Superplastic Behavior of Al-4.5Mg-0.46Mn-0.44Sc Alloy Sheet Produced by a Conventional Rolling Process

This article describes the superplastic behavior of the Al-4.5Mg-0.46Mn-0.44Sc alloy. The investigated alloy was produced by casting and was conventionally processed to form a sheet with a thickness of 1.9 mm and an average grain size of 11 μm. The superplastic properties of the alloy were investigated using a uniaxial tensile testing with a constant cross-head speed and with a constant strain rate in the range 1 × 10⁻⁴ to 5 × 10⁻² s⁻¹ at temperatures from 390 to 550 °C. The investigations included determinations of the true-stress, true-strain characteristics, the maximum elongations to failure, the strain-rate sensitivity index m, and the microstructure of the alloy. The m-values determined with the strain-rate jump test varied from 0.35 to 0.70 in the temperature interval from 390 to 550°C and strain rates up to 2 × 10⁻² s⁻¹. The m-values decreased with increased strain during pulling. The elongations to failure were in accordance with the m-values. They increased with the temperature and were over 1000%, up to 1 × 10⁻³ s⁻¹ at 480 °C and up to 1 × 10⁻² s⁻¹ at 550 °C. A maximum elongation of 1969% was achieved at an initial strain rate of 5 × 10⁻³ s⁻¹ and 550 °C. The results show that the addition of about 0.4 wt.% of Sc to the standard Al-Mg-Mn alloy, fabricated by a conventional manufacturing route, including hot and cold rolling with subsequent recrystallization annealing, results in good superplastic ductility.     

AZ41镁合金超塑性成形特性

研究AZ41镁合金在热轧(无后续热变形)条件下的显微组织变化,以确定其在超塑性成形工艺中的适用性,并确定最佳成形参数.采用高温拉伸试验和热气体胀形试验对材料在不同应变速率(1×10?1～1×10?3 s?1)和温度(350～450℃)下的成形性进行评估.利用GOM Aramis相机进行圆形网格分析,了解峰值应变和材料减...     

Study on high strain rate superplasticity of A 6061Al alloy composite reinforced with 30 Vol.% AlN particulate

An investigation on the superplastic behavior of 30 vol.% AlNp/6061Al composite prepared by powder metallurgy (PM) techniques was carried out. Superplastic tensile tests of the composite were performed at strain rates ranging from 10° to 10⁻³ s⁻¹ and at temperatures from 823 to 893 K. A fine-grained structure prior to superplastic testing was obtained by hot rolling after extrusion. The highest total elongation to failure of 438% was achieved at a temperature of 863 K and at an initial strain rate of 1.67×10⁻¹ s⁻¹ and the highest value of the strain rate sensitivity index (m) was 0.42 for the composite. Differential thermal analysis (DTA) was used to investigate the possibility of any partial melting in the vicinity of optimum superplastic temperatures. The formation of a liquid phase is attributed to the melting of the Al-Si eutectic phase at the surface of the AlN particulates at elevated temperatures, as determined by electron probe microanalysis (EPMA). The influence of the microstructure and the fracture behavior on the superplastic behavior of the composite was studied by transmission electronic microscopy (TEM) and scanning electron microscopy (SEM). A large number of matrix filaments were present at the fracture surfaces of the specimens when superplastic deformation of the composite was performed under the optimum superplastic test conditions. The presence of dislocations and fine recrystallized grains in the test specimens suggested that they play an important role in the high-strain-rate superplasticity for this composite.     

Superplastic behavior of a TiAl-based alloy

Superplastic behavior under the conditions of a temperature range from 850 to 1075°C and strain rates varying from 8×10⁻⁵ to 1×10⁻³ s⁻¹ was investigated for Ti–33Al–3Cr–0.5Mo (wt%) alloy with a very fine grain size obtained by the multi-step thermal mechanical treatment. The results show that the TiAl-based alloy with a hot-deformed fine grain size possesses good superplasticity. It exhibits a strain rate sensitivity coefficient of 0.9 at a strain rate of 3×10⁻⁵ s⁻¹ and temperature from 1000 to 1075°C. Moreover, the strain rate sensitivity coefficient is stable during the hot deformation, and a tensile elongation of 517% was obtained at 1075°C and a strain rate of 8×10⁻⁵ s⁻¹. The superplastic behavior of the present fine-grained TiAl-based alloy can be explained by the local strain hardening and high m value during the tensile deformation. Microstructure evolution in the superplastic deformation was also discussed.     

