Producing a Non-dendritic Structure Metal by Using Rheocasting udMethod for Developing The Semisolid Forming Processin Order to udImprove a Conventional Casting Process

摘要

This work was conducted to produce non-dendritic (globular) structure udsemisolid metal. It was related to long term objective of the research to apply udsemisolid forming technology for producing automotive component. Technology for udsemisolid forming involves preparation of globular structure of semisolid metal and udtransfering directly into a die for component shaping. Semisolid forming technology udgives opportunity to produce automotive component with high integrity and tight uddimensional control. udMaterial processed in this study was Al-6,23% Si alloy. In this research, udglobular stucture was obtained by mechanical stirring of molten metal during udsolidification. Rotating rod stirred the melt for short periods and then removed. The udrod cools the alloy below its liquidus temperature to intiate solidification while udstirring the melt. Process parameters of rheocasting that investigated were preheat udtemperature of stirring rod (200 udoudC, 300 udoudC, 400 udoudC and 500 udoudC), stirring depth (30 udmm, 40 mm, 50 mm and 60 mm) and stirring rod material (cupper, carbon steel and udgraphite). Microstructure of rheocasting result was examined to obtain value of udgrain shape factor. Shape factor is used to quantify grain sphericity. Shape factor is ud1 refers to a perfectly spherical (globular) morphology, while shape factor = 0 refers udto complex shape. udThe work result shows that the rheocaster machine able to produce globular udsemisolid metal with shape factor value above 0.58.Shape factor value and grain udsize increases with increasing of preheat temperature of stirring rod. The highest udshape factor 0,7 was obtained at preheat temperature 500 udoudC. At preheat udtemperature 400 udoudC, depth of stirring rod was not found to have siginificant effect on udspherecity of primary αgrain. Increasing of depth of stirring rod from 30mm to 60 udmm slightly increased shape factor from 0.64 to 0.68. Stirring rod material also was udnot found to have significant effect on spherecity of primary αgrain. Graphite rod udproduced shape factor 0,66 and cupper rod produced shape factor 0,62. At stirring uddepth of steel rod 50 mm, rotation speed 200 rpm and preheat temperature 440 udoudC – ud470 udoudC, rheocasting produced globular structure of semisolid metal that could be udcasted by conventional casting.