The effect of Gd on the recrystallisation,texture and deformation behaviour of magnesium-based alloys

A series of binary magnesium-based alloys have been prepared with Gd concentrations between 0.22 and 4.65 wt.% Gd. These alloys were processed by hot rolling in order to refine the microstructure and examine the recrystallisation behaviour. The addition of small amounts of Gd was found to significantly decrease the recrystallised grain size and at higher alloy concentrations nucleation of recrystallisation became more strongly inhibited, but the growth rate remained largely unchanged. The effect of Gd concentration on solute strengthening was quantified and it was found that strengthening of the prismatic slip system above 100 MPa could be achieved through alloying with Gd. A fivefold increase in ductility also resulted from Gd addition, and this was attributed to changes in the recrystallisation texture.     

Microstructure,texture and grain boundaries character distribution evolution of ferritic stainless steel during rolling process

In order to better understand the texture, microstructure and grain boundaries character distribution evolution of ferritic stainless steel, the texture, microstructure and grain boundaries character distribution of ferritic stainless steel (hot rolled sheet, cold rolled sheet and annealing sheet) with 11 wt%Cr content were studied using X-ray diffraction and electron back scattered diffraction technique. The texture of the hot and cold rolled sheets has a through-thickness texture gradient. In the center layer of the hot and cold rolling sheet, α-fiber texture was observed which was attributed to ideal plane strain deformation. Close to the surface a Gross orientation was detected which was attributed to shear deformation. During annealing, the γ-fiber was formed attributed to recrystallization process. The microstructure of the hot and cold rolled sheets was non-homogeneous through the sheet thickness, while, the microstructure of annealing sheets was homogeneous through the sheet thickness. Grain boundaries character distribution results show that there are many low angle grain boundaries in hot and cold rolled sheets and many high angle grain boundaries and coincidence site lattice after annealing. The above results indicated that the changes in texture are closely related to the grain boundaries type.     

异步热轧对钛合金Ti-6Al-4V微观组织及力学性能的影响

通过异步/同步热轧实验研究了异步热轧工艺对钛合金显微组织和力学性能的影响。实验表征了试样的显微组织、力学性能、断口形貌和微观取向。实验结果表明,复杂应变路径较之简单应变路径能更好的细化晶粒及同时提高强度和塑性,并且表层晶粒小于中心晶粒。异步轧制工艺相比同步轧制能更好获得细小晶粒。异步轧制试样的强度及塑性值高于同步轧制试样相应值,提高异步速比可提高强度及塑性值。异步轧制试样的塑性变形机制可能是滑移,而同步轧制试样塑性变形机制为滑移或孪晶。     

Processing,microstructure and property aspects of a spraycast Al–Mg–Li–Zr alloy

This paper describes a microstructural and property investigation of an Al–5.31Mg–1.15Li–0.28Zr alloy produced by spraycasting and downstream processing. Following a dispersoid precipitation treatment of 4 h at 400 °C, samples were hot compressed at strain rates of 2, 1, 0.2 and 0.1 × 10⁻² s⁻¹ at temperatures between 250 and 475 °C. Electron backscattered diffraction showed a strong dependence of recrystallised grain size on deformation temperature. At 250 °C and faster strain rates at 325 °C, a network of fine recrystallised necklace grains formed by progressive lattice rotation. At 325 °C at slow strain rates and at 400 °C and higher, dynamic recrystallisation occurred by discontinuous nucleation and growth at regions of microscopic strain localisation such as grain boundaries and triple points. The microstructures from small-scale hot compression experiments were compared with larger forgings under similar conditions and microstructural evolution was broadly similar. Mechanical properties of larger-scale forgings exceeded the targets for mechanically alloyed Al–Mg–Li alloy AA5091.     

