Surface modification of die casting mold steel by a composite technique of hot-dipping and plasma electrolytic oxidation

The hot dipping process of pure aluminum on H13 steel substrates followed by plasma electrolytic oxidation（PEO） was studied to form alumina ceramic coatings for protective purpose.H13 steel bars were first dipped in pure aluminum melts,and then,a reactive iron-aluminum intermetallic layer grew at the interface between the melt and the steel substrate.The reactive layer was mainly composed of intermetallic Fe-Al（Fe₂Al₅）;the thickness of aluminum layer and Fe-Al intermetallic layer were mainly influenced by dipping time（1.5～12.0 min） and dipping temperature（710～760 ℃）.After PEO process,uniform Al₂O₃ ceramic coatings were deposited on the surface of aluminized steel.The element distribution,phase composition and morphology of the aluminized layer,and the ceramic coatings were characterized by SEM/EDS and XRD.The distribution of hardness across the composite coating is demonstrated,and the maximum value reaches 1864 HV.The thermal shock resistance of the coated sample is also well improved.