The influence of tensile direction on the mechanical properties of directionally solidified Al-4.5wt.% Cu alloys was examined and compared with the analyses. Angular variations of the elastic constants (Young's modulus and Poisson's ratios) qualitatively agreed with the analysis with the Voigt average and the finite element method. An angular variation of the yield strength agreed with the analysis with the Sachs average except when the angle between the tensile direction and the growth direction of columnar crystals was about π/4 rad. At this angle, the grain boundary slip had to be considered. An angular variation of the tensile strength was explained by the three fracture mechanisms of composites.
