Effect of Microstructure on Cavitation during Hot Deformation of a Fine-Grained Aluminum-Magnesium Alloy as Revealed through Three-Dimensional Characterization

Chang, Jung-Kuei; Taleff, Eric M.; Krajewski, Paul E.

doi:10.1007/s11661-009-0061-5

Cited by 15 publications

(10 citation statements)

References 38 publications

(52 reference statements)

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“…A decrease in tensile ductility is also expected at very low Z values, Z less than approximately 10 7 s À1 , because of an increasing propensity toward cavitation development. [9,11,13,40,41] Figure 4 presents data for the Q parameter as a function of the Zener-Hollomon parameter. The Q parameter, a convenient measure for the amount of flow localization occurring at fracture in tension, [40] compares the reduction in area (q) with the theoretical reduction in area in the absence of necking:…”

Section: B Deformation Responsementioning

confidence: 99%

Abnormal Grain Growth and Recrystallization in Al-Mg Alloy AA5182 Following Hot Deformation

Chang

Takata

Ichitani

et al. 2010

Metall Mater Trans A

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Abnormally large grains have been observed in Al-Mg alloy AA5182 sheet material after forming at elevated temperature, and the reduced yield strength that results is a practical problem for commercial hot-forming operations. The process by which abnormal grains are produced is investigated through controlled hot tensile testing to reproduce the microstructures of interest. Abnormal grains are shown to develop strictly during static annealing or cooling following hot deformation; the formation of abnormal grains is suppressed during plastic straining. Abnormal grains grow by static abnormal grain growth (SAGG), which becomes a discontinuous recrystallization process when abnormal grains meet to form a fully recrystallized microstructure. Nuclei, which grow under SAGG, are produced during hot deformation by the geometric dynamic recrystallization (GDRX) process. The mechanism through which a normally continuous recrystallization process, GDRX, may be interrupted by a discontinuous process, SAGG, is discussed.

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Section: B Deformation Responsementioning

confidence: 99%

Abnormal Grain Growth and Recrystallization in Al-Mg Alloy AA5182 Following Hot Deformation

Chang

Takata

Ichitani

et al. 2010

Metall Mater Trans A

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“…When reviewing the efforts on tensile testing of superplastic materials, one needs not to look for long before realising the disagreements among researchers on the issue. Selected examples of recent efforts in the field show that investigators adopt test specimens with different gauge lengths; varying from as long as 25.4 mm, to as short as 4 mm [1][2][3][4][5][6][7][8][9][10]. Moreover, the discrepancies are not limited to gauge length; they cover gauge width, gauge length-to-width ratio, fillet radius, and even the size of the grip region.…”

Section: Introductionmentioning

confidence: 99%

Optimum Specimen Geometry for Accurate Tensile Testing of Superplastic Metallic Materials

2010

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The high temperatures and large strain limits associated with superplastic materials amplify the possibility of the tensile test outcomes being sensitive to the shape and size of the specimen geometry. In spite of that, the disparities in the specimen geometries used throughout the numerous efforts on characterising this unique class of materials are rather astonishing. There is an urge to evaluate the dependency of a superplastic tensile test on specimen geometry, before a much-needed universally-adopted standard specimen can be designed; which is the main objective of this comprehensive experimental investigation. More than 20 geometries, covering multiple variations in gauge length, gauge width, grip length and grip width values, are tested at identical conditions, and the corresponding material behaviour is compared in terms of deformation uniformity, material flow and the extracted stress/strain curves. The results reveal the influences of each geometrical parameter, as well as their combined effects, and guide the selection of an optimum specimen geometry for accurate and unified tensile testing of superplastic metallic materials.

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“…The slow forming rates and high forming temperatures lead to many problems, such as reduced tool life and high heating demands. In particular, mechanical properties of the formed products are poor due to the microstructural defects and large amounts of cavitation induced [13][14][15][16][17]. Moreover, the high-temperature requirement limits the application in forming of the alloys that are sensitive to oxidation, especially for titanium alloys at elevated temperature.…”

Section: List Of Symbolsmentioning

confidence: 99%

“…The grain growth rate [11] and the amount of cavitation [14] increase with decreasing strain rate. The influence of microstructure on cavitation development has been investigated by Chang et al [15] extensively.…”

Section: Characteristics Of Aluminum Alloys With Superplasticity (A) mentioning

confidence: 99%

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Superplastic-like forming of lightweight alloys

Liu¹

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Conventional superplastic forming (SPF) is attractive for the current industrial fabrication of precision, large and complex-shaped sheet-metal components. This process requires a fine-grained material and is carried out at high temperatures (typically above 500º C for aluminum alloys and 900º C for titanium alloys) and slow forming rates (mostly strain rate slower than 10-3 s-1). To address these limitations, an advanced sheet-forming process has been designed by combining hot drawing and superplastic forming (namely gas forming) in a one-step operation to establish a fast forming technology. The process together with a nonisothermal heating system is referred to as superplastic-like forming. The aim of this work is to investigate (i) the relationship between process parameters, material draw-in and thickness distribution and (ii) the microstructural evolution, deformation mechanism and post-forming properties during forming. Target materials are commercial grade AA5083 and Ti-6Al-4V alloys. Tensile tests were performed for both materials to determine the optimal deformation conditions, i.e. temperature and strain rate. The flow stress data of AA5083 were used in the calibration of a material model for finite element modeling (FEM). The results showed that AA5083 can deform with reasonable flow stress and tensile elongation at 400º C and a strain rate of 2×10-3 s-1 and that Ti-6Al-4V alloy possesses good forming capability at 800º C and a strain rate of 10-3 s-1. A rectangular die cavity with multiple steps was used to demonstrate different amounts of material draw-in and surface expansion of the formed part in superplastic-like forming. The punch geometry was designed and validated through a parametric study during hot drawing. The measured drawing limits were used to determine the sheet ABSTRACT II size for hot drawing. The optimal dimensions of AA5083 and Ti-6Al-4V sheets are 200×200 and 210×210 mm 2 , respectively. The non-isothermal heating system is expected to maintain the sheet at a lower global (furnace) temperature. Meanwhile, a higher local temperature in specific zones, i.e. die radii, ensures that the material there has more ductility to flow. For AA5083, the entire forming was conducted at a global temperature of 400º C, but the material close to the die radii was selectively heated to 420º C. During superplastic-like forming of Ti-6Al-4V alloy, the global and local temperatures were 800 and 820º C, respectively. After completion of forming AA5083 in 8 min, a final part with maximum percentage thinning of 40% at the outward corners and 137% surface expansion was achieved. The forming of Ti-6Al-4V alloy was completed in 16 min, exhibiting a maximum percentage thinning of 54% at the outward corners and the surface expansion of 130%. Stress gradients and the corresponding strain rate differences at the outward corners in the forming sheet led to thinning gradient and plastic straining as a result of geometric inhomogeneity as demonstrated through finite element simulations of hot drawing and gas formi...

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Effect of Microstructure on Cavitation during Hot Deformation of a Fine-Grained Aluminum-Magnesium Alloy as Revealed through Three-Dimensional Characterization

Cited by 15 publications

References 38 publications

Abnormal Grain Growth and Recrystallization in Al-Mg Alloy AA5182 Following Hot Deformation

Abnormal Grain Growth and Recrystallization in Al-Mg Alloy AA5182 Following Hot Deformation

Optimum Specimen Geometry for Accurate Tensile Testing of Superplastic Metallic Materials

Superplastic-like forming of lightweight alloys

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