阳极氧化6061铝合金在工业海洋大气环境长周期暴晒时的腐蚀行为

The outdoor exposure tests of anodized 6061 aluminum alloy in sulfuric acid and boron-sulfuric acid were carried in industrial-marine atmospheric environment at Qingdao for five years. The effects of two different anodizing methods on the corrosion behavior and mechanism of 6061 aluminum alloy were investigated by means of the surface and cross-section morphology observation, mass loss method, the corrosion products analysis, mechanical properties testing and fracture analysis. The results show that the average corrosion rates of the anodized alloy in sulfuric acid and boron-sulfuric acid decrease by 70.2% and 45.4% after five-year exposure in the industry-marine atmospheric environments, respectively, compared to the naked alloy. The loss of yield strength decrease by 69.5% and 11.0%, and the loss of elongation decrease by 71.8% and 41.0%. Thus, the anodic treatment weakened corrosion and the effect of sulfuric acid anodizing is much better than for the boron-sulfuric acid anodizing. The high concentration of chloride ions in the industry-marine atmosphere in Qingdao plays an important role in the destruction of the oxide films and in inducing the pitting corrosion. Due to the pitting on the grain boundaries, the intergranular corrosion initiated. The sulfide in the atmosphere can penetrate into the grain boundary region along with the corrosive medium, which aggravate the propagation of the intergranular corrosion. The anodized film has an effective hindrance for chloride ions penetrating to the matrix, and the effect of anodizing in sulfuric acid is better, which can effectively inhibit the initiation and propagation of intergranular corrosion, thereby reduce the loss of strength and plasticity of 6061 aluminum alloys.