Solid Solution Treatment On 7050 Aluminum Alloy Thick Plate To The Microstructure And Properties Of High Impact

7050aluminum alloy combined with high specific strength, fracture toughness and stress corrosion resistance is produced as thick plate and widely used in the aerospace industry. Much attention has been paid to achieve a combination of higher properties and uniform macroscopic properties of7050aluminum alloy thick plates. The distribution of microstructures through the thickness of the rolled7050aluminum alloy plate with thickness of200mm, and the effects of single-stage, double-stage solution treatment on the microstructures and properties of the thick plate were investigated. Hardness and electrical conductivity testing, ambient temperature tensile testing, exfoliation corrosion testing, slow strain rate testing, optical microscopy, scanning electron microscopy and transmission electron microscopy were used for investigation and analysis of microstructures, mechanical and corrosion resistance properties of the plate surface,1/4thickness and core. The main conclusions are as follows:(1)The Surface location of the rolled7050aluminum alloy plate, characterized by large deformation and small grains, distributes AlZnMgCu phase particles uniformly. While at1/4thickness and core locations of the rolled plate, smaller deformation, larger grains, as well as considerably coarse S and Al7Cu2Fe phase particles are observed. The second phase particles are relatively more tiny at1/4thickness location, compared with the core. The maximum difference of tensile strength through the thickness of the rolled plate attains11%.(2) With the increasing of solution temperature from440℃to490℃, the coarse particles decrease during single-stage solution, while the volume fraction of the recrystallized grains increases. Thus, the hardness of the plate increases first, and then decrease, finally decreases again. Meanwhile the electrical conductivity varies in the opposite. The optimal single-stage solution temperature is470℃.(3)After single-stage solution treatment of470℃/2.5h, the tensile strength of the aged7050plate markedly decreases first and then increases, finally decreases again through the thickness. And at1/4thickness of the plate the lowest strength exhibits. After double-stage solution treatment of440℃/1h+490℃/0.5h, most AlZnMgCu and S phases are dissolved. Compared to single-stage solution treatment, volume fraction of the second phase particles declines from2.45%to0.51%at1/4thickness location, and the tensile strength of561MPa increases by12.5%. Double-stage solution treatment increases the mechanical properties of the plate due to the finer precipitates in the matrix, and the property difference through the thickness is reduced.(4)7050aluminum alloy plate with double-stage solution treatment of440℃71h+490℃/0.5h has an enhanced resistance to exfoliation corrosion, the average corrosion depth at the core of the plate decreases from232μm to158μm. Double-stage solution treatment causes optimization of the size and distribution of the grain boundary precipitates, reduction of the coarse second-phase particles and refinement of the sub-grains, which improves the stress corrosion cracking resistance of the plate in short-transverse direction, and increases the tensile strength and elongation.