Power ultrasonic treatment of molten metal
At present, in order to obtain fine and fine structure, various external fields (magnetic field, electric field and ultrasonic vibration treatment of metal melt technology are very active. Among them, power ultrasonic treatment of metal melt technology has a significant effect on the refinement of metal solidification structure.
The technology of power ultrasonic treatment of molten metal is during the solidification of the molten metal or before the solidification of the molten metal. The method of applying ultrasonic vibration to the metal melt to control the structure and performance of the metal during solidification. Compared with the traditional inoculation and metamorphism treatment technology, the power ultrasonic treatment of the metal melt technology is used to control and refine the metal solidification structure. It can avoid the pollution of the environment and the metal material itself, so the power ultrasonic treatment of the liquid metal melt is one of the effective methods to obtain excellent structure and performance castings, and it is the main way to tap the potential of high-tech materials.
Mechanism of Melt Treatment
The sound wave with a frequency above 20kHz or the wave generated by the vibration frequency of an object in this range can be called ultrasonic, which is both a form of wave and a form of energy, and a mechanical wave propagating in a media medium. It is the threshold of the wave. After exceeding a certain value, it interacts with the sound transmission medium and can change or even destroy the state, nature and structure of the sound transmission medium. Change objects or physical properties. The cavitation effect and acoustic flow effect of ultrasound are mainly used.
Ultrasonic cavitation effect
Cavitation is a physical phenomenon caused by ultrasonic waves. It is the main reason why ultrasonic waves can refine metal melts. . When ultrasound is used
When used in a molten metal, the gas solubility of the molten metal is reduced and a large number of tiny bubbles are formed. In this process, the tiny bubbles in the molten metal are activated under the action of power ultrasound, which will produce a series of dynamics. process. With the continuous action of ultrasound, the cavitation bubbles will gradually increase. When the cavitation bubbles exceed a certain threshold, the cavitation bubbles will instantly collapse, and the energy in the cavitation bubbles will be released instantaneously, resulting in high temperature and high pressure in a small area, forming structural fluctuations And energy fluctuations, increase the nucleation rate of the alloy, and initiate crystallization.
Ultrasonic sound flow effect
During the propagation of the ultrasonic wave in the molten metal, due to the absorption and loss of the molten metal, there will be attenuation when the ultrasonic wave propagates in the melt, therefore. The limited amplitude attenuation will form a certain sound pressure gradient from the tool head, and the strong shock wave will bring the broken crystal embryo to each part of the melt.
Part, at the same time, the temperature field and composition of the molten metal will be more uniform during the flow process, and it will have a certain stirring effect on the molten metal.
Processing application
In the process of metal melt processing, power ultrasound has a unique acoustic effect. After applying power ultrasound, the solidification structure of the ingot can be
From coarse columnar crystals to uniform and fine equiaxed crystals. At the same time, the segregation will also be improved, reducing or eliminating forming defects, and improving the metal structure and casting properties. Different ultrasonic process parameters and some other experimental conditions will affect the ultrasonic effect. The process parameters that affect the effect of ultrasonic refinement mainly include ultrasonic power, ultrasonic vibration time, and ultrasonic vibration temperature.
Application during solidification
The high temperature generated by ultrasonic cavitation helps to improve the wettability between the reinforcing phase and the base alloy, and solves the problem of the particles and the base alloy being fully wetted by the mechanical stirring and easy to agglomerate. Moreover, the acoustic current effect plays an important role in accelerating mass transfer, heat transfer, destroying the boundary layer, and promoting the dispersion of reinforcements. Therefore, the application of power ultrasound in the solidification process of metal matrix composites has received extensive attention.
