The microstructure uniformities and mechanical properties of the 2219 Al–Cu alloy ring should be further improved. By whole-process analysis and partial quantitative analysis, this paper studies the ...microstructure evolution and its influence on the mechanical properties of the 2219 Al–Cu alloy rings undergoing rolling deformation with different deformation temperatures. The results indicate that, when the rolling temperatures are from hot condition to warm condition, the increase of the sub-grain amount leads to more grain refinement after heat treatment; the elongation values clearly increase. The single Goss texture with high volume fraction is changed to be more varieties after heat treatment, having no significant effect on transverse and normal strengths for each sample. The Al
2
Cu phases became more dispersed and fragmented, leading to more dissolve, which results in denser precipitates; the yield strengths gradually increase. In addition, the comprehensive properties of the sample on the border are slightly stronger than those on the core, especially for the warm rolling samples.
Graphical Abstract
The mechanical properties of large 2219 Al–Cu alloy rings need to be further improved with the diameter of the launch vehicle being more than 10 m. In this study, the effects of cold rolling (CR) and ...cold compression on microstructure evolution and the comprehensive mechanical properties of such rings were compared. The evolution of dislocation characteristics, grain structure, second phase, and the mechanical properties of the T8-aged samples were examined. Results show that compared with CR, because of deformation characteristics, cold compression deformation induces less increase in dislocation densities; however, the increase in dislocation densities on the core was higher than at other positions, resulting in a more uniform grain structure and elongation in the axial and radial direction. The cold compression deformation contributes to the uniform dissolution of the secondary phase, resulting in denser precipitates, and thus improved strength. Brittle fractures occur in fewer CR samples because of the longer moving distance of the Al matrix. In summary, both CR and cold compression can improve the mechanical properties. However, the cold-compressed sample exhibits more uniform microstructure and higher comprehensive mechanical properties (the radial elongation increased from 7.1 to 11.2%; the in-plane anisotropy decreased from 36.6 to 8.9%), without any brittle fractures, because of more uniform metal flow.
2219 Al alloy is an important material for manufacturing launch vehicles, and its grain structure has a substantial effect on the performance of storage tank transition rings. In this work, warm ...compression tests (100–350 °C) of 2219 Al alloy were carried out, a grain refinement model of warm deformation was established, and the evolution and thermal stability of the static recrystallized grain size
D
were analyzed. The results showed that static recrystallization is the main mechanism of grain refinement, and that the nucleation rate and grain refining effects were significantly improved by decreasing the deformation temperatures (
T
). The established model was found to be accurate, and the predicted and experimental values exhibited high degrees of coincidence. When
T
and the amount of deformation (Δ
d
) were respectively 150 °C and 70%, the value of
D
was reduced from 60 μm to 21 μm. Additionally, when the solution treatment time was increased from 0 to 4 h, there was a slight change in the values of
D
(high thermal stability) when
T
was lower than 250 °C and Δ
d
was greater than 20%, but they significantly increased when Δ
d
was less than 10%.
Graphic Abstract
In this paper, the effects of different deformation temperatures T and deformation amount Δd on average grain size D of 2219 Al alloy forgings were investigated, and the evolution rule and thermal stability of D were analyzed. The research results showed that static recrystallization was the main mechanism for grain refinement of 2219 forgings, and the nucleation rate and grain refining effects were improved by increasing Δd and decreasing T. Warm compression was conducive to accumulating higher-density dislocations, storing more deformation energy, generating more high energy distortion points. Hence, increasing the recrystallization nucleation rate and decreasing grains growth velocity. Furthermore, the thermal stability of grain sizes increased with the decreasing recrystallization grain size and uniformity. Because there is a low energy difference between fine and uniform grains (the interface energy was very low), which led to slow grain boundary migration speed and restraining grain growth even at high temperatures.
2219 Al–Cu alloy transition rings are widely used in launch vehicles. However, the coarse and agglomerated second-phase Al
2
Cu particles significantly deteriorate the mechanical properties and ...ductility of 2219 Al–Cu alloy rings manufactured by traditional thermal deformation processes. In this study, cryogenic deformation (− 190 °C) is applied for the manufacturing of 2219 Al–Cu alloy rings to alleviate this problem. The effects on the evolution of second-phase Al
2
Cu particles and the mechanical properties of the T8-aged samples were examined in comparison with the results of room-temperature (25 °C) and conventional thermal deformation at 480 °C. The results indicate that cryogenic deformation can effectively produce high-density dislocations and strongly crush coarse particles, promoting the dissolution of Al
2
Cu particles and improving their distribution in the Al matrix when combined with subsequent solution treatment and rolling processes. As the deformation temperature was decreased from 480 to −190 °C, the area fraction of the coarse particles was decreased from 1.55 to 0.47%, while their mean size was decreased from 11.8 to 8.3 μm. Correspondingly, the uniformity and density of the precipitates after T8 aging were improved. Thus, the mechanical properties of the T8-aged samples were improved with decreasing deformation temperatures; the average ultimate tensile strength, yield strength, and elongation were increased by 20 MPa, 22 MPa, and 3.1% at room temperature.
