*7.7. Energy Dispersive Spectroscopy (EDX) Analysis of the Cast AA6111 Alloy*

Energy dispersive spectroscopy (EDX) analysis confirmed the presence of Al, Cu, Mg, and Si, in AA6111 alloy, as shown in Figure 14. Furthermore, there is a negligible macro-segregation of alloying elements in the cast strip, as shown in the chemical element's maps, obtained at 15 KV excitation voltage. This is caused by the rapid solidification of molten AA6111 alloy in the HSBC process, which resulted in a homogenous microstructure with fine equiaxed grains. Additionally, the elemental maps provide us with details of the chemical nature of the secondary phases. EDX analyses revealed that inter-metallics dispersed throughout the cast structure are rich in Cu and Mg, whereas the elongated inter-metallics found at the grain boundaries are concentrated in Si, Cu, and Mg.

#### *7.8. Surface Roughness Measurement*

The surface waviness of the top/bottom sides of the strip was determined using a Nanovea 3D profilometer (Nanovea, Irvine, California, United States). This technique works on the principle of measuring the physical wavelength of light and directly relating it to a specific height. This ensures accurate measurement of surface roughness/finish [20]. The scan length for all the measurements was 25 mm, whereas the scan speed was 0.1 mm/s. Ten random locations were selected for surface roughness measurements. These locations were randomly selected from all over the strip. The surface profiles are almost identical to one another. The upper surface roughness lies within the 125 μm (0.125 mm) range, as shown in Figure 15a, which is considerably smaller than the DC cast product roughness, i.e., 0.45 mm for AA5182 aluminium alloy (Figure 16a,b) [21]. Additionally, pinholes/blowholes were not detected on the surface of the cast strip (Figure 16c,d), unlike continuously cast products, which possessed defects on their surfaces, and require surface grinding prior to hot rolling [21].

**Figure 14.** (**a**) Intermetallics distributed within grains and at grain boundaries (1000×). (**b**,**c**) Elemental maps showing the chemical content of the intermetallics.

**Figure 15.** 3D profilometry results: (**a**) strip top surface roughness and (**b**) strip bottom surface roughness.

**Figure 16.** Strand surface morphologies of direct chill of (**a**) AA3004 (Al-1%Mn-1%Mg), (**b**) AA5182 (Al-4.5%Mg) [21], (**c**) surface morphology of AA6111 (Al-1.1%Si-1%Mg-0.45%Mn), 250 mm wide strip produced via the HSBC process. (**d**) Surface morphology of AA6111 (Al-1.1%Si-1%Mg-0.45%Mn), covering the central 80 mm length of the strip produced via the HSBC process.

The strip bottom surface roughness was also measured, and lay in the 20 μm range, as shown in Figure 15b. As evidenced by the results of the line scans, the bottom surface quality is much superior to the top surface. This fact is credited to the fact that the molten metal is in direct contact with the moving belt, and conforms to its shape, during the solidification process. On the other hand, the top surface of the cast strip is exposed to the atmosphere and is affected by disturbances in the flows of the molten metal.
