Study Of High-voltage Anode Deposition Process Of Aluminum And Its Alloys

Research actuality, technologic characteristic, application foreground and research signification of anodic deposition under high voltage are reviewed on the base of studying Lots of literature at home and abroad. Moreover, the basic knowledge of anodic deposition is generalized.In the part of experiment research. The anodic deposition experiment under high voltage and large electric current is conducted respectively for aluminum in mixed organic acid and LY12 aluminum alloy in mixed organic acid, Na2W04 and additive. It is mainly studied of what effects of electrolyte composition, initial current density and oxidation time have on oxidation and film property. The condition of forming excellent film is found through a lot of experiment. The film which is formed by anodic deposition under high voltage in different conditions is analyzed by XRD, SEM and ES. Then the mechanism of anodic deposition under high voltage and large electric current for aluminum and LY12 aluminum alloy is discussed on the base of those illustrated above.Experiment research and theoretical analysis shows that sleek and compact film with high hardness and large thickness can be acquired by anodic deposition technique under high voltage and large electric current. The most suitable conditions of anodic deposition for aluminum in mixed organic acid is the mixed acid concentration 1~5g/L, initial electric current density 12~24A/dm2 and oxidation time 20~50 minutes. The low concentration of mixed organic acid is beneficial to get film with high hardness quickly. Contrarily, high acid concentration will lead to long oxidation time and low hardness. When the initial electric current is elevated properly, the hardness of film can increase accordingly. Whereas, with electric current elevated, the dissolution of film becomes violently, so the highest electric current density is limited to 24A/dm2. Extending oxidation time, the hardness and thickness of film will be elevated. But when oxidation time surpasses 40 minutes, the film will grow slower, evendecrease slightly. For anodic oxidation of LY12 aluminum alloys under high voltage and large electric current, the mixed organic acid play main role in forming film, the function of Na2WO4 is to distribute electric current evenly on surface of anode, the effect of additive on oxidation is to restrain the emergence of arc. The hest electrolyte composition for anodic deposition of LY12 aluminum is the mixed acid concentration 4 - 8g/L, Na2WO4 0. 2~0. 3g/L, additive 0. 2~0. 3g/L In order to acquire harder and thicker anodic film for LY12 aluminum alloys, higher initial electric current is beneficial, hut the film will be broke down quickly by the striking of electron when initial current density is higher than 17. 8 A/dm2, which limits shorter oxidation time and thinner thickness. The suitable current density should be controlled in the scale of 13. 3 - 22. 2A/dm2. When oxidation time is extended, the harder and thicker film can be acquired accordingly, but when oxidation time is more than 40 minutes, the growth of film becomes slower, even negative change. So the most suitable oxidation time should be controlled between 30 minutes and 40 minutes.The XRD analysis of aluminum film formed in mixed organic acid shows that the film is non-crystal structure and composed by A1(OH)3, A100H and A1203. The SEM analysis found that there are many holes and flaws caused by internal stress on the surface. These holes and flaws may be active spot where deposition takes place preferentially. The SEM analysis on transect surface indicates that the film is a monolayer but non-porous layer structure, and composed by many rhombic column which stack up till the surf act; in a way of interlaced arrange. The film connects wiLli substrate in a jagged interlocking pattern, which provides a firm combination mode. The KS test shows that the atom proportion of Al and 0 in the film increases along with forming film completed. For the film of LY12 aluminum alloys produced by anodic deposition under high voltage and larg...