METHOD AND APPARATUS FOR RHEO-PROCESSING OF SEMISOLID METAL ALLOYS

摘要

Due to the high cost of feedstock and equipment for the thixocasting process, the general trend internationally has been to develop new more economically viable rheocasting processes. The aim of the current project was to develop the equipment and process for the production of SSM slurry. The equipment had to be versatile and economical so that it could be incorporated into existing HPDC facilities. The CSIR, SA, developed a rheocasting system to produce a billet per minute. An experimental trial on shot weights between 500g to 4kg has been achieved successfully. The slurry is produced in cylindrical stainless steel cups using controlled cooling and induction heating/stirring. A356 aluminium alloy was used to evaluate the process and equipment. The temperature profile of the billet was found to be very uniform and with a maximum variation of 4°C. Microstructural analyses of 60mm diameter, 200mm long and 90mm diameter, 200mm long billets revealed an average grain size of 68μm and shape factor of 1.43, and 85μm and 1.52 respectively. The average yield strength, tensile strength and elongation of HPDC specimens after T6 heat treatment was determined to be 286MPa, 334MPa and 6.2% respectively.