Effect Of Ultrasonic On-line Processing Of Aluminum Melt On Microstructure And Properties Of Slab In Continuous Casting And Rolling

Continuous casting and rolling is an efficient aluminum strip production process.However,unlike steel plate,as-cast aluminum billet has no homogenization process before direct rolling.Therefore,the quality of the billet has a great influence on the performance of the final hot rolled strip.Applying ultrasonic to melt is an advanced melt treatment technology.The research shows that applying ultrasonic can refine the microstructure,improve the uniformity and improve the effect of segregation process.Therefore,in order to reduce the microstructure defects of as-cast billet,combined with the actual production process of continuous casting and rolling,ultrasonic wave was applied to the continuous casting and rolling process of 1030 B aluminum sheet for the first time in this paper,at the same time,ultrasonic was applied at the outlet of the degassing box,the outlet flow groove of the filter box and the molten pool of the front box to carry out the experimental study of multi-pass ultrasonic treatment of aluminum alloy melt.In the process of production,the application of ultrasonic treatment melt at the groove position is generally referred to as the pre-treatment.The sound pressure field distribution of the four-source ultrasonic in the front box molten pool is simulated.The changes of microstructure and properties of 1030 B aluminum plate after melt ultrasonic treatment were analyzed by experiments.The activation of refiner by ultrasonic and the cavitation mechanism of aluminum melt are discussed.The main research contents of this paper are as follows:(1)The melt samples from the outlet of degassing tank and filtration tank were tested,and the macroscopic distribution law of Ti element content was analyzed.The results show that the distribution of Ti element is more uniform,the content of Ti element is increased,and the calculated macrosegregation rate is also relatively reduced.The distribution of Ti element content in the matrix was detected by SEM.It was found that the microdistribution of Ti element content was more uniform under ultrasonic action.The grain size was calculated and compared.The grain refinement of the sample in the flow tank increased by more than 20% after ultrasonic application.It indicates that the synergistic effect of ultrasonic and refiner can improve the refining effect.Ultrasonic makes the distribution of Ti element more uniform,increases the number of effective nucleation,and activates Al Ti B refiner.(2)A four-source ultrasonic cavitation simulation analysis was carried out for 1030 B aluminum alloy continuous casting and rolling.The calculation model of sound pressure in aluminum melt was established,and the distribution law of ultrasonic sound pressure in aluminum melt was obtained.The proportion of cavitation area on the section was calculated to be 17.64%.The solidification microstructure of the sample before and after applying ultrasonic to the molten pool was analyzed,and it was found that the refinement rate was 32.35%,which verified that the cavitation effect of ultrasonic on the molten pool refined the grain structure.Based on the simulation results,the mechanism of ultrasonic cavitation fine grain was discussed,it is analyzed that the intense shock wave and microjet caused by the collapse of cavitation bubbles have a cleaning effect on the surface of refined particles and reduce the wetting angle.A large number of inert finer particles were activated as the core to increase the nucleation rate.On the other hand,the collapse of cavitation bubbles will absorb heat from the surrounding melt,resulting in local undercooling,which can also increase the number of effective nucleation,thus resulting in grain refinement of the final crystal structure.(3)The microstructure and properties of continuous casting and rolling plate under conventional and ultrasonic intervention were compared and analyzed.The results show that the fineness of cast plate is between20% and 30% and that of rolled plate is between 10% and 20%;Moreover,the enrichment of coarse second phase in some areas is improved,and the area fraction of the second phase of the cast plate and the rolled plate decreases by 43% and 44% on average.At the same time,the mechanical properties and corrosion resistance of the cast plate and rolled plate were tested,and it was found that the mechanical properties of the cast plate and rolled plate were improved to a certain extent after the application of ultrasonic.The melt of 1030 B strip was treated by ultrasonic wave at several key positions during continuous casting and rolling.The grain size,composition distribution,mechanical and corrosion resistance ofthe product have been improved to varying degrees.The research work and conclusion have reference and guiding value to promote the application of ultrasonic and improve the quality of aluminum strip.