Plastic deformation technology of high strength deformed magnesium alloy

The traditional plastic deformation technology of magnesium alloys is relatively poor at high temperature, so a plastic deformation technology of high strength wrought magnesium alloys is designed. Firstly, the slip surface and slip direction which affect the properties of magnesium alloy are analyzed, then the rolling finite element is simulated, the simulation results are visualized, and the simulation information required by the user is output. The results show that the temperature rise decreases with the increase of initial deformation temperature, the average grain size decreases and the uniformity of grain size distribution increases gradually due to dynamic recrystallization, and the cumulative strain and strain distribution in the strain field increases gradually with each pass due to the existence of shear stress in the stress field.

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Plastic Deformation of Electrodeposited Nanocrystalline Ni-W Alloys at High Temperatures

Materials Science Forum ◽

10.4028/www.scientific.net/msf.561-565.1295 ◽

2007 ◽

Vol 561-565 ◽

pp. 1295-1298

Author(s):

Hitoshi Yokoyama ◽

Tohru Yamasaki ◽

Takeyuki Kikuchi ◽

Takeshi Fukami

Keyword(s):

Plastic Deformation ◽

Grain Size ◽

Plastic Strain ◽

Tensile Stress ◽

Initial Period ◽

Shear Bands ◽

High Strength ◽

Tensile Test Specimen ◽

Average Grain Size ◽

Static Tensile

High-strength nanocrystalline Ni-W alloys containing 16.9 at. % W with average grain size of about 6 nm in diameter has been obtained by electrodeposition. At room temperature, the nominal tensile strength of the alloy was attained to about 1600 MPa, while the plastic strain before fracture was a very low value of 0.05 %. In this case, highly localized shear bands were observed near the fractured surface of the tensile test specimen. When the samples were annealed at 300 °C under a static tensile stress of 327 MPa, the plastic strain was largely increased at the initial period of annealing and then tended to saturate, i.e., 0.54 % for 2 h, respectively. Grain size of the Ni-W alloys was almost saturated to 10 ~ 15 nm after annealing at 300°C for 2 h. It may be expected that the high tensile stress during grain growth might be effective to obtain the large uniform plastic deformation of nanocrystalline Ni-W alloys.

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Structural Transformations and Mechanical Properties of Metastable Austenitic Steel under High Temperature Thermomechanical Treatment

Metals ◽

10.3390/met11040645 ◽

2021 ◽

Vol 11 (4) ◽

pp. 645

Author(s):

Igor Litovchenko ◽

Sergey Akkuzin ◽

Nadezhda Polekhina ◽

Kseniya Almaeva ◽

Evgeny Moskvichev

Keyword(s):

Plastic Deformation ◽

Grain Size ◽

High Temperature ◽

Austenitic Steel ◽

Structural Transformations ◽

Initial State ◽

Twin Boundaries ◽

Metastable Austenitic Steel ◽

Average Grain Size ◽

Heating Up

The effect of high-temperature thermomechanical treatment on the structural transformations and mechanical properties of metastable austenitic steel of the AISI 321 type is investigated. The features of the grain and defect microstructure of steel were studied by scanning electron microscopy with electron back-scatter diffraction (SEM EBSD) and transmission electron microscopy (TEM). It is shown that in the initial state after solution treatment the average grain size is 18 μm. A high (≈50%) fraction of twin boundaries (annealing twins) was found. In the course of hot (with heating up to 1100 °C) plastic deformation by rolling to moderate strain (e = 1.6, where e is true strain) the grain structure undergoes fragmentation, which gives rise to grain refining (the average grain size is 8 μm). Partial recovery and recrystallization also occur. The fraction of low-angle misorientation boundaries increases up to ≈46%, and that of twin boundaries decreases to ≈25%, compared to the initial state. The yield strength after this treatment reaches up to 477 MPa with elongation-to-failure of 26%. The combination of plastic deformation with heating up to 1100 °C (e = 0.8) and subsequent deformation with heating up to 600 °C (e = 0.7) reduces the average grain size to 1.4 μm and forms submicrocrystalline fragments. The fraction of low-angle misorientation boundaries is ≈60%, and that of twin boundaries is ≈3%. The structural states formed after this treatment provide an increase in the strength properties of steel (yield strength reaches up to 677 MPa) with ductility values of 12%. The mechanisms of plastic deformation and strengthening of metastable austenitic steel under the above high-temperature thermomechanical treatments are discussed.

