In-situ melting assessment of AZ91D magnesium alloy investment casting
Thesis (Ph.D (Mechanical Engineering))
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| Format: | Thesis |
| Language: | English |
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Universiti Teknologi Malaysia
2024
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| Online Access: | https://openscience.utm.my/handle/123456789/1421 |
| _version_ | 1825623323769307136 |
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| author | Jafari, Hassan |
| author_facet | Jafari, Hassan |
| author_sort | Jafari, Hassan |
| collection | OpenScience |
| description | Thesis (Ph.D (Mechanical Engineering)) |
| first_indexed | 2024-12-08T06:29:49Z |
| format | Thesis |
| id | oai:openscience.utm.my:123456789/1421 |
| institution | Universiti Teknologi Malaysia - OpenScience |
| language | English |
| last_indexed | 2024-12-08T06:29:49Z |
| publishDate | 2024 |
| publisher | Universiti Teknologi Malaysia |
| record_format | dspace |
| spelling | oai:openscience.utm.my:123456789/14212024-12-01T10:01:06Z In-situ melting assessment of AZ91D magnesium alloy investment casting Jafari, Hassan Magnesium alloys Materials science Thesis (Ph.D (Mechanical Engineering)) In this research, a new technique in casting of magnesium alloy using ceramic shell investment casting process was explored. AZ91D granules were charged into shell investment mould and heated at different temperatures (650-800°C) and times (30 and 60 min) in air as well as argon gas with and without flux comprising MgCl2, KCl and CaF2. Field emission scanning electron microscopy, energy dispersive Xray spectroscopy and X-ray diffraction analysis were used to characterise the products. The results showed that with increasing heating temperature and time, significant increase in oxide/metal ratio with no development of molten pool was observed when no protected atmosphere was used. However, thermal analysis proved that the granules melted but remained in isolation due to being encapsulated by oxides, which prevented the melted granules from merging into a pool of molten metal. Even though heating in argon atmosphere prevented oxidation, prolonged heating did not produce complete melting due to the high surface tension between the liquid droplets. Further experiments were conducted using flux-argon combination in different amounts of flux (0.5, 1.0, 1.5 and 2.0 wt.%) and application conditions: on top of the granules, bottom of the mould, inner surface of the mould and mixed with the granules. The results revealed that applying 1.5 and 1.0 wt.% flux on the top of and mixed with the granules, respectively, produced comparatively best results. Thermal analysis showed that 30 min heating time is sufficient to melt the granules completely. Black residue with nodular morphology of the mould-metal reaction product formed on casting surface was found to be of the same alloy. Mg2Si, Mg3N2 and AlN in black oxide proved the reaction occurred between the alloy and shell material and air during cooling, while their absence and the presence of K6MgO4 and MgF2 in the white residue confirmed less reaction occurred due to the formation of a protective barrier at the mould-metal interface. Investigation on the effect of heating temperature (650-775°C) and shell thickness on the reaction revealed that heating of the granules mixed with flux in argon atmosphere at 650°C in thin mould suppressed the mould-metal reaction and produced casting with good surface quality. Thermal analysis showed that use of thinner moulds increased melting temperature arrests by enhancing the heating rate and providing higher solidification rates that were favourable for in-situ melting of magnesium alloy. Results also showed that shell mould permeability was found ineffective in suppressing the reaction at 650ºC. Castings produced using this technique possessed large grain size but very low level of casting defects as well as high homogeneity of microstructure Faculty of Mechanical Engineering 2024-12-01T01:42:11Z 2024-12-01T01:42:11Z 2012 Thesis Dataset https://openscience.utm.my/handle/123456789/1421 en application/pdf application/pdf application/pdf Universiti Teknologi Malaysia |
| spellingShingle | Magnesium alloys Materials science Jafari, Hassan In-situ melting assessment of AZ91D magnesium alloy investment casting |
| title | In-situ melting assessment of AZ91D magnesium alloy investment casting |
| title_full | In-situ melting assessment of AZ91D magnesium alloy investment casting |
| title_fullStr | In-situ melting assessment of AZ91D magnesium alloy investment casting |
| title_full_unstemmed | In-situ melting assessment of AZ91D magnesium alloy investment casting |
| title_short | In-situ melting assessment of AZ91D magnesium alloy investment casting |
| title_sort | in situ melting assessment of az91d magnesium alloy investment casting |
| topic | Magnesium alloys Materials science |
| url | https://openscience.utm.my/handle/123456789/1421 |
| work_keys_str_mv | AT jafarihassan insitumeltingassessmentofaz91dmagnesiumalloyinvestmentcasting |