Reduction of Elongation Anisotropy in Cold-Rolled and Annealed Al-7%Si Alloy Strips Fabricated by Vertical-Type High-Speed Twin-Roll Casting

Vertical-type high-speed twin-roll casting is a candidate method to realize up-grade recycling of aluminum, in which cast alloy is used to produce wrought alloy products due to its rapid solidification. Using A356 aluminum alloy (Al-Si-Mg) strips to produce wrought alloy sheets requires isotropy and high ductility for good formability. However, the elongation of the cold-rolled and annealed A356 strips after vertical-type high-speed twin-roll casting is different in the rolling direction (RD) and the transverse direction (TD) of the strips. In this study, strips of pure Al, Al-2% Si, and Al-7% Si alloys were fabricated by vertical-type high-speed twin-roll casting to investigate the effect of eutectic Si particles on the elongation anisotropy of the cold-rolled and annealed strips. The effect of increasing the rolling reduction rate of the strips on the reduction of the elongation anisotropy was examined. Elongation anisotropy was not observed in pure Al, whereas it was observed in Al-2% Si and Al-7% Si, and it was more pronounced in Al-7% Si. Although the eutectic Si particles were randomly distributed in the RD cross section, they were oriented in the RD in the TD cross section. When the strip was loaded in the TD, the voids that formed around the eutectic Si particles were often connected perpendicular to the load direction during the tensile test, and the elongation decreased. To reduce the elongation anisotropy, it is necessary to create a uniform distribution of eutectic Si particles in both the RD and TD cross sections. Tandem vertical-type high-speed twin-roll casting was used to fabricate a thick strip while maintaining the rapid cooling rate. In the clad strips, elongation increased in the TD, and the elongation anisotropy was reduced. Anisotropy was not observed in the five-layer clad strip because the eutectic Si particles were uniformly distributed by the increase in the rolling reduction rate due to the increase of the initial strip thickness.