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Superplasticity at Intermediate Temperatures of ZK60 Magnesium Alloy Processed by Indirect Extrusion

Metals ◽

10.3390/met11040606 ◽

2021 ◽

Vol 11 (4) ◽

pp. 606

Author(s):

César Palacios-Trujillo ◽

José Victoria-Hernández ◽

David Hernández-Silva ◽

Dietmar Letzig ◽

Marco A. García-Bernal

Keyword(s):

Magnesium Alloy ◽

Magnesium Alloys ◽

Deformation Mechanism ◽

Extrusion Direction ◽

Grain Boundary Sliding ◽

Mg Alloys ◽

Homogeneous Microstructure ◽

Texture Measurement ◽

Average Grain Size ◽

Zk60 Magnesium Alloy

Magnesium alloys usually exhibit excellent superplasticity at high temperature. However, many Mg alloys have poor formation ability near room temperature. Therefore, preparation of Mg alloys with suitable microstructures to show low or intermediate temperature superplasticity is an important goal. In this work, the superplastic behavior at intermediate temperatures of a commercial ZK60 magnesium alloy processed by indirect extrusion was investigated. After extrusion, the alloy showed a refined and homogeneous microstructure with an average grain size of 4 ± 2 μm. Overall texture measurement indicated that the alloy showed a strong prismatic texture with the highest intensity oriented to pole ⟨101¯0⟩. A texture component ⟨1¯21¯1⟩ parallel to the extrusion direction was found; this type of texture is commonly observed in Mg alloys with rare earth additions. Tensile tests were performed at temperatures of 150, 200, and 250 °C at three strain rates of 10−2, 10−3, and 10−4 s−1. A very high ductility was found at 250 °C and 10−4 s−1, resulting in an elongation to failure of 464%. Based on calculations of the activation energy and on interpretation of the deformation mechanism map for magnesium alloys, it was concluded that grain boundary sliding (GBS) is the dominant deformation mechanism.

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A Physical-Based Plane Stress Constitutive Model for High Strength AA7075 under Hot Forming Conditions

Metals ◽

10.3390/met11020314 ◽

2021 ◽

Vol 11 (2) ◽

pp. 314

Author(s):

Fulong Chen ◽

Haitao Qu ◽

Wei Wu ◽

Jing-Hua Zheng ◽

Shuguang Qu ◽

...

Keyword(s):

Grain Size ◽

Aluminum Alloy ◽

Plane Stress ◽

Metal Forming ◽

Electron Backscatter Diffraction ◽

High Strength ◽

Material Model ◽

Hot Forming ◽

Industrial Processing ◽

Average Grain Size

Physicallybased constitutive equations are increasingly used for finite element simulations of metal forming processes due to the robust capability of modelling of underlying microstructure evolutions. However, one of thelimitations of current models is the lack of practical validation using real microstructure data due to the difficulties in achieving statistically meaningful data at a sufficiently large microstructure scale. Particularly, dislocation density and grain size governing the hardening in sheet deformation are of vital importance and need to be precisely quantified. In this paper, a set of dislocation mechanics-based plane stress material model is constructed for hot forming aluminum alloy. This material model is applied to high strength 7075 aluminum alloy for the prediction of the flow behaviorsconditioned at 300–400 °C with various strain rates. Additionally, an electron backscatter diffraction (EBSD) technique was applied to examine the average grain size and geometrical necessary dislocation (GND) density evolutions, enabling both macro- and micro- characteristics to be successfully predicted. In addition, to simulate the experienced plane stress states in sheet metal forming, the calibrated model is further extended to a plane stress stateto accuratelypredict the forming limits under hot conditions.The comprehensively calibrated material model could be used for guidinga better selection of industrial processing parameters and designing process windows, taking into account both the formed shape as well as post formed microstructure and, hence, properties.

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Novel grain refinement of AZ91E magnesium alloy and the effect on hot tearing during solidfication

10.32920/ryerson.14649522.v1 ◽

2021 ◽

Author(s):

Abdallah Elsayed

Keyword(s):

