An improved process for grain refinement of large 2219 Al alloy rings and its influence on mechanical properties

doi:10.1016/j.jmst.2018.09.007

Abstract

Abstract:

The large 2219 Al alloy rings used to connect propellant tank components of a satellite launch vehicle to each other are conventionally manufactured by radial-axial ring rolling at 460 °C with 50% deformation, but often suffer from coarse elongated grain and low ductility. An improved process (hot ring rolling at 460 °C with 30% deformation, then air cooling to 240 °C, followed by ring rolling at 240 °C with 20% deformation) was tested for ring manufacturing. The corresponding microstructure evolution and mechanical properties of the produced rings were studied. The results show that the improved process can successfully be applied to manufacture the large 2219 Al alloy rings without formation of macroscopic defects, resulting in a product with fine and uniform grains after heat treatment. The fracture mechanism of both rings was mainly intergranular fracture. With the resulting grain size refinement due to the improved process, more homogeneous slip occured and the crack propagation path became more tortuous during the tensile testing process. Thus, the elongation in all three orthogonal directions was greatly improved, and the axial elongation increased from 3.5% to 10.0%.

Key words: 2219 Al alloys, Large rings, Ring rolling, Grain refinement, Mechanical properties

Hailin H, Youping Yi, Shiquan Huang, Yuxun Zhang. An improved process for grain refinement of large 2219 Al alloy rings and its influence on mechanical properties[J]. J. Mater. Sci. Technol., 2019, 35(1): 55-63.

Figures/Tables 11

Fig. 1. Schematic of manufacturing process: (a) conventional process; (b) improved process.

Fig. 2. Forming principle of radial-axial ring rolling.

Fig. 3. Schematic of sampling: (a) cutting test block; (b) cutting samples for tensile testing and microstructure observation.

Fig. 4. EBSD images (a1, b1) and grain boundary misorientation distributions (a2, b2) of ring after radial-axial rolled under conventional (a1, a2) and improved (b1, b2) processes.

Fig. 5. TEM images of the ring after being radial-axial rolled in conventional (a) and improved (b) processes.

Fig. 6. EBSD results of ?3350?mm 2219 Al alloy large rings after heat treatment: (a1, a2) conventional process; (b1, b2) improved process.

Fig. 7. Optical micrographs of heat-treated ring manufactured by improved process: (a) schematic of sampling locations; (b) OM microstructures at different locations.

Fig. 8. TEM bright-field images and corresponding SAED pattern showing matrix precipitates (a1, b1) and grain boundary precipitates (a2, b2) of T8-aged rings obtained near [001]Al zone axis under conventional (a1, a2) and improved (b1, b2) processes.

Fig. 9. Tensile properties of T8-aged rings manufactured by two different processes.

Fig. 10. SEM images of tensile-fractured surfaces of large 2219 Al alloy rings manufactured by two different processes: (a) conventional process; (b) improved process; (c) high magnification at intergranular cracking zones; (d) EDS analysis of particles.

Fig. 11. Schematic of crack propagation: (a) coarse grain structure produced by conventional process; (b) fine grain structure produced by improved process.

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