformation ability and poor corrosion resistance, hinder their use. AZ31rolled plates are selected as the research materials in this paper, and their corrosion resistance are improved by building the micro-nano hierarchical structure on magnesium alloys surface to generate the super-hydrophobicity for the latter problem. This could make magnesium alloys play a better role in automotive industry and aerospace,3C industry.A simple and efficient method for fabricating a super-hydrophobic film on magnesium alloys has been developed using oxalic acid etching, chemical silvering and self-assembly treatments; furthermore, the chemical reaction mechanism has been revealed in the article. Then contact angles and morphology of the super-hydrophobic coating are characterized by Optical Contact Angle Measuring Device and field emission scanning electron spectroscopy, respectively. And the electrochemical impedance spectroscopy is measured using Autolab electrochemical workstation. These results show that the treated magnesium alloy surface exhibits high hydrophobicity with an apparent contact angle of153¡ãand contact angle hysteresis of4¡ã. The super-hydrophobic film is covered with serried and uniform micro-spherical structures with a average diameter of about2¡«3¦Ìm, which are composed of irregularly arranged nano-plates with the thickness of90¡«100nm. The unique micro-nano hierarchical structures can trap a lot of air to form an extremely thin layer of air cushion between water and substrate, and the air cushion becomes a very effective block of the penetration of water molecules. Comparing with untreated magnesium alloys, the corrosion resistance of treated magnesium alloys in0.1mol/L NaCl aqueous solution is significantly improved by the super-hydrophobic film, and the film is positive enough to prevent the pitting corrosion between film and substrate.Besides, the effects of super-hydrophobic structure on buoyancy of magnesium alloys and cryogenic treatment on coating-substrate adhesion, wear resistance for the super-hydrophobic film. At last I hope that fabrication of super-hydrophobic films on magnesium alloys and their relevant properties in this article do provide some helpful basic data or ideas for follow-up work of this topic and other research projects.
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