| Aluminum-lithium alloy,one of the most ideal and new structural materials,is considered to be the main aerospace vehicle in the 21st century due to its light weight,high specific stiffness and high specific strength,excellent low-temperature properties,fatigue resistance,and excellent ductility.It is more suitable for the development of modern aerospace technology.However,due to the low hardness,poor wear resistance,and low corrosion resistance of aluminum-lithium alloys,their widespread application in various industrial fields has been limited.Micro-arc oxidation technology is a new type of environmentally friendly surface treatment technology.The film can grow in situ on the surface of the alloy and has a good combination with the substrate,high hardness,good corrosion resistance and wear resistance.It is a promising surface strengthening technology.This article takes 2195 aluminum-lithium alloy as the research object.In the silicate-phosphate alkaline composite electrolyte,micro-arc oxide films were prepared with different parameters by three different power supply modes:DC steady current,single pulse steady current,and double pulse steady current.The surface and cross-section morphology,elemental phase composition of the film layer under various parameters were analyzed by SEM?XRD?EDS and other analytical testing methods;and the film layer was analyzed by surface roughness meter,electrochemical workstation,friction and wear tester,etc.The properties of surface roughness,corrosion resistance and wear resistance were explored,and the effect mechanism of micro-arc oxidation on film performance under different power modes was explored.The results show that micro-arc oxide films with different current densities and different oxidation times prepared under the DC constant current power mode.When the current density is low,the film surface contains more elongated holes and the film layer is thinner.As the current density increases to 6A/dm2,the pores of the film layer decrease,and a cake-like molten oxide is formed on the surface,resulting in an increase in density;however,as the current density increases to a certain extent,the discharge pore size increases,the film layer becomes loose and porous,and the surface roughness gradually increases;The main elements of the film layer include Al,O,Si and other elements.The main constituent phases of the film layer are?-Al2O3and a small amount of?-Al2O3.According to the wear morphology of the oxide film,it is known that the wear mechanism of the film layer is mainly fatigue wear and slight abrasive grain wear;the average minimum friction coefficient is about 0.68,and the minimum wear rate is 0.0769×10-3mm3/N·m;the film has the strongest corrosion resistance when the current density is 4A/dm2,the self-corrosion current density is3.334×10-8A·cm-2,and the dense layer resistance value Rbis 2.300×106?·cm2.Compared with the oxide film prepared in the DC mode at the same time and current density,the oxide film prepared in the single pulse constant current mode with different pulse frequencies has little change in the main constituent elements and phase composition.The main surface morphology of the oxide film is a round cake,the pores are reduced and the surface of the film layer is denser,so the corrosion resistance is significantly increased.The corrosion current density at the frequency of300 Hz is 1.040×10-8A·cm-2.The impedance value Rbis 5.073×107?·cm2,which is about 20 times that of the DC mode oxide film.The wear resistance of the micro-arc oxide film is significantly reduced compared with the best in the DC steady current mode.The minimum wear rate is 0.1089×10-3mm3/N·m.The wear microcosmic morphology of the film contains a large amount of wear debris.The wear mechanism is mainly adhesive wear.Oxide films with different negative current densities prepared in the double-pulse steady-current mode form a similar"lobe-like"surface morphology that is different from other power modes;as the negative current density increases,the surface roughness increases first and then decreases(From 0.93 to 1.40 and then to 1.13),and the overall film layer becomes smoother;compared with other power modes,the film layer becomes more dense and uniform,and the abrasion resistance is generally improved.The minimum wear rate is 0.0655×10-3mm3/N·m.The corrosion resistance of the film layer decreases first and then increases with the increase of the negative current density.When the current density is 5A/dm2,the corrosion resistance of the film is the strongest.The self-corrosion current density is 7.153×10-8A·cm-2,and the resistance of the dense layer Rbis 1.524×107?·cm2. |
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