Chemical bonding

AlCl₃ has simple covalent bonding because the aluminium cation is so small and highly charged (3+) that it has an extremely high charge density. This charge density distorts the electron cloud of the anions (Cl-) to such a large degree that the bonding is considered as covalent. This is why AlCl₃ vapourises at room temperature, because it only has weak van der waal's intermolecular forces.

but in AlCl₃.6H₂O the H⁺ will make ionic bonding with the Cl ^-

so the AlCl₃ is covalent but AlCl₃.6H₂O is ionic!