Phase Composition and Superplastic Behavior of a Wrought AlCoCrCuFeNi High-Entropy Alloy

A cast AlCoCrCuFeNi high-entropy alloy was multiaxially forged at 950°C to produce a fine homogeneous mixture of grains/particles of four different phases with the average size of ~2.1 μm. The forged alloy exhibited unusual superplastic behavior accompanied by a pronounced softening stage, followed by a steady-state flow stage, during tensile deformation at temperatures of 800°C–1000°C and at strain rates of 10^?4–10^?1 s^?1. Despite the softening stage, no noticeable strain localization was observed and a total elongation of up to 1240% was obtained. A detailed analysis of the phase composition and microstructure of the alloy before and after superplastic deformation was conducted, the strain rate and temperature dependences of the flow stress were determined at different stages of the superplastic deformation, and the relationships between the microstructure and properties were identified and discussed.     

High-strain-rate superplasticity of the Al–Zn–Mg–Cu alloys with Fe and Ni additions

During high-strain-rate superplastic deformation, superplasticity indices, and the microstructure of two Al–Zn–Mg–Cu–Zr alloys with additions of nickel and iron, which contain equal volume fractions of eutectic particles of Al₃Ni or Al₉FeNi, have been compared. It has been shown that the alloys exhibit superplasticity with 300–800% elongations at the strain rates of 1 × 10^–2–1 × 10^–1 s^–1. The differences in the kinetics of alloy recrystallization in the course of heating and deformation at different temperatures and rates of the superplastic deformation, which are related to the various parameters of the particles of the eutectic phases, have been found. At strain rates higher than 4 × 10^–2, in the alloy with Fe and Ni, a partially nonrecrystallized structure is retained up to material failure and, in the alloy with Ni, a completely recrystallized structure is formed at rates of up to 1 × 10^–1 s^–1.     

High-temperature deformation behavior and processing map of 7050 aluminum alloy re]20101008

The high-temperature deformation behavior and processing map of 7050 aluminum alloy were investigated by tensile tests conducted at various temperatures (340, 380, 420, and 460 °C) with various strain rates of 10⁻⁴, 10⁻³, 10⁻², and 0.1 s⁻¹. The results show that the instability region with a peak power dissipation efficiency of 100 % occurs at the low deformation temperature region of 340 °C to 380 °C and high strain rates (>10⁻³ s⁻¹). The 7050 aluminum alloy exhibited a continuous dynamic recrystallization domain with power dissipation efficiency of 35% to 60 % in the deformation temperature range of 410 °C to 460 °C and the strain rate range of 10⁻⁴–10⁻³ s⁻¹. The domain with a power dissipation efficiency of 35 % to 50 % occurring at high deformation temperatures and strain rates was interpreted to represent dynamic recovery. Dynamic recovery and continuous dynamic recrystallization provide chosen domains for excellent hot workability.     

Superplastic behavior of a powder metallurgy TiAl alloy with a metastable microstructure

Superplasticity in a powder metallurgy (P/M) TiAl alloy (Ti–47Al–2Cr–1Nb–1Ta) with a metastable B2 phase coexisted with a fine-grained γ+α₂ duplex structure has been studied. Alloy samples were tested at temperatures ranging from 650 to 1100°C, and at strain rates ranging from 10⁻⁶ to 10⁻⁴ s⁻¹. An elongation of over 300% was obtained at a strain rate of 2×10⁻⁵ s⁻¹ and at a temperature of 800°C, which is close to the ductile-to-brittle transition temperature of the alloy. This is in contrast to the prior observations of superplastic behavior of TiAl alloys in which a typical temperature of 1000°C is usually required for achieving superplasticity. It is suggested that the occurrence of low-temperature (800°C) superplasticity in the present alloy is primarily due to the presence of a metastable B2 phase in addition to a fine-grained (α₂+γ) duplex microstructure. The metastable B2 phase continues to decompose into fine-grained α₂ and γ phases, which promotes grain boundary sliding during superplastic deformation. The retained fine B2 grains accommodate the sliding strains to reduce the propensity of cavitation at grain triple junctions and thus delay the cavitation and fracture process.     

