We present a time-resolved magneto-optical imaging study of YBa2Cu3O7-δ coated conductors in alternating current regime. The evolution of the magnetic flux density distribution in the superconducting samples is imaged at small steps of the phase of the applied AC current. The flux penetration during the phase evolution is inhomogeneous due to the grain structure of the coated conductor. A quantitative analysis of the images show how grain boundary network affects the overall behavior of the flux and current density evolution.