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1、AlZnMnSiCuNiFe杂质余量5.66.40.200.260.50.050.0080.0010.0040.02Mg Because of the magnesium alloy electric wheel hub surface area is larger, general above 0.4 m2, require micro-arc oxidation power supply is bigger, this subject adopts the lanzhou university of technology institute of materials and develop

2、ment of MAO - 300 type nc micro-arc oxidation production device （figure 1） micro-arc oxidation on magnesium alloy wheel casting processing, its similar to ordinary anodic oxidation equipment, including special high-voltage power supply, micro-arc oxidation alkaline solution of electrolytic tank, mix

3、ing system, cooling system, workpiece with stainless steel plate for peer electrode.With micro-arc oxidation method in sodium silicate and sodium hydroxide electrolyte fluid system in the preparation of magnesium alloy wheel casting oxide ceramic membrane, the concrete technological process first se

4、t oxidation process parameters and the alkaline tank sodium silicate solution, the cleaning after micro-arc oxidation of magnesium alloy wheel casting into cell 15 20 min, clean with clear water tank 2 4 min, add hot water in hot water （80 , 10 15 min）, closed, then cool in the cold water tank 2 min

5、, hoisted out drainage, drying, examine the hub. After micro-arc oxidation treatment must be closed by hot water, formed by micro-arc oxidation discharge holes so the distribution of the channel and the surrounding a large number of micro cracks will be closed, prevent oxygen to cause oxidation. Aft

6、er completion of micro-arc oxidation, from after micro-arc oxidation on magnesium alloy wheel casting intercept film sample were analyzed, and to facilitate test analysis, request samples made of circular plate, so the sample interception location choice among wheels, most is shown in figure 2. Usin

7、g scanning electron microscope analysis of oxide filmFigure 1 MAO - 300 type nc micro-arc oxidation power supplyFigure 2 after micro-arc oxidation magnesium alloy wheel hub casting and interception of membrane layer analysis sampleThree micro-arc oxidation process parameters on the quality of the fi

8、lmBased on the research of the sample and analysis of micro-arc oxidation technology is, in fact, the substrate magnesium magnesium oxide. Figure 3 for the dimension of samples before and after oxidation appearance schematic simulation, which is suitable for ceramic oxide film a outward growth, name

9、ly the increase of size part, b is the depth of the internal oxidation to the matrix, a and b interface for initial sample surface position, h for the total thickness of oxide film.Figure 3 samples dimension changes before and after micro-arc oxidation diagramLarger influence on test has a positive

10、voltage, frequency, duty cycle, current density and oxidation time on the process parameters. Due to the electric casting of magnesium alloy surface area is larger, micro-arc oxidation micro-arc discharge must be formed in the surface can occur after a certain thickness of oxide film, so the formati

11、on of the oxide film is needed for the voltage doesnt need much, the current is larger, the oxide film formation and the process of thickening, often accompanied by current and voltage mutation. When the oxide film thickness reaches a certain degree, the need to increase the voltage on both ends of

12、the workpiece, usually at around 150 V in the micro arc discharge between the workpiece and the electrolyte. Increased with the increase of voltage, current, micro-arc density is more and more close, more and more bright, and micro-arc constantly beating, basically, the current and voltage, linear i

13、ncrease about 180 V voltage, the density of micro-arc basically meet the technological requirements, the current growth slowly. When the thickness of oxide film reaches a certain electricityFrom electric casting magnesium alloys is not hard to find in the micro-arc oxidation test result analysis, mi

14、cro-arc oxidation in the process can be divided into two steps, namely the oxide film formation stage and the stage of micro-arc oxidation film discharge, the formation of oxide film phase as the initial stage, the stage of the supply voltage is small, and after the film to produce micro-arc dischar

15、ge requires high voltage, for magnesium alloy electric casting the large workpiece with micro-arc oxidation processing surface area is larger, the film for a long time, to a large extent affected the production efficiency.Experimental results also found that the dc power of oxide film faster than pu

16、lse power, in the absence of micro arc discharge, oxide film layer is not dense, it can be seen from appearance, need again with pulse power supply for micro-arc oxidation discharge, the oxide film become more dense. In order to improve the production efficiency, to meet the needs of industrial prod

