Casting and Analysis of Squeeze Cast Aluminium Silicon Eutectic Alloy

237 Pages·2006·29.91 MB·English

Casting and Analysis of
Squeeze Cast Aluminium
Silicon Eutectic Alloy
Matthew Smillie
A thesis presented in partial fulfilment
of the requirements for the degree of
Doctor of Philosophy
in
Mechanical Engineering
at the
University of Canterbury,
Christchurch, New Zealand.
2006

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Figure 1 Squeeze cast aluminium silicon eutectic alloy, differential interference con-
trast illumination at 50x magnification. A combination of small, hard crystals of primary
silicon, partially modified aluminium silicon eutectic, and soft primary aluminium den-
drites are shown by the contrast in polishing relief revealed using differential interference
contrast illumination.

ABSTRACT
Squeeze casting is the practise of solidifying metals under mechanically ap-
plied pressure via a slow displacement of a die volume. It has been shown
that squeeze casting enhances the mechanical properties of cast metals.
Research into other high integrity casting processes has shown that using
techniques that enhance melt quality can further increase the mechanical
properties. Therefore a bottom-tapped, bottom-fed squeeze casting ma-
chine was designed and built around a pre-existing squeeze casting die de-
signed for uniaxial pressure application. This was used to obtain quantita-
tive metallurgical and microstructural information on the squeeze castings
produced, including the effects of common micro-alloying additions of stron-
tium modifier and titanium modifier on the microstructure and hardness of
a commercial aluminium silicon eutectic alloy. These were examined using a
Taguchi design of experiments approach. It was found that squeeze casting
reduced porosity and secondary dendrite arm spacing and increased hard-
ness, and reduced or eliminated increases in porosity and secondary dendrite
arm spacing associated with micro-alloying addition. The size of possibly
deleterious iron-rich precipitates was reduced, and the morphology of such
precipitates changed to a possibly less deleterious form without further alloy
additions of manganese. It was also found that melt control and handling is
essential for consistent quality of castings in the production of small volume
squeeze castings, such as the ones produced in this experimental work.

For my wife, Fleur.

ACKNOWLEDGEMENTS
The author would like to acknowledge the following:
Dr John Smaill and Dr Milo Kral: For their supervision, instruction
and advice.
Julian Philips, Ken Brown, Paul Wells, Scott Amies, Bruce Sparks
and Otto Bolt: For the fabrication of the many parts, and replace-
ments thereof, of the experimental casting rig.
Kevin Stobbs, Mike Flaws and Hugh Mobbs: For their help in the
Materials Laboratory, the foundry and the Microscope Laboratories.
CWF Hamilton & Company Limited: For the supply of commercial
LM6 alloy and alloy additions used in this research.
New Zealand Aluminium Smelters Limited: For their financial sup-
port in the form of the New Zealand Aluminium Smelters Limited
Research Scholarship in 1996 and 1997.
Andrew Lintott, Rodney Elliot, Janna van Hasselt, and espe-
cially Charlotte Overton: For their friendship and support.