Rheological Behavior Of In-situ TiAl₃/ZL101 Aluminum Matrix Composites Prepared By Ultrasonic Vibration

Since the 1970 s, semi-solid metal forming has garnered attention as a promising technique for near net shape forming of components with aluminum alloys. In contrast with conventional casting, semi-solid metal forming has many advantages such as simple processing, energy conservation, high efficiency and low production cost. Several methods have been developed to prepare semi-solid slurries, such as the mechanical stirring, the electromagnetic stirring, the cooling slope casting process and the ultrasonic vibration. In recent years, ultrasonic vibration has been used to produce semi-solid slurry. In this process, the surface of melt is not be broken during ultrasonic vibration. This has several advantages, including refined grains and a more uniform melt. Therefore, in this paper, semi-solid TiAl₃/ZL101 aluminum matrix composite slurry was prepared by ultrasonic vibration. The effects of ultrasonic vibration on the morphology of the slurry were investigated. Besides, the apparent viscosity of the slurry was measured using a rotational viscometer. The results showed that when ultrasonic vibration temperature decreased, the size of primary α-Al particles increased and the shape of primary α-Al particles changed from spheroids to rosettes. With the increase of ultrasonic vibration time, the size of primary α-Al particles decreased initially and increased afterwards. The size of primary α-Al particles decreased with the increasing of ultrasonic power. When ultrasonic vibration temperature was 608 ℃, ultrasonic power was 1000 W, ultrasonic time was 60 s, primary α-Al particles exhibited spherical shapes with the size of 62 μm and the shape coefficient of 0.8. Moreover, the apparent viscosity of the slurry increased as the TiAl₃ fraction or solid fraction increased, and decreased with increasing ultrasonic power. Based on the experimental data, this study established a rheological model of semi-solid TiAl₃/ZL101 composites prepared by ultrasonic vibration:In addition, we used VS2005 software to compile the rheological model into Flow 3D software and then simulate the process of semi-solid TiAl₃/ZL101 slurry forming using Flow 3D software. In order to optimize parameters of semi-solid metal forming, the casting temperature, the injection speed and the die temperature were chose for orthogonal experimental design. The simulation results of the velocity field, the pressure filed and the surface defect were studied, the results showed that the quality of the part forming at semi-solid condition was better than that of the part forming at liquid condition, the velocity field and the pressure filed distribute uniformly at semi-solid condition. High casting temperature and die temperature can guarantee the good flow ability of the semi-solid slurry, this can prepared high quality casting. On the other hand, the slurry has high velocity of filling with high injection speed, this can get the high quality part. Considered all simulation results, the best parameters of semi-solid metal forming was the casting temperature of 600 ℃, the injection speed of 2 m/s and the die temperature of 200 ℃. Based on simulation results, the semi-solid die casting experiment were carried out to verify the reliability of simulation results.