Hot deformation mechanisms in Ti-5.5Al-1Fe alloy

The mechanisms of hot deformation in the alloy Ti-5.5Al-1Fe have been studied in the temperature range 750 to 1150 °C and with the true strain rate varying from 0.001 to 100 s⁻¹ by means of isothermal compression tests. At temperatures below β transus and low strain rates, the alloy exhibited steady-state flow behavior, while, at high strain rates, either continuous flow softening or work hardening followed by flow softening was observed. In the β region, the deformation behavior is characterized by steady-state behavior at low strain rates, yield drops at intermediate strain rates, and oscillations at high strain rates. The processing maps revealed two domains. (1) In the temperature range 750 to 1050 °C and at strain rates lower than 0.01 s⁻¹, the material exhibits fine-grained superplasticity. The apparent activation energy for superplastic deformation is estimated to be about 328 kJ/mole. The optimum conditions for superplasticity are 825 °C and 0.001 s⁻¹. (2) In the β region, a domain occurs at temperatures above 1100 °C and at strain rates from 0.001 to 0.1 s⁻¹ with its peak efficiency of 47% occurring at 1150 °C and 0.01 s¹. On the basis of kinetic analysis, tensile ductility, and grain size variation, this domain is interpreted to represent dynamic recrystallization (DRX) of β phase. The apparent activation energy for DRX is estimated to be 238 kJ/mole. The grain size (d) is linearly dependent on the Zener-Hollomon parameter (Z) per the equation

Superplasticity in cast A356 induced via friction stir processing

Superplasticity was investigated in friction stir processed A356 alloy at temperatures of 470–570 °C and initial strain rates of 3 × 10⁻⁴–1 × 10⁻¹ s⁻¹. Maximum superplastic elongation of 650% was obtained at 530 °C and an initial strain rate of 1 × 10⁻³ s⁻¹ where a maximum strain rate sensitivity of 0.45 was observed.     

The hot formability of an Al-Cu-Mg-Fe-Ni forging disk

The high temperature formability of AA2618-T61 forged disk was studied by means of tensile test over temperatures and strain rates ranging from 100 to 400°C and 3 × 10⁻⁵ −3 × 10⁻³ s⁻¹, respectively. The constitutive equations of the material were calculated based on an Arrhenius-type equation and the ductility of the material was evaluated considering elongation and percent reduction of area. The results showed that both kinds of softening mechanisms, dynamic recovery and dynamic recrystallization, occurred during high temperature deformation of the alloy. Strain rate sensitivity of the material was evaluated in all the deformation conditions and the obtained values were used to calculate the apparent activation energy.     

Superplastic deformation of SiCp/2024 Al composite fabricated by spray atomization and codeposition

In this paper, data are presented on the microstructure and superplastic deformation mechanics of an aluminum alloy, 2024, containing 10 vol% SiC particles. The material was fabricated by spray atomization and codeposition. The properties were studied after pretreatment by isothermal hot compression and isothermal hot forward extrusion (extrusion ratio 10.0). The experimental results show that the strain-rate sensitivity index (m-value) is 0.48 and the limit elongation (the elongation at fracture) is 345 % during superplastic uniaxial tension. The optimum conditions for superplastic behavior are 753 K of deformation temperature and 1.0 × 10⁻³ s⁻¹ of initial strain rate. Superplasticity may result from the fine grain size and the well-distributed SiC particles during superplastic uniaxial tension. Moreover, the simple and convenient pretreatment used in this paper is easily applied to industrial practice.     

