Measurement of temperature inside die and estimation of interfacial heat transfer coefficient in squeeze casting

As an advanced near-net shape technology, squeeze casting is an excellent method for producing high integrity castings. Numerical simulation is a very effective method to optimize squeeze casting process, and the interfacial heat transfer coefficient(IHTC) is an important boundary condition in numerical simulation. Therefore, the study of the IHTC is of great significance. In the present study, experiments were conducted and a "plate shape" aluminum alloy casting was cast in H13 steel die. In order to obtain accurate temperature readings inside the die, a special temperature sensor units(TSU) was designed. Six 1 mm wide and 1 mm deep grooves were machined in the sensor unit for the placement of the thermocouples whose tips were welded to the end wall. Each groove was machined to terminate at a particular distance(1, 3, and 6 mm) from the front end of the sensor unit. Based on the temperature measurements inside the die, the interfacial heat transfer coefficient(IHTC) at the metal-die interface was determined by applying an inverse approach. The acquired data were processed by a low pass filtering method based on Fast Fourier Transform(FFT). The feature of the IHTC at the metal-die interface was discussed.

Experimental study and cellular automaton simulation on solidification microstructure of Mg-Gd-Y-Zr alloy

The solidification microstructure of Mg-Gd-YZr alloy was investigated via an experimental study and cellular automaton(CA)simulation.In this study,stepshaped castings were produced,and the temperature variation inside the casting was recorded using thermocouples during the solidification process.The effects of the cooling rate and Zr content on the grain size of the Mg-Gd-Y-Zr alloy were studied.The results showed that the grain size decreased with an increase in the cooling rate and Zr content.Based on the experimental data,a quantitative model for calculating the heterogeneous nucleation rate was developed,and the model parameters were determined.The evolution of the solidification microstructure was simulated using the CA method,where the quantitative nucleation model was used and a solute partition ceoefficient was introduced to deal with the solute trapping in front of the solid-liquid(S/L)interface.The simulation results of the grain size were in good agreement with the experimental data.The simulation also showed that the fraction of the eutectics decreased with an increasing cooling rate in the range of 2.6-11.0℃·s^(-1),which was verified indirectly by the experimental data.