铝合金在HEDP电解液中的阳极氧化行为及膜层结构

Anodizing behavior and film microstructure of aluminum alloy in HEDP electrolyte

选用羟基乙叉二膦酸(HEDP)为电解液对1060铝合金进行阳极氧化,分析了其在恒压氧化过程中的电流变化特征;借助FESEM、EDS、XRD等分析了氧化膜的微观结构、化学组成及其演变过程,探讨HEDP阳极氧化膜的生长机制;通过动电位极化曲线评价HEDP阳极氧化处理铝合金的耐蚀性。结果表明:HEDP体系中铝合金阳极氧化膜的形成是一个电化学成长与化学溶解的动态调整过程。HEDP阳极氧化膜与硫酸阳极氧化膜类似,也呈双层结构;外层为蜂窝孔状结构,只是孔径略大;内层为壁垒型结构,但明显更厚;膜层主要由非晶态Al_(2)O_(3)组成,同时多孔层中含有一定量的水合Al_(2)O_(3)。随着氧化时间的延长,孔径和孔隙率会不断增大;氧化30 min时,膜层厚度为4~5μm,表面孔径为110~120 nm,阻挡层厚度约154 nm。HEDP阳极氧化膜大幅提升了1060铝合金的耐蚀性,且膜层厚度相当时,其耐蚀性优于铬酸阳极氧化膜。

The hydroxy ethylidene diphosphonic acid(HEDP)was used as the electrolyte to anodizing the 1060aluminum alloy.The changing characteristics of current during the constant-voltage anodizing was analyzed.Besides,the evolution process of the microstructure and chemical composition of anodic film with oxidation time were analyzed by means of FESEM,EDS and XRD,the growth rule of anodic film in HEDP electrolyte was comprehensively discussed.Meanwhile,the corrosion resistance of aluminum alloy anodized in HEDP system was evaluated by potentiodynamic polarization curve.The results show that the formation of anodic film during the constant-voltage oxidation for 1060 aluminum alloy in HEDP electrolyte is a dynamic adjustment process of electrochemical growth and chemical dissolution.HEDP anodic film also presents a typical double-layer structure,which is similar to sulfuric acid anodic(SAA)film.The outer layer is a honeycomb pore structure,and the inner layer is a barrier structure;but its pore size is slightly larger and the barrier layer is significantly thicker comparing to SAA film.The film is mainly composed of amorphous Al_(2)O_(3),and the porous layer also contains a certain amount of hydrated Al_(2)O_(3).In addition,the pore size and porosity will continue to increase with the extension of oxidation time.When 1060 aluminum alloy is anodized for 30 min,the thickness of anodic film is about 4-5μm,the pore size of the film is about 110-120 nm,and the thickness of barrier layer is about 154 nm.HEDP anodic film greatly improves the corrosion resistance of 1060 aluminum alloy,and its corrosion resistance is better than that of chromic acid anodic(CAA)film with the same thickness.