Editorial

4 pages, 347 KiB

Open AccessEditorial

Superplasticity and Superplastic Forming

by Donato Sorgente

Metals 2021, 11(6), 946; https://doi.org/10.3390/met11060946 - 11 Jun 2021

Cited by 2 | Viewed by 2037

In both academic and industrial research endeavours, driving forces are essential to keep the interest alive for a specific topic [...] Full article

(This article belongs to the Special Issue Superplasticity and Superplastic Forming)

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Research

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17 pages, 4863 KiB

Open AccessArticle

Experimental Analysis and Behaviour Modelling of the Deformation Mechanisms of a Ti-6242S Alloy under Hot and Superplastic Forming Conditions

by Longqiu Song, Anzu Ii, Laurie Despax, Hatsumi Onishi, Hiroaki Matsumoto, Vincent Velay and Vanessa Vidal

Metals 2020, 10(12), 1599; https://doi.org/10.3390/met10121599 - 29 Nov 2020

Cited by 4 | Viewed by 1393

Abstract

In this work, the hot deformation characteristics of a near-

α

Ti-Al-2SnZr-2Mo alloy (Ti6242 alloy) with a Fine-Grained (FG) microstructure (

d_{α}

= 2.86

μ

m) were investigated at two levels of temperature, T = 730

^{\circ}

C and T = 840 [...] Read more.

In this work, the hot deformation characteristics of a near-

α

Ti-Al-2SnZr-2Mo alloy (Ti6242 alloy) with a Fine-Grained (FG) microstructure (

d_{α}

= 2.86

μ

m) were investigated at two levels of temperature, T = 730

^{\circ}

C and T = 840

^{\circ}

C. The initial microstructure consists of equiaxed nodules of the

α

phase as well as some

α

lamellae sparsely distributed and separated by thin layers of the BCC

β

phase. For both temperatures, three strain rates (

10^{- 4}, 10^{- 3}, 10^{- 2} s^{- 1}

) were analysed during loading. Moreover, the microstructural evolution (

α

size and morphology) was also evaluated by conducting interrupted tensile tests. The different tensile testing conditions greatly influence the stress-strain response of the material as well as the microstructure evolution. Indeed, various phenomena can take place such as elongation of the grain structure, globularization, dynamic recrystallization and grain growth of the equiaxed areas depending on the temperature, the strain rate and the strain level. The FG Ti6242 alloy exhibits interesting superplastic ductility at T = 840

^{\circ}

C. At this temperature either a very gradual flow softening (at higher strain rate) or flow hardening (at lower strain rate) can be observed and are related respectively to one or more of the following mechanisms: lamellae globularization, DRX and grain growth. At the intermediate strain rate, both mechanisms, strain hardening and softening, coexist. At T = 730

^{\circ}

C, the onset of the

α

lamellae globularization was only promoted at low strain rate. A mechanical behavior model was developed in the temperature range of 730–840

^{\circ}

C, which was able to take into account all the observed phenomena: viscosity, softened behavior and strain hardening. Constitutive equations were calibrated from the stress-strain responses and microstructural observations, and the computed results were in good agreement with the experiments. Full article

(This article belongs to the Special Issue Superplasticity and Superplastic Forming)

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12 pages, 295 KiB

Open AccessArticle

Dimensional Analysis of Superplastic Processes with the Buckingham Π Theorem

by Luis García-Barrachina and Antonio J. Gámez

Metals 2020, 10(12), 1575; https://doi.org/10.3390/met10121575 - 25 Nov 2020

Cited by 7 | Viewed by 2176

Abstract

This work applies the Buckingham

Π

theorem from dimensional analysis on superplastic processes in order to obtain laws of behaviour in a simple way. For this reason, a mathematical background is developed. The particular behaviour of superplastic materials makes it necessary to adapt [...] Read more.

This work applies the Buckingham

Π

theorem from dimensional analysis on superplastic processes in order to obtain laws of behaviour in a simple way. For this reason, a mathematical background is developed. The particular behaviour of superplastic materials makes it necessary to adapt the way in which these are treated, modelling them by a viscosity function of the strain-rate. Then, dimensional analysis is applied on a set of free-inflation tests in order to obtain a formula that defines the forming time as single function of geometric and material variables. Dimensional analysis allows us to reduce the number of variables to analyse from six to only three. Finally, two different forming time estimators are compared to measure the accuracy of our method, showing a significant improvement over previous methods. Full article

(This article belongs to the Special Issue Superplasticity and Superplastic Forming)

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18 pages, 18909 KiB

Open AccessArticle

The Effect of Material Properties on the Accuracy of Superplastic Tensile Test

by Sergey Aksenov and Vadim Mikolaenko

Metals 2020, 10(10), 1353; https://doi.org/10.3390/met10101353 - 10 Oct 2020

Cited by 6 | Viewed by 2308

Abstract

Tensile testing is widely used for the mechanical characterization of materials subjected to superplastic deformation. At the same time, it is known that the obtained flow data are affected by specimen geometry. Thus, they characterize the specimen rather than the material. This work [...] Read more.

