Microstructure Transition And Corrosion Resistance Of Thermal Sprayed AlCoCe Coatings Under High Current Pulsed Electron Beam

Aluminum-based amorphous alloys have excellent mechanical properties and corrosion resistance.Currently,they are mostly used as coating materials in the field of material protection.However,due to the relatively low cooling rate of thermal spraying technology and the limitation of the coating micro-structure,the coating has not yet become a complete amorphous state.High current pulsed electron beam modification technology can remelt the coating surface to achieve amorphous transformation of the material by high current and short pulse electron beam.In this paper,AlCoCe alloys and powders were prepared,and then AlCoCe alloy coatings were prepared on Q235 substrate by high velocity oxygen-fuel thermal spraying technology.Finally,the coatings were remelted by high current pulsed electron beam.The changes of microstructure and corrosion resistance of the coatings during the process were studied by structural characterization and corrosion experiments,and the relationship between structure and corrosion resistance were studied.The AlCoCe alloy in this paper is in complete crystalline state and its composition is within the range of amorphous formation.Its corrosion resistance is poor.The order of corrosion resistance of each phase is Al₈Co₂Ce,Al₁₁Ce₃,Al/Al₁₁Ce₃eutectic phase,Al₉Co₂,Al.In addition,the self-corrosion potential of AlCoCe alloy is more negative,so it can be used as cathodic protection material for Q235 carbon steel.In the AlCoCe alloy powders prepared by gas atomization technology,the small particle size powders have preliminary amorphous structure under the effect of high cooling rate.The coating prepared by high velocity oxygen-fuel thermal spraying also has a certain amount of amorphous composition,but the coating structure has lamellar structure and rough surface.The immersion experiment shows that the coatings can form a good cathodic protection for bare carbon steel matrix.After 90 days immersion,a dense protective film composed of oxides or hydroxides of Fe,Al,Ce and other elements was formed on the surface of exposed carbon steel matrix.After 8 pulses of high current pulsed electron beam,a dense and homogeneous amorphous layer was formed on the surface of the coating.With the increasing number of pulses,the cooling rate decreased due to the heating of the substrate,which led to the appearance of crystal structure in the surface treatment layer.Because of the large thermal gradient between the treatment layer and the bottom coating,there are a number of cracks in the surface treatment layer.The results of electrochemical corrosion test show that the surface treatment layer after HCPEB treatment has excellent corrosion resistance,but the corrosion medium can penetrate into the coating through the cracks on the treatment layer,resulting in the sublayer corrosion.The self-corrosive current of the sealed thermal spraying coatings and surface remelting coatings is significantly lower than that of the unsealed samples,indicating that the corrosion resistance of the samples after sealing treatment has been significantly improved.The composite structure of thermal spraying coating and amorphous treatment layer can form a better protective effect on Q235 carbon steel matrix.Its main protective effects are shown in three aspects:mechanical protection,cathodic protection and release of corrosion inhibitor ions(Ce³⁺).