Stress corrosion crack initiation and propagation characteristics of 7xxx high-strength Al alloy

摘要

High-strength 7xxx aluminum alloy is widely used in aerospace and ocean engineering as structural materials, causing a risk of stress corrosion crack (SCC) in equipment [1]. Different from previous works, the slow strain rate tensile (SSRT) and constant load tensile (CLT) tests were innovatively designed in c onjunction, and the electrochemical activity of metal surfaces under different deformation states was analyzed by in-situ electrochemical test in this work. Stress distribution simulated by the finite element method (FEM) and mechanical experiments equippe d with in -situ electrochemical analysis are utilized to research the SCC mechanism of 7xxx Al alloys in simulated marine environments that contain corrosive Cl −. The results showed that different deformation states caused varying degrees of stress concentr ations on the 7xxx sample after a slow strain rate test (SSRT) and constant load test held for 12 h in the simulated marine environment. The strain concentration coefficient (Kε) of the plastic deformation sample was higher than that of the elastic deformation sample, due to the larger aspect ratio (width D/depth d) of its pits. The severe plastic deformation sample (ε s=12.5%) had the highest SCC susceptibility, exhibiting large -scale and dense SCC crack generation due to micro -texture transformation and pa ssive film defects.