2021 Volume 71 Issue 2 Pages 112-120
To predict hot tearing during DC (direct chill) casting by thermal stress analysis, cooling rate dependence of viscous properties in semi-solid state are indispensable. However, those at cooling rates of DC casting had not been obtained in the past. In this study, a tensile test device with high frequency induction heating that can control the cooling rate was developed. By using this device, the viscous properties were obtained on Al-5mass%Mg alloy at 1 K/s and 5 K/s. To determine those, two methods were employed. The first method was to determine those from relationships between the maximum true stress, σmax and the true strain rate, έmax. The method suggested by Matsushita was employed as the second method. It was found that the viscous properties obtained by each methods were different at 1 K/s. This should be because the true strain rate was increased due to the formation of micro-damage inside the test piece at σmax. The viscous properties of those that did not experience micro-damage were independent of the cooling rate. This should be because the degree of microsegregation was similar at the two cooling rates resulting in no difference in solid fractions.
