Growth direction and Si alloying affecting directionally solidified structures of Al-Cu-Si alloys

The roles of growth direction and Si content on the columnar/equiaxed transition and on dendritic spacings of Al-Cu-Si alloys still remain as an open field to be studied. In the present investigation, Al-6 wt-%Cu-4 wt-%Si and Al-6 wt-%Cu alloys were directionally solidified upwards and horizontally under transient heat flow conditions. The experimental results include tip growth rate and cooling rates, optical microscopy, scanning electron microscopy energy dispersive spectrometry and dendrite arm spacings. It was found that silicon alloying contributes to significant refinement of primary/secondary dendritic spacings for the upward configuration as compared with corresponding results of the horizontal growth. Experimental growth laws are proposed, and the effects of the presence/absence of solutal convection in both growth directions are discussed.