Study Of Preparatin, Physical And Chemical Properties Of Microarc Oxidation Coating On 5754 Al-Mg Alloy

As world energy and resources of the increasing tension,call for energy conservation and weight reduction, fall energy, durability and environmental protection are becoming higher and higher, light aluminium alloy of magnesium metal has become more extensive scope of application,but the lower hardness, prone to erosion and anyway, it quickly becomes visible. Microarc oxidation (MAO) is an advanced technique of processing material by means of high energy density. MAO coatings of aluminium alloy have intensively attracted the attention of many research groups due to its desirable characteristics. In recent years,the relevant articles report has become more and more, aluminium surface technology research organizations with a wide range of perspectives. In this paper. MAO technology has been used to producing MAO coating on aluminium alloy using a constant working voltage. In addition, a comprehensive, systematic study has been proceed with the changing rules of the coating growth characteristics and physical and chemical properties under different process parameters' conditions. At the same time, a comprehensive, systematic study has been proceed with the changing rules of the coating growth characteristics and physical and chemical properties on different Aluminum Magnesium Alloy.The study of this paper is divided into the three following parts:In the first part of the paper, the effect of different electrolyte system (Na₂SiO₃, Na₃PO₄ and NaAlO₂) and concentration on solution conductivity, the critical voltage, growth characteristics, microstructure and phase component of MAO coatings has been studied. Optimized the electrolyte wich using in the MAO process through the conclusion of MAO coatings characteristics, that is electrolyte of NaAlO₂. Affter that, the effect of temperatures.PH value and concentration on growth characteristics, microstructure and phase component of MAO coatings has been studied. The experiment results show that:by using the DC power supply and keeping the voltage constant, the solution conductivity reduced gradually in various electrolyte systems with the increase of solution concentration. The solution conductivity of Na2SiO3 and Na3PO4 increased linearly, but in the NaAlO₂. when the concentration is lower than 15g/L. the solution conductivity increased linearly, when the concentration is higher than 15g/L. the solution conductivity increased slowly. The critical voltage reduced gradually in various electrolyte systems with the increase of solution concentration. Further more, the critical voltage reduced rapidly in the Na3PO4 electrolyte system, slowly in the NaAlO₂. In these 3 kinds of treatment liquid, the thickness and the unevenness of the MAO coat increase with the increase of the liquid concentration. The MAO coat in Na3PO4 liquid has the highest thickness and growing rate, while the MAO coat in Na2SiO3 liquid has the lowest thickness and growing rate. In the Na2SiO3 liquid system, the smoothness of the MAO coat is not good, micro holes on the coat has a larger size but smaller density:the smoothness of the MAO coat is very poor, even sheds sometimes; and in the Na3PO4 liquid system, the MAO coat has the best quality compares to other 2 liquid system, which has the best smoothness and the smallest micro hole size.γ-Al2O3 andα-Al2O3 compose the MAO coat, but the content of which is different in these 3 kinds of treatment liquid. In the Na3PO4 system,α-Al2O3 has a lower content in the MAO coat, while in the Na2SiO3 and NaAlO₂ system, the content ofα-Al2O3 is much more higher. In the NaAlO₂ liquid system, temperature affects the thickness of the MAO coat remarkably. When 20°≤T≤50℃, the thickness increases slowly with the temperature went higher; while when 50℃≤T≤70℃, the thickness leans with the temperature went higher. Higher the temperature is. bigger the micro hole size and unevenness are. and lower the micro hole density is. However, the temperature has little affection to the MAO coat's XRD spectrum. In the NaAlO₂ liquid system, the thickness of the MAO coat increases with the increase of the treatment liquid PH linearly. Higher the PH is, more proportion ofα-Al2O3 is in the coat.In the 2nd part, the MAO treatment electronic parameters are analysis which includes voltage, frequency, duty cycle and time. All these parameters can affect the growing character, surface pattern and phase structure of MAO coat. Experiments show that:with the voltage goes higher, the thickness of the MAO coat and the size of micro hole on the coat increase. When 450V≤U≤550V, the unevenness of the MAO coat increase. When 550VV≤U≤650V, the unevenness of the MAO coat decrease,γ-Al2O3 diffraction peak decreases gradually, andα-Al2O3 diffraction peak increases gradually. With the increase of pulse frequency, the coat thickness and micro hole size and unevenness decrease, but the micro hole density increase.γ-Al2O3 diffraction peak decreases gradually,α-Al2O3 diffraction peak increases gradually. With the increase of duty cycle, the coat thickness and micro hole size and unevenness increase, but the micro hole density decrease.α-Al2O3 diffraction peak increases gradually, however.γ-Al2O3 diffraction peak does not change much. With the increase of treatment time, the coat thickness and micro hole size and unevenness increase. When in. the micro hole density increase with the time increase. When in, the micro hole density decrease with the time increase.α-Al2O3 diffraction peak decreases gradually, however,γ-Al2O3 diffraction peak does not change much.In the 3rd part.first of all. treat the 3 kinds of Al-Mg alloy with MAO,and compare and analysis the characters of its MAO coat in different parameters. Secondly, the physics and chemistry characters of the 3 kinds of alloy MAO coat are anglicized. The experiment shows that, with the concentration increase, the coat thickness of 5083 alloy and 5754 alloy increase linearly, when the treatment liquid concentration increase above 15g/L. the coat thickness of 5052 increase slowly. In the same treatment liquid concentration,5754 alloy has the thickest coat,5083 alloy has the second thickest coat,5052 alloy has the thinnest coat. Rockwell hardness of the 3 kinds of alloy MAO coat increase with it. The Rockwell hardness of 5754 alloy has the highest increasing rate. After MAO treatment, the corrosion resisting performance of the 3 kinds of alloy raise remarkably. However, when the concentration reach 15g/L. the corrosion resisting performance of the 3 kinds of alloy decrease a little. In the same treatment concentration. MAO coat of 5083 alloy have the highest corrosion resisting performance, the MAO coat of 5052 alloy has the poorest corrosion resisting performance. With the voltage raise, the thickness of them increases. In which.5754 has a higher increasing rate. Rockwell hardness 3 kinds of alloy MAO coat increase. and the 5754 alloy MAO coat has a higher hardness increasing rate. When U>500V. the hardness of 5754 MAO coat is remarkably higher than which of 5052 alloy. In the same corrosion time, corrosion resisting parameter of 3 kinds of alloy MAO coat increase with the treatment voltage when U≤550V. However, when 550V20min. the Rockwell hardness of 5052 and 5754 went down except 5083. When the treatment time increase from 5min to 10min. the corrosion resisting parameter increase greatly. However. when the time reach 10min. the corrosion resisting parameter no longer increase any more.