Under The Conditions Of High Strength Aluminum Alloy Stress Corrosion Behavior And Electrochemical Behavior

Aluminum alloy has wide applications in the aircraft industry because of its high strength to density ratio and great response to precipitation hardening, but there also is an basilic problem as other metals. It maybe occur SCC which lead to a vital accident due to the interaction of mechanical and environmental factors.In the present paper, the effect of different constant tensile stress and immersion time on the corrosion behaviors of AA7075-T6, AA7075-RRA, AA2024-T6 and AA2024-T4 under tensile stress in 3.5wt%NaCl solution,as well as the mechanism was investigated by SEM, TEM and EDAX. Subsequently, the PDS and current noise under constant potential of the four alloys in 3.5wt% NaCl solution were innovationally mearsured, and then open otential of PDS was simulated and the characteristics with parameters of EN in the process of corrosion was analysed by FFT. The effect of stress on the parameters of SPD was illustrated. The main conclusions are as following:The unstressed AA7075-T6 and AA7075-RRA were domainated with pits going with a little intergranular corrosion in 3.5% NaCl solution.The pits of AA7075-T6 developed into larger dimension and the intergranular corrosion penetrated into the matrix with the stress increased. While the stress mainly led the pits of AA7075-RRA to become denser and increasing in size, which showed severe general corrosion.The primary form of corrosion for AA2024-T6 was pitting and intergranular corrosion in 3.5% NaCl solution. Larger dimension of pits were developed because of stress, at the same time pits penetrated into the matrix in the hole and developed into intergranular corrosion. The AA2024-T4 was domained with pitting corrosion in 3.5% NaCl solution. Stress induced larger dimension of pits. There were pits lay noncontinuously along the grain boundary when the stress got to 240MPa. The effect of stress on the corrosion of AA2024-T6 was great, especially the penetration into the matrix. It was suggested that tensile stress had greater effect on the corrosion of AA2024-T6 than on AA2024-T4.The open potential and the breakdown potential of the four alloys were lower and the current was higer at a given potential with the growing stress which accelerated the anode dissolution.The white noise W of AA2024-T4 and AA2024-T6 turned to be larger with the increased stress under the same constant potential, as well as with the growing polarized potential. It showed that white noise W While could reflect the corrosion.In addition, provided that the current noise of AA2024-T6 under constant polarized potential had showed a fluctuation frequency with stress, the corrosion cracks along the grain boundary was occurred and aggravated more severly with the higher fluctuation frequency.The white noise W got larger with the rised stress which meaned more severly aggravated for AA7075 under the same heat treatment condition. While stress had a little effect on the white noise W of AA7075-RRA below 250 MPa, accordingly stress had a little effect on the corrosion.