变形Mg-1.5Zn-xCe合金织构及室温成形性能

实验研究了不同Ce元素含量对变形Mg-1.5Zn合金的织构及室温成形性能的影响.结果表明:在相同的热轧和退火工艺处理后,添加不同含量的Ce元素均可以有效弱化镁合金织构强度.Mg-1.5Zn合金中添加质量分数为0.2%的Ce元素后表现出了优异的室温成形性能,织构强度最大值仅为2.20,织构沿着横向分裂,并且基面法向即c轴沿着横向发生约为±35°偏转,室温下轧向方向延伸率达到23.2%,埃里克森杯突值为5.46,平面各项异性系数Δr=0.01;然而,Mg-1.5Zn合金中添加质量分数分别为0.5%和0.9%的Ce元素后,织构强度增加,埃里克森杯突值减小,由于在合金中生成了粗大的第二相粒子,使得Mg-1.5Zn-xCe合金的室温成形性能变低.      

Deformation microstructures in titanium sheet metal

A metallographic study has been made of the microstructures produced by room temperature deformation of 0.6mm thick commercially pure titanium sheet metal in uniaxial, plane strain and biaxial tension. Deformation twinning becomes increasingly important as the deformation mode changes from uniaxial through plane strain to equibiaxial tension, and is more significant for strain transverse to the rolling direction than for strain in the longitudinal direction. In uniaxial tension, 1122 twins are dominant in longitudinal straining, while 1012 twins dominate in transverse straining. In plane strain and equibiaxial straining, 1012 twinning is suppressed and largely replaced by 1122 twinning. The observed changes in twin occurrence and type are attributed to the interaction of the imposed stress system and the crystallographic texture of the rolled sheet, which alters the distribution of the grain basal-plane poles with respect to the operative stress axes. In uniaxial tension parallel to the longitudinal direction, twins favored by ‘c’ axis compression are produced, while in the transverse direction twins favored by ‘c’ axis tension appear. In plane strain and biaxial tension the dominant stress is through-thickness compression, which produces twins favored by ‘c’ axis compression in nearly all cases. The alterations in twin orientation and numbers are associated with changes in stress-strain behavior. As twin volume fraction increases and twins are aligned more closely to the principal stress axis, the instantaneous work-hardening rate tends to stabilize at a nearly constant value over a large strain range. Formerly Chief Metallurgist, The APV Company.     

Effects of yttrium on recrystallization and grain growth of Mg-4.9Zn-0.7Zr alloy

Recrystallization and grain growth in Mg-4.9Zn-0.7Zr and Mg-4.9Zn-0.9Y-0.7Zr alloys as a function of temperature on deformation were investigated with regards to hot rolling and annealing. The influence of yttrium addition on the microstructure was examined by X-ray diffraction （XRD）, optical microscopy （OM）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）. The results indicated that yttrium addition promoted nucleation of recrystallization during hot rolling process. The grain size of Mg-4.9Zn-0.7Zr alloy samples grew significantly with annealing temperature （300-400 ℃） and holding time （0-120 min）, while the microstructure of the alloy with yttrium addition remained unchanged and fine. The activation energy of grain boundary migration for Mg-4.9Zn-0.9Y-0.7Zr alloy samples （56.34 kJ/mol） was higher than that for Mg-4.9Zn-0.7Zr （42.66 kJ/mol） owing to the pinning effect of Y-containing particles. The proposed growth models of recrysta/lized grains for the two studied alloys conformed well to E. Robert＇s grain-growth equation. Besides, the ultimate strength and yield strength of the alloys with yttrium addition were improved with good plasticity.     

The Influence of Strain Path on Rare Earth Recrystallization Textures in a Magnesium-Zinc-Rare Earth Alloy

In this study, the effect of strain path on texture evolution during cold rolled and annealing of hot rolled Mg-Zn-Rare-Earth (RE) alloy (ZEK100) sheet has been investigated. Strain path during cold rolling has been varied by changing rolling direction with respect to the original hot rolling (HR) direction of the sheet. Cold rolling either parallel or perpendicular to the HR direction leads to spread and split of basal poles in the transverse direction (TD) during annealing, characteristic of Mg-Zn-RE alloys. However, when the sheet is continuously rotated between cold rolling passes, this texture spread is not produced. It is demonstrated that a change in dislocation activity, as predicted by crystal plasticity modeling, cannot explain the unusual textures developed in Mg-Zn-RE alloys. Instead, the role of strain path in determining shear band evolution is considered to be critical. When shear bands are suppressed by continuously rotating the specimen, the distinct Zn-RE texture is not produced. Furthermore, it is demonstrated the dominance of the TD spread grains emerges gradually during recrystallization, leading to the final observed texture.

