Corrosion Resistance And Anodic Oxidation Of Al-Li Alloy

Al-Li alloys can replace convention aluminum alloy, have been widely applied in aviation, aerospace, marine and other industries because of their excellent properties such as low density, high strength to weight ratio, good corrosion and fatigue resistance, fitting ductility. However, Li is a metallic element with strong activity, which makes Al-Li alloys in wet and salt spray environment prone to intergranular corrosion, exfoliation corrosion and stress corrosion and other destroys. This paper analyze the effect of different heat treatment technology on the corrosion resistance of Al-Li alloys, use anodic oxidation method to produce anodic oxidation film on Al-Li alloys surface, can greatly increase the corrosion resistance of Al-Li alloys, extend the service life and broaden application scope.The composition, microstructure and mechanical properties of Al-Li alloys were observed and tested under different heat treatment. The intergranular and exfoliation corrosion sensitivity of Al-Li alloys were determined and the effect of heat treatment were investigated by using electrochemical techniques. With the increasing of aging time, the certain rules are followed: elongation decreased gradually, the hardness and tensile yield strength continued to increase, reached a peak in aging 40h and then decreased slowly; obvious grain precipitation zone appeared, and gradually widened; Al-Li alloys corrosion potential and resistance tended to decline, the sensitivity of intergranular corrosion and exfoliation corrosion tended to grow, corrosion extent became more prominent and corrosion resistance lower and lower.A dense anodic oxidation film of Al2O3 was prepared on the surface of Al-Li alloy in 15% H2SO4 electrolyte, that hardness is between 80～250HV, and that thickness is between 5～20μm. Surface morphology of the anodic oxidation shows porous shape which arrange orderly and distribute densely, pore wall is hexagonal, cavity is circular, pore diameter size is 50 ~ 100nm. With the increase of current density, the thickness and hardness of anodic oxidation film rise first and then reduce, grain size becomes smaller, the pore diameter size and pore wall thickness of porous surface increase gradually; With the prolonging of oxidation time, the hardness rises first and then reduces, the thickness increases gradually, grain size become smaller too, the pore diameter size and pore wall thickness of porous surface also continue to increase.The immersion corrosion, drop corrosion and salt spray corrosion tests showed that the corrosion damage of Al-Li alloy began from the grain boundaries, with the increase of current density and oxidation time, the corrosion resistance of anodic oxidation film first enhanced and then weakened. The optimum processing parameters for anodic oxidation were in current density of 2A/dm2, oxidation time of 60min, sealing time of 20min by boiling water.