The DSC thermal analysis curve of 7075 aluminum alloy was tested in the experiment. According to the thermal analysis curve, different temperatures (460, 475, 490, 505, 520 and 535 ℃) were set for isothermal solution treatment for 2 hours respectively. The effect of solution temperature on Microstructure and hardness properties of 7075 alloy was studied, so as to determine the best solution temperature.
Figure 1 shows the microstructure of 7075 rheo squeeze casting parts at different solution temperatures (solution time: 2h), and the solution temperatures are 460, 475, 490, 505, 520 and 535 ℃, respectively. Using image pro plus, three straight lines were cut to get the average grain size. It can be seen from table 5.2 that the grain size of the material changes in different degrees after solution treatment. Before heat treatment, the average grain size of the material is 33.1 μ m, and after solution treatment, the average grain size of the sample increases from 33.4 μ m to 41.1 μ m, 54.1 μ m and 57.1 μ m, respectively. By comparing the average grain size of the sample, it can be seen that the grain size gradually increases with the increase of solution temperature and solution time, and the curve distribution of the grain size with the change of solution temperature is shown in Figure 2.