17、uction, suggest early low voltage adjustable dc constant voltage power supply are available to set up the initial oxidation film, forming a complete insulation film in place to ensure that the first phase, and the oxide film in the late discharge can use digital pulse type adjustable power supply, i

18、t can shorten the artifacts of micro-arc oxidation time.The size of the current density in a certain extent reflects the intensity of micro-arc oxidation, strongly affect the resulting performance of the micro arc oxidation ceramic layer. The duration of oxidation also seriously affects the coating

19、corrosion resistance: oxidation time is too short, although generated mainly the dense layer, but the film is too thin, dont have good corrosion resistance; After oxidation time is too long, at some time, with the increase of time, although the overall film thickness increases, but the increase is a

20、 loose layer, layer density and thinning trend, does not favor the coating corrosion resistance, also not economic. The density of micro arc also related with the pulse frequency, when the pulse frequency increases, the density of micro arc also gradually increased. Will have the electric field set

21、up suddenly, can produce micro arc. In the basic process parameters such as electrolyte concentration, duty ratio and pulse number of uncertain, the arc voltage is constant commonly, so when the frequency increases, the sustain micro-arc voltage frequency increases, the micro-arc density will increa

22、seFour micro-arc oxide film layer structure characteristicsAfter micro-arc oxidation of magnesium alloy wheel hub interception by Mef3 large metallurgical microscope observation of the sample, the micro-arc oxide film surface morphology as shown in figure 4. Can be seen from the figure in the wheel

23、hub surface layer is made up of many tiny small volcanic cone （figure protuberant part around the holes） in dendritic combination, constitute the mesh structure. Small volcanic cone center has a small hole, this is the electrolyte reaction with matrix micro-arc discharge channel, namely when the mic

24、ro-arc spewed molten oxide channel. In addition, because the current micro area local plasma channel is different that differ by the size of the hole, big hole are also distributed around a large number of micro cracks, the generation of micro cracks often related to the stress that exist in the fil

25、m. With SSM Analysis Analysis software 6 to analyze the surface density, including 25 m film for sample, the hole surface area ratio of 18%, that of micro-arc oxidation film density is better.Figure 4 magnesium alloy wheel hub micro-arc oxide film layer surface morphologyFigure 5 AM60B magnesium all

26、oy micro-arc oxidation film section morphology by SEMFigure 5 is through JMS - 6700 - f field emission scanning electron microscopy （sem） observed the micro-arc oxide film layer section morphology photos. Figure 5 shows the average film thickness of about 22 （including m, the oxide film and substrat

27、e with good, decomposition of a distinct, density on the interface is good, no big holes. By figure 5 can also see, micro-arc oxide film by the outermost layer of loose layer, the inside of the transition layer and layer in between density of three parts, the transitional layer is the interface film

28、 layer and substrate, holes and other defects existing in the loose layer, dense layer is the key to improve its corrosion resistance.Figure 6 is obtained by Phlip X pert X-ray diffractometer AM60B magnesium alloy wheel hub of micro-arc oxidation film XRD spectrum, according to the intensity of diff

29、raction peak accumulation analysis shows that the matrix of Mg peak relatively obvious, the main phase of micro-arc oxidation coating is cubic structure of MgO style, surface with Mg2Si2O4 and MgAl2O4 spinel phase, according to the test conditions that may also contain SiO2, MgF2 and small amounts o

30、f Mg （OH） 2, and the oxide of Al, K and Na. Studies have shown that MgAl2O4 and Mg2Si2O4 can improve the wear resistance of ceramic layer and MgO style the corrosion resistance of ceramic layer play a very important role. This is the micro-arc oxide film performance is higher than the root cause of

31、the anode oxidation membrane performance. In addition, micro-arc oxidation ceramic layers of low porosity, and to improve the corrosion resistance of the coatings; Ceramic layer from the substrate on the growth, combined with matrix closely, therefore, is not easy to fall off. In addition, the techn

32、ology can generate uniform film both inside and outside the material surface layer, expand the scope of application of micro-arc oxidation.Figure 6 AM60B magnesium alloy micro-arc oxidation film XRD spectrumFive To detect the corrosion resistance of the micro-arc oxide film layerIn order to meet the requirements of the use of electric cars, mic