The effects of vortex gate design on mechanical strength of thin section casting of LM 25 (Al---7Si-0.3Mg) aluminum casting alloy
Aluminum alloy castings are being used progressively more in safety-critical applications in the automotive and aerospace industries. During the production of aluminum ingots and castings, the surface oxide on the liquid is folded in to produce crack-like defects (bifilms), porosities that are...
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| Format: | Thesis |
| Language: | English |
| Published: |
2012
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| Subjects: | |
| Online Access: | http://eprints.uthm.edu.my/2472/1/24p%20ZAID%20ALI%20SUBHI.pdf |
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| Summary: | Aluminum alloy castings are being used progressively more in safety-critical
applications in the automotive and aerospace industries. During the production of
aluminum ingots and castings, the surface oxide on the liquid is folded in to produce
crack-like defects (bifilms), porosities that are extremely thin and tiny or big, but can
be extremely extensive, and so constitute seriously detrimental defects. To produce
castings of sufficient quality, it is, therefore, important to understand the mechanisms
of the formation of defects in aluminum melt flow through the gating system. Gating
system design is an essential element in casting process which affects significantly
the molten metal flow behavior, heat transfer and solidification of the melt. The good
quality casting product could be achieved by using an optimum gating design. This
study has employed Vortex gate design of LM25 (Al—7Si-0.3Mg) thin section
casting to determine the effect of Vortex and Conventional gate design on
mechanical properties and porosity distribution pattern. Numerical simulation by
ADESTEFAN v.10 package was used to identify the molten metal flow behavior in
the mold cavity which is physically could not be detected by unaided eye. The X-Ray
Radiography test used to examine in general the distribution of defects in thin casted
part. 3-Point bending test was applied to measure the flexural strength of the casted
alloy material. The scattering of flexural strength has been quantified by Weibull
statistics approach. The microstructure inspection was observed using both, the
optical microscope micrographs and scanning electron machine (SEM) tests.
Numerical simulation results showed a smooth and non turbulent flow of the Vortex
gate design. The liquid metal in vortex entering the mould cavity is helped by gravity
for a good free surface condition during filling, reducing the danger of entrapment of
any free surface film. Furthermore, experimental results showed that casting product
with vortex gate leads to excellent improvement of average flexural strength and
reduction of porosity and cracks defects relying on the feature of swirled flow inside
the vortex gate. The ‘virtual’ experiment using a computational modeling package
and the ‘physical’ experiment were found to be in reasonable agreement. 377$
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