Microstructure of Al-2%Si and Al-6%Si Strips Cast Using Vertical-Type High-Speed Twin-Roll Caster

Al-2%Si and Al-6%Si were cast at a roll speed of 30 m/min and a roll load of 5 N/mm using a vertical-type high-speed twin-roll caster. The rolls were suddenly stopped during casting and the molten metal was solidified. The effect of Si content on the microstructure at the cross section near the roll bite was investigated using Weck’s reagent. The cross section of the Al-2%Si strip consisted of five layers (one center layer, two middle layers, and two surface layers) at the roll bite and that of the Al-6%Si strip consisted of three layers (one center layer and two side layers). The a-Al in the center layer was globular for both Al-2%Si and Al-6%Si. The relative thickness of the center layer for Al-6%Si was greater than that for Al-2%Si. In Al-2%Si, the surface layer had a very fine chill-zone microstructure. The Si solid-solution content in the α-Al in the surface layers and the center layer was less than that in the middle layers in the Al-2%Si strip.