Microstructural evolution and superplastic deformation behavior of fine grain 5083Al (original) (raw)
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Microstructure changes in superplastically deformed ultrafine-grained Al-3Mg-0.2Sc alloy
Letters on Materials
Experiments were conducted on an ultrafine-grained Al-3wt.%Mg-0.2wt.%Sc alloy to characterize the microstructure changes occurring during large tensile deformation at elevated temperature within a transition between superplasticity and creep. The coarse-grained material was subjected to equal-channel angular pressing at room temperature using a die which had a 90° angle between the channels. The billets were rotated by 90° in the same sense between each pass in the processing route Bc. The billets were subsequently pressed by 2 and 8 passes. Microstructure was investigated by scanning electron microscope equipped with an electron back scatter diffraction unit. Microstructure analysis showed that the movement of dislocations and the growth of grains were restricted by Al3Sc coherent precipitates formed during stabilizing annealing at 623 K for 1h. It was found that deformation behaviour of investigated Al alloy was influenced by inhomogeneity of microstructure and deformation-induced coarsening of grains. The fracture behaviour was affected by cavity formation due to high local concentration of plastic deformation at the triple points and inefficient accommodation processes of grain boundary sliding. The results showed that total tensile deformation is a consequence of a various mechanisms occurring at different stages of tensile deformation. The superplastic tensile deformation was predominantly realized by grain boundary sliding and formation of mesoscopic shear bands. The role played by grain boundary sliding is discussed.
Deformation behavior of fine-grained 5083 Al alloy at elevated temperature
Transactions of Nonferrous Metals Society of China, 2009
The microstructure evolution of the fine-grained 5083 Al alloy was investigated in annealing temperature range of 150−300. Then the effects of the different annealed microstructures on high-temperature deformation behavior were further studied. The results indicate that the initial recrystallization temperature is about 200. By tensile tests at 380−570 and in strain rate range of 4.17 10 −4 −1.0 10 −2 s −1 , the optimum superplastic parameters are obtained as follows: the annealed temperature 250 , the tensile temperature 550 and the strain rate 4.17 10 −4 s −1. With the aid of scanning electronic microscopy (SEM), the fractography of the alloy after the superplastic deformation was analyzed. The results reveal that intergranular cavities with fine size and homogeneous distribution are beneficial to superplastic deformation.
Analysis of Void Growth During Superplastic Deformation of Commercial AL5083 Alloy
Iranian Journal of Science and Technology, Transactions of Mechanical Engineering, 2017
Superplastic alloys and metals possess the ability to undergo large uniform strains prior to failure. A number of materials are subject to the cavitation during superplastic deformation. Cavitation usually leads to either the undesirable post-forming characteristics or to the premature tensile failure. It is also apparent that the cavities can preexist in the form of cracks and decohered interfaces, which develop during thermo-mechanical processing necessary to produce the superplastic microstructures. Evidently, extensive cavitation imposes significant limitations on their commercial application. The material constitutive equation constants of commercial AL5083 alloy contain strength coefficient, and strain rate sensitivity index is determined by superplastic bulge forming tests for 400, 450, 500, 550°C. By comparing the results of a deformed sample, good accordance between experimental and FEM results is observed. Using the calculated values for C and m parameters, the effect of material properties such as the cavity growth rate, strain rate sensitivity index, strain hardening exponent and number of intentionally preexisted voids on specimens voids growth subject to the tensile deformation and to the biaxial deformation has been determined numerically. The tensile tests have been simulated by the FEM software ABAQUS v6.9 using commercial aluminum 5083 alloy that presents superplastic properties at temperatures in the range 400-550°C. The simulations are implemented at 400, 450, 500 and 550°C. The results of the numerical prediction obtained are in good agreement with the results of the experiments done by some other authors.
Superplastic characteristics of fine-grained 7475 aluminum alloy
Journal of Materials Engineering and Performance, 2006
A 7475-aluminum alloy was subjected to a thermomechanical heat treatment that resulted in a final recrystallized grain size on the order of 10 µm. Tensile specimens of dimensions 10 × 4 × 2.3 mm were machined such that the tensile axis was parallel to the rolling direction. Tensile tests were carried out at high temperatures in the range of 773 to 803 K at different cross-head speeds corresponding to initial strain rates in the range of 10−4 to 10−2 s−1. Elongations of several hundred percent were observed at strain rates of −3 s−1. The correlation between flow stress and strain rate suggests that the strain rate sensitivity m is close to 0.5 at the lower strain rates. The value of m decreases to ≈0.2 at high strain rates. The decrease in m suggests a transition in the rate-controlling process from superplastic deformation (m ≈ 0.5) to dislocation creep (m ≈ 0.2) with increasing strain rate. The calculated activation energies in the two deformation regions are consistent with the suggested rate-controlling processes.
Influence of predeformation on microstructure evolution of superplastically formed Al 5083 alloy
2017
Cavitation is the main defect encountered during superplastic forming (SPF) of thin sheet aluminum alloys. In the present paper, the influence of preforming operation (cold or hot) on the superplastic forming ability and quality of 1.6-mm-thick sheet of 5083 SPF aluminum alloy is investigated. Specifically, grain size evolution and the characteristics of the cavitation process are discussed as a function of prior deformation and the preforming temperature. Optical and field emission gun scanning electron microscopy (FEG-SEM) were used to study the characteristics of the cavities and microstructure evolution. Image processing was used to measure the surface and volume fractions of the cavities. The results indicate that hot preforming leads to a lower number of cavities per unit surface compared to cold preforming prior to the SPF operation. However, the average cavity sizes and the average grain size are higher in the case of hot preforming compared to cold preforming, which lead to...