Mechanical Properties ◽

Grain Size ◽

Magnesium Alloy ◽

Grain Refinement ◽

Magnesium Alloys ◽

Hot Tearing ◽

Grain Refining ◽

Grain Refiner ◽

Structural Applications ◽

Hot Tearing Susceptibility

For the A1-5Ti-1B grain refiner, the addition of 0.1 wt.% provided a 68 % reduction in grain size as compared to the unrefined AZ91E alloy at a holding time of five minutes. Grain growth restriction by TiB₂ particles was the source of grain refinement. With the addition of A1-5Ti-1B, only a small reduction in hot tearing susceptibility ws observed because large TiA1₃ particles bonded poorly with the eutectic and blocked feeding channels.The addition of 1.0 wt.% A1-1Ti-3B provided a grain size reduction of 63% as compared to the unrefined AZ91E alloy at a holding time of five minutes. The grain refinement with A1-1Ti-3B addition was attributed to a combination of TiB₂ grain growth restriction and A1B₂ nucleating sites. A significant reduction in hot tearing susceptibility was observed with A1-1Ti-3B addition as a result of a higher cooling rate and shorter local soldification time as compared to the AZ91E alloy. The reduction in hot tearing susceptibility was attributed to the good interface between eutectic and TiB₂ particles. Both grain refiners demonstrated a good resistance to fading during the holding times investigated. In addition, the AZ91E + A1-5Ti-1B and AZ91E + A1-1Ti-3B castings showed much fewer dislocation networks as compared to the untreated AZ91E casting.The development of efficient A1-Ti-B refiners can also improve castability of magnesium alloys. In addition, the fade resistant A1-Ti-B grain refiners can reduce operating costs and maintain productivity on the foundry floor. Thus, magnesium alloy with A1-Ti-B treatment have the potential for more demanding structural applications in the automobile and aerospace industries. Vehicle weight in the aerospace and automotive industries directly impacts carbon emissions and fuel efficiency. An increase in the use of lightweight materials for structural applications will result in lighter vehicles. Low density materials, such as magnesium (1.74 g/cm³) are a potential alternative to aluminium (2.70 g/cm³), to reduce component weight in structural applications.However, current magnesium alloys still do not have adequate mechanical properties and castability to meet the performance specifications of the automotive and aerospace industries. Grain refinement can significantly improve mechanical properties and reduce hot tearing during permanent mould casting. Recently, Al-Ti-B based grain refiners have shown potential in grain refining magnesium-aluminum alloys such as AZ91E. This study investigates the grain refining efficiency and fading of A1-5Ti-1B and A1-1Ti-3B in AZ91E magnesium alloy and their subsequent effect on hot tearing.The grain refiners were added at 0.1, 0.2, 0.5 and 1.0 wt.% levels. For the grain refinement and fading experiments, the castings were prepared using graphite moulds with holding times of 5, 10 and 20 minutes. For the hot tearing experiments, castings were produced representing the optimal addition level of each grain refiner. The castings were prepared using a permanent mould with pouring and mould temperatures of 720 and 180 ºC, respectively. The castings were characterized using SEM, TEM, optical microscopy and thermal analysis.

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Paradox of Strength and Ductility in Metals Processed Bysevere Plastic Deformation

Journal of Materials Research ◽

10.1557/jmr.2002.0002 ◽

2002 ◽

Vol 17 (1) ◽

pp. 5-8 ◽

Cited By ~ 858

Author(s):

R. Z. Valiev ◽

I. V. Alexandrov ◽

Y. T. Zhu ◽

T. C. Lowe

Keyword(s):

Mechanical Properties ◽

Plastic Deformation ◽

Grain Size ◽

Yield Strength ◽

Mechanical Behavior ◽

High Strength ◽

High Ductility ◽

Elongation To Failure ◽

Failure Ductility ◽

Strength And Ductility

It is well known that plastic deformation induced by conventional forming methodssuch as rolling, drawing or extrusion can significantly increase the strength of metalsHowever, this increase is usually accompanied by a loss of ductility. For example, Fig.1 shows that with increasing plastic deformation, the yield strength of Cu and Almonotonically increases while their elongation to failure (ductility) decreases. Thesame trend is also true for other metals and alloys. Here we report an extraordinarycombination of high strength and high ductility produced in metals subject to severeplastic deformation (SPD). We believe that this unusual mechanical behavior is causedby the unique nanostructures generated by SPD processing. The combination ofultrafine grain size and high-density dislocations appears to enable deformation by newmechanisms. This work demonstrates the possibility of tailoring the microstructures ofmetals and alloys by SPD to obtain both high strength and high ductility. Materialswith such desirable mechanical properties are very attractive for advanced structuralapplications.

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Influence of Diffusion Bonding for Superplasticity Magnesium Alloys with the Fore and Post Treatment

Materials Science Forum ◽

10.4028/www.scientific.net/msf.551-552.169 ◽

2007 ◽

Vol 551-552 ◽

pp. 169-172

Author(s):

Yan Dong Yu ◽

C.W. Wang

Keyword(s):

Grain Size ◽

Magnesium Alloy ◽

Surface Treatment ◽

Magnesium Alloys ◽

Diffusion Bonding ◽

Ageing Time ◽

Post Treatment ◽

Ageing Temperature ◽

Experiment Study ◽

Shearing Strength

Influence of surface treatment to diffusion bonding before joining was analyzed during the process of magnesium alloys diffusion bonding. We processed diffusion bonding by using ZK60 rolling superplasticity magnesium alloy sheets with thickness 1.5mm and grain size 8.9$m. Joint was carried out ageing strengthening by experiment study to increase its shearing strength. Ageing strengthening performance was researched under ageing temperature 150-190 °C and the ageing time 6-48h. The results showed: diffusion bonding joints’ shearing strength had enhanced in some degrees and reached 86% of basal strength when the ageing temperature is 160 °C and the ageing time is 24h. It showed that the magnesium alloy joint’s strength could be greatly improved by ageing strengthening.

