The displacement of casting is defined as the displacement of nodes caused by solidification shrinkage and punch pressing. As shown in Fig. 1 (A-D) and Fig. 1 (E-H), the displacement distribution nephogram of aluminum alloy and magnesium alloy castings under the applied pressure of 70MPa is shown. At the same time, under the action of the punch, the upper surface of the casting moves down with the punch. As shown in Figure 1, the displacement distribution of aluminum alloy casting is more uniform than that of magnesium alloy casting, which is similar to the pressure distribution, because the reasons for these phenomena are the same.
Figures 2 and 3 (a) show the positions a and B. the displacements of these two positions on magnesium alloy and aluminum alloy castings are shown in Figure 3 (a). According to the discussion, position B is the top corner position of the casting, and it is the earliest and hardest position for solidification. This position will always support the punch, so it will move with the punch, and the displacement of position B represents the displacement of the punch. As shown in Figure 3, the displacement of position a is the same as that of position B at the beginning. For magnesium alloy, the divergence occurs in 18S, while for aluminum alloy, the divergence occurs in 26S. After bifurcation, the displacement of position a is greater than that of position B. At this time, for aluminum alloy and magnesium alloy, the pressure of the central part of the casting is reduced to 0 MPa. As the solidification proceeds, position a and punch are separated due to solidification shrinkage.
According to the results of numerical simulation and discussion, it can be seen that the pressure in the center of the casting disappears before the solidification is completed during the squeeze casting experiment with the applied pressure of 70MPa. Therefore, shrinkage defects are likely to occur in the center of the casting. In addition, the pressure in the center of magnesium alloy casting disappears earlier than that of aluminum alloy, and the solidified shell of magnesium alloy is harder than that of aluminum alloy. Therefore, the probability of shrinkage defects in the center of magnesium alloy casting should be higher than that of aluminum alloy casting. As shown in Figure 4, it is the defect distribution of the central interface of the casting. For magnesium alloy, visible shrinkage defects appear in the center of the casting, but not for aluminum alloy, which is in good agreement with the results of numerical analysis.
