| In recent years, as a kind of lightweight alloy, aluminum alloy has been used in many fields, such as automobile, aerospace and so on, which adapted to the need for lightweight. At the same time, the manufacturing of large parts with complex shapes put forward higher requirements for the existing forming methods. 2219 aluminum alloy is a lightweight and high-strength alloy. Due to its good low-temperature mechanical properties, fracture toughness, welding property and anti stress corrosion performance, it was widely used in the aerospace field, such as the fuel tanks of large carrier rocket. But the room-temperature plasticity of 2219 aluminum alloy is poor, and there are problems such as low forming limit and easy to crease in the conventional deep drawing forming. Therefore, the conventional forming method of the large parts with complex shapes was divided the part into several small parts, forming them fist, then weld them into the target parts through the friction stir welding(FSW). Although the method guarantee the overall strength of the parts, the uniform organization and existence of welding defects in the weld area greatly reduced the reliability.In order to solve this problem, this paper proposed a method of welding the sheets first, then adjusting the microstructure and properties of the welded joint by thermo-mechanical treatment, and finally forming integrally. Taking 2219 aluminum alloy as the research object, this paper researched the influence of the welding parameters, heat treat ment parameters, the influence of deformat ion on the microstructure and mechanical propert ies of welded jo ints, providing a theoret ical support for the forming of large parts with complex shapes by 2219 aluminum allo y tailor welded blanks(TWBs).Combined the mechanical property tests, the effect of welding parameters and heat treatment temperature on the properties of FSW welded joints was given. Within the reasonable low welding speed parameters, mechanical propert ies o f welded joints were similar. The overall elongation can reach 20% and was slightly lower than the base material. The yield strength decreased slightly after heat treatment; with the increase of heat treatment temperature, the jo ints’ yield strength and tensile strength did not changed slightly. The elongation significantly decreased when the heat treatment temperature higher than 350℃. And the fracture zone also changed from the base materials zone to weld zone. The deformation o f weld zone increased gradually.Studied the influence of different deformation by single direction tension and multi-pass rolling on the mechanical properties and microstructure of welded joints. It was found that the mechanical properties of the specimens with small tensile strain and 350℃ treatment temperature were not significantly decreased, and the microstructure was close to the as-weld specimens.And with the large rolling deformation and 350℃ heat treatment, the weld zone grain grew up, the base metal grain refined and the overall organization became uniform. A s a result, the tensile strength was higher than the base material and the elongation was close to that of the base material.Simulation Research on the bulging and drawing of FSW TWBs was studied by finite element simulation software. With the increase of heat treatment temperature, the limit bulging height of the sheet increased slightly. In the experiments, the limit bulging height of the two-time bulging process with 350℃ intermediate heat treatment increased by 12%. The deep drawing numerical simulation of the semi-sphere part was carried out, it was found that the existence of the weld zone had little influence of the thickness. Finally formed the large size semi-sphere drawing parts with no defects, the main process parameters were 12 MPa liquid chamber pressure and 6000 k N blank holder force. |
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