Small Fatigue Crack Behavior and Life Prediction of Pre-Corroded 2024-T62 Aluminum Alloy

摘要

In this paper, initiation and growth behavior tests of small fatigue crack in laboratory air and aqueous 3.5% NaCl were conducted using non-corroded and pre-corroded SENT specimens for 2024-T62 Aluminum alloy. In order to compare with the corresponding small cracks, large crack growth tests for non-corroded and corroded specimens with different prior corrosion times were performed. Variation of pre-corrosive pit sizes with corrosion time was also studied. The results show that for fatigue specimens with pre-corrosive pits, small cracks initiated from the corrosion pits in both laboratory air and aqueous 3.5% NaCl, and initiation lives of small cracks (a≤60μm) are below 25% of total fatigue lives. For non-corroded fatigue specimens in laboratory air, small cracks initiated naturally from voids of the material, and initiation lives of small cracks (a≤25μm) are below 20% of total fatigue lives. An obvious small crack effect was found at R=-1 for non-corroded material in laboratory air. However, the same effect was not found at R=0.06 for the non-corroded material in laboratory air, and for the corroded material in both laboratory air and aqueous 3.5% NaCl at R=-1 and 0.06. And effect of environment on growth of small cracks that initiated from pre-corrosive pits was not found for Al2024-T62. The similar tendency was also found in large crack growth tests. Moreover, effect of prior corrosion time on large crack growth rates was not found to be in existence for this material. By assuming a pre-corrosive pit as an initiating surface crack, the commercial software FASTRANII and AFGROW were used to predict fatigue lives of corroded specimens with different prior corrosions. The predictions were found to agree reasonably with the tests.