Aluminum Alloy Ultrasonic Coagulation Dissolved Pool Flow Numerical Simulation And Experimental Research

Treating aluminum melt by ultrasonic field is the international research hotspot in nowadays and a new direction of future casting technique.Caviation and acoustic streaming in the melt induced by ultrasound can improve ingot's solidification structure and mechanical property obviously.This paper took aluminum ultrasonic casting as penetration point and the main study was shown as follows:1,By measuring the displacement amplitude of the ultrasonic radiator and using the multi-media transmission theory,the sound pressure field distribution in the aluminum alloy melt induced by the radiator was calculated.After analyzing the cavitation theory and the influencing factors of cavitation threshold,combined with the sound pressure field distribution of the melt,the area 30mm down below the radiators face was assigned to be the efficient cavitation area in the melt under the laboratory condition.2,The expression of Eckart streaming driving force was obtained by theoretical analysis of the Eckart streaming phenomenon in the melt and derivating the fluid equations considering the second order parameters.CFD software Fluent was used to numerical simulating the phenomenon of the 7050 aluminum alloy melt in the crucible while ultrasonic sonicating.Acoustic streaming driving force was got by calculating the acoustical absorption coefficient in the melt.Then the driving force was added to Fluent's computational process using UDF.The simulation results were as follows: large-scale Eckart streaming phenomenon was produced in the flowable area of the crucible by ultrasound of 170W output power.High velocities were not characteristic of acoustic streaming.The axis velocities in the liquid phase along the radiator face's axis increased at first and then reduced to zero at the crucible's bottom.The maximum value of the axis velocities simulated was in the same order of magnitude with the one calculated by classic Eckart steaming equation,but in the different position. The maximum axis velocity did not increase linearly with the driving force.The increasement of driving force influenced the temperature field and acoustic streaming field.The maximum axis velocity increased with the increasement of container scale rapidly,but when the container went larger,it began to increase slowly.3,According to simulation conditions,ultrasonic vibration was imposed during the crucible casting of aluminum alloy.Results showed there was an obvious borderline in the area from the radiator's face to the boundary of the ingot,combining with the analysis of cavitation field and the numerical simulation results,acoustic streaming phenomenon was proved to have contribution to the refined area of the ingot indirectly. Reaults of semi-continuous casting of aluminum alloy using ultrasounic vibration proved that ultrasound produced same refining effect in semi-continuous casting area.We can find that acoustic streaming phenomenon had little contribution in semi-continuous casting tests for enlarging the refined region after contrasting the flow field caused by casting mouth with acoustic streaming flow field.