Tensile testing is widely used for the mechanical characterization of materials subjected to superplastic deformation. At the same time, it is known that the obtained flow data are affected by specimen geometry. Thus, they characterize the specimen rather than the material. This work provides the numerical analysis aimed to study how the material flow behavior affects the results of tensile tests. The simulations were performed by the finite element method in Abaqus software, utilizing user-defined procedures for calculation of forces acting on the crossheads. The accuracy of tensile testing is evaluated by the difference between the input material flow behavior specified in the simulations and the output one, obtained by the standard ASTM E2448 procedure based on the predicted forces. The results revealed that the accuracy of the superplastic tensile test is affected by the material properties. Even if the material flow behavior follows the Backofen power law, which is invariant for the effective strain, the output stress–strain curves demonstrate significant strain hardening and softening effects. The relation between the basic superplastic characteristics and the tensile test errors is described and analyzed. Full article

(This article belongs to the Special Issue Superplasticity and Superplastic Forming)

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12 pages, 3971 KiB

Open AccessFeature PaperArticle

Process Development for a Superplastic Hot Tube Gas Forming Process of Titanium (Ti-3Al-2.5V) Hollow Profiles

by Ricardo Trân, Franz Reuther, Sven Winter and Verena Psyk

Metals 2020, 10(9), 1150; https://doi.org/10.3390/met10091150 - 25 Aug 2020

Cited by 20 | Viewed by 3059

Abstract

Tube forming technologies based on internal forming pressures, such as hydroforming or hot tube gas forming, are state of the art to manufacture complex closed profile geometries. However, materials with excellent specific strengths and chemical properties, such as titanium alloys, are often challenging [...] Read more.

Tube forming technologies based on internal forming pressures, such as hydroforming or hot tube gas forming, are state of the art to manufacture complex closed profile geometries. However, materials with excellent specific strengths and chemical properties, such as titanium alloys, are often challenging to shape due to their limited formability. In this study, the titanium alloy Ti-3Al-2.5V was processed by superplastic hot tube gas forming to manufacture a helically shaped flex tube. The forming process was investigated in terms of process simulation, forming tool technology and process window for the manufacturing of good parts. Within a simulation study, a strain rate optimized forming pressure–time curve was defined. With the newly developed tool design, forming temperatures up to 900 °C and internal forming pressures up to 7 MPa were tested. A process window to manufacture good parts without necking or wrinkling has been successfully identified. The experiment data showed good agreement with the numerical simulations. The detailed study of the process contributes to an in-depth understanding of the superplastic forming of Ti-3Al-2.5V during hot tube gas forming. Furthermore, the study shows the high potential of superplastic hot tube gas forming of titanium alloys for the manufacturing of helical flex tubes and bellows. Full article

(This article belongs to the Special Issue Superplasticity and Superplastic Forming)

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10 pages, 2433 KiB

Open AccessArticle

Using High-Pressure Torsion to Achieve Superplasticity in an AZ91 Magnesium Alloy

by Roberto B. Figueiredo and Terence G. Langdon

Metals 2020, 10(5), 681; https://doi.org/10.3390/met10050681 - 22 May 2020

Cited by 20 | Viewed by 2732

Abstract

An AZ91 magnesium alloy (Mg-9%, Al-1% Zn) was processed by high-pressure torsion (HPT) after solution-heat treatment. Tensile tests were carried out at 423, 523, and 623 K in the strain rate range of 10⁻⁵−10⁻¹ s⁻¹ to evaluate the occurrence [...] Read more.

An AZ91 magnesium alloy (Mg-9%, Al-1% Zn) was processed by high-pressure torsion (HPT) after solution-heat treatment. Tensile tests were carried out at 423, 523, and 623 K in the strain rate range of 10⁻⁵−10⁻¹ s⁻¹ to evaluate the occurrence of superplasticity. Results showed that HPT processing refined the grain structure in the alloy, and grain sizes smaller than 10 µm were retained up to 623 K. Superplastic elongations were observed at low strain rates at 423 K and at all strain rates at 523 K. An examination of the experiment data showed good agreement with the theoretical prediction for grain-boundary sliding, the rate-controlling mechanism for superplasticity. Elongations in the range of 300–400% were observed at 623 K, attributed to a combination of grain-boundary-sliding and dislocation-climb mechanisms. Full article

(This article belongs to the Special Issue Superplasticity and Superplastic Forming)

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20 pages, 6237 KiB

Open AccessArticle

An Accurate Constitutive Model for AZ31B Magnesium Alloy during Superplastic Forming

by Guangwen Dai, Firas Jarrar, Fahrettin Ozturk, Jamal Sheikh-Ahmad and Zemin Li

Metals 2019, 9(12), 1273; https://doi.org/10.3390/met9121273 - 28 Nov 2019

Cited by 6 | Viewed by 2424

Abstract

Accurate constitutive material models are essential for the realistic simulation of metal forming processes. However, for superplastic forming, mostly the material models found in the literature are based on fitting of the simple power law equation. In this study, an AZ31B constitutive model [...] Read more.