Influences of temperature and Sn-addition on microstructural evolution of Ag during FSW

ABSTRACT

The microstructural evolutions of pure Ag and Ag-0.75 wt-%Sn during rapid cooling friction stir welding (FSW) were examined. At the lower welding temperature of FSW conditions, the annealing twinning was highly suppressed and the microstructural evolution was dominated by the discontinuous dynamic recrystallisation (DDRX) via the high angle boundary (HAB) bulging. The fully recrystallised microstructure was remarkably finer than that formed through the frequent annealing twinning at the higher welding temperature. Moreover, the Sn-addition caused the HAB bulging due to the inhibition of dynamic recovery and decreased mobility of grain boundaries. With decreasing the ratio of the peak temperature to the recrystallisation temperature, the dominant grain refinement mechanism is implied to change from the annealing twinning to the DDRX.     

Flow stress and microstructural evolution in as rolled AZ91 alloy during hot deformation

1　INTRODUCTIONMgalloysarethelightestconstructionmaterialsformanyengineeringcomponentsduetotheirlowdensity ,higherductilityandsuitablestrength[13] .However ,Mgalloyshavepoorformabilityandlimit edductilityatroomtemperaturebecauseofitsHCPstructure[4 ] .Therefore ,itisrequiredforMgalloystobedeformedatwarmtemperature(>4 98K ) [5] ,es peciallyatelevatedtemperature ,whenprismaticslipisactivatedsothattheformalityofMgalloyscanbeimprovedintermsofhighductilityandmakesiteasytosimplifythedesignandm…     

������Ʒ����������ȱ�ݳ���Ԥ����ʩ

 冷轧板最主要的质量问题就是表面缺陷,亮带缺陷是目前首钢冷轧板最为常见的表面问题。通过研究不同亮带表面缺陷形貌及亮带处缺陷形貌、发生规律、元素构成、以及全流程缺陷的遗传性,分析了首钢冷轧亮带缺陷的主要原因,包括连铸坯皮下夹渣、皮下气泡、氧化铁皮压入以及辊印等因素。     

薄板坯连铸连轧超薄规格板带技术及其应用进展

在简要介绍我国薄板坯连铸连轧生产技术发展的基础上, 重点介绍了我国热轧薄规格板带的市场及应用现状, 分析了CSP线生产超薄规格高强板带的工艺、FTSR线生产超薄规格板带的进展、半无头轧制技术生产超薄规格板带涉及的关键技术以及高质量薄规格板带技术开发生产应用情况。最后指出: 薄规格、超薄规格热轧板带在节能减排、"以热代冷"提高产品附加值方面具有一定的市场空间, 但需要主动积极开拓市场; 需要解决相关工艺机理及工艺控制上的关键技术, 并进行全面技术集成与创新, 才能大批量稳定生产薄规格、超薄规格板带。     

Development of efficient production routes based on strip casting for advanced high strength steels for crash-relevant parts

Twin roll strip casting can be an effective alternative to produce high manganese TWIP steel, which provides extraordinary mechanical properties. In the work presented, 1.5–3 mm thin hot strips with up to 30 wt% manganese were produced directly from the melt and further processed to cold strip. An adapted thermo-mechanical treatment, consisting of cold rolling with or without subsequent annealing, enables to adjust different material states, such as recrystallised or strengthened state, and thus to tailor the mechanical properties. As an example for the superior crash behaviour of high manganese TWIP steels, dynamic crash tests were carried out using cold rolled Fe–29Mn–0.3C steel in different material states.     

�������ֱ�����������ȱ�ݵij������������

在热轧卷板的生产过程中,通过表面质量在线检测系统检测到热轧卷板的表面存在着类似"划线状"的缺陷。通过对该缺陷宏观图、化学元素、成分检测、金相组织分析和生产跟踪分析,确定了该纵向裂纹缺陷是由钢坯的拉裂引起的,从而对钢坯的生产工艺进行了调整,减少钢坯拉裂后,减少了钢板的纵向裂纹缺陷,避免了大量经济损失。     

挤压比对Mg—Zn—Zr—RE合金组织和性能的影响

研究了不同挤压比对铸态Mg-5．4Zn-0．3Zr-0．98RE镁合金微观组织和力学性能的影响。研究表明,当挤压比较小时,微观组织呈现出粗晶和细晶组成的混晶组织;随着挤压比增加到16,微观组织发生完全再结晶,获得均匀、细小的再结晶组织。动态再结晶是铸态镁合金Mg-5．4Zn-0．3Zr-0．98RE晶粒细化的机制。在挤压温度为250℃,挤压比为16时,合金获得的力学性能最好,抗拉强度为345MPa,屈服强度为223MPa,断后伸长率为21．4％。     

