Evolution and performance of a MgO/HA/DCPD gradient coating on pure magnesium

•HA tends to aggregate together while DCPD changes from narrow bar to plate-like.•Plate-like DCPD weakens the bonding between PEO layer and CaPh compounds.•The corrosion resistance increases first and then drops with the deposition time.•The morphology of precipitated HA highly depends on the originated structures.•Phase conversion impedes the initial cell adhesion but then has limit influence.