| Magnesium alloy is the lightest metallic structural material in engineering application at the present time. Due to its high strength: weight ratio, high damping characteristics, high thermal conductivity, high dimensional stability, good machinability and electromagnetic shielding characteristics, magnesium alloy is widely used in many applications. Unfortunately, magnesium has a high chemical reactivity that would easily induce the occurrence of corrosion in environment, which hindered its wide use greatly. One of the protective techniques is organic coating which is low cost and simply processed. It is a good protective measure to improve the corrosion resistance of magnesium alloy surface. But the inhibitors and antirust pigments in organic coatings were studied rarely. In this paper, inorganic inhibitor, organic inhibitor and traditional antirust pigment that can inhibit corrosion of magnesium alloy in epoxy coating were searched. By means of dynamic potential polarization, inhibition effect of 1‰,3‰,5‰sodium molybdate, sodium phosphate and potassium nitrate were studied for the AZ91D magnesium alloys in 3% NaCl solution. It was found that 3‰sodium phosphate and 3%o nitrate of potash play a good inhibitor role. And then the effect on protective properties of epoxy coatings with 3%o sodium phosphate and 3%o potassium nitrate on magnesium alloy were studied by immersion test and electrochemical impedance spectroscopy (EIS). The experimental results showed that coating with 3%o sodium phosphate and 3%o nitrate accelerated the corrosion of magnesium alloy compared with epoxy varnish coating.By means of immersion test and EIS, the corrosion inhibition of imidazole(IM), thiourea,1,4-butynediol, hexamethylenetetramine, sodium diethyldityiocarbamate (DDTC), benzotriazole (BTA), sodium dodecylbenzensulfonate (SDBS) with different contents in epoxy coatings to the AZ91D magnesium alloy was studied. It showed 1% 1,4-butynediol and 0.5% DDTC can improve the protective properties of coatings on the magnesium alloy.In this thesis, epoxy coatings with different antirust pigments were brushed on the surface of AZ91D magnesium alloy. By means of immersion test, EIS, dynamic potential polarization, open circuit potential monitoring and XPS, iron oxide red, zinc chromate, nano TiO2 et.al 7 pigments were studied for their effect on protective properties of the organic coating on AZ91D magnesium alloy. The results indicated that 20% or 30% zinc chromate,20% aluminium tripolyphosphate, and 20% nano TiO2 can improve the protective properties of the coatings apparently. |
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