| The effect of various rheological parameters on the thixotropic behaviors of the A357 Al alloy was studied using a Searl type high temperature viscometer. The viscometer was designed to cover wide range of cooling rate(1-20℃/min) and to apply high shear rate up to 1100/s so that thixotropic behaviors exhibited during the actual semi-solid forming alloy can be simulated. Thixotropy of the slurry was measured as a function of solid faction, shear rate, and time at rest. According to the isothermal test results, steady state viscosities at a given solid fraction and shear rate were significantly lower than those measure during continuous cooling. Areas of the hyateresis loops, which can be used as a measure for thixotropy, increased with increasing volume fraction of solid and required to reach the maximum shear rate. |
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