Graphic Abstract
Optimization of forging process to improve the microstructure and mechanical properties of 2195 Al–Cu–Li alloy forgings is an urgent issue. In this study, a homogenized 2195 alloy ingot was subjected ...to multi-directional forging (MDF), annealing, and forging at 500 °C, 420 °C, and 240 °C with a 50% reduction in cross-sectional area, followed by a T8 heat treatment (involving solution, quenching, cold compression, and aging). The microstructural evolution during the process and the final mechanical properties in three orthogonal directions were examined. The results showed that the grain structures of the alloy were significantly refined after MDF by dynamic recrystallization (DRX), but the structure was thermally unstable and formed coarse grains during subsequent annealing by static recrystallization (SRX). The T8-treated samples forged at 500 °C, 420 °C, and 240 °C obtained fine and uniform grain structures by DRX, inhomogeneous grain structures by partial SRX, and uniform, equiaxed grain structures by full SRX, respectively. The average grain size of the forging increased with decreasing forging temperature because more significant SRX occurred for the forging that was deformed at lower temperatures. The grain structures had minimal influence on precipitation behavior and strength but had a significant influence on elongation. The fine and uniform grain structures improved the elongation; whereas, the inhomogeneous grain structures, which contained extremely large grains, significantly deteriorated the elongation. The uniform, equiaxed grain structures decreased the anisotropy in three orthogonal directions and maintained fine elongation even though the average grain size of the forging was the largest.
Graphic Abstract
Large 2219 Al–Cu alloy transition rings are extensively utilised in launch vehicles. However, coarse-grained structures and agglomerated Al
2
Cu second-phase particles considerably decrease the ...ductility of large 2219 Al–Cu alloy rings manufactured using the conventional hot rolling process. In this study, 10%–40% warm rolling deformation was applied to elucidate the evolution of grain structures, characteristics of the Al
2
Cu second-phase particles, and the influencing mechanisms of ductility. The results indicate that increased warm rolling deformation can facilitate dynamic recrystallisation and yield more sub-grains, which leads to the appearance of numerous finer and more equiaxed recrystallised grains after solution heat treatment; however, the homogeneity of the grain structure is decreased. With increased warm rolling deformation, Al
2
Cu second-phase particles are more dispersed and more completely fragmented; furthermore, the dispersed and fragmented Al
2
Cu particles are more thoroughly dissolved during solution heat treatment. By the combined action of grain structures and second-phase particles, the main fracture mode transitions from intergranular fracture into transcrystalline fracture. This results in elongation in the axial and circumferential directions increasing steadily with increased warm rolling deformation; elongation in the radial direction initially increases, and finally decreases due to the appearance of glide planes. Samples that experience a warm rolling deformation of 30% exhibit the best overall elongation.
Graphical Abstract
The 2195 aluminum alloy has been widely utilized in the aerospace field, of which dynamic recrystallization microstructures have a substantial effect on the mechanical properties of aerospace parts. ...In this study, 2195 aluminum alloy was compressed at 300–520 °C using a Gleeble 3500-GTC thermo-mechanical testing system. The discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) behavior of 2195 aluminum alloy at medium/high temperature was studied. The results demonstrated that during medium temperatures (300–360 °C) deformation the main softening mechanism was DDRX, and at high temperatures (420–520 °C), it was CDRX. CDRX of 2195 aluminum alloy involved three types of subgrain-forming mechanisms: dislocation tangling to form subgrains, microscopic shear bands to form subgrains, and the coalescence of two small subgrains to form larger subgrains. In addition, several recrystallized grains underwent geometric dynamic recrystallization (GDRX) at high temperature and extensive deformation (480 °C-80% or 520 °C-60%).
•DDRX occurred in 2195 aluminum alloy at medium temperature.•CDRX occurred in the alloy at high temperature.•Continuous dynamic recrystallization is based on 3 subgrain forming mechanisms.•GDRX occurs during large deformation at high temperatures for 2195 aluminum alloy.
