Britnell, David John (1996) Pressure assisted segregation in squeeze cast aluminium alloys. PhD thesis, University of Warwick.

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Abstract

A study has been conducted into Pressure Assisted Macrosegregation during the
squeeze casting of an aluminium alloy, LM25, and an aluminium based silicon
carbide particulate metal matrix composite. The squeeze casting process is
particularly prone to this type of segregation which results in large areas of
solute rich material in the final casting.
The fundamental causes of the segregation have, until now, not been fully
understood. This has restricted the use of squeeze casting as it was believed
that the cause was a fundamental manufacturing weakness.
An existing squeeze casting facility at Warwick was used to produce cast
samples for study. The facility produces simple tensile test bars. Inserts for the
die were designed to specifically produce the segregation within the castings.
Thermocouples were threaded through the die wall and placed within the
casting to enable the recording of the thermal history during solidification.
Samples were taken from the castings, mounted, ground and polished for study
via an optical microscope.
A mechanism for the formation of the segregation is proposed. The primary
causes of the segregation are shown to be surface tension, of the molten alloy,
and the design of the component. The widespread belief that this form of
segregation is a fundamental weakness of the squeeze casting process is
therefore shown to be false.
A theoretical model to a first approximation of the segregation, using the Young
and Laplace equation is given. Using the pressure difference across a thin film
the minimum web width, or radius of a corner, for no significant segregation can
be found.
The model is expanded and presented in a graphical form which is easy to
understand and provides the designer with some tools to enable a sound casting
to be produced. By sensible design the segregation phenomenon can be
significantly reduced and in some cases eliminated completely.

Item Type:	Thesis (PhD)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Library of Congress Subject Headings (LCSH):	Founding, Aluminum founding, Aluminum alloys, Aluminum castings
Official Date:	March 1996
Dates:	Date Event March 1996 Submitted
Institution:	University of Warwick
Theses Department:	School of Engineering
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Neailey, Kevin ; Smith, Tony E.
Sponsors:	Engineering and Physical Sciences Research Council (EPSRC) ; Rover Group (Firm)
Extent:	xix, 209 leaves
Language:	eng

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