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Research on Formability and Microstructure of Aa6061 Tubes at Elevated Temperatures

Author: ShaoFei
Tutor: YuanShiJian
School: Harbin Institute of Technology
Course: Materials Processing Engineering
Keywords: Aluminum alloy High Temperature Tensile Hot bulging Fractography Microstructure
CLC: TG379
Type: Master's thesis
Year: 2010
Downloads: 132
Quote: 0
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Abstract


Growing number of applications in the automotive, aircraft aluminum profiled section parts. Room temperature formability of aluminum tubing seriously restricted the application of aluminum alloy parts. Pipe thermal state pressure forming method is an effective way to solve the problem. Annealed 6061 aluminum alloy extruded tube for the study, one-way through along the pipe axial tensile test, test pipe temperature mechanical properties, mechanical properties of parameter variation with temperature and strain rate; dual power function to strengthen the modeling of high-temperature plastic constitutive of the test pipe; observed under different temperature tensile fracture surface analysis of fracture types and mechanisms under different temperature. The results show that the flow stress of the aluminum alloy increases with the decrease of temperature and strain rate increases;, high temperature constitutive model can better describe the aluminum alloy high-temperature plastic deformation behavior; tensile fracture toughness of microvoid accumulation fracture, intergranular fracture appears brittle fracture at 550 ℃. Hot free bulging experiments, test different temperatures pipe internal pressure formability, bursting pressure and bulging rate variation with temperature; observe the bulging of the pipe under different temperature fracture morphology, and axial tensile fracture morphology compared. The results show that as the temperature increases, the bursting pressure monotonically decreasing; bulging first increases and then decreases the rate of 425 ° C bulging; increase in the number of dimples with increasing temperature, change into deep, the temperature is too high when sectional oxidation and overfiring organization. Technical analysis by electron backscatter diffraction (EBSD) the axial and circumferential pipe bulging tissue. Hot bulging process, the initial fine equiaxed grains grow significantly; become increasingly evident as the temperature increases, the grain oriented, elongated along the deformation direction, in 450 ℃ fibrous tissue; crystal The boundary of recrystallized grains also appear grew elongated phenomena; the grain internally generated a large number of uneven distribution of sub-structures as the temperature increases. Bulging along the axial deformation amount The larger parts hardness is higher than near the end parts of the tube along the ring to close the fracture is higher than the hardness of the part away from the fracture; bulging temperature hardness bulging pipe impact not large. By axial tensile test and bulging experiments, a preliminary study of the mechanical properties of the pre-6061 aluminum alloy extruded tube deformation and bulging performance. The results show that the strength of the 6061 aluminum alloy extruded tube significantly improved after pre-deformation at room temperature, almost no plastic deformation capability, the wall thickness of the pipe is very uneven. However, with the improvement of the test temperature, the pipe deformation capacity significantly improved, bulging rate of more than 60% of the limit under the conditions of 500 ℃ still available.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metal pressure processing > Extrusion > Non-ferrous metal and alloy extrusion
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