Inhibiting Effect Of A MG-Rich Primer On Pitting Corrosion Of LY12 Aluminum

Aluminium alloy is widely used in aerospace, military, automotive industry because of its low density, high strength, easy to process and the largest storage. On account of popularization of aluminium and responding to the call from government, It should be a priority for all to improve working life. Among numerous protection methods of aluminium alloy, Mg-rich coating on aluminium alloy with pitting corrosion was studied. The cathodic protection from Mg-rich coating to aluminum alloy was be investigated. It is researched what effects Mg-rich coating with scratch on aluminum alloy. Finally the corrosion resistance was be surveyed when magnesium powder was blended of different size of aluminum powder.Firstly the potentiodynamic scanning method is used to make pitting corrosion on LY12 aluminium alloy surface. Samples in analogous degree of pitting was chosen. The samples coated with Mg-rich primer and epoxy primer was measured by EIS after immersion in 3wt% NaCl solution. Results showed that the Mg-rich coating could reduce the open circuit potential of aluminum alloy and maintain it stable for an extended period, showing obviously the effect of cathdic protection. The time for the Al matrix to be corroded was significantly prolonged. On the Al substrate with pits the dissolution rate of Mg particles in the coating increases, which would protect the substrate more effectively. With the Mg-rich coating the pits on the substrate surface showed no obvious changes, indicating that the Mg-rich primer could inhibit the generation and development of pitting corrosion on aluminum alloy to some extent.Manufacturing artificial cross scratches have been made on Mg-rich coating in aluminum alloy surface and epoxy coating, the area of artificial control defects was immersed in 3wt%NaCl solution for EIS test. The results showed that the sample with epoxy coating has appeared corrosion after 1h, there were detachments between primer and substrate after 48 hours. The time of appearing corrosion in sample with Mg-rich coating is 288hours which showed that magnesium powder on aluminum alloy defect has protected aluminium alloy. Magnesium powder could inhibit development of scratch.Magnesium powder with different particle size of aluminum powder as pigment is added to epoxy resin coating with controlling 2:3 ratio of the mass fraction of magnesium powder and aluminum powder to get magnesium aluminum composite coating. Then put the coating on the LY12 aluminum alloy surface to study its corrosion resistance. Machu test showed that in the strong corrosion solution, corrosion resistance of Mg-rich was better than magnesium aluminum composite coating because of the truth that magnesium powder has strong reactivity, cathodic reduction reaction was easier to be occurred compared with magnesium aluminum composite coating. Electrochemical test and immersion test showed that the working life of coating with added in 17μm aluminum powder has prolonged 888 hours. It was caught that adding with aluminum had no effects on protection of magnesium powder from open circuit potential analysis.