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Dissertation
Influence of process parameters on microstructure and mechanical properties of lost foam aluminum castings
Doctor of Philosophy (Ph.D.), Drexel University
1991
DOI:
https://doi.org/10.17918/00008560
Abstract
A fundamental analysis was conducted to evaluate the metallurgical quality of aluminum castings produced by the lost foam process. Test castings were produced for a variety of processing conditions and analyzed to determine the microstructural parameters and mechanical properties. Various defects have been identified and characterized. The effects of grain refinement and modification on microstructure and mechanical properties have also been evaluated. It has been shown that the thermal gradients established during the filling of the mold have a significant effect on the solidification behavior. Both dendrite arm spacing (DAS) and grain size vary inversely with the distance from the ingate. The morphology and distribution of interdendritic phases varies along the length of flow. A segregated region containing a high concentration of alloying elements may be observed near the metal front. Bulk porosity levels in the casting are comparable to the values measured in green sand castings. Lost foam castings may contain large amounts of surface porosity and porosity near the metal front. Excessive glue at joints seems to contribute to the evolution of porosity in the casting. Other defects such as folds, laps and black inclusions may also be present in the casting. It has been shown that liquid degradation products have a critical role in determining casting quality. A pouring temperature of the order of 730 to 750[degrees]C and terminal flow velocity of 9 to 14 cm/s may be necessary to minimize defect formation. A minimum of 0.15% Ti is necessary to achieve substantial grain refinement. Optimum concentration of Sr for obtaining a fine and fibrous eutectic Si structure in the casting are between 0.01 to 0.015%. Mechanical properties of lost foam castings are better than or equal to the values measured in green sand castings, but are inferior to the properties in permanent mold castings.
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Details
- Title
- Influence of process parameters on microstructure and mechanical properties of lost foam aluminum castings
- Creators
- Libo Wang
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xxi, 240 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Materials (Science and) Engineering (Metallurgical Engineering) [Historical]; College of Engineering (1970-2026); Drexel University
- Other Identifier
- 991021888997604721