**2. An Overview of Previous Studies Conducted on HSBC Metal Feeding Systems**

Many variants of the feeding system have been investigated by researchers at McGill Metals Processing Centre, to date. They can be classified into two types of the metal delivery systems; either single-impingement or multi-impingement, based on how many times the molten metal encounters obstacles before reaching the cooling substrate, as shown in Figure 2 [2,3]. In a single impingement feeding system, the molten metal is abruptly stopped by the horizontally moving belt, since there is no intermediate obstacle in its way, which could decrease its kinetic energy. As a result, the molten metal tends to penetrate back into the quadruple region, i.e., the region where melt, refractory, air, and belt coexist, as determined by Sa Ge et al. [3], for the casting of plain carbon steel, employing a single impingement feeding system (Figure 3a) [3]. If the backflow is too excessive, it may lead to skull formation, thereby curtailing further casting as determined experimentally.

**Figure 2.** Different feeding systems for HSBC process, (**a**) Double impingement, (**b**) single impingement [1–4].

**Figure 3.** (**a**) Simulated flow of the molten plain carbon steel in single impingement feeding system, showing back-flow into the quadruple region; molten phase is colored red, fully solidified shell is in blue, and the partially solidified zone is in between [3], (**b**) Numerical simulations did not predict any back flow of molten Al-Mg-Sc-Zr into the quadruple region; the molten phase is coloured red, air is represented in blue. The numerical simulations were supported by experiments in these studies [13].

Additionally, it has been shown by Sa Ge [13], that a single impingement feeding system can be used to produce Al-Mg-Sc-Zr alloy strips, without any backflow into the quadruple region (see Figure 3b), as was found for steel casting. This could be due to the low density of Al-Mg-Sc-Zr alloy and a higher contact angle, i.e., a lower wettability between liquid Al-Mg-Sc-Zr and the alumina refractory [13].

In both these studies, the molten metal flowing over the moving belt was considered as being nearly iso-kinetic, a condition in which the velocities of the molten metal and belt approach each other. Furthermore, the as-cast thickness of the produced strips was ~3 mm [3,5].

As explained above, excessive backflow of molten metal into the quadruple region is not desired. This can be conveniently prevented by employing a double-impingement feeding system in the HSBC process [14]. In a double impingement feeding system the molten metal dispensing from the refractory nozzle slot first interacts with a 45◦ inclined refractory plane, followed by its second interaction with the moving belt, on to which it begins to solidify [14]. In this way, the final impact of the molten metal with the moving belt is not as rapid and abrupt, as it would be for a single-impingement feeding system [4]. Furthermore, in a double-impingement feeding system, the flow of the molten metal over the inclined refractory plane and the moving belt is entirely gravity-driven, unlike the variant of the single-impingement feeding system reported by Sa Ge for the casting of Al-Mg-Sc-Zr. For that, the flow of the molten metal is impeded by the refractory front wall, as shown in Figure 3b [13]. During continuous operation, the refractory material may abrade and embed small particles into the pool of molten metal. This could significantly decrease the bulk quality of the cast strip.

In this research study, non-isokinetic feeding of molten metal over the moving belt has been considered. This is significantly different from our group's previous research studies, for which only near iso-kinetic feeding was considered, as discussed above. Under non-isokinetic feeding conditions, as in the present case (the belt/side dam speed is considerably slower, i.e., 0.3 m/s, as compared to the molten metal velocity at the nozzle slot outlet, i.e., 2 m/s). The strip produced under this condition has ~6 mm thickness, which is thicker as compared to the strips obtained under iso-kinetic feeding (~3 mm). This allowed us to perform substantial hot deformation in order to produce a 1 mm, or lower, thickness of strip. Hot deformation is necessary, as it transforms the cast dendritic structure into fine equiaxed grains, leading to a far more uniform distribution of alloying elements throughout the sheet material. Another purpose of hot reduction is to squash/weld any pores, if present, in the cast strip, so as to improve its mechanical properties [15].

### **3. Objectives of the Present Research**

The objective of this research study is to produce high-quality AA6111 aluminum alloy strips 250 mm wide, ~6 mm thick. Additionally, molten metal flow in a double-impingement feeding system has been analyzed under non-isokinetic feeding. Under these experimental conditions, the molten metal was observed to be flowing inwards, i.e., towards the center of the strip. This can usefully eradicate center shrinkage cavity defects formed otherwise. In order to investigate this phenomenon, a three-dimensional mathematical model was developed using Fluent software (14.5, Ansys, Inc., Canonsburg, PA, USA, 1970), and its accuracy was evaluated against experimental data. Thanks to these numerical simulations, we now understand the complex interaction of the molten metal with the inclined refractory plane and the moving belt that leads to the phenomenon of the molten metal's inward flow.

A horizontal single belt pilot caster installed at MetSim Inc., Montreal, QC, Canada, was used for the casting experiments. However, several modifications were applied to the existing caster, as it was not capable of producing 250 mm wide strips. These included the design of a new alumina refractory nozzle slot (250 mm wide and 3 mm thick), increasing the cooling capability of the moving steel belt, needed to completely solidify molten AA6111 strip before it exits the moving belt. Additionally, the caster modifications included enlarging the strip guidance system, and, lastly, the extension of the length and width of the run-out table, so as to accommodate the wider strip exiting the caster.
