Elastic scattering cross sections of the 89Y(α,α)89Y reaction have been measured at energies Ec.m.=15.51 and 18.63 MeV. The high-precision data for the semimagic N=50 nucleus 89Y are used to derive a local potential and to evaluate the predictions of global and regional α-nucleus potentials. The variation of the elastic α-scattering cross sections along the N=50 isotonic chain is investigated by a study of the ratios of angular distributions for 89Y(α,α)89Y and 92Mo(α,α)92Mo at Ec.m.≈15.51 and 18.63 MeV. This ratio is a very sensitive probe at energies close to the Coulomb barrier, where scattering data alone is usually not enough to characterize the different potentials. Furthermore, α-cluster states in 93Nb=89Y⊗α are investigated.