*7.6. Characterization of the AA611 Alloy Cast Strip*

A microstructural study has been carried out to analyze the quality of the cast strips. The samples for optical microscopy were ground down to 1200 grid, and then electropolished/etched using 2% perchloric acid (HClO4) in alcohol. Micro images were taken using a Leica DM IRM optical microscope (Leica Microsystems, Concord, ON, Canada) and a TM3030 Scanning Electron Microscope (Hitachi, Pleasanton, CA, US). The microstructure consisted of fine equiaxed grains throughout the thickness of the strips (see Figure 13). The microstructure also contains porosities at various locations within the cast strip, very similar to DC cast product. The average grain size of the strip was found to be 85 μm, as shown in Figure 13.

**Figure 13.** *Cont.*

**Figure 13.** (**a**) Microstructure at the center of the strip (50×); (**b**) polarized micrograph (50×); (**c**) intermetallics observed at the grain boundaries as well as inside the grains (500×).

The inter-metallics are also observed to be distributed inside the grains, as well as at the grain boundaries of the cast microstructure, as shown in Figure 13c. X-ray micro-analyses revealed that inter-metallics dispersed throughout the cast structure have the following stoichiometry: Al17Cu2Mg3Si3, Al20Cu2Mg2.5Si5, whereas the elongated inter-metallics distributed at the grain boundaries are in the category of Al17(CuMg)2(FeMn)Si2 or Al25(CuMg)4.5(FeMn)Si5 [16,17]. These phases are clearly observed in the Figure 13c, at a higher magnification of 500×.