Accurate constitutive material models are essential for the realistic simulation of metal forming processes. However, for superplastic forming, mostly the material models found in the literature are based on fitting of the simple power law equation. In this study, an AZ31B constitutive model that takes into account microstructural evolution is introduced. This model takes into account grain growth and cavity formation in addition to strain and strain rate hardening. The model parameters were calibrated using the results of high temperature bulge forming tests and microstructural analysis. The Taguchi optimization method was used in the fitting process. In order to verify the model, simulations of the superplastic forming of two different geometries were carried out, and the results were compared with those obtained experimentally. Results show that the proposed model can accurately predict the formed geometry and thickness distribution. Full article

(This article belongs to the Special Issue Superplasticity and Superplastic Forming)

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12 pages, 4476 KiB

Open AccessArticle

The Effect of Isothermal Multi-Directional Forging on the Grain Structure, Superplasticity, and Mechanical Properties of the Conventional Al–Mg-Based Alloy

by Anastasia V. Mikhaylovskaya, Anton D. Kotov, Mikhail S. Kishchik, Alexey S. Prosviryakov and Vladimir K. Portnoy

Metals 2019, 9(1), 33; https://doi.org/10.3390/met9010033 - 02 Jan 2019

Cited by 24 | Viewed by 3870

Abstract

The current study observed a grain structure evolution in the central part and periphery of the sample of an Al–Mg–Mn-based alloy during isothermal multidirectional forging (IMF) at 350 °C with a cumulative strain of 2.1–6.3 and a strain per pass of 0.7. A [...] Read more.

The current study observed a grain structure evolution in the central part and periphery of the sample of an Al–Mg–Mn-based alloy during isothermal multidirectional forging (IMF) at 350 °C with a cumulative strain of 2.1–6.3 and a strain per pass of 0.7. A bimodal grain size distribution with areas of fine and coarse grains was observed after IMF and subsequent annealing. The grain structure, mechanical properties, and superplastic behavior of the samples subjected to IMF with a cumulative strain of 6.3 and the samples exposed to IMF with subsequent cold rolling were compared to the samples exposed to a simple thermo-mechanical treatment. The micro-shear bands were formed inside original grains after the first three passes. The fraction of recrystallized grains increased and the mean size decreased with an increasing cumulative strain from 2.1 to 6.3. Significant improvements of mechanical properties and superplasticity were observed due to the formation of a homogenous fine grain structure 4.8 µm in size after treatment including IMF and subsequent cold rolling. Full article

(This article belongs to the Special Issue Superplasticity and Superplastic Forming)

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12 pages, 5011 KiB

Open AccessArticle

Finite Element Simulation of High-Speed Blow Forming of an Automotive Component

by Omid Majidi, Mohammad Jahazi and Nicolas Bombardier

Metals 2018, 8(11), 901; https://doi.org/10.3390/met8110901 - 03 Nov 2018

Cited by 10 | Viewed by 5331

Abstract

High-speed blow forming (HSBF) is a new technology for producing components with complex geometries made of high strength aluminum alloy sheets. HSBF is considered a hybrid-superplastic forming method, which combines crash forming and gas blow forming. Due to its novelty, optimization of the [...] Read more.

High-speed blow forming (HSBF) is a new technology for producing components with complex geometries made of high strength aluminum alloy sheets. HSBF is considered a hybrid-superplastic forming method, which combines crash forming and gas blow forming. Due to its novelty, optimization of the deformation process parameters is essential. In this study, using the finite element (FE) code ABAQUS, thinning of an aluminum component produced by HSBF under different strain rates was investigated. The impact of element size, variation of friction coefficient, and material constitutive model on thinning predictions were determined and quantified. The performance of the FE simulations was validated through forming of industrial size parts with a complex geometry for the three investigated strain rates. The results indicated that the predictions are sensitive to the element size and the coefficient of friction. Remarkably, compared to a conventional power law model, the variable m-value viscoplastic (VmV) model could precisely predict the thickness variation of the industrial size component. Full article

(This article belongs to the Special Issue Superplasticity and Superplastic Forming)

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