*3.4. Discussion*

According to the experimental research in this paper, it can be concluded that the ultrasonic bending vibration improves the refinement efficiency of the Al-Ti-B refiner. Compared with the conventional casting and rolling strip with the 0.18 wt% Al-Ti-B refiner, the grain size of the ultrasonic casting and rolling strip with the 0.18 wt% Al-Ti-B refiner or 0.12 wt% Al-Ti-B refiner are smaller, the precipitated phases are dispersed, the distribution is uniform, and the mechanical properties are also improved. Moreover, after the cold rolling of the casting and rolling strip, the effect of the ultrasonic bending vibration on the improvement of the microstructure and properties of the aluminum alloy strip is inherited.

Al-Ti-B refiner plays an important role in the grain refinement of the aluminum alloy, and the refinement effect of the refiner is largely determined by the size and shape of the TiB<sup>2</sup> particles and TiAl<sup>3</sup> phase. The fine and uniformly distributed TiAl<sup>3</sup> phase and the dispersed and isolated TiB<sup>2</sup> particles are all helpful in improving the refining effect of the refiner [29,30]. TiB<sup>2</sup> particles inoculated into the melt through the Al-Ti-B master alloys are able to enhance the heterogeneous nucleation of α-Al grains [31–33]. However, TiB<sup>2</sup> particles are small in size and easy to aggregate into clusters, which are difficult to separate when added into the melt metal. Due to their high density and being

easy to deposit, TiB<sup>2</sup> particles basically lose the role of the nucleation core, reducing the refining efficiency and becoming inclusions, thus reducing the quality of the aluminum products [34,35].

The ultrasonic bending vibration induced by the L-shaped ultrasonic rod into the aluminum melt in the launder will produce a significant acoustic flow effect, which will produce an obvious stirring and scouring effect in the aluminum melt. This causes the TiB<sup>2</sup> particles to be evenly distributed in the aluminum melt, reduces the aggregation and precipitation of the TiB2, and makes the effect of the grain refinement more obvious. At the same time, the stirring effect of the ultrasonic bending vibration can promote the diffusion of the alloy elements in the aluminum melt and solid solution in the aluminum matrix, reduce the micro segregation, and inhibit the formation of coarse compounds, thus strengthening the matrix.

However, when the amount of Al-Ti-B refiner is reduced from 0.18 wt% to 0.09 wt%, even if it has the effect of the ultrasonic bending vibration the microstructure and properties of the 1060 aluminum alloy cast rolling strip and its subsequent cold rolling strip will deteriorate. This shows that the ultrasonic energy applied in the continuous casting and rolling process of the 1060 aluminum alloy in this paper cannot completely replace the role of the Al-Ti-B refiner. However, it can also be found from the text that when the amount of Al-Ti-B refiner is reduced from the conventional 0.18 wt% to 0.12 wt%, the microstructure and properties of the 1060 aluminum alloy cast rolling strip and its subsequent cold rolling strip are better than those of the conventional. The ultrasonic energy applied in this paper can reduce by the 1/3 amount of Al-Ti-B refiner used during continuous casting and rolling of the 1060 aluminum alloy, which is conducive to reducing the production costs.
