Research On Mechanical Behavior And Simulation And Experiment Of Superplastic Forming Of 5083 Aluminum Alloy

With environmental and energy issues becoming increasingly acute, the major transportation manufacturers are speeding up research and development of lightweight vehicles. As an ideal material of lightweight for airplane, spacecraft, and automobile, aluminum alloy has become hot spots of research and development by the aerospace industry and automotive industry. But aluminum alloy is difficult to form at room temperature that restricts its application. However, superplastic forming of aluminum alloy is one of the most effective methods to slove that problem at present. Therefore, aluminum alloy was carried out the research on mechanical properties and the technology of superplastic forming. First of all, the constant strain rate uniaxial tension method was used to study the plastic and superplastic properties of materials at different temperatures under various strain rates, determine the optimal forming parameters and establish constitutive model of materials as the temperature change. And then, the pressure control algorithm was improved in superplastic bulging simulation and the simulation was applied to analyze the influence of the friction and elements type on forming results. In addition, Superplastic differential temperature drawing was also simulated firstly in MARC software through secondary development for a detailed disscussion on impacts of blank geometry, blankholder gap, temperature difference and friction coefficient on sheet drawing performance. Finally, based on simulation, three sets of experiments mold and forming process were designed to carries out bulging test, constant temperature and differential temperature drawing experiments, respectively. And experiments results were compared with the simulation one.Mechanical behavior of 5083 aluminum alloy was investigated through the constant strain rate tests at temperature of 100 ~ 535℃and strain rate of 0.013 ~ 0.00005s-1. Superplastic flow was achieved with a maximum tensile elongation of 397% at 525℃, 0.0002s-1 strain rate. The result shows that AA5083 has a lower elongation which reduces with increasing strain rate and is not indicated superplasticity below 200℃. Above 250℃, AA5083 shows superplasticity and its elongation increases with rising the temperature and behaves strain rate sensitivity. The curve of flow stress decreases with rising the temperature and increases with increasing the strain rate, which basically shows three phenomena: strain hardening, dynamic steady-state flow between strain hardening and strain softening and strain softening. The performance level of the phenomena is different as the temperature or strain rate vary. The strain rate sensitivity index m was measured with the constant-strain-rate technique and was influenced by the strain and strain rate. The strain hardening exponent n was determined by that Hollomon empirical formula fitted strain-hardening stage of true stress - true strain curves. A constitutive equationusing up-dated viscoplasticity equation of AA5083 was established at temperature of 100 ~ 525℃and strain rate of 0.013 ~ 0.008s-1. The results show that the predicted values are in good agreement with the experimental data.With improvement of the default pressure control algorithm in MARC, the superplastic bulging simulation was carried out AA5083 bracket. The results show that the geometric model of parts has a significant impact on the distribution of thickness so that components should be designed to avoid the small fillet radius, large aspect ratio, and the shape mutation. The optimized pressure load algorithm controls the deformation rate in critical regions of the part and improves the sheet forming properties leading to more uniform thickness distribution. It was discussed that the impact of solid element, shell element, and membrane element simulation on the sheet thickness distribution and the pressure - time curve. The simulation results show that shell element is the most suitable to simulate the sheet deformation. In addition, the improvement of lubrication conditions in superplastic bulging ameliorates the sheet flow property.Superplastic differential temperature drawing was firstly successfully simulated in MARC through secondary development with the changed model of AA5083 bracket and die. The parts drawing ratio was analyzed and showed that the conventional drawing could not make the parts in one step forming. The simulation result reveals the superplastic differential temperature drawing is able to the bracket, in which technology there are die in 525℃, punch in 150℃, blank holder gap of 1.05 ~ 1.1 times of the sheet thickness, the optimized blank, and the drawing speed of 0.1mm/s. And the workpiece has a uniform thickness distribution, high enough for request and lowwer thinning ratio than one of superplastic bulging in that simulation forming. It was analyzed that the impact of the blank holder gap on the material flow, blank holder force, and drawing force. And it was also investigated that the effect of the temperature difference between die and punch, and friction coefficient on improving the performance of drawing.In the basis of simulation on superplastic bulging and differential temperature drawing, AIRBUS brackets were performed expermental study. The optimization and default load curves through bulging simulation were used to control gas pressure load of experiments. The results show that pressure of the default curve is loaded too fast so that the workpiece has an over large deformation rate and a serious thickness reduction to fracture. However, the optimized load curve successfully form AA5083 bracket in the experiment which is in good agreement with simulation results. But thickness of the workpiece is thinned seriously and non-uniform distribution. Superplastic differential temperature drawing was carried on according to that simulation results. The experimental results show that differential temperature drawing process, the optimized blank shape, no flange and the mutations shape designed in the workpiece model improve the drawing formability of the workpiece and the uniform thickness distribution, which is similar with the simulation results. At last, there were comparation of workpiece thickness among superplastic bulging, superplastic differential temperature drawing, and constant temperature drawing.