     

Texture,Structure, Mechanical Properties,and Deformability of MA2-1pch Magnesium Alloy Rolled Sheets Preliminarily Subjected to Direct Extrusion or Equal-Channel Angular Pressing and Annealing

The textural and structural evolution in MA2-1pch magnesium alloy sheets fabricated from initial workpieces after (1) hot direct extrusion or (2) equal-channel angular pressing performed by route B_c in four passes at 245°C and subsequent recrystallization annealing is investigated during warm rolling and subsequent uniaxial tension. The same sharp basal texture, but different structures with different average grain sizes and fractions of twinned grains form in sheets (made of two different workpieces) after warm rolling. Subsequent uniaxial tension arranges basal planes in the sheets made from workpiece 2 along prismatic directions. Modeling of texture within the framework of a thermoactivation model shows that the texture changes due to the activation of prismatic slip. Structural evolution during uniaxial tension in the sheets made of workpiece 2 is accompanied by more intense twinning than that in the sheets made of workpiece 1. These textural and structural changes are responsible for the enhanced mechanical properties and the deformability parameters of the sheets fabricated from workpiece 2.     

Microstructure and Texture Evolution in a Yttrium-Containing ZM31 Alloy: Effect of Pre- and Post-deformation Annealing

Microstructure and texture evolution of as-extruded ZM31 magnesium alloys with different amounts of yttrium (Y) during pre- and post-deformation annealing were examined with special attention given to the effect of Y on recrystallization. It was observed that the extruded ZM31 alloys exhibited a basal texture with the basal planes parallel to the extrusion direction (ED). The compression of the extruded alloys in the ED to a strain amount of 10 pct resulted in c-axes of hcp unit cells rotating toward the anti-compression direction due to the occurrence of extension twinning. Annealing of the extruded alloys altered the microstructure and texture, and the subsequent compression after annealing showed a relatively weak texture and a lower degree of twinning. A reverse procedure of pre-compression and subsequent annealing was found to further weaken the texture with a more scattered distribution of orientations and to lead to the vanishing of the original basal texture. With increasing Y content, both the extent of extension twinning during compression and the fraction of recrystallization during annealing decreased due to the role of Y present in the substitutional solid solution and in the second-phase particles, leading to a significant increase in the compressive yield strength.     

Role of Alloying Elements in the Mechanical Behaviors of An Mg-Zn-Zr-Er Alloy

The mechanical behavior of the as-extruded and heat-treated Mg-1.5Zn-0.6Zr and Mg-1.5Zn-0.6Zr-2Er alloys was investigated and correlated with microstructure evolution. Deformation mechanisms are detailed. No evidence of twinning was observed under compression in the Er-bearing alloy throughout the grain size range of ~5 to 27 μm at a strain rate of 0.001 or 1/s. The compressive yield strength followed a Hall–Petch relation with a slope of ~10.3 MPa/mm^1/2. Er played a major role in the pyramidal 〈c+a〉 slip that was identified as a dominant plastic deformation mechanism. The CRSS for 〈c+a〉 slip system was greatly reduced and was 98 MPa in the as-extruded alloy. While it did not change the mechanical response of the Mg-1.5Zn-0.6Zr-2Er alloy, annealing was found to promote dissolution of Zn in the Mg matrix, leading to an increase in CRSS for extension twinning in the heat-treated Mg-1.5Zn-0.6Zr alloy. As a result, twinning was only observed under a higher strain rate of 1/s in compression. The CRSS for extension twinning for the heat-treated alloy with a grain size of ~28 μm was estimated to be 40 MPa, a bit lower than that for the Er-bearing alloy of the same grain size, which was 42 MPa.     

