The Heat Treatment & Surface Treatment of AZ91D Magnesium Alloy
| Autor: | Hao-Jan Tsai, 蔡浩然 |
|---|---|
| Rok vydání: | 2007 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 95 AZ91D has higher content of aluminums, it can precipitate the β phase(Al12Mg17) of BCC structure in the magnesium base of HCP with the proper heat treatment. Because of this precipitates are located slip plane（0001）under the room temperature, this kind of precipitates can not resisted the dislocation to slide very effective and it caused the purpose of precipitation hardening are very limited. In consequence, this study will use the different heat treatment ways which like T6 treatment（solid solution＋aging hardening）、T8 treatment（solid solution＋TMT＋aging hardening）and T9 treatment（solid solution＋aging hardening ＋TMT）on AZ91D magnesium alloy（As－Extruded）and survey the morphological distribution of samples after solid solution treatment、aging hardening treatment、TMT； and then, comprehend the effect of hardness and tensile strength for AZ91D magnesium alloy. The experimental result shows, the magnesium alloy of AZ91D is in the rising that after T6, T8 and T9 treatment are achieved with its hardness value will be obvious, especially T8, T9 treatment, It can make Al12Mg17 produced the discontinuous particle precipitates directly by the TMT, make its distributed evenly in the magnesium base, and then improve the effect of precipitation hardening. Can know by the result of tensile test, after T6 treatment, 200 degrees Centigrade of aging hardening temperature makes tensile strength value that can be obviously higher than the extruded magnesium alloy；and then, the T8、T9 treatment can also find the tensile strength of the two is higher than the extruded magnesium alloy, superior to the tensile strength value that T6 treatment. In consequence, after comprehensive hardness and result of tensile test, AZ91D extruded magnesium alloy can change morphological distribution ofβ phase(Al12Mg17) by the TMT to reach higher strength. The corrosion resistance of magnesium alloys was, however, very poor. Without proper corrosion-prevention treatment, their applications can be severely restricted, In this study, DC magnetron sputtering was used to deposit a thin film of photo-catalytic TiO2 on AZ91D Mg-alloy to enhance the corrosion-resistance and photo-catalytic properties of the AZ91D substrate. Experimental results showed that the contact angles of AZ91D surface, when coated with a thin film of TiO2, decreased substantially down to 5° after exposure to UV light, From the experimental of photo-catalytic activity via methyllene blue, can knows that the methylene blue were catalyzed by TiO2 film，thus exhibiting photo‐induced hydrophilicity effect. On the other hand, the potentiodynamic polarization curves indicated that the corrosion potential of TiO2-deposited AZ91D was higher than that of the uncoated AZ91D Mg-alloy. While for TiO2-deposited samples this data suggested an increase in the intrinsic corrosion resistance, the current density of the TiO2-deposited samples was much higher than that for the uncoated samples. The overall corrosion resistance of TiO2-deposited samples deteriorated as compared with that of the uncoated samples. FE-SEM observation of the TiO2 thin film showed polycrystalline structure characteristics of anatase phase, as well as the presence of pinholes on the TiO2 thin film. EDS analysis revealed the pinholes to be locales of incomplete deposition, which caused accelerated corrosion by Galvanic corrosion effect, on the other hand, AZ91D substrate which coated TiO2 film to use voltage and which coated TiO2 film after conversion coating both can advanced the corrosion resistance of magnesium alloys. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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