| Treating metal melt by ultrasonic field is an effective method of improving casting ingot solidification structure and material mechanical property. It is the international research hotspot in nowadays and a new direction of future casting technique. This paper took aluminum ultrasonic casting as penetration point and the main study was shown as follows:1,The whole ultrasonic vibration equipment had been studied. First, according to the theory of electricity-force-acoustic analogy, admittance circles in different load cases were measured by using admittance analyzing apparatus. Based on them, the variational rules of resonant frequency F_s and mechanical quality Q_m of the vibration system were studied. The results showed: F_s and Q_m both decreased with the increase of load temperature and viscosity and working depth of tool rod; with load cross section area increased, first order F_s increased and second order F_s has a little decreased, but it had a less effect on Q_m. On this basis, the optimum electrical matching of the vibration system and generator was confirmed. Second, based on the discussion of resonance breaking of vibration equipment, the circuit working theory of quondam generator was analyzed and improving scheme of power source suited to ultrasonic casting.2,For the problems of that the end face of present tool rod was flat, sound wave radiated in a small scale and its influencing zone was small, which is bad for ultrasonic casting, the optimum design of end face was made according to Snell law and with all of the comprehensive consideration of shape of metal liquid sump in semi-continuous casting, the distribution of sound intensity and using efficiency of sound energy considered. The modal analysis and validation of tool rod was carried out by using finite element software Marc. It was found that the longitudinal vibration frequencies of unimproved and improved tool rod were almost uniform, which assured that the improved tool rod could be used matching the quondam vibration system.3,The energy transmission property of ultrasonic in treating metal melt, two major functionary mechanism of grain refining by ultrasonic and the effect of ultrasonic on the process of nucleus and growth of crystal were described, which provided a academic basis for the proceeding of experiments and their results analysis.4,The casting ingot structure refining laws of the different ultrasonic powers, temperatures, depth and ways of applying vibration and cooling methods during ultrasonic treating process were discussed. Ultrasonic action area and mechanical property of casting ingot were also analyzed. Experiment results showed: there existed an optimal ultrasonic power 170W and temperature range of applying vibration 800～660℃in grain refinement by ultrasonic; it was good for grain refinement when cooling intensity decreased properly; the depth of applying vibration should not be too great, otherwise the vibrating intensity would decreased and grain refining effect would be weakened; the refining effect acquired with intermittent vibration would be better than that with continuous vibration when the time and temperature of applying vibration selected reasonable; ultrasonic acting distance was related to different casting load cases; by ultrasonic treatment, mechanical property of casting ingot was increased and its structure and composition were also prone to homogenization, which was good for second machining.Through the study above, some variational rules of vibrating property of the vibration system and matching laws of technical parameters during ultrasonic casting were acquired. It has certain guide value for power ultrasonic effective treating metal melt used in industrial filed. |
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