Deformation in wrought Mg−9Wt Pct Y

Considerable tensile-compressive yield strength anisotropy is normally associated with textured wrought magnesium alloys.¹ The ease of {1012} twinning is responsible for the lower compressive yield strengths of these materials. In Mg-9 wt pct Y, however, approximately equal tensile and compressive yield strengths of about 50 ksi have been previously reported.² This investigation was performed to study the deformation of wrought Mg-9 wt pct Y with the purpose of understanding its unusual isotropic behavior. It was found that almost no {1012} twinning occurs in this alloy, thus accounting for the absence of anisotropy. Initial plastic deformation both in tension and compression occurs almost entirely by slip, primarily on the basal plane. Subsequent deformation occurs by a combination of slip and {1121} twinning with short {1012} twins appearing only occasionally.     

Microstructure and Texture Evolution During Sub-Transus Thermomechanical Processing of Ti-6Al-4V-0.1B Alloy: Part I. Hot Rolling in (α + β) Phase Field

In the current study, the evolution of microstructure and texture has been studied for Ti-6Al-4V-0.1B alloy during sub-transus thermomechanical processing. This part of the work deals with the deformation response of the alloy by rolling in the (α + β) phase field. The (α + β) annealing behavior of the rolled specimen is communicated in part II. Rolled microstructures of the alloys exhibit either kinked or straight α colonies depending on their orientations with respect to the principal rolling directions. The Ti-6Al-4V-0.1B alloy shows an improved rolling response compared with the alloy Ti-6Al-4V because of smaller α lamellae size, coherency of α/β interfaces, and multiple slip due to orientation factors. Accelerated dynamic globularization for this alloy is similarly caused by the intralamellar transverse boundary formation via multiple slip and strain accumulation at TiB particles. The (0002)_α pole figures of rolled Ti-6Al-4V alloy shows “TD splitting” at lower rolling temperatures because of strong initial texture. Substantial β phase mitigates the effect of starting texture at higher temperature so that “RD splitting” characterizes the basal pole figure. Weak starting texture and easy slip transfer for Ti-6Al-4V-0.1B alloy produce simultaneous TD and RD splittings in basal pole figures at all rolling temperatures.     

Grain Size Effects on Primary,Secondary, and Tertiary Twin Development in Mg-4 wt pct Li (-1 wt pct Al) Alloys

Grain size effects on three generations of twins were investigated in extruded Mg-4 wt pct Li (-1 wt pct Al) alloys using electron-backscatter diffraction. Samples with three distinct grains sizes, yet the same texture and applied strain were analyzed. With these variables fixed, we show that compression and double twinning decrease substantially with decreasing grain size. We find that compression twinning exhibits a stronger grain size effect than tension twinning, whereas the compression twinning to double twinning transition is independent of grain size.     

Strain-Rate Sensitivity,Tension-Compression Asymmetry,r-Ratio,Twinning, and Texture Evolution of a Rolled Magnesium Alloy Mg-1.3Zn-0.4Ca-0.4Mn

Metallurgical and Materials Transactions A - In this work, the deformation response, texture evolution, and twinning development of a magnesium (Mg) alloy, Mg-1.3Zn-0.4Ca-0.4Mn, for biocompatible...     

Effect of Ca Addition on the Intensity of the Rare Earth Texture Component in Extruded Magnesium Alloys

Extruded Mg alloys usually display strong basal fiber textures, which are related to poor formability. Inspired by the texture weakening effect of the addition of rare earths (RE) to Mg alloys, two Mg-Ca alloys were designed and a range of extrusion conditions were explored in attempts to reproduce this effect. Constant strain rate and strain rate change compression tests were performed on the specially prepared Mg-0.5Ca and Mg-1Ca alloys. Dynamic strain aging (DSA) was observed to take place in both alloys over a well-defined temperature and strain rate range. Seven extrusion trials were then carried out on the Mg-0.5Ca alloy within and external to the DSA range of conditions. From the resulting textures and microstructures, it is concluded that the 〈11?21〉 (RE) texture component is formed when extrusion is carried out while DSA is taking place. The occurrence of this type of texture weakening is attributed to the promotion of recrystallization within the shear bands formed when the rate sensitivity is negative. The latter in turn arises because of the DSA taking place in the presence of solute Ca.     

