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Non-contact ultrasonic study on thixotropic alloys
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Idris, Azmi (1995) Non-contact ultrasonic study on thixotropic alloys. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b1399504~S15
Abstract
Thixotropic metals have better fluid flow behaviour in the semi-solid state
when compared to conventional metals and have been increasingly used commercially
for the production of high quality engineering components using the technique of
thixoforming. However in industrial production, there is no proper quality control
system available at present to monitor the softness or to estimate the percentage of
solid/liquid fractions of the metal before it is forged into the required shapes. Due to
the existence of a temperature gradient within the sample when heated in the RX
furnace a bulk measurement is needed.
This thesis examines the capability of non-contact ultrasound to make acoustic
wave measurements in to the semi-solid state. In particular we have identified pulsed
laser generation and EMAT reception as being the most appropriate approach. The
Nd: YAG laser has proved capable of generating broadband ultrasound and a
water-cooled spiral coil permanent magnet EMAT an efficient detector of both shear
and longitudinal waves. The system enables both the longitudinal and shear waves to
be detected simultaneously. Investigations have been conducted on various thixotropic
metals ranging from lower melting temperature Al-Si alloys (≃570°C) to the higher
melting point M2 tool steel (≃1200°C). A Cu-Sn alloy that has a melting temperature
of around 830°C was also used for the investigation. Due to the high price and
difficulty in obtaining the thixotropic materials preliminary measurements were carried
out on non-thixotropic Al-Si alloys and a commercial mild steel. A water-cooled shear
EMAT, furnace systems and an ultrasonic cell have been designed and constructed for
the thesis. The experiment was carried out in a through transmission arrangement with
the laser and the EMAT on epicentre. The experimental work is presented in chapters
4 to 6. Chapter 4 covers the investigation on the Al-Si alloys, chapter 5 covers
investigations on the higher melting point materials, and chapter 6 presents
investigations into the efficiency of the chosen laser-EMAT system and analyses
systematic errors.
The laser-EMAT system has proved capable of making measurements not only
in the partially molten state but also in the fully molten state with sample temperatures
up to 1140°C. The sudden drop in the longitudinal wave to shear wave transit time
ratio indicates that the onset of melting could be detected. Since the ratio depends only
on the temperature and the percentage of solid and liquid present in the sample and is
independent of the sample dimensions it could be a suitable parameter for monitoring
the percentage of liquid/solid fractions necessary for thixoforging. However work has
yet to be carried out in the industrial environment to prove the capability of the system
in monitoring the softness of the metal during thixoforming.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QC Physics | ||||
Library of Congress Subject Headings (LCSH): | Thixotropy -- Quality control, Ultrasonic imaging, Nd-YAG lasers | ||||
Official Date: | January 1995 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Physics | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Palmer, Stuart B. | ||||
Sponsors: | Lucas Automotives Ltd. Advanced Engineering Centre | ||||
Extent: | xiv, 129 leaves | ||||
Language: | eng |
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