TOPIC:Cornflour, Ketchup and Parts for Cars: A Review of Semi-Solid Processing
Professor Helen V. Atkinson
Fellow of the Royal Academy of Engineering
Head of the Mechanics of Materials Group and Head of Department, Department of Engineering, University of Leicester.
The thixotropic behaviour of semi-solid metals was first discovered by Flemings and his group at MIT in the early 1970s. When alloy was stirred as it solidified, and then reheated into the semi-solid state, it behaved in a surprising way; on shearing it flowed with the consistency of heavy machine oil but when allowed to stand it could be handled like a solid. This behaviour (which is very like that of tomato ketchup) was then exploited in a family of semi-solid processing techniques, including:- thixoforming, thixoforging, thixocasting, rheocasting and rheoforming. ‘Thixomolding’ (based on injection moulding) is used by numerous companies, particularly in Japan and the US to produce magnesium alloy components e.g. for portable computers and cameras, but it is not suitable for aluminium alloys. Aluminium alloys have been widely produced for automotive applications, mainly by thixocasting and thixoforming-type processes.
In the last few years, there has been a great increase in interest in semi-solid processing in China, India and other countries with many new ideas under investigation. This lecture will review the current situation.