Mechanisms of phase and structural transformations and texture formation in titanium alloy sheet semiproducts

Inverse pole figures are used to analyze texture formation in sheet semiproducts made from titanium alloys of various classes. The role of the mechanisms of phase and structural transformations in texture formation has been revealed. A VT6 alloy is used as an example to study the texture formation during hot, warm, and cold rolling of high-alloy α + β titanium alloys. Hot rolling followed by cooling is shown to form the β → α transformation texture. Warm or cold rolling of α + β titanium alloys leads to the (0001)〈hkio〉 deformation texture of the α phase, and subsequent annealing in the two-phase field results in the transformation texture with a strictly determined orientation distribution of α-phase crystallites due to the shear mechanism of α-phase nucleation. Specifically, the 〈10\(\overline 1 \)0〉 orientation is parallel to the rolling direction, the [0001] direction is parallel to the transverse direction, and the {11\(\overline 2 \)0} planes are parallel to the rolling plane. Thermohydrogen treatment in combination with rolling is shown to form nano-and submicrocrystalline structures with a virtually textureless α phase in VT6 sheet semiproducts. As a result, the anisotropy of the mechanical properties of the sheet semiproducts produced by this new combined hydrogen technology decreases sixfold.     

The Microstructural, Textural, and Mechanical Properties of Extruded and Equal Channel Angularly Pressed Mg-Li-Zn Alloys

The microstructural and textural evolution of the Mg-6Li-1Zn (LZ61), Mg-8Li-1Zn (LZ81), and Mg-12Li-1Zn (LZ121) alloys were investigated in the as-extruded condition and after being equal channel angularly pressed (ECAPed) for one, two, and four passes. The shear punch testing technique was employed to evaluate the room-temperature mechanical properties of the extruded and ECAPed materials. Microstructural analysis revealed that the grain refinement in both LZ61 and LZ121 alloys could be achieved after multipass ECAP through the continuous dynamic recovery and recrystallization process. For the LZ81 alloy, however, the occurrence of Li loss in the four passes of ECAP condition partly offsets the grain refining effect of the ECAP process by increasing grain size and volume fraction of the α phase. Textural studies in both LZ61 and LZ81 alloys indicated that the developed fiber texture after extrusion could be replaced by a typical ECAP texture, where the basal planes are mainly inclined about 45 deg to the extrusion axis. The increased volume fraction of the β phase in LZ81 significantly affected the α-phase texture by decreasing the intensity of the maximum orientations of the basal and prismatic planes in all deformation conditions, compared with the LZ61 alloy. It was also observed that the abnormal grain growth might be promoted by the strong texture developed in the extruded LZ121 alloy. This texture became more randomized when the number of ECAP passes increased. The SPT results showed that the shear yield stress, ultimate shear strength and normalized displacement in all studied alloys were improved through the grain refinement strengthening caused by ECAP. It was also established that increasing Li content decreased the shear strength and enhanced the shear elongation in all deformation conditions.     

Deformation Structure of Unidirectionally Compressed Ultrafine-Grained Mg-3Al-1Zn Alloy

Ultrafine-grained (UFG) Mg-3Al-1Zn (AZ31) alloys with gain sizes ranging from 0.46 to 3.22 μm were prepared by equal channel angular pressing (ECAP) and annealing. The deformation structure of UFG AZ31 alloy resulting from uniaxial compression was studied by optical and electron microscopy. The deformation was noted to proceed with the development of shear bands (SBs), which has not been reported in an UFG hcp metal. Characterization of these SBs was performed, and comparison with the SBs formed in UFG bcc and fcc metals was given. { 10[`1]2} \{ 10\bar{1}2\} tension twins inside SBs were found in all specimens compressed, irrespective of the grain size. Discussion on the limiting grain size of twinning in the UFG AZ31 alloy is also given.     

