Study On Hdrogen Degassing Effect Of Ultrasonic Vibration On Both Liquid Melt And Semi-solid Slurry Of Al Alloy

As an environmental friendly technology, ultrasonic vibration has attracted a lot of attention. Many researches have been taken on the ultrasonic degassing effect in the liquid metal melt. In recent years, the combination of the technologies of ultrasonic vibration and semi-solid metal processing has been realized. So, it is fairly important to study the degassing effect of ultrasonic vibration in the semisolid metal slurry.In this paper, a fast hydrogen-measuring technology of aluminum melt has been used to study the hydrogen content variation in the hypoeutectic aluminum-silicon alloy A356 and a new type of high silicon aluminum alloy named SPR alloy Al-20Si-2Cu-1Ni-0.6Re when dealt with ultrasonic vibration in both the liquid temperature and semi-solid temperature. It was also studied from the variation of density and porosity of the samples through reduced pressure tests.In different conditions of melt or slurry temperatures and initial hydrogen contents before ultrasonic vibration, the degassing effect of ultrasonic vibration has been studied. The results show that in the semi-solid temperature range of both A356 and Al-20Si-2Cu-1Ni-0.6Re, ultrasonic vibration does have an obvious degassing effect. As the initial hydrogen content decreases, the ultrasonic degassing efficiency of A356 decreases, while it has nearly no influence on Al-20Si-2Cu-1Ni-0.6Re. The degassing effect of both alloys increases in the following sequence of treatments, only ultrasonic vibration, only argon gas and the combination of the above two.The influence of ultrasonic vibration time on the hydrogen content variation of A356 and Al-20Si-2Cu-1Ni-0.6Re alloy under liquid and semi-solid temperature has been studied. The ultrasonic vibration power is 1.2 kW,time range is 0 to 120 s. To A356 alloy, when dealt with ultrasonic vibration under the liquid temperature 650℃and semi-solid temperature 613℃, the hydrogen content of the melt or slurry decreases when vibration time increases. The best vibration time under the liquid temperature and semi-solid temperature is determined to be 120 s and 60 s respectively, on which the ultrasonic degassing efficiency is 47.4% and 21.6%. And to Al-20Si-2Cu-1Ni-0.6Re alloy, under the liquid temperature 710℃and semi-solid temperature 680℃, the hydrogen content of the melt or slurry first decreases when the vibration time increases, then as the time increases further, the hydrogen content increases. When under the liquid temperature, the vibration time needed to degas the high silicon aluminum alloy Al-20Si-2Cu-1Ni-0.6Re is shorter than hypoeutectic aluminum alloy A356. And under the semi-solid temperature, in the same vibration time, the former degassing effect is better than the latter.The influence of ultrasonic vibration power on the hydrogen content variation of Al-20Si-2Cu-1Ni-0.6Re alloy under liquid and semi-solid temperature has been studied. The ultrasonic vibration time is 90 s, power range is 0 to 1600 W. When treated by ultrasonic vibration under the liquid temperature 710℃and semi-solid temperature 680℃, the hydrogen content first decreases when the vibration power increases, then as the power increases further, the hydrogen content increases slightly. The degassing effect of the liquid and semi-solid temperature is considerably the same, and the highest degassing efficiency of both can reach to 37%.The principle of ultrasonic degassing was discussed. It points out that it is the co-action result of cavitation and acoustic streaming effects of ultrasonic sound in the melt and semi-solid slurry. To the semi-solid slurry of aluminum alloy, acoustic streaming can improve the metal's flow property, and then increase the action range of cavitation, so to improve the ultrasonic degassing effect. The reason why high silicon aluminum alloy can attain a good ultrasonic degassing effect under both liquid and semi-solid temperature is the high content of silicon and the powerful acoustic streaming induced by high power ultrasonic vibration. Both can greatly improve the flow property of the melt and semi-solid slurry.