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Effect of Micro-Arc Oxidation on Corrosion Behavior of Friction Stir Welding Joint of 7075 Aluminium Alloy

Author: LiuJing
Tutor: FuRuiDong
School: Yanshan University
Course: Materials Science
Keywords: Friction Stir Welding Micro-arc oxidation 7075 Tensile properties Stress corrosion
CLC: TG407
Type: Master's thesis
Year: 2010
Downloads: 191
Quote: 0
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Abstract


In this paper, micro-arc oxidation (MAO, also known as PEO) in 7075 high strength aluminum alloy friction stir welded joints in the surface of the plasma electrolytic oxidation, using immersion test , continuous neutral salt spray test , electrochemical test , such as corrosion and stress corrosion test measured by means of MAO 7075 after friction stir welded joints of corrosion were evaluated to determine the optimal MAO process . Scanning electron microscopy (SEM) observations of welded joints after MAO microscopic corrosion morphology ; electrochemical workstation with ceramic layers of different composition measured polarization curves ; MAO by optical microscopy after fracture of welded joints position ; using X-ray (XRD) MAO ceramic layer analysis phase composition ; tensile test evaluation using MAO on the mechanical properties of welded joints . The results showed that: the electrolyte system in phosphate , sodium phosphate, 50 g / l, sodium hydroxide, 2 g / l as the best formulations based electrolyte , the current density 5 A/dm2, oxidation time was 15 min for the best the MAO parameter ; the soaking test, continuous electrochemical test and neutral salt spray test , it is determined in the base electrolyte by adding a certain amount of K2Cr2O7 was the best corrosion resistance of the electrolyte . In the neutral salt spray test continuous , MAO FSW after the corrosion resistance of welded joints was significantly higher than that of the original MAO welded joints ; in stress corrosion test, stress corrosion in the early MAO ceramic layer etching can play a role in isolation , no welded joints of MAO appears crack turtle , but MAO not prevent the occurrence of stress corrosion ; the tensile test at room temperature , MAO FSW after slightly less than the tensile strength of the welded joint without MAO welded joint tensile strength , and the elongation has increased. MAO position of the weld joint fracture had no effect ; during stretching into the middle , MAO ceramic layer loose layer off, but the dense layer and the buffer layer and the substrate with good ; tensile fracture was ductile fracture characteristics .

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Welding, metal cutting and metal bonding > Welding general issues > Mechanical properties of welded joints and Intensity
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