4. Discussion4.1. Effect of the cooling rate on the microstructureA change in the microstructure with the solidification rate isclearly observed in Figs. 3 and 4. The samples that solidified withlow cooling rate such as BC and TR show a microstructure characterized by the segregation of Sn at the a-Al grain boundaries. As thecooling rate increases, by using the melt spinning technique, it isobserved a transition from a b-Sn segregation at the a-Al grainboundaries microstructure to a more homogeneous distribution ofrounded b-Sn particles embedded in the refined a-Al grain matrix.The melt-spun ribbons have different cooling rate at both surfaces(WS and GS) which make a microstructure gradient with graincoarsening from the WS towards the GS. The surface at the WS hasthe finest microstructure along the thickness of the melt-spunribbons. The surface at the GS, as this quenches in inert gas, themicrostructure is coarser than the one at the WS.