镁合金表面微弧氧化/氧化石墨烯/硬脂酸复合超疏水涂层在不同盐雾条件下的腐蚀过程

Corrosion behavior of superhydrophobic micro-arc oxidation/graphene oxide/stearic acid composite coating on magnesium alloy under different salt spray test conditions

[目的]研究镁合金表面超疏水复合涂层在标准中性盐雾(35℃)、45℃的中性盐雾和模拟海水盐雾3种试验条件下的腐蚀过程。[方法]在AZ91D镁合金表面先后采用微弧氧化、电沉积和自组装技术制备了微弧氧化/氧化石墨烯/硬脂酸(MAO/GO/SA)超疏水复合涂层。[结果]在3种盐雾试验条件中,复合涂层出现腐蚀坑前都能维持超疏水状态,水接触角保持在150°左右。出现腐蚀坑后,标准中性盐雾条件下涂层的水接触角比其他两种盐雾条件下降得更慢。极化曲线测试结果表明,复合涂层的腐蚀电流密度比镁合金基体降低了3个数量级。3种盐雾条件下试验192 h后,复合涂层的腐蚀电流密度仍比镁合金基体低,但标准模拟海水盐雾试验后试样的腐蚀电流密度增速最快,涂层最先被腐蚀。[结论]MAO/GO/SA超疏水复合涂层具有优异的耐蚀性,能够有效阻止介质对镁合金基体的腐蚀,令镁合金基体的腐蚀速率降低。

[Introduction]The corrosion of a superhydrophobic composite coating on the surface of magnesium alloy under three salt spray test conditions i.e.standard neutral salt spray test at 35°C,neutral salt spray test at 45°C,and simulated seawater salt spray test was studied.[Method]The micro-arc oxidation(MAO),electrodeposition of graphene oxide(GO),and self-assembly with stearic acid(SA)were carried out with AZ91D magnesium alloy as the substrate to form a superhydrophobic MAO/GO/SA composite coating.[Result]The composite coating showed superhydrophobicity in all three salt spray tests prior to the formation of corrosion pits,with a water contact angle of approximately 150°.Following the appearance of corrosion pits,the water contact angle of the specimen under standard neutral salt spray condition was decreased slower than that under other salt spray conditions.The results of polarization curve measurement showed that the corrosion current density of the composite coating was three orders of magnitude lower than that of the magnesium alloy substrate.After 192 hours of salt spray test under different conditions,the corrosion current density of the specimen with the superhydrophobic composite coating was lower than that of the AZ91D magnesium alloy substrate.However,the corrosion current density of the simulated seawater salt spray test specimen was increased at the fastest rate,and the composite coating on this specimen was the first to be corroded.[Conclusion]The superhydrophobic MAO/GO/SA composite coating has excellent corrosion resistance,protecting the magnesium alloys effectively from corrosion in corrosive media and reducing the corrosion rates of magnesium alloys.