ABSTRACT
In this study, CoCrAlY-Al2O3/TiO2 ceramic and Al 、 NiCrAl metal anticorrosion 、wear-resisting coatings were prepared on the surface of AZ91D magnesium alloys by the method of flame spraying 、flame add plasma spraying and electric arc spraying.Study on the preparation of the coating and Performance. Morphologies observed coating by using the optical microscopy,scanning electron microscopy (SEM). Use line scan and the spectrum analysis of the coating composition and integration, use metallographic image analysis system measuring the porosity of the coating. Using a thermal shock test of the coating and substrate bonding strength, dry friction and wear test the wear resistance of the ceramic coating. Salt water immersion test used to detect the corrosion resistance of coatings. Preparation of the arc spraying and Al, NiCrAl metal corrosion coating for the electrochemical corrosion test, drawing from the anode polarization curves,analysis of electrochemical corrosion testing.
The results show that: as long as proper process control,using thermal spraying in magnesium alloy surface preparation ceramic, metal coating is entirely achievable. The determination of plasma-sprayed ceramic coatings for the porosity of 5.42%, flame sprayed ceramic coatings porosity of 13.77%, arc spraying metal coating porosity of 9.68%, all in the normal range. EDX analysis and lines scanning show that the coating and the substrate between the elements to spread and intensity of a combination of higher metallurgical.Coating thermal shock experiment proved the ability of anti-cold cycle of good, proven coating and the substrate with a higher intensity. Friction and wear experiments show that the wear resistance of ceramic coating is better than quenching 45＃ steel, greatly improving the wear resistance of the surface of magnesium alloy. Experiments show that the salt water immersion metal, and ceramic-coated have greatly improved magnesium alloy corrosion resistance properties of the matrix.
Preparation of the arc spraying of metal corrosion coating for electrochemical corrosion experiments, the anode polarization curves show that: the NiCrAl and Aluminum metal coatings had well passivation phenomena in the corrosion mediator of 3.65%NaCl+5%H2SO4 aqueous solution. The passivation intervals were -0.3～0.6v and 0.2～0.7v,respectively. The working current of Aluminum coating was 0.38A, and the working current of NiCrAl coating was only 0.043A.
Several methods of thermal spray coating system in the comparison found: Preparation of the plasma-sprayed ceramic coatings in the micro-hardness, wear resistance, porosity,light intensity are superior flame spraying of the ceramic coating. Preparation of the metal arc spray coating and the substrate with the highest intensity, NiCrAl metal coating is superior to the corrosion resistance of Al metal coating.
KEY WORDS: Magnesium alloy, thermal spraying, porosity, wear corrosion resistance,passivation
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