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Improvement of Strength and Ductility by Combining Static Recrystallization and Unique Heat Treatment in Co-20Cr-15W-10Ni Alloy for Stent Application

Materials Science Forum ◽

10.4028/www.scientific.net/msf.1016.1503 ◽

2021 ◽

Vol 1016 ◽

pp. 1503-1509

Author(s):

Kosuke Ueki ◽

Soh Yanagihara ◽

Kyosuke Ueda ◽

Masaaki Nakai ◽

Takayoshi Nakano ◽

...

Keyword(s):

Heat Treatment ◽

Grain Size ◽

Static Recrystallization ◽

High Strength ◽

Small Variation ◽

Grain Structure ◽

Fine Grain ◽

High Temperature Short Time ◽

Average Grain Size ◽

Strength And Ductility

The Co-20Cr-15W-10Ni (CCWN, mass%) alloy has excellent corrosion resistance and strength-ductility balance and is applied in almost all balloon-expandable stent platforms. To further reduce the invasiveness of stent placement, it is necessary to reduce the diameter of the stent. That is, both high strength and high ductility should be achieved while maintaining a low yield stress. In our previous studies, it was discovered that low-temperature heat-treatment (LTHT) at 873 K improves the elongation of the CCWN alloy. In this study, we focused on the grain refinement by swaging and static recrystallization to improve the strength of the alloy. The as-swaged alloy was recrystallized at 1373–1473 K for 100–300 s, followed by LTHT. A fine grain structure with an average grain size of 3–17 μm was obtained by static recrystallization. The η-phase (M12X-M6X type precipitates, M: metallic elements, X: C and/or N) formed during the recrystallization at 1373–1448 K. The alloys recrystallized at 1448 and 1473 K had a homogeneous structure with a small variation in the grain size. On the other hand, the alloys recrystallized at 1373 and 1423 K had an inhomogeneous structure in which fine and coarse grains were mixed. Both the strength and ductility of the CCWN alloy were improved by combining high-temperature short-time recrystallization and LTHT.

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Microstructural Control of 7075 Al Wrought Alloys through Thixoextrusion Route

Materials Science Forum ◽

10.4028/www.scientific.net/msf.510-511.362 ◽

2006 ◽

Vol 510-511 ◽

pp. 362-365 ◽

Cited By ~ 2

Author(s):

Young Ok Yoon ◽

Hyung Ho Jo ◽

Jin Kyu Lee ◽

Dong In Jang ◽

Shae K. Kim

Keyword(s):

Grain Size ◽

Liquid Fraction ◽

Isothermal Holding ◽

High Strength ◽

Industrial Applications ◽

High Productivity ◽

Die Life ◽

Average Grain Size ◽

Low Energy Consumption ◽

Holding Temperature

Thixoextrusion, one of the thixoforming processes, has advantages of high productivity, reduction of the extrusion pressure, extension of the die life, and cost saving owing to its low energy consumption compared with the conventional extrusion processes. Especially, thixoextrusion process is expected to be very effective for hard-to-form materials with high strength. The present study focuses on 7075 Al wrought alloy to investigate the potential industrial applications of the thixoextrusion process. The microstructural evolution of 7075 Al wrought alloy for thixoextrusion was investigated with respect to isothermal holding temperature and time in the partially remelted semisolid state. The results showed that the liquid fraction increased with increasing isothermal holding temperature and time while the average grain size was inversely proportional to isothermal holding temperature and time up to 5min. However, there was no big change of liquid fraction and average grain size with respect to isothermal holding temperature and time. The important fact that the liquid fraction and average grain size were almost uniform after 5 min holding time is considered very useful for thixoextrusion in terms of process control.

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Monte Carlo Simulation of Seebeck Coefficient and Electrical Conductivity in Thermoelectrics

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.709.176 ◽

2013 ◽

Vol 709 ◽

pp. 176-179 ◽

Cited By ~ 2

Author(s):

Jian Li

Keyword(s):

Electrical Conductivity ◽

Monte Carlo Simulation ◽

Grain Size ◽

Monte Carlo ◽

Seebeck Coefficient ◽

Ground State ◽

Proposed Model ◽

Average Grain Size ◽

Polycrystalline Ceramics ◽

Simulation Results

we proposed a scheme for simulating the electronic and thermoelectric properties of polycrystalline ceramics. The simulation results show that the ground state electrons are easily confined in the largest grain. In addition, with the increasing average grain size, the Seebeck coefficient decreases while the electrical conductivity increases monotonically. The simulation results agree well with the available experimental results. Therefore, the proposed model is proved to be a promising approach for thermoelectric investigations.

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