Prediction and Experimental Validation of Cooling Rate Dependence of Viscoplastic Properties in a Partially Solidified State of Al–5 mass%Mg Alloy

Abstract

To predict hot tearing in direct chill (DC) casting and shape casting of aluminum alloys using thermal stress analysis, cooling rate dependence of viscoplastic properties in a partially solidi ed state is indispensable. Based on viscoplastic properties determined from experiments, this study develops a method to predict the temperature dependence of viscoplastic properties at an arbitrary cooling rate through the Clyne-Kurz microsegregation model. For validation of the developed method, tensile tests were performed on Al-5 mass%Mg alloy in a partially solidi ed state at three cooling rates. Results show good agreement between the predicted values and experimentally obtained values, which demonstrates that the developed method is effective for predicting the cooling rate dependence of viscoplastic properties.

Effect of Temperature Field and Mechanical Properties of Casting on Prediction of Hot Tearing Tendency Using FEM Thermal Stress Analysis

“…The average expansion coefficient was determined from the following experimentally obtained results in an earlier work. During solidification, an Al4%Mg alloy contracts by around 0.2% during solidification 32) in the temperature range between 570°C, which is consistent with the ZST, 14,26,27) and the solidus (448°C). Figure 3(b) presents the thermal strain at each temperature range which reproduces the contraction behavior described above.…”

“…14,26,27) Under the cooling conditions used for this study, it was confirmed that the ZST of the alloy has almost no cooling rate dependence. 14) The temperature at the occurrence of hot tearing T HT was determined from the experimentally obtained thermal load described in section 2.1, i.e. the temperature at which the first derivative of the loadtime curve is the maximum.…”

“…2,22) However, within the cooling rate range of changes found in this study, the cooling rate effect on the grain size is negligible. Therefore, the difference in the hot tearing tendencies observed in this study should be caused by not the grain size but other factors (e.g., differences in both the temperature field of casting and intensity of micro segregation of the major solute element 14) ).…”

“…The elastic Poisson's ratio and the average expansion coefficient (reference temperature: 25°C) were obtained using computational thermodynamics software. 3.4.2 Temperature range from the solidus to the ZST (448¯T¯570°C) Plots for both the Young's modulus 26) and two creep parameters 14,26,27) were obtained previously using a tensile testing device during solidification. The elastic Poisson's ratio was obtained using computational thermodynamics software.…”

“…Actually, experimentally obtained results 13) demonstrate that the alloy strength during partial solidification depends on the cooling rate. Moreover, the cooling rate dependence was reported 14) for the two creep parameters of both n and A in eq. (1), which describes the inelastic deformation behavior of an AlMg alloy during partial solidification.…”