2013 年 63 巻 9 号 p. 310-317
In order to predict the hot tearing during DC casting by using thermal stress analysis, constitutive equations in both solid–liquid coexisting and below solidus of alloy are inevitable. However, previous constitutive equations used in hot tearing predictions have no less than one problem as follows. (1) Testing methods of obtaining material constants weren't appropriate. Firstly, elastic strain reversibility was unconfirmed. Secondary, flat distribution of temperature in gauge length of specimen wasn't guaranteed. Thirdly, strain was measured from not local strain but cross head displacement. Fourth, the melt-back phenomenon was unavoidable in partial melting method which was caused by homogenization of segregation structure. (2) Temperature dependence of strain rate sensitivity of stress wasn't considered. (3) Some material constants were not obtained experimentally but guessed. In this study, elasto-viscoplastic constitutive equations (Hooke's and Norton's laws) for both partial solidification and below solidus were developed. In order to obtain material constants experimentally, two tensile tests which the problem (1) was solved were conducted using Al–5mass%Mg alloy. They were partial solidification tensile tests (above solidus) and high temperature tensile test with high frequency induction (below solidus). Then, temperature dependence of elastic, viscoplastic properties were investigated and material constants were obtained. Furthermore, they were compared with other previous testing methods.
