After determining 475 ℃ as the best solution temperature, four 15 × 15 × 15mm heat-treated samples were taken from 8 and 12 parts respectively. 1.5h, 2h, 2.5h and 3H were selected for water quenching at different holding time. The transfer time is less than 10s and the water temperature is room temperature.
It can be seen from the metallographic structure chart 1 of 7075 rheo squeeze casting parts under different solution time that when the solution time is 1 h, most of the second phase particles in the structure still gather at the grain boundary and are not fully dissolved. When the solution time is 2 h, the grain boundary becomes fine and most of the second phase particles melt into the matrix. The average grain size is about 39.3 μ M. With the increase of time, the grain boundary becomes blurred, the grain size grows up and the grains tend to merge. Figure 2 shows the grain size change curve of 7075 rheo squeeze casting parts under different solution time. It can be seen from Figure 2 that when the solution time is 2 h, the grain size reaches the minimum, and then becomes coarse with the extension of time.