2.4.1. Microstructure Analysis of the Cast Rolling Strip Samples

The 20 × 20 × 6 mm samples were cut at a distance of 20 mm from the edge of the cast rolling strips. The samples were ground and polished in the MP-2B polishing machine and the morphology, size, and distribution of the precipitated phases were observed using a Phenom fully automatic scanning electron microscopy (Phenom-world BV, The Netherlands). Then, the electrolyte (19 mL water, 38 mL concentrated sulfuric acid, 43 mL phosphoric acid) was prepared for anodic coating. The current was controlled at 0.2 A, the temperature was controlled at 20 ◦C~30 ◦C, and the surface was observed every 30 s. After the grains appeared, the pictures of the grains on different sides of the cast rolling strip samples were obtained by a metallographic microscope (OLYMPUS DSX500 metallurgical microscope (Olympus, Japan)).