Theoretical predictions and experimental verification of surface grain structure evolution for AA6061 during hot rolling

Finite element modeling of a hot-rolled 6061 aluminum alloy was performed with the software package DEFORM^TM 2-D in order to predict the localized state variables: temperature, strain, strain rate and stress. The state variables were then incorporated into a new dynamic recrystallization (DRX) model that considers both continuous dynamic recrystallization and geometric dynamic recrystallization to predict grain structure evolution near the rolled surface. The performed DRX simulation was verified by experimental results from hot-torsion and hot-rolling experiments from the literature. The recrystallized grain structure evolution along the surface of hot-rolled AA6061 was predicted with reasonable accuracy.     

镀锡板表面白条缺陷原因分析及改进措施

客户在使用首钢镀锡板时发现带钢表面存在白条缺陷,严重影响产品美观和使用,通过对缺陷进行扫描电镜等微观分析、工艺优化及试验跟踪,明确了白条缺陷的根本成因是热轧带钢表面的氧化麻点压入。通过优化钢坯加热工艺、优化精轧高压水除鳞、机架间冷却水和轧辊防剥落水开启制度等改进措施,基本消除了热轧带钢表面氧化麻点压入,有效控制了镀锡板表面白条缺陷的发生,提高了产品质量。     

Evolution of recrystallisation texture and microstructure in low alloyed titanium sheets

The evolution of microstructure and crystallographic texture in low alloyed titanium sheets, initially deformed by 80% cold rolling, are investigated at different stages of the recrystallisation process. Optical and transmission electron microscopies, as well as X-ray diffraction and EBSD are used to provide information about recrystallisation mechanisms and kinetics. Orientation Density Function (ODF) differences are used to quantitatively compare recrystallised and deformed states. The main texture features of the deformed state evolve only slightly during the primary recrystallisation. The major changes in texture result from secondary recrystallisation or grain growth. Primary recrystallisation can be roughly separated into two stages. The first one is very fast and corresponds to the appearance of new grains in about 80% of the material volume. The second stage is more sluggish. It corresponds to the disappearance of the so-called “white grains”, which did not twin during deformation due to their stable orientation near {ϕ₁=0°, φ=45°, ϕ₂=0°}. Recovery is an important mechanism throughout the process and deformation heterogeneities must be taken into account for a good understanding of the recrystallisation in titanium.     

Microstructure and tensile properties of AM50A magnesium alloy prepared by recrystallisation and partial melting process

Prior to thixoextrusion, the microstructural evolution of semi-solid AM50A magnesium alloy prepared by the recrystallisation and partial remelting (RAP) route was investigated. The effect of compressive ratio on microstructure of semi-solid AM50A magnesium alloy was studied. Furthermore, tensile properties of thixoextruded components were determined. The results showed that the occurrence of recrystallised grains was closely associated with the location of the first liquid formed above the solidus. With prolonging holding time, deformed microstructure was penetrated, causing fragmentation, which resulted in the decrease of average grain size. Moreover, prolonging holding time was favorable for the improvement of the degree of spheroidization due to the increase in the amount of liquid. With the increase in compressive ratio, the size of solid grain decreased, the degree of spheroidization was improved during partial remelting, and the tensile properties of thixoextruded AM50A components were improved. The tensile properties for AM50A magnesium alloy thixoextruded from starting material produced by the RAP route were better than those of the same alloy produced by die-casting and thixomolding.     

Hot-deformation behaviors of AZ31 alloys with different initial states

The hot-deformation behaviors of three types of AZ31 samples,extruded sheet,hot rolled sheet and cast rod were studied. These samples had different initial grain size and texture.Compression deformation of these samples was carried out using a Gleeble 1500D under a series of thermal deformation conditions.Microstructure and texture of the initial and deformed samples were examined using electron backscatter diffraction(EBSD) techniques.The flow curves for all these three types of samples shifted upward w...     

