The Al based alloys (Al-3 wt%Si, Al-3 wt%Cu and Al-1 wt%Ti) were prepared using metals of 99.99% high purity in the vacuum atmosphere. These alloys were directionally solidified upward with a constant growth rate (V = 0.008 mm/s) at the different temperature gradients (G = 1.1-6.8 K/mm) and also with a constant temperature gradient (G) in a wide range of growth rates (0.008-0.499 mm/s) with a Bridgman type directional solidi. cation furnace. The microstructure parameters (primary dendrite arm spacing, gimel(1), secondary dendrite arm spacing, gimel(2), dendrite tip radius, R, andmushy zone depth, d, were measured from both transverse and longitudinal section of the specimens as a function of G and V. The dependence of microhardness (H(V)) on the solidi. cation process parameters (V and G) and the microstructure parameters were determined by using linear regression analysis in the Al based alloys. The results obtained in this work have been compared with the previous similar experimental results obtained for binary or ternary alloys. (C) 2008 Elsevier B.V. All rights reserved.