Superplastic deformation behaviour of friction stir processed 7075Al alloy

Commercial 7075Al rolled plates were subjected to friction stir processing (FSP) with different processing parameters, resulting in two fine-grained 7075Al alloys with a grain size of 3.8 and 7.5 μm. Heat treatment at 490 °C for 1 h showed that the fine grain microstructures were stable at high temperatures. Superplastic investigations in the temperature range of 420–530 °C and strain rate range of 1×10⁻³–1×10⁻¹ s⁻¹ demonstrated that a decrease in grain size resulted in significantly enhanced superplasticity and a shift to higher optimum strain rate and lower optimum deformation temperature. For the 3.8 μm 7075Al alloy, superplastic elongations of >1250% were obtained at 480 °C in the strain rate range of 3×10⁻³–3×10⁻² s⁻¹, whereas the 7.5 μm 7075Al alloy exhibited a maximum ductility of 1042% at 500 °C and 3×10⁻³ s⁻¹. The analyses of the superplastic data for the two alloys revealed a stress exponent of 2, an inverse grain size dependence of 2, and an activation energy close to that for grain boundary self-diffusion. This indicates that grain boundary sliding is the main deformation mechanism for the FSP 7075Al. This was verified by SEM examinations on the surfaces of deformed specimens.     

Deformation Mechanisms of Ti-6Al-4V During Tensile Behavior at Low Strain Rate

A superplastic Ti-6Al-4V grade has been deformed at a strain rate of 5 × 10⁻⁴ s⁻¹ and at temperatures up to 1050 °C. Structural mechanisms like grain boundary sliding, dynamic recrystallization, and dynamic grain growth, occurring during deformation, have been investigated and mechanical properties such as flow stress, strain hardening, and strain at rupture have been determined. Dynamic recrystallization (DRX) brings on a decrease in the grain size. This could be of great interest because a smaller grain size allows a decrease in temperature for superplastic forming. For DRX, the driving force present in the deformed microstructure must be high enough. This means the temperature must be sufficiently low to ensure storing of enough dislocation energy but must also be high enough to provide the activation energy needed for DRX and to allow superplastic deformation. The best compromise for the temperature was found to be situated at about 800 °C; this is quite a bit lower than the 925 °C referenced in the literature as the optimum for the superplastic deformation. At this medium temperature the engineering strain that could be reached exceeds 400%, a value high enough to ensure the industrial production of complex parts by the way of the superplastic forming. Microstructural, EBSD, and mechanical investigations were used to describe the observed mechanisms, some of which are concurrent. This article was presented at the AeroMat Conference, International Symposium on Superplasticity and Superplastic Forming (SPF) held in Seattle, WA, June 6-9, 2005.     

Superplastic deformation of a heat-resistant Al–Cu–Mg–Ag–Mn alloy

The superplastic behavior and deformation mechanism of a heat-resistant Al–Cu–Mg–Ag–Mn alloy prepared by ingot metallurgy was investigated by using optical microscopy, scanning electron microscopy and transmission electron microscopy. It is shown that the Al–Cu–Mg–Ag–Mn alloy shows good superplastic properties at temperatures higher than 450 °C and strain rates lower than 10^?2 s^?1. A maximum elongation-to-failure of 320% was observed at 500 °C and 5 × 10^?4 s^?1, where the corresponding strain rate sensitivity index m is 0.58 and the flow stress σ is 5.7 MPa. Microstructure studies revealed that the observed superplastic behavior resulted from severe grain elongation rather than grain boundary sliding. It is suggested that this phenomenon may provide a new concept for developing superplastic materials.     

Temperature and grain size dependence of superplasticity in a Zn−0.3wt.%Al alloy

The superplastic deformation behavior of quasi-single phase Zn-0.3 wt. %Al was investigated. A series of load relaxation and tensile tests was conducted at various temperatures ranging from RT (20 °C) to 200 °C. The recently proposed internal variable theory of structural superplasticity was applied. The flow curves obtained from load relaxation tests were shown to consist of contributions from interface sliding (IS) and accommodating plastic deformation. In the case of quasi-single phase Zn-0.3 wt.% Al alloy with an average agrain size of 1 μm, the IS behavior could be described as a viscous flow process characterized by a power index of M_g=0.5. A large elongation of about 1400% was obtained at room temperature and the strain rate sensitivity parameter was about 0.4. Although relatively large-grained (10 μm) single phase alloy showed a high value of strain rate sensitivity comparable to that of fine-grained alloy at very low strain rate range, IS was not expected from the analysis based on the internal variable theory of structural superplasticity at room temperature. As the temperature increased above 100 °C, however, the contribution from IS was observed at a very low strain rate range. A high elongation of ∼400% was obtained in a specimen of 10-μm-grain-size at 200 °C under a strain rate of 2×10⁻⁴/sec. Jointly appointed at Center for Advanced Aerospace Materials (CAAM)     

