| Nowadays, with the development of aerospace industry, aluminum alloys forgings especially these with H-shape section as well as vertical and horizontal structure have been widely used. Due to their bad working environment and usually bearing large load, these forgings are required to have higher dimensional accuracy, good streamline distribution and better comprehensive properties. Therefore, research on forming process, heat treatment and relief of quenching residual stresses is crucial to improve the properties of aluminum alloys.In this work, the hot forming processes of forgings with h-shape were researched via hot compression and actual production. Morever, based on mechanical tensile under room temperature, fracture toughness test, residual stress test, optical micro-structure and scanning electron micro-structure, effects of solution temperature, quenching medium as well as quenching transfer time on the second-phase, grain structure, materials strength and fracture toughness properties were revealed. Meanwhile, the values and distribution of residual stresses under different quenching processes were studied as well. Furthermore, though pressing experiment under room temperature and finite element method, influence of different cold pressing process on quenching residual stresses was discussed. The main conclusions are as follows:(1) Though hot compression experiment, carried out on Gleeble-1500 with the strain rate 0.01-10s-1 and temperature 300-450?,the true stress-strain curves of 7050 aluminum alloys were investigated. Besides, according to regression analysis of the compression date and hyperbolic sine Arrhenius equation, the constitutive relation represented by variable Z was established and it was applied in mathematical analysis subsequently.(2) The optimization of hot forming variables for h-shape forgings were proposed based on response surface method(RSM), it was verified to be feasible though actual production with optimized parameters. Due to combination of mathematical simulation and RSM, hot forming was researched and the optimized parameters were achieved via analyzing the mechanism of defects, unfilled, partial draining and non-uniform deformation, appearing in hot deformation.(3) Effects of different solution temperature on micro-structure and properties of 7050 aluminum alloys were investigated and revealed. The observations demonstrate that the second-phase particles has been dissolved into Al matrix during the solution process, the amount of second-phase particles decrease gradually and keep invariant finally with the solution temperature increasing while the volume fraction of recrystallized grains increase. Thus, the strength and fracture toughness increase firstly and then decrease with the solution temperature increasing, the peak achieves when the solution temperature was 470?with ?b ?0.2 KIC of 567 Mpa, 512 Mpa, and 37.2MPa·m1/2, respectively.(4) The influence of different quenching medium and quenching transfer time on the microstructures and properties of 7050 aluminum alloy were studied and revealed. The volume fraction of the second phase particles is significantly affected by the various quenching medium and quenching transfer time while a little influence on the organization form of after quenching. Among the four quenching medium, the volume fraction of the second phase particles is minimum under salt bath quenching, therefore, it possesses good mechanical property after aging, compared with quenched in water and 20% PAG solvent; Owing to the largest of the second phase particle after quenching in air,its mechanical property is the worst. Besides, when quenched in water, with the increase of quenching transfer time, the volume of the second phase particles increases, while the mechanical properties decrease.(5) The effect of different quenching medium and quenching transfer time on the quenching-induced residual stress of the H section of 7050 aluminum alloy forging were studied and revealed. Generally, the tensile stress is transformed into compressive stress for the surface of aluminum alloy forging, while compressive stress is transformed into tensile stress on quenching for the center of aluminum alloy forging after quenching. The quenching-induced residual stress was mainly focus on the transition fillet region, and increase with the increase of the thickness of reinforcing plate. In addition, the forging surface quenching-induced residual stress increases with the increase of transition fillet while the interior of quenching-induced residual stress decreases. Among the four quenching medium, Compared the forging with 20% PAG solvent quenching, the residual stress quenched in air was smallest, besides, both quenched in water and NaCl have larger residual stress. With the increase of quenching transfer time, the residual stress of quenched transition fillet region of the forging became smaller and smaller.(6) The effect of different cold-press processes on quenching residual stress of the H section of 7050 aluminum alloy forging were investigated. The numerical simulations confirmed the best cold-press process which the top of reinforcement and fillet simultaneously compressed, then, the forging web was compressed. The optimized dies can effectively control the whole cross section of quenching residual stress, and reduce to under 40 Mpa. With the increase of molding capacity, the residual stress initially decreases and then increase. When 3% molding capacity, the residual stress reached to the smallest. The surface residual stress of mold specimen after experimental result was consistent with numerical simulation, and the error between experimental and numerical simulation is within 30 Mpa, which suggested numerical simulation method had high precision to predict quenched residual stress. |
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