2219 Al alloy has been used to manufacture the launch vehicle storage tank transition ring, but the large ring obtained in conventional manufacturing processes still suffers from severely ...agglomerated coarse second phase particles and poor mechanical properties. An improved process (forging at 510 °C with 20% deformation and at 240 °C with 50% deformation, then rolling at 240 °C with 30% deformation, followed by solid solution at 538 °C for 4 h and T8 treatment) for 2219 Al alloy large ring manufacturing was proposed, and the corresponding simulation tests were carried out. The evolution of Al2Cu second phase particles and the mechanical properties of the produced workpieces were investigated. The results showed that the degree of crushing, dissolution, and precipitation of Al2Cu particles were significantly improved in the improved process, and the area fractions of Al2Cu coarse second phase particles after saddle forging and rolling were significantly reduced, leading to 2.4 times increase in area fraction of the θ′ phase after T8 treatment. More homogeneous slip occurred during the tensile testing process and intergranular fracture was the main fracture mechanism. The tensile strength σb, yield strength σs, and elongation δ in the radial direction of the 2219 workpieces were increased to 491 MPa, 388 MPa, and 13.1%, where were increases of 11%, 14%, and 68%, respectively. The uniformity in σb, σs, and δ of the 2219 workpieces increased by 57%, 38%, and 64%, respectively.
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•Thermomechanical treatment for improving properties of 2219 Al-Cu alloy is studied.•Dislocation tangles around Al2Cu particles form preferential recrystallization nucleation ...sites.•High dislocation density promotes dissolution of Al2Cu particles during solution treatment.•Grain refinement occurs and higher-destiny precipitates form during new process.•New TMT process leads to improved strength, elongation, and low anisotropy.
An improved thermomechanical treatment, which included 50% hot deformation at 440°C, 10% cold predeformation at 25°C, and a subsequent heat treatment (solution, 2.5% cold deformation and aging treatment), was performed on 2219 Al alloy forgings. For comparison, a 2219 Al alloy forging was also manufactured using the conventional process, which involved 50% hot deformation at 440°C and a subsequent heat treatment. The evolution of the microstructures of the forgings during the treatments and their final mechanical properties were evaluated. A large number of Al2Cu particles were formed during the hot-deformation process. Further, tangled dislocation structures were formed around these particles after 10% cold deformation in the forging manufactured by the improved process, resulting in a significant grain refinement during the solution treatment because of particle stimulated nucleation as well as a weakened texture. In addition, more coarse Al2Cu particles dissolved into the Al matrix during the solution treatment in the case of the forging subjected to the improved treatment, because the tangled dislocation structures promoted the dissolution of these particles, thus increasing the density of the precipitates after T8-aging. The forging manufactured by the improved treatment exhibited a higher ultimate tensile strength (by 34.3 MPa), higher yield strength (by 43.2 MPa), and significantly lower anisotropy, as well as improved elongations in the axial and radial directions (lower-performance directions).
2195 aluminum alloy is widely used to manufacture the external tanks of space shuttles and aircraft skins, and its mechanical properties are substantially affected by dynamic recrystallization ...occurring in its microstructure. In this study, hot compression experiments were performed on 2195 aluminum alloy to investigate its dynamic recrystallization (DRX) behavior. The results indicated that discontinuous (DDRX) and continuous dynamic recrystallization (CDRX) both occurred in the alloy from 300 °C to 520 °C at strain rates of 0.01–10 s−1. The microstructure analysis revealed that DDRX grains formed at grain boundaries, while CDRX grains appeared in the triangular grain boundary region with transition grain boundaries or within grains. The dominant DRX mechanism changed from DDRX to CDRX when the strain was greater than 1.2. Moreover, at higher temperatures or lower strain rates, the number of CDRX grains increased, while the number of DDRX grains decreased. Finally, to quantitatively describe the DDRX and CDRX kinetics of 2195 aluminum alloy, the critical conditions were used to establish a composite kinetics model that was consistent with the experimental results, and which suitably predicted the volume fraction of DRX grains formed via the two different DRX mechanisms.
•A strain of 1.2 was the transition point between the two recrystallization mechanisms for 2195 aluminum alloy under thermal compression.•Upon increasing the temperature or decreasing the strain rate, CDRX grains increased, while DDRX grains decreased.•Critical conditions of dynamic recrystallization were found and the critical stress, critical strain and other stress of model were established.•A composite kinetics model was proposed by considering the characteristics of DDRX and CDRX.
