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Formation Mechanism and Tribological Properties of Micro-arc Oxidated Coating on Aluminium

Author: GaoCheng
Tutor: XuJinYong
School: Guilin University of Electronic Science and Technology
Course: Mechanical Design and Theory
Keywords: Micro-arc oxidation Al2O3 ceramic membrane Control process Al2O3/TiO2 composite ceramic film Formation mechanism Wear resistance
CLC: TG174.453
Type: Master's thesis
Year: 2010
Downloads: 92
Quote: 0
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Abstract


In order to improve the wear resistance of the aluminum surface to extend the life of the aluminum parts, aluminum micro-arc oxidation treatment in the silicate system electrolyte, the aluminum alloy surface in situ generation layer of ceramic membrane. SEM, XRD, EDS analysis of the microstructure of the ceramic membrane, phase composition and phase components of the system to study the wear resistance of ceramic membrane sandpaper friction environment. The main contents and conclusions are as follows: (i) Al 2 O 3 ceramic membrane ⑴ change of the electronic control parameters determine the the pulse instantaneous discharge energy increase or decrease trend, thereby affecting the ceramic film growth The rate of the fast and slow. When more than 30 m (2) the thickness of the ceramic film began to appear layered, dense layer ratio exceeds 35%, up to 86%, with the increase in the thickness of the ceramic membrane, the dense layer and the thickness of the loose layer were increased, but the ratio between the two is reduced . (3) microscopic surface of the ceramic membrane was rich pore structure and the discharge pore diameters ranging from a few hundred nm to more than a dozen m, the surrounding the round pie oxide condensate traces of; discharge of the high-energy, a large number of molten oxide sputtering to the surface particle micelles. ⑷ obtained ceramic membrane containing 3Al 2 the O 3 2SiO 2 (mullite), α-Al 2 O 3 and γ-Al 2 O 3 three primary mullite the electrolyte molten alumina sintered role the product of part of the γ-Al 2 O 3 at high temperatures is irreversibly converted to the α-Al 2 O 3 point to the surface direction, by the base body, the α-Al 2 the O 3 content decreased, the γ-Al 2 O 3 content increased. ⑸ high negative voltage conducive electrophoresis to eliminate the positive pulse period and a silicic acid colloid adsorbed on the surface of the ceramic membrane, the dense formation of the ceramic membrane surface. ⑹ 60 min constant current oxidation ceramic membrane surface roughness Ra of no more than 6.8 m. ⑺ dispersed ceramic membrane surface hardness, more than 800 HV up to 1600 HV, too thin and too thick ceramic film does not have a high hardness. The electronic control parameters ⑻ draw the better system: constant current oxidation mode - positive current density of 12 A / dm 2 1 5 A / dm 2 < / sup>, the negative current density of 4 A / dm 2 5 A / dm 2 , the pulse frequency of 500 Hz 6 00 Hz, pulse duty 0.15 0 .20, oxidation time 45 min 7 5 min; constant voltage mode - a positive voltage the 460 V 5 < / sup> 20 V, negative voltage to 60 V 8 0 V, pulse frequency 500 Hz 6 00 Hz, pulse duty 0.15 0 . 20, oxidation time 30 min 6 0 min. ⑼ a two-stage study control process - 30 min constant current (16 A / dm 2 ) 15 min constant voltage (510 V) this method enables both having ceramic membrane in the early high growth rate, but also in the late fine to repair ceramic membrane surface. (Ii) Al 2 O 3 / TiO 2 composite ceramic film for the first time in the electrolyte add TiO 2 nano powder, Al 2 O 3 / TiO 2 ceramic composite membrane obtained under conditions with the same electronic control parameters Al 2 < / sub> O 3 ceramic membranes compared: ⑴ growth rate of 16.9% faster. ⑵ TiO 2 nano powder conducive dense ceramic membrane surface, the compaction of the cross-section. (3) composite ceramic film in addition to containing α-Al 2 O 3 γ-Al 2 O 3 and mullite stone, but also contain a small amount of Al 2 TiO 5 and anatase TiO 2 . ⑷ microscopic increase the hardness 162 HV, the strengthening effect of nano the TiO 2 powder. (Iii) the first waterproof sandpaper friction environment abrasion characteristics of ceramic membrane friction test results showed: (1) whether water lubricated friction or dry friction, ceramic membrane with 1000 # waterproof sandpaper grinding show excellent resistance grinding performance, dry friction wear resistance of the ceramic membrane than the aluminum alloy matrix increased by 5.3-fold increased 94-fold in water lubricated friction. ⑵ Al 2 O 3 ceramic film loose layer, compact layer and Al 2 O 3 / TiO 2 the wear composite ceramic film speed contrast approximates 4:1:1.86. (3) and aluminum alloy friction speed and load on the wear rate of the ceramic membrane. ⑷ different roughness of the ceramic membrane under initial wear rate, stable friction stage there is little difference. ⑸ Al 2 O 3 / TiO 2 friction coefficient of the composite ceramic membrane in 0.21 0 .22 between, and Al 2 O 3 ceramic membrane of 0.40 0 .45 between.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology > Inorganic complex layer of protection > Ceramic stratified
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