- Title
- Computational analysis and cavity optimisation to achieve directional solidification in a cast aluminium alloy [Al7SiMg] component
- Creator
- Nohanyaza, Melikhaya
- Subject
- Metal castings
- Subject
- Automobiles -- Materials
- Subject
- Alloys
- Subject
- Light metal alloys
- Date Issued
- 2018
- Date
- 2018
- Type
- Thesis
- Type
- Masters
- Type
- MEng
- Identifier
- http://hdl.handle.net/10948/22913
- Identifier
- vital:30141
- Description
- The study at hand focussed on A356.0 industrial and high production die casting alloy. Since the birth of metal casting, numerous researchers have addressed the multiple phenomena that influence the casting quality and mechanical properties of castable alloys. This study harnessed research findings on A356.0 alloy and the aluminium family as a whole, to improve the casting soundness of the component already in the production process. The local foundry showed interest in understanding solidification and quality of A356.0 alloy fluxed with NaCl+KCl melt cleaning flux plus 4 of TiB2 5:1 master alloy grain refining rods and A356.0 alloy processed with KCl+Ti (presumably KCl+TiB2) grain refining flux plus 4 of TiB2 5:1 master alloy rods. Numerical analysis was used to define the progressive nature and directional solidification of the alloy using MAGMA5. MAGMA5.3 virtual optimisation capabilities were used for development of future component casting methods and procedures to solve macro- and microporosity evident on the casting. To find a direct link between the virtual and foundry environment, a preliminary study was conducted on a simple foundry stage of cone billet casting for both alloys with and without mould/casting interface coating. The findings indicated that A356.0 maintained its shrinkage volume percentage at mould temperatures above 300 °C, but progressively increased at temperatures below. Furthermore, thermal insulation coat (also used on Right Hand Side [RHS] mould of the foundry component) influenced the shrinkage distribution on the casting while localised at the centre on non-coated mould/casting interfaces for both KCl+Ti and NaCl+KCl melt fluxed A356.0 at similar percentage shrinkage for mould temperatures greater or equal to 300 °C. Near thin foundry castings for both flux treatments indicated similar mechanical properties at similar casting stages. The mechanical properties of both conditions seemed to degrade as a function of die casting period. Secondary dendrite arm spacing microstructure parameter for NaCl+KCl and KCl+Ti fluxed alloy averaged 40 μm and 35 μm respectively across all test zones. However, individual SDAS definitions per test zone indicated possible micro segregation on NaCl+KCl fluxed alloy and instantaneous solidification as a result of constitutional supercooling on alloys fluxed with KCl+Ti alloy. The growth rate solidification parameter was symmetrical about the centre of the component, where the centre of the component experienced an exponential drop from the top (away from the filling gate) to the bottom (near the filling gate) of the component. A virtual approach to tooling geometrical design indicated a weak influence on both micro- and macroporosity. However, the introduction of low thermal capacity, high heat transfer at Left Hand Side [LHS] tooling and a new cooling system arrangement indicated a higher influence in achieving sound casting. Knowledge gained in this study will improve local foundry competitiveness and introduce cost effective virtual approach foundry developments. The study will also introduce new methods for industrial research and position Nelson Mandela University as a leader in this field.
- Format
- xxx, 184 leaves
- Format
- Publisher
- Nelson Mandela University
- Publisher
- Faculty of Engineering, the Built Environment and Information Technology
- Language
- English
- Rights
- Nelson Mandela University
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