The quality of wheel shaped rheo squeeze casting parts is closely related to the extrusion filling speed, pouring temperature, mold temperature and other factors. The process parameters of 7075 aluminum alloy wheel shaped squeeze casting were optimized by orthogonal experiment with AnyCasting simulation software. In the experiment, the pouring temperature, mold filling speed and mold temperature were simulated by three factors and three levels orthogonal experiment.
(1) Probabilistic defect parameter simulation results. As shown in Figure 1, JT represents the pouring temperature, CV represents the filling speed, and MT represents the mold temperature (all subsequent figures in this section are marked with this code). According to the simulation results, when the pouring temperature is 635 ℃, the filling speed is 0.2m/s, and the mold temperature is 200 ℃, the probability defect parameter distribution is the least, and the quality of squeeze casting parts is excellent.
(2) Combined defect simulation results. As shown in Figure 2, combined defects refer to the defects caused by uneven temperature gradient and cooling rate, mainly including uneven stress, hot cracking and other defects. It can be seen from the figure that from the defects of temperature gradient and cooling rate, when the pouring temperature is 635 ℃, the mold filling speed is 0.2m/s, and the mold temperature is 200 ℃, the distribution of combined defect parameters is the least, and the quality of squeeze casting parts is good.
(3) The simulation results of oxide defects are shown in Figure 3. In terms of oxide defects, when the pouring temperature is 620 ℃, 635 ℃, the filling speed is 0.2m/s, and the mold temperature is 150 ℃ and 200 ℃, the distribution of oxide defects in the two groups (group 2 and group 5) is the least, and the quality of squeeze casting parts is better.
(4) The curve comparison between filling fraction and velocity is shown in Figure 4. Among them, four curves represent the change of filling velocity of alloy melt at four sensor positions, yellow represents position 1, blue represents position 2, green represents position 3, and red represents position 4 (center part of squeeze casting parts). It can be seen from the figure that when the filling speed is 0.08m/s (Experiment 1.4.7), the flow velocity of alloy melt at each position begins to change continuously, and the former is discontinuous pulsating velocity change; when the filling speed is 0.2m/s (Experiment 2.5.8), the velocity at four sensor positions intersects smoothly, and when the flow reaches 2.2m/s, the velocity at each sensor position is stable When the filling velocity is 0.4m/s (Experiment 3.6.9), the flow velocity at positions 4 and 3 increases sharply at the beginning of filling, and when the filling velocity reaches 40%, the alloy melt basically fills the top of the cavity, positions 1 and 2 The filling velocity at the filling point increases rapidly to nearly 80 cm / s, and then decreases when the filling rate reaches 90%. However, the velocity deviation between position 1, 2 and position 3, 4 is still large (the pressure gradient is also large), and it is easy to produce liquid segregation and other defects. Therefore, 0.2m/s is the best from the point of view of mold filling rate, which can obtain better quality of squeeze casting parts, and the parts should be designed as the castings with uniform wall thickness as far as possible.
(5) Analysis of the optimal process parameters. Based on the above simulation results, the distribution of defects such as probability defect parameters, combined defect parameters, oxides and the relationship between filling velocity and filling fraction at different positions of the middle section of squeeze casting parts are considered. During the cooling process, most of 7075 alloy will produce hot cracks and inclusions. Therefore, the combined defect parameters affected by temperature gradient distribution and cooling rate and oxide defects are the main reference. In order to avoid the residual stress caused by uneven temperature and cooling shrinkage, and even hot cracks, the best process parameters are as follows: pouring temperature 635 ℃, mold filling speed 0.2m/s, mold temperature 200 ℃.
(6) Comparative test analysis. When the pouring temperature is fixed at 635 ℃ and the mold temperature is 200 ℃, the mold filling speed is 0.08m/s and 0.2m/s, respectively. Cut from the middle part of the part, grind it with sandpaper, and then corrode it with 180g / L sodium hydroxide solution for 13 minutes. Rinse it with clean water immediately, and then put it into 25% nitric acid solution by volume to remove the black alkali corrosion products on the surface. The comparison between experiment and simulation is shown in Fig. 5 and 6. When the mold filling speed is 0.08m/s, the location of the crack defect is corresponding to the probability defect location in the simulation results. The main reason is that the temperature gradient and the stress after cooling are caused by the slow mold filling speed. When the filling speed was optimized to 0.2m/s, no such defects were found.
