| Preparing hard anode oxidation film in low concentration of sulfuric acid electrolyte of 6061 Aluminum sheet was studied in this topic, which aimed at increasing film thickness and hardness, at the same time, economizing the production costs and reducing environmental pollution. Because of its excellent properties, Aluminum alloy has the biggest usage and the widest application. However, Aluminum is very active and has more negative corrosion potential, it corrodes totally and seriously. Hence in order to expand the application range and extend service life, anodizing or surface coating is needed. Traditionally, electrolyte of hard anodizing contains 15% 30% (wt. %) sulfuric acid, which has high costs and goes against environmental protection. What's more, it is very difficult to improve the mechanical properties of the oxide film. Hungarian scholars got film with excellent properties in low concentration of sulfuric acid electrolyte, but it is not been used in practice. Our team did some studies about oxidation technology, but not involved the growth pattern. This topic, in the basis of traditional theories and preliminary work, growth pattern of anodic film in low concentration of sulfuric acid electrolyte was studied, which in order to obtain relevant oxidation technology of high-performance film.In this paper, effects of sulfuric acid concentration, oxidation time, oxidation temperature and current density parameters on oxide film growth mode, film thickness, hardness and surface roughness were studied. Scanning Electron Microscope (SEM) and computer image analyzer microscope (XJP-6A) were used to analyze the microstructure of oxide film; Energy Dispersed X-ray spectrometer (EDX) was used to test the kinds and contents of component elements. Digital cladding thickness gauge (TT230), computer display type manual turret micro-hardness (MVC-1000JMT1) and TR200 roughmeter were applied to measure film thickness, hardness and surface roughness.According to the existing theories, this paper discussed and analysed the experiment results, which were as follows:⑴Unlike conventional porous membrane, the growth of oxide film can be divided into early and late stages. In the early stage, anodic oxide film generates and expands in the form of particles on the local area of substrate surface at first. With the increase of oxidation time, particles generate and expand constantly on the surface of substrate where it has not oxidized yet. Finally the whole surface is covered by particles to form complete Al2O3 film. In the late stage, the oxide film at the interface of particles corrodes and breakdown under the action of the electric field, then mass transfer and film form fast. Oxide film grows quickly in the way of this growth pattern, which film grows alternately at the interface of particles.⑵In the oxidation process, with the increase of the concentration of sulfuric acid, the values of film thickness, hardness and surface roughness decrease; As the oxidation time increasing, the values of film thickness, hardness and surface roughness increase; with the increase of electrolyte temperature, the values of film thickness first increase and then decrease, but the values of film hardness decrease. The results show that in the electrolyte which contains 3% (wt. %) sulfuric acid, when the temperature is minus 2 degrees, current density is 4 A/dm2 and the oxidation time is 50min, the film can have excellent properties. The values of film thickness, hardness and surface roughness are 47μm, 510HV and 1.472.⑶Oxidation film of 6082 pistons are got in 3% H2SO4 (Wt. %) electrolyte, at minus 2 degrees, 4A/dm2 and 70min. The film is very compact. The max values of film hardness and thickness are 520HV and 90μm. This technology can not only improve the values of film thickness and hardness, but also economize the production costs and reduce environmental pollution, which can comply with the development needs of low-carbon society. |
PDF Full Text Request