Figure 1 (A-D) and figure 1 (E-G) show the solidification of aluminum and magnesium alloy castings at different times during squeeze casting. The red part represents the melt part, and the gray part represents the solidified part. It can be seen from the figure that the solid fraction of magnesium alloy casting is higher than that of aluminum alloy casting at the same time. Fig. 2 shows the variation of solid fraction with time in the whole casting.
For the squeeze casting experiments, the working conditions are the same except for the alloy types. In order to make the numerical simulation results comparable with the experimental results, the only difference between the numerical models of magnesium alloy and aluminum alloy castings is the alloy type. The latent heat of magnesium alloy and aluminum alloy can be obtained from pandat database, and their values are 373 kJ kg-1 and 452 kJ kg-1 respectively. Because the latent heat of magnesium alloy is much smaller than that of aluminum alloy, the solidification of magnesium alloy is faster than that of aluminum alloy under the same working condition, which is verified by the numerical simulation results.
Faster solidification means more severe shrinkage. As shown in Fig. 3, the interface heat transfer coefficient of magnesium alloy at condition 1 and 2 decreases sharply at 19S, which is quite different from that of aluminum alloy at condition 2 and 3. At this moment, the pressure at the casting die interface has disappeared, and solidification shrinkage has become the most important factor affecting the contact state of the casting die interface. As shown in Figure 5.6, the solidification of aluminum alloy castings is slower than that of magnesium alloy, and the castings in condition 2 and 3 of aluminum alloy are slower than that in condition 1, so the solidification shrinkage of magnesium alloy castings in condition 1 and 2 is stronger than that of aluminum alloy castings in condition 2 and 3. This means that the interface contact state of magnesium alloy castings in condition 1 and condition 2 deteriorates more severely, and the interface heat transfer coefficient will decrease faster.
It can be seen from the above discussion that the solidification rate has a great influence on the solidification shrinkage. The solidification shrinkage is a very important factor affecting the interface contact state.