# Study on interface heat transfer in squeeze casting process

In the solidification process of squeeze casting, on the one hand, due to the cooling of the casting, the metal not only has phase transformation, but also has cooling shrinkage. At the same time, the mechanical properties of the metal are greatly affected by the temperature change, so with the cooling of the casting, its mechanical properties will also have a great change, thus affecting the internal stress distribution of the casting; on the other hand, under the effect of external force, the mechanical properties of the casting will change greatly The change of deformation and stress distribution will directly affect the heat transfer at the interface between the casting and the die, and then affect the temperature distribution inside the casting. Therefore, the temperature field and stress field of the casting affect each other during the whole solidification process, which makes the heat transfer at the interface between the casting and the die in squeeze casting very complicated.

In this paper, the heat transfer coefficient of the casting mold interface in aluminum alloy squeeze casting process was studied. The temperature of different positions of the casting and the mold was measured by experiment. The temperature of each measuring point inside the casting and the mold was fitted by polynomial curve, and the surface temperature of the casting and the mold was obtained by extrapolation. Then the heat flow through the interface was calculated by using the temperature difference of different positions of the mold, and the interface was obtained Heat transfer coefficient. The results show that the heat transfer of the interface in squeeze casting process is not only related to the extrusion pressure, but also related to the temperature of the interface.

The effect of extrusion pressure on heat transfer coefficient of A356 aluminum alloy during squeeze casting was studied by using inverse algorithm. At each time step, the assumed interfacial heat transfer coefficient is used to solve the temperature field, and then the value of heat transfer coefficient is corrected by comparing the actual value with the calculated value at a specific temperature measuring point, so as to obtain the interfacial heat transfer coefficient in this time step. Through the above inverse calculation process, the interfacial heat transfer coefficient of squeeze casting solidification process was obtained, and the relationship between the peak value of interfacial heat transfer coefficient and extrusion pressure was described.

The interface heat transfer coefficient of squeeze casting under different pressures was studied by inverse algorithm. The results show that the peak values of interface heat transfer coefficient are 3858.65, 6718.96, 7250.82 and 8020.44 wm-2k-1 when the extrusion pressure is 0, 25, 50 and 75 MPa, respectively.

The research group of Professor Henry Hu of Canada studied the influence of interface pressure on the interface heat transfer coefficient through experiments. However, they only fit the functional relationship between the peak value of interfacial heat transfer coefficient and the peak value of interfacial pressure and temperature, and did not study the relationship between the interfacial heat transfer coefficient and the changing interfacial pressure with solidification. As a direct influence on the interface contact state, the interface pressure not only changes with time, but also has different distribution in space due to the different pressure transmission in different positions of the die. Therefore, it is very important to study the relationship between the interface pressure and the interface heat transfer coefficient for studying the interface heat transfer behavior of squeeze casting. 