Synergistic Effect Of Ultrasonic Field And AlTiC Refiner On Grain Refinement And Its Mechanism Research

Abstract:Ultrasonic casting and conventional casting were compared in experiment, we measured the cooling curves of aluminum melt during solidification process and calculated the undercooling degree difference. Metalloscope was used to measure the grain size of ingot solidification organization with different AlTiC refiner addition, and DSC measurement was used to calculate the difference in undercooling degree, these results were used to discuss the undercooling nucleation model of TiC particles. We detected the distribution of main alloying elements in aluminum alloy ingot casting, as well as to the AlTiC refiner on the effect of ultrasonic in the aluminum melt by using EPMA and SEM, direct reading spectrometer. The research indicates that:1. Ultrasonic vibration can produce local temperature fluctuations inside the aluminum alloy melt, the temperature fluctuation amplitude caused by ultrasonic cavitation is2-6℃in experiment. The temperature fluctuation increases the initial nucleation temperature from638.4℃to644.5℃, which brings the nucleation process of melt forward. During the undercooling nucleation stage, the temperature fluctuation can increase the degree of undercooling to increase the rate of nucleation, and in the dendrite growth process, can fusing the secondary dendrite arm to increase the nucleation core. Compare the nucleation rate calculated by undercooling degree with grain density counted by crystallite size distribution, we conclude that the increase of nucleation rate is not only caused by undercooling nucleation under the effect of ultrasonic.2. The microstructure is refined with Al-5Ti-0.2C refiner and has the best effect with0.5%addition, continue to add content of Al-5Ti-0.2C refiner, it can’t improve ingot refinement effect of solidification organization. The DSC results show that the cooling curves make some difference:the nucleation undercooling degree and maximum undercooling degree of the melt are both decreased with the increase of Al-5Ti-0.2C refiner addition but decreased little once the addition is over0.5%. 3. The refinement rate is44%with0.5wt.%A1-5Ti-0.2C refiner during the solidification of7085aluminum alloy, the refinement rate is76%with AlTiC refiner and ultrasonic field, applying ultrasonic increases32%refinement rate. EPMA element surface scanning results show that after applying ultrasonic Ti and C elements are relatively evenly distributed inside the crystal, concentrations of Ti and C elements in the grain boundary decrease significantly. SEM element line scan results show that applying ultrasound makes Zn, Mg, Cu solute elements distributed relatively evenly in the aluminum melt, the constitutional undercooling degree of TiC particles increases and local variations of undercooling degree decrease during nucleation. Using direct reading spectrometer to detect the elements of ingot cross section, the results show that ultrasonic effect makes the refiner more evenly distributed in the aluminum melt, and Zn, Mg, Cu element of macro segregation rate are relatively reduced, the TiC particles are uniform distributed in the melt, which is helpful to form a uniform fine equiaxed grain structure.