Processing maps for hot working of a P/M iron aluminide alloy

The hot working behavior of a Fe–24 wt.% Al iron aluminide alloy processed by the powder metallurgy route has been studied in the temperature range 750–1150°C and strain rate range 0.001–100 s⁻¹ by establishing processing maps at different strains in the range 0.1–0.5. The features in the processing maps have changed with strain suggesting that the mechanisms of hot deformation are evolving with strain. Early in the deformation (strain of 0.1), the map exhibited a single domain with a peak efficiency of power dissipation of about 44% occurring at about 1100°C and a strain rate of about 0.03 s⁻¹. This domain represents dynamic recrystallization (DRX) of the initial material possibly causing a substantial grain refinement. With increasing strain, a bifurcation has occurred giving rise to two domains: (1) at strain rates lower than about 0.1 s⁻¹ and temperatures above 1000°C, superplastic deformation has occurred, and (2) at strain rates higher than about 10 s⁻¹ and temperatures above 1125°C, DRX has occurred. The material exhibited flow localization at lower temperatures and higher strain rates. On the basis of the processing maps, the optimum processing routes available for hot working of this material are outlined.     

Microstructure effects on the forgeability of Zn-22Al eutectoid alloy

The forgeability of Zn-22Al eutectoid alloy with two types of microstructure has been studied by using a Gleeble simulation machine. Experimental results showed that the fine-grained Zn-22Al eutectoid alloy possessed excellent forgeability. The flow stress was only 11.5 MPa at 200°C in a compressive strain rate of 0.006 s⁻¹ and then remained constant during the whole forging process. However, the compressive stress-strain curves of lamellar Zn-22Al eutectoid alloy were drastically higher than that of fine-grained Zn-22Al eutectoid alloy tested in the same forging conditions. The stress-softening phenomenon and oscillatory behavior exhibited in these stress-strain curves of lamellar Zn-22Al eutectoid alloy may be attributed to the dynamic recovery (and/or recrystallization) effect at elevated temperatures.     

Effect of Cu on the Superplastic-like Behavior of Coarse-Grained Al-Mg Alloys

In this study, the effect of Cu content on the superplastic-like behavior of Al-Mg alloys in coarse grain size condition has been studied. Five hot-rolled Al-Mg alloys with different Cu concentrations (0.5, 1.0, 1.5, and 2.0?wt.%) and without Cu were prepared. Tensile test specimens were machined parallel to the rolling direction. High-temperature elongation to failure tests were performed under a constant cross-head speed condition at different strain rates and temperatures. Grain size refinement is observed as Cu addition increases. Maximum tensile elongation of 373% could be achieved in the Al-4.5%Mg-1.5%Cu alloy with an average grain size of 28???m at 500?°C and 1?×?10^?2?s^?1. Grain size refinement after superplastic deformation was also observed.     

TA15合金高低温恒应变速率拉伸变形行为对比研究

为进一步研究钛合金超塑性变形行为,对TA15合金在变形温度700~900 ℃、应变速率1×10?2~1×10?4 s?1条件下进行恒应变速率拉伸实验,对比不同温度、不同应变速率下合金的变形行为。结果表明:TA15合金在初生等轴α相平均尺寸15 μm的条件下,拉伸试样的伸长率为73.3%~250.0%;在850 ℃、1×10?4 s?1变形条件下,试样伸长率最高;在700~750 ℃下,合金表现出的峰值应力较大;在750 ℃、1×10?4 s?1变形条件下,试样伸长率为183.3%。合金试样仅在高温及低应变速率条件下出现稳态流变阶段,该阶段持续时间越长,合金的伸长率越高。变形后的TA15合金组织均发生不同程度的长大,经高温、低应变速率的变形,试样组织粗化现象最为明显。