| 6061 aluminum alloy is one of the Al-Mg-Si series alloys, which has medium strength. It can be used in building decoration, transportation, aerospace and other fields because of good plastic, processing properties and corrosion resistance. Al 6061 alloy is adopted by mainstream semiconductor equipment manufacturers widely. The main manufacturer is Alcoa Company, because other company can not produce the 6061 alloy meeting the needs of semiconductor devices, although they can support aluminum alloy to apply in the aviation, architecture, vehicle, and vessel. The domestic parts were crossed seriously in working process because the density and uniformity of oxidation film that can be obtained by the surface treatment, is poor. The real reason of the poor film is un-uniform microstructures and coarse second phases. The key decision of oxidation film quality is the quality of the aluminum matrix. In order to obtain high quality 6061 aluminum alloy, the homogenization and forging before oxidation need be optimized. In this paper, the variation of the second phase and grain size were investigated. Specially, the effect of the second phase and grain size on oxidation film was researched deeply. The main conclusions are as follows:(1) The main second phase is Mg2Si and AlFeSi in Al 6061 alloy. In the anodic oxidation procession, Mg2Si made the pinhole in the film after it be dissolved as anode phase, while AlFeSi made loosen film after it remained in the film as cathode phase.(2) Homogenization made Mg2Si solution and AlFeSi phase transition, which can reduce the harmful effects of second phase on the film, to improve the quality of oxide film. 560℃-580℃was the suitable temperature range on condition thatβ-AlFeSi transited to theα-AlFeSi. The iron-rich phase transited more fully when the holding time reached 24 horns, however over-extending holding time had no obvious effect on the uniformity. Two-stage homogenization (560℃×24h+580℃×24h) was better than single-stage homogenization.(3)β-AlFeSi had more harmful effects on the film than the granularα-AlFeSi. In the homogenization procession, the transition of iron-rich phase was beneficial to obtain the granularα-AlFeSi. There were two transformation forms during the whole homogenization. The one was precipitation from the Al matrix, for smallα-AlFeSi phase. The other one was phase transition transformation thatβ-AlFeSi transformed intoα-AlFeSi with high ration of Fe/Si by losing Si.(4) The reasonable end forging temperature was 360℃for 6061 alloy. The lower end forging temperature can lead to coarse grain that affect not only the various mechanical properties, but also bring about piebald with different shades.(5) The forging can crush the strip or chain second phase to make AlFeSi phase spheroidize and distribute evenly, which was beneficial to enhance the transparency and hardness of the oxide film. On this oxidation condition, the second phase whose size is bigger than 5μm can impede the growth of anodic oxide film, resulting in the uneven thickness of film and the weaken binding force with Al substrate.
|
PDF Full Text Request