Comparing Studies On Corrosion Resistance Of Mg-Al Rich Coating And H900 Coating On Aluminum Alloy

Aluminum alloys are often applied to aerospace,marine and automotive industries due to their low density,good corrosion resistance and thermal conductivity.However,the usage of aluminum alloys is limited by their poor corrosion resistance,in the harsh environments.Aluminum alloys can be effectively protected by protective coatings.Therefore,in order to improve the protective performance of the coatings,various techniques for the modification of the coatings were investigated.In this thesis,through EIS,SEM,Machu test,cross scratch test and neutral salt spray test,the corrosion resistance of Mg-Al rich epoxy coating and H900 antirust epoxy coating was investigated.After 90 days of immersion test,the OCP for all the samples coated with H900 coating is higher than that of the substrate,and the OCP for all the samples coated with 20Mg30Al decreased to about-0.91 VSCE that is more negative than the OCP of the substrate alloy.Therefore,H900 coating behaved mainly the shielding effect and the Mg-Al rich coating behaved both the cathodic and the shielding effects.After 245 days of immersion test,the EIS result shows the impedance value of the H900 samples with 105±5 μm coating thickness decreased from 1010Ω to 107Ω cm2.After 245 days’ immersion test,the EIS result shows,the impedance value of the samples with 105±5 μm Mg-Al coating decreased from 1010 Ω to 105Ω cm2.Therefore,the results show that at room temperature H900 behaved somewhat better than Mg-Al rich coating.The effect of temperature on the two coatings was studied.For H900 coating,after 70 days immersion test at 40 ℃,the EIS result shows that the coating impedance value decreased from 1010 Ω to 105Ω cm2,this indicates that the physical aging of H900 coating is intense at 40 ℃ and the coating deteriorated fast than at room temperature.For specimen coated with Mg-Al rich coating,after 70 days immersion test at 40 ℃,the impedance value decreased from 1010 Ω cm2 to about 3x 105 Ω cm2.This indicates that although at room temperature the impedance of Mg-Al rich coating decreased faster than that of H900 coating,but at 40 Ω NaCl solution the service life of Mg-Al rich coating was longer.The metallic particles in the coating,which are high temperature resistant,may played important role.