Superplastic behavior of fine and ultra fine-grained AA5083 Al alloy was examined using the shear punch test. To achieve fine-and ultra fine-grained microstructures, a relatively new severe plastic deformation (SPD) process, namely Double Equal Channel Lateral Extrusion (DECLE) was employed. The strain rate sensitivity indices (m) of samples were evaluated after 1, 2, 4, and 6 passes for shear strain rates in the range of 3 × 10 −3 to 3 × 10 −1 s −1 and temperatures in the range of 573 to 673 K. For microstructural observations, TEM images together with the corresponding SAED patterns were prepared and utilized. A considerable increase in the m-value was observed after the first pass of the operation for all testing temperatures. The best condition for achieving a good superplasticity for the alloy was found to be a single pass DECLE at 673 K in the strain rate range of 10 − 2 to 10 − 1 s − 1. This process condition resulted in an m-value of 0.43, indicative of a high strain rate superplastic deformation behavior. Further passes of the SPD process did not show any sign of superplasticity until the last pass of the operation, during which the m-value slightly increased, compared with the previous pass.
High-temperature deformation in a superplastic 7475 Al alloy with a relatively large grain size
Materials Science and Engineering: A, 1995
Tensile tests were conducted on a superplastic 7475 Al alloy having a grain size of 14 pm, which is relatively larger than that of conventional micrograin superplastic alloys, at temperatures in the range of 723-789 K. The objective of the present investigation was to examine the possible rate-controlling mechanisms that govern superplastic deformation of the alloy at both intermediate and low stresses. The values of the stress exponent and the activation energy, as well as microstructural observation, indicate that deformation of the alloy at intermediate stresses is rate-controlled by lattice diffusion. At low stresses, the stress exponent and the activation energy are higher than those at intermediate stresses. The mechanical behaviour at low stresses may be attributed to the existence of a threshold stress which strongly depends on temperature. The origin of the threshold stress is discussed in terms of the various dislocation-particle interaction models that have been proposed for the creep of dispersionstrengthened alloys. The present analysis reveals that the mixed climb model can qualitatively explain the very strong temperature dependence of the threshold stress, but not quantitatively. Therefore an alternative explanation is suggested for the very strong temperature dependence of the threshold stress on the basis of the role played by interface diffusion in recreating the dislocation core segment that is smeared out following attachment of dislocation to the dispersoids.
MATERIALS TRANSACTIONS, 2004
A series of tensile testing was carried out on the ultrafine grained 5083 Al alloy, which was fabricated by equal channel angular pressing (ECAP) with different ECAP strains, at low temperature superplastic (LTS) temperature of 548 K. This investigation was aimed at examining the effect of the ECAP strain inducing different microstructure in the alloy on the deformation mechanisms at LTS regime. The most distinguishable microstructural evolution by increasing the ECAP strain from 4to4 to 4to8 was an increment of a portion of high angle boundaries while the (sub)grain size remained almost unchanged. The sample after 4 passes (a strain of 4)didnotexhibitLTS,butsuperplasticelongationswereobtainedinthesampleafter8passes(astrainof4) did not exhibit LTS, but superplastic elongations were obtained in the sample after 8 passes (a strain of 4)didnotexhibitLTS,butsuperplasticelongationswereobtainedinthesampleafter8passes(astrainof8). An analysis of the mechanical data in light of the standard deformation mechanisms revealed that deformation of the sample after 4 passes was governed by dislocation climb while grain boundary sliding attributed to LTS of the sample after 8 passes. The difference of the deformation mechanisms in the present case was discussed in terms of the microstructures developed under different ECAP strains.
High-strain-rate superplasticity in bulk cryomilled ultra-fine-grained 5083 Al
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2006
The ductility and creep of bulk ultra-fine-grained (UFG) 5083 Al (grain size ∼440 nm) processed by gas atomization, cryomilling, and consolidation were studied in the temperature range 523 to 648 K. Also, the creep microstructure developed in the alloy was examined by means of transmission electron microscopy (TEM). The ductility as a function of strain rate exhibits a maximum that shifts to higher strain rates with increasing temperature. An analysis of the experimental data indicates that the true stress exponent is about 2, and the true activation energy is close to that anticipated for boundary diffusion in 5083 Al. These creep characteristics along with the ductility behavior of 5083 Al are a reflection of its creep behavior as a superplastic alloy and not as a solid-solution alloy. In addition, the observation of elongations of more than 300 pct at strain rates higher than 0.1 s−1 is indicative of the occurrence of high-strain-rate (HSR) superplasticity. Microstructural evidence for the occurrence of HSR superplasticity includes the retention of equiaxed grains after deformation, the observation of features associated with the occurrence of grain boundary sliding, and the formation of cavity stringers. Grain size stability during the superplastic deformation of the alloy is attributed to the presence of dispersion particles that are introduced during gas spraying and cryomilling. These particles also serve as obstacles for dislocation motion, which may account for the threshold stress estimated from the creep data of the alloy.