| In many specific industries, to meet special performance requirements, it must be used in aluminum and its alloys, aluminum and its alloys, but lower surface hardness, corrosion resistance and poor wear resistance, thermal shock resistance is poor, restricted application of aluminum alloy. Can be processed by surface treatment to improve the comprehensive performance of aluminum alloy. Oxidation in the anodic oxidation process developed on the basis of the new surface treatment technology, micro-arc oxidation film has high hardness, corrosion resistance and insulation resistance and good wear resistance, high thermal shock resistance, oxide film and the substrate combined with strong advantages, greatly improved the application of aluminum alloy.Micro-arc oxidation (MAO), also known as micro-plasma oxidation (MPO) or anodic spark deposition (ASD), also known as plasma-enhanced electrochemical surface ceramic (PECC) is adjusted by controlling the electrolyte and the corresponding electrical parameters of the combination of aluminum, magnesium, titanium and its alloys depend on micro-plasma discharge generated by the instantaneous high temperature high pressure, through chemical, electrochemical, thermal chemistry, plasma chemistry, the role of reaction under the surface of the substrate in situ growth of the oxide ceramic membrane technology. The formation of micro-arc oxidation film can be divided into the following four stages:the first phase of the initial formation of amorphous films. Anodic film formation process with the same electrode system to follow Faraday's law, electrolyzer voltage and current follows Ohm's law, the sample surface oxide layer of thin transparent insulating film, under low pressure, can prevent the passage of the surface current, also known as the barrier layer. The second phase of spark discharge stage. As voltage increased, the breakdown barrier layer, charged particles accelerated by high voltage electric field created by the collision with other atoms "electronic avalanche" phenomenon of the formation of sparks, through the breakdown of material into the matrix channel within the complex after the reaction, the formation of new non-amorphous oxide film thickness of oxide film. The third stage of the formation of ceramic membrane. As the voltage increases, micro-plasma discharge produces high temperature and pressure, to form amorphous oxide film dissolves, and the rapid cooling in the condensed electrolyte environment, the first surface of ceramic particles in the sample, with the constant breakdown surface, the formation of ceramic particles continuously grow up to touch the way to bypass the formation of ceramic coatings. As the breakdown always occurs in parts of the film is weak, so the formation of the ceramic coating is uniform. The fourth stage ceramic membrane growth. With the oxidation time, oxidation film formed by continuous dissolution and, in the micro-arc oxidation film growth rate is greater than the dissolution rate, the ceramic membrane is constantly growing thicker, the oxide film dissolves in the membrane More weak layer formed on the surface area is more prone to oxidation, so that continued growth of the film thickness, until it reaches a balance of growth and dissolution, the oxide film to stop the growth of micro-arc oxidation process is over.This article is about the process of Aluminum Alloy Research. Testing process is a huge project, choose a reasonable test method can play a multiplier effect, so this paper applies computer technology to the oxidation test, the use of orthogonal experimental design for micro-arc oxidation and data analysis. Orthogonal design is the use of normalized orthogonal table, the proper design of the pilot program and effectively analyze test results, the optimal formulation and process conditions, and thus may be better to design a pilot program of scientific method. Orthogonality principle is the scientific basis of orthogonal table, orthogonal with "balanced with" and "neat" in its features, from a large number of full-scale testing program, a representative for the small number of selected test point, the system into a neat arrangement of standardized forms.This paper studies the main film-forming agent to sodium silicate electrolyte oxidation experiment, the orthogonal design experiment in micro-arc oxidation process the application, use the overall balance method and variance analysis of test data analysis micro-arc oxidation ceramic oxide film growth law, the factors on the ceramic oxide film growth, as well as the factors that influence the test target size, while analysis of variance in the emphasis of the sodium silicate concentration and voltage micro arc oxidation The interaction of oxide film growth. Test by scanning electron microscopy (SEM) morphology of the ceramic oxide films were analyzed, using 631-type microhardness and the hardness of the oxide film thickness measurements of oxide film on the ceramic thermal shock resistance, corrosion resistance was tested.Tests show that the electrolyte concentration on the oxidation process significantly affected all parameters. Different concentrations of electrolyte, oxidation of the voltage difference that the surface current density. With concentration, the micro-arc oxidation arc voltage decreases, the sample surface current density is increased, and tend to a limit.Test showed that all factors (electrolyte concentration and voltage micro arc oxidation) on the test indicators (hardness and thickness) was significant. Sodium-based film-forming agent in the electrolyte, the concentration of which Na2SiO3 hardness and thickness of the ceramic membrane greatest impact on the two indicators, micro-arc oxidation voltage and the second impact H3BO3 concentration, KOH concentration of influence again, H2O2 concentration impact is minimal. The five-factor test for four-level orthogonal design of micro-arc oxidation process, and with the overall balance method and variance analysis to evaluate, select Na2SiC>3 concentration of 6g/L, H3BO3 concentration of 1.5g/L, KOH concentration of 0.5g/ L, H2O2 concentration X4, micro-arc oxidation voltage of 360V for the optimal process plan. The optimal process plan on LY12 aluminum alloy oxidation treatment to obtain a dense layer of hardness 1700HV, the total thickness of about 200μm uniform distribution of micro-arc oxidation ceramic coating.Test showed that the micro-arc oxidation ceramic coating surface of the pores reduces the corrosion resistance of the film, by sealing treatment can greatly improve its corrosion resistance, at room temperature, the treated samples were immersed 10% HCl,10% NaCl,10% NaOH solution in 80 hours, the specimen is almost no change in weight before and after corrosion. Micro-arc oxidation film with good thermal shock resistance, resistance to 600℃-20℃heat shock-shock cold shock 15, but the film without cracks, loss, blistering and other damage phenomena. |
PDF Full Text Request