Effect of Rare Earth Cerium on Yield Strength Anisotropy of Al-Li Alloy Sheet and Its Theoretical Prediction

Traceadditionofrareearthinto 2 0 90Al Lialloyisoneofthemeasurestoimproveitslowductilityandtoughness .Al Lialloysheetwithstrongcrystallo graphictexturehasbeenknowntohaveunusuallyhigheryieldstrengthanisotropythanconventionalalu minumalloys[1～3] .However ,ithasnotbeennormallyrecognizedsofarabouttheeffectofceriumonthisanisotropyofAl Lialloy .Someinvestigationsonheat treatableAl Lialloysshowthattheyieldstrengthanisotropyof 2 0 90sheetalloyisdefinitelyassociatedwiththevolumefractionofT1precipita…     

Influence of Nd and Y additions on the corrosion behaviour of extruded Mg-Zn-Zr alloys

To improve the corrosion resistance of wrought magnesium alloys through rare earth (RE) additions, the corrosion behaviour of Mg-5Zn-0.3Zr-xNd (x=0, 1, and 2; wt%) and Mg-5Zn-0.3Zr-2Nd-yY (y=0.5 and 1; wt%) alloys in a 5wt% NaCl solution was investigated using immersion test and electrochemical measurements. The results of immersion test show that Mg-5Zn-0.3Zr-2Nd alloy exhibits the best corrosion resistance among the tested alloys. Electrochemical measurements show that secondary phases in RE-containing Mg-5Zn-0.3Zr alloys behave as less noble cathodes in micro-galvanic corrosion and suppress the cathodic process. The additions of Nd and Y into Mg-5Zn-0.3Zr alloy also improve the compactness of the corrosion product film and are beneficial to the corrosion resistance.     

Influence of transverse rolling on the

The influence of transverse rolling passes on the recrystallization texture was investigated in an effort to strengthen the {111} 〈uvw〉 type components and reduce the intensity of the {100} 〈0vw〉 components, improve the uniformity of the microstructure, and refine the grain size in high-purity tantalum plate. Tantalum, from three different ingot breakdown processes, received an additional 80 pct reduction in the transverse direction (perpendicular to the ingot centerline) in the processing schedule prior to final annealing. This work investigated the influence of the additional transverse rolling passes on the development of texture in the as-rolled tantalum and also in rolled plus annealed tantalum. After annealing, the tantalum plates had significantly strengthened {111} 〈uvw〉 crystallographic orientations, not only for the side forged process, but also for the upset and side forged tantalum. For tantalum processed by extrusion, the transverse rolling did not improve the final recrystallized texture.     

Constitutive Behavior of Commercial Grade ZEK100 Magnesium Alloy Sheet over a Wide Range of Strain Rates

The constitutive behavior of a rare-earth magnesium alloy ZEK100 rolled sheet is studied at room temperature over a wide range of strain rates. This alloy displays a weakened basal texture compared to conventional AZ31B sheet which leads to increased ductility; however, a strong orientation dependency persists. An interesting feature of the ZEK100 behavior is twinning at first yield under transverse direction (TD) tensile loading that is not seen in AZ31B. The subsequent work hardening behavior is shown to be stronger in the TD when compared to the rolling and 45 deg directions. One particularly striking feature of this alloy is a significant dependency of the strain rate sensitivity on orientation. The yield strength under compressive loading in all directions and under tensile loading in the TD direction is controlled by twinning and is rate insensitive. In contrast, the yield strength under rolling direction tensile loading is controlled by non-basal slip and is strongly rate sensitive. The cause of the in-plane anisotropy in terms of both strength and strain rate sensitivity is attributed to the initial crystallographic texture and operative deformation mechanisms as confirmed by measurements of deformed texture. Rate-sensitive constitutive fits are provided of the tensile stress–strain curves to the Zerilli–Armstrong[1] hcp material model and of the compressive response to a new constitutive equation due to Kurukuri et al.[2]     

Effect of alloying elements on the formation of rolling texture in Mg-Nd-Zr and Mg-Li alloys

The effect of alloying on the texture of Mg-Nd-Zr and Mg-Li alloy sheets is studied using pole and inverse pole figures. The basal texture intensity in rolling of Mg-Nd-Zr alloys is shown to be substantially decreased due to the precipitation of dispersed intermetallic Mg₁₂Nd phase particles. As a result, the workability characteristics during deep drawing can be increased. Lithium alloying causes the formation of a prismatic rolling texture, which is unusual for magnesium alloys, as a result of the phase transformation of the lithium-based bcc phase into the magnesium-based hexagonal close-packed phase that obeys the Burgers orientation relationships.