Research On Structure And Properties Of Cold Sprayed Aluminum And Micro-arc Oxidation Film On AZ31 Magnesium Alloy

Magnesium alloys are applied in automobile,aviation,aerospace,electronics industries due to their low density and excellent mechanical and physical properties.However,the poor corrosion and wear resistance of magnesium alloys limit their application as structural materials.Cold spray（CS）technology is an economic and environmentally friendly surface treatment technology,which has been successfully applied to the corrosion protection of magnesium alloys,but it has not solved the problem of poor wear resistance of magnesium alloys.In this work,a pure Al coating andα-Al₂O₃ particle reinforced Al-50%Al₂O₃composite coating were deposited on AZ31 magnesium alloy by cold spray technology,respectively and then,micro-arc oxidation technology was used to transform the top of the cold spray coating into alumina ceramic film.The microstructure and phase compistion of the coatings was characterized by scanning electron microscopy,transmission electron microscopy and X-ray diffraction,respectively.The hardness,corrosion,wear and cavitation resistance of the coatings were tested by a microhardness tester,electrochemical workstation,ball-on-disk tribometer,wheel abrasion testing machine and ultrasonic vibratory cavitation device.The effects of the addition of Al₂O₃ particles on the microstructure and properties of the pure Al coating were investigated.The effects of the microstructure of cold sprayed coatings on micro-arc oxidation process,film morphology and properties were studied.The results show that the Al-50%Al₂O₃ composite coating exhibited more compact microstructure,higher hardness,bond strength and wear resistance but less deposition efficiency in comparison to the pure Al coating.The corrosion current density of the composite coatings(2.36×10^-7A/cm²)was similar to that of the pure Al coating(1.19×10^-7A/cm²),but was about three orders of magnitudes less compared to the AZ31 magnesium alloy(2.56×10^-4A/cm²),therefore both the pure Al coting and Al-50%Al₂O₃ composite coating can significantly improve the corrosion resistance of magnesium alloys.After micro-arc oxidation（MAO）treatment in a low concentration sodium aluminate electrolyte,ceramic films composed ofα-Al₂O₃ andγ-Al₂O₃ were formed on both the pure Al and the Al-50%Al₂O₃ coatings,which further improved the corrosion and wear resistance of the coatings.In addition,the MAO film generated on the Al-50%Al₂O₃ coating showed higher speed of growth,sliding and abrasive wear as well as cavitation resistance,but less corrosion resistance compared with the MAO film generated on the pure Al coating.Double coatings produced by CS+MAO processes can significantly increase the corrosion and wear resistance of the AZ31magnesium,which is expected to expand the application scope of the magnesium alloys in production practice.