| Magnesium alloys are widely used in high-tech fields such as aerospace,marine,and automobiles due to its excellent physical and mechanical properties.However,magnesium alloy has low hardness,poor wear resistance and corrosion resistance,which greatly limits its application in actual working conditions.Cold spraying is a relatively novel surface treatment technology that can provide superior corrosion protection for magnesium alloys,but it does not have significant advantages in improving the hardness and wear resistance of magnesium alloys.Plasma electrolytic oxidation is an effective ceramic coating growth process,which can significantly improve the hardness and wear resistance of valve metals.In this work,first,a 1 wt.%carbon nanotube-reinforced aluminum(1 wt.%CNT-Al)composite composite powder was prepared using the polymer pyrolysis coupled high-energy ball milling(PPCVD-HEBM)process.Then,a pure Al coating and a 1 wt.%CNT-Al composite coating were deposited on the surface of the AZ91 magnesium alloy substrate by cold spraying technology.Finally,the cold spray coating is treated with PEO to construct a cold spray+PEO duplex coating structure.The morphology,structure,phase composition and element content of cold spray powder,cold spray coating and PEO coating were studied by using environmental scanning electron microscopy(SEM),field emission transmission electron microscopy(TEM),Raman spectroscopy,X-ray diffraction(XRD)and thermogravimetric analysis(TGA).The mechanical properties and wear and corrosion resistance of the coating are analyzed by comprehensive nanomechanical performance tester,electrochemical workstation and dry sliding friction and wear tester.The main research is the preparation of CNT-Al composite powder and the influence of the introduction of CNT on the microstructure and phase structure,mechanical properties,wear resistance and corrosion resistance of cold sprayed Al-based metal coatings and Al2O3-based ceramic coatings.The results show that the PPCVD-HEBM process is a relatively novel and effective method for preparing CNT-Al composite powder.Further using cold spray technology,it was formed into a CNT-Al composite coating on the AZ91 magnesium alloy substrate and found that:Due to the strengthening effect of CNT with high hardness and high modulus in Al matrix,the average hardness and elastic modulus of cold-sprayed CNT-Al composite coating are 1.66 GPa and 77.6 GPa,respectively,which are 112.8%and 11.7%higher than those of pure Al coating;CNT inhibits the propagation of cracks in the Al-based coating and fills the micropores in the coating,so that the corrosion current density of the CNT-Al composite coating is only 2.030×10-6 A/cm2.It is half of the pure Al coating(4.661×10-6 A/cm2),and it is 2 orders of magnitude lower than the AZ91 magnesium alloy substrate(1.126×10-4 A/cm2),which significantly improves the corrosion resistance of the magnesium alloy substrate;The wear rate of CNT-Al composite coating is 9.34×10-4mm3/N·m,which is one order of magnitude lower than that of pure Al coating(3.50×10-3 mm3/N·m)and AZ91magnesium alloy matrix(1.16×10-3 mm3/N·m),respectively,due to CNT's self-lubrication and isolation effect,and has significant advantages in wear resistance.After PEO treatment of the cold spray coating,CNT-Al+PEO and Al+PEO duplex coatings were successfully prepared on AZ91 magnesium alloy.Compared with cold spraying coating,the composite properties of cold spraying combined with PEO coating are significantly improved.In addition,CNT-Al+PEO double coating has better mechanical properties and wear resistance than Al+PEO duplex coating.However,the CNT-containing duplex coating contains an obvious porous layer,which makes the corrosion resistance of the CNT-Al+PEO duplex coating slightly worse. |
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