Study On The Microstructure And Fatigue Crack Growth Property Of 2E12 Aluminum Alloy Sheet

As an important aviation materials,2524 aluminum alloy was mainly used in the aircraft's skin, the wing lower panels and other key positions, and successfully applied in the Boeing 777, Airbus A380 aircrafts,2E12 aluminum alloy was developed at the basis of 2524 by further reducing the impurity content of Fe and Si. The microstructure, conventional mechanical properties, fatigue crack growth rate and micro-crack growth path of domestic 2E12-T3 and imported 2524-T3 alloy were evaluated by OM, SEM (EBSD), TEM, EDS, DSC, Hardness Testing, Conductivity Testing, Tensile performance testing at room temperature, fatigue crack growth rate testing and other methods, etc, and obtained the main reasons of effect on the fatigue property of pre-made 2E12 aluminum alloy, then proposed the optimize program of the preparation process, and took a evaluation of fatigue crack propagation performance for the improved 2E12-T3 aluminum alloy, and obtained the domestic 2E12-T3 aluminum alloy which basically achieved the imported 2524-T3 fatigue level, the test results and conclusions obtained are as follows:The grains of domestic 2E12-T3 alloy were homogeneous and minute with more seriously recrystallized, and were approximately equiatxed, but the imported 2524-T3 alloy presented the rolled fibrous tissue, which were approximately equiatxed, the former was more seriously recrystallized; both of them were distributed with a little undissolved coarse second phase in the matrix, AlCu or AlCuMg and iron-rich phase; more middle-size Al20Cu2Mn3 club-shaped particles were observed in 2E12-T3 alloy with more close space in them; And with the same heat-treatment state for T3 state, the aging precipitated strengthening phase was the GP zone, which was coherent with the matrix.The fatigue crack growth rate of domestic 2E12-T3 alloy was significantly higher than imported 2524-T3 aluminum alloy, and the fractures had the significant differences, the fracture of 2E12-T3 alloy was relatively flat with the small striation space and a few of dimples,2524-T3 alloy was more rough and obviously rugged with the bigger striation space and more dimples at the fracture.The main difference between domestic 2E12-T3 and imported 2524-T3 alloy was the degree of recrystallization in microstructure, in order to reduce the recrystallization of domestic 2E12-T3, a low temperature annealing process could be added the front of the last one cold rolling annealing, the high accumulated strain energy would be fully released, while the deformation structure was reserved.By comparison with imported 2524-T3 alloy, the grains characteristic of improved 2E12-T3 aluminum alloy had come about an obvious change, and obtained the same fibrous-like tissues with 2524-T3 alloy, then a more prominent phenomena was observed in the improved 1.2mm-thick 2E12-T3 aluminum alloy, whose length-width ratio was about 6. Therefore, the microstructure of improved 2E12-T3 alloy had basically achieved the level of imported 2524-T3 alloy. By the evaluation of fatigue crack growth performance for the improved 2E12-T3 aluminum alloy, adding intermediate annealed process could effectively slow the crack growth rate and extend the remained fatigue life of domestic 2E12-T3 alloy, particularly, the fatigue crack growth rate curve of 1.2mm-thick improved 2E12-T3 alloy was almost coincided with 2524-T3 alloy, whose remained fatigue life reached up to 4.10×104cycles, it was only lower than the imported 2524-T3 alloy about 3%. Therefore, the fatigue performance of improved 2E12-T3 alloy basically achieved the level of imported 2524-T3 alloy.