Microstructure and Elongation Anisotropy of Cold Rolled and Solution Treated A356 Alloy Strips Fabricated via High-Speed Twin-Roll Casting

A356 alloy strips fabricated via high-speed twin-roll casting were cold rolled at the reductions of 0%, 12%, 30%, 50% and 73% and then solution treated at 793 K for 1 h. Microstructure observations and tensile tests were performed for the processed strips. Upon increasing the reduction from 0% to 50%, an improvement in elongation with significant anisotropy was observed; the elongation along the transverse direction was inferior to that in the rolling direction. However, on further reduction up to 73%, this anisotropy was eliminated and an elongation above 20% was achieved. This behavior is caused by the characteristic changes occurring in the second-phase particles that are located in the mid-thickness region of the strip. To achieve a high elongation without anisotropy, a process for refining the coarse particles in the mid-thickness region of the twin-roll-cast strips and homogeneously dispersing them into the matrix needs to be developed.