304奥氏体不锈钢应变诱发马氏体的研究

用X射线衍射(XRD)、磁针法、力学性能和显微分析研究了商用热轧态和冷轧态304奥氏体不锈钢在不同变形方式下应变诱发马氏体的行为。结果表明:304钢热轧态由于存在多量碳化物和组织不均匀性,其奥氏体稳定性低,拉伸应变诱发马氏体量达40%,冷轧(固溶)态组织均匀、奥氏体稳定性高,拉伸应变诱发马氏体量仅9%;304冷轧板材扩孔、杯突成形时其切向和径向的二向拉应力有助于γ→α’转变,诱发马氏体量(30%～35%)多于单向拉应力的拉伸诱发马氏体量(8%～10%)。对于冷轧304不锈钢,在20%以上拉伸工程应变的驱动下才能较明显地诱发马氏体。304明显的强化效果(△σ达320～400 MPa)来自应变硬化和马氏体相变强化两方面:冷轧304钢的强化主要来自应变硬化本身;热轧304钢的强化不光有应变硬化的贡献,还有应变诱发的多量马氏体的重要贡献,而且后者是主要的。     

热轧钢带边裂形成原因分析及控制

边裂是热轧钢带生产过程中出现的边部缺陷.通过对边裂的统计分析、租轧坯低倍缺陷分析、边裂的三维向显微组织的分析,对其形成原因及机理进行了研究.结果表明:钢坯缺陷使钢的致密性降低,使氧易于渗透并发生氧化,这是热轧带出现边裂的主因；强宽展及不均变形等轧制条件促使粗轧坯内部缺陷的扩展、氧化,这是边裂产生的外因；提出加强钢水中气...     

һ�ֹ�������TRIP590���������������

传统的TRIP590冷轧带钢因硅含量较高,表面质量很难达到高级轿车的要求.为了满足高级轿车对力学性能和表面质量的严格要求,通过硅、铝及其他合金元素的精确匹配,开发了一种硅铝复合的TRIP590高强度汽车用钢.介绍了该钢种试制方法和过程,首先将热轧带钢通过酸轧机组生成冷硬带钢,冷硬带钢再通过连续退火机组生成最终冷轧产品.对实物组织形态、力学性能和表面质量进行了分析和比较,研究结果表明,采用硅铝复合成分控制和相应的工艺制度,可以生产出力学性能和表面质量双优的TRIP590高强钢,满足高级轿车的使用要求.     

Recrystallisation towards a single texture component in heavily cold rolled tungsten (W) sheets and its impact on micromechanics

In this study, we present the recrystallisation behaviour of heavily cold rolled tungsten sheets and show that the material recrystallises towards a single texture component, i.e. the rotated cube component {001}<110>. This result is remarkable as it distinguishes from the classical concept of recrystallisation and is likely to have a strong impact in various fields in science and technology.The thermal stability of as-rolled tungsten sheets featuring a thickness reduction of 98% (i.e. 4.1 in the logarithmic notation) was investigated. Annealings were performed in a vacuum and in the temperature range of 400 °C (673 K) to 2000 °C (2273 K) for a time period of 6 min up to 500 h. The annealing-induced evolution of the microstructure is displayed by hardness (HV0.1) and electron backscatter diffraction (EBSD) measurements. The results show that after an annealing of 6 min at 800 °C (1073 K), the hardness drops from 666 ± 6.3 to 625 ± 7.9 HV0.1.The evolution of the hardness is fitted by classical kinetic models for recovery (logarithmic kinetics) and recrystallisation. The apparent activation energy of half of the hardness loss, E_ΔHV/2, was found to be 356 kJ/mol (3.69 eV), which can be associated with the activation energy of grain boundary diffusion in tungsten.Furthermore, the hardness data allows for the distinction between two stages. In stage I, the material rapidly develops an equiaxed grain structure by the break-up and spheroidisation of the high aspect ratio grains. We do not observe the formation of nuclei in the classical sense. Moreover, the recrystallisation processes can be described as grain growth. We suggest the dominant driving force to be the reduction of the internal stored energy. Finally, the transition from stage I to stage II is caused by the onset of abnormal grain growth.