Modeling of microstructural evolution during dynamic recrystallization in coarse Nb microalloyed austenite

The aim of the current study was to investigate the microstructural evolution during dynamic recrystallization in coarse Nb microalloyed austenite in thin slab direct rolling （TSDR） processing. A model was developed to predict the change of the austenite grain size during the dynamic recrystallization, by using the law of mixtures. The equations initially developed for partial static recrystallization were used for partial dynamic recrystallization, by adjusting the value of the constant. The results show that the change of the austenite grain size can be reasonably described by using the equations developed according to the law of mixtures.     

Dynamic Recrystallization Prediction During Double Cup Extrusion by Cellular Automata Coupled with Finite Analysis Method

In order to investigate the microstructure evolution during a hot extrusion process, a cellular automata （CA） coupled with finite element method （FEM） was developed to numerically simulate the dynamic recrystallization （DRX）. Firstly, the cellular automata model was modified by introducing thermomeehanical parameters under the isothermal hot compression conditions. Then, the modified CA was verified by the experimental average grain size which was obtained by the hot compression of cylindrical specimens. After that, the modified CA was used to predict the microstructure evolution during a double cup extrusion by combining with the finite element method. The results showed that the strain rate and the temperature are sensitive to the average grain size while the strain can affect the DRX fraction greatly. In addition, the CA model can predict the final microstrueture successfully and is able to simulate the DRX phenomenon for a wide range of deformation conditions. It also revealed that the results obtained by CA model are consistent with the ones acquired by finite element analysis.     

Characterization of microstructure evolution and mechanical properties of the spray-deposited AZ31 magnesium alloy

The cylindrical billets of a Mg-3Al-1Zn (AZ31) alloy were synthesized by spray deposition processing. The microstruc-ture evolution and mechanical properties of the alloy were investigated. The results reveal that the microstructure of the AZ31 alloy is refined significantly by spray deposition processing. A homogeneous and equiaxial-grain structure with an average grain size of 17 μm is obtained. Further grain refinement with an average grain size of 5 μm is attributed to dynamic recrystallization during e...     

微观组织预测技术在热成型过程中的应用

为了进一步推动微观组织预测技术领域的科学研究,推广该技术在热成型生产中的应用,对热成型过程中奥氏体晶粒变化过程的数学模型进行了系统归纳和研究,主要包括金相组织晶粒初始尺寸、动态再结晶、静态再结晶、晶粒长大以及温度补偿等效时间的数学模型.结果表明:运用有限元技术成功预测组织成分具有现实的科学价值.微观组织预测技术在生产中的成功运用,不仅可以提高产品质量,还可以大幅度降低生产成本.     

Friction stir processing of thixoformed AZ91D magnesium alloy and fabrication of surface composite reinforced by SiC<Subscript>p</Subscript>s

The microstructural evolution characteristics of the thermomechanically affected zone (TMAZ) alloy during friction stir processing (FSP) of thixoformed (TF) AZ91D alloy were investigated. Simultaneously, a surface composite layer reinforced by SiC particles (SiC_ps) was prepared on the alloy by FSP and the corresponding tribological properties were examined. The experimental results indicate that dynamic recrystallization and mechanical separation (including splitting and fracture of the primary grains) are the main mechanisms of grain refinement for the TMAZ. A composite surface reinforced by uniformly distributed SiC_ps was prepared on the alloy. Compared with the corresponding permanent mould casting alloy and the TF alloy without composite surface, the TF alloy with composite surface has the highest wear resistance and lowest friction coefficient.     

热模拟技术优化X80管线钢热轧工艺

用Gleeble 1500D热模拟实验机,对X80管线钢进行单道次双道次以及多道次压缩实验,找出动态再结晶的临界应变量和未再结晶区,在未再结晶区内优化精轧道次轧制工艺,通过抑制道次间的静态再结晶累积应变,在多道次轧制过程中使其在最后一道次超过临界应变量发生动态再结晶,从而避免晶粒大小不均并实现晶粒细化.     

Simulation of dynamic recrystallization for aluminium alloy 7050 using cellular automaton

The prediction of microstructure evolution plays an important role in the design of forging process. In the present work, the cellular automaton (CA) program was developed to simulate the process of dynamic recrystallization (DRX) for aluminium alloy 7050. The material constants in CA models, including dislocation density, nucleation rate and grain growth, were determined by the isothermal compress tests on Gleeble 1500 machine. The model of dislocation density was obtained by linear regression method based on the experimental results. The influences of the deformation parameters on the percentage of DRX and the mean grain size for aluminium alloy 7050 were investigated in details by means of CA simulation. The simulation results show that, as temperature increases from 350 to 450 °C at a strain rate of 0.01 s⁻¹, the percentage of DRX also increases greatly and the mean grain size decreases from 50 to 39.3 μm. The mean size of the recrystallied grains (R-grains) mainly depends on the Zener-Hollomon parameter. To obtain fine grain, the desired deformation temperature is determined from 400 to 450 °C. Foundation item: Project(2005CB724105) supported by the Major State Basic Research Program of China; Project(IRT0549) supported by Program for Changjiang Scholars and Innovative Research Team in University     

Friction Stir Processing of Thixoformed AZ91D Magnesium Alloy and Fabrication of Surface Composite Reinforced by SiC_ps

The microstructural evolution characteristics of the thermomechanically affected zone (TMAZ) alloy during friction stir processing (FSP) of thixoformed (TF) AZ91D alloy were investigated. Simultaneously, a surface composite layer reinforced by SiC particles (SiCps) was prepared on the alloy by FSP and the corresponding tribological properties were examined. The experimental results indicate that dynamic recrystallization and mechanical separation (including splitting and fracture of the primary grains) are ...     

600MPa级冷轧双相钢的组织再结晶演变规律

为了指导600MPa级冷轧双相钢后期热处理工艺的制定,利用金相显微技术和硬度测试对冷轧双相钢的组织再结品演变规律作研究。分析再结晶过程对实验钢组织的影响,以及此过程中硬度的变化,建立静态再结晶体积分数模型。实验表明：对于冷轧双相钢而言,再结晶温度一定,随退火时间增加,组织中再结晶的体积分数急剧增加,直至保持在一平台,达到完伞再结品;保温时间一定情况下,随着退火温度的逐渐升高,组织发生再结晶的速度更快;再结晶模型计算值与实测值吻合较好。     

钛合金薄壁筒形件热强旋宏微观成形规律研究进展

钛合金薄壁筒形件是航空航天等重要领域迫切需要的高性能轻量化构件,强力旋压成形技术是实现该类构件整体化高性能精确成形的一种有效途径。然而,钛合金筒形件强旋是多场耦合、多参数作用下的多道次热成形过程,变形过程中极易产生隆起、喇叭口和破裂等宏观缺陷,且会诱发复杂的组织演化,改变组织形态与特征参数,进而影响筒形件的力学性能。为此,国内外学者针对钛合金薄壁筒形件热强旋宏微观成形规律开展了大量研究。本文从旋压变形规律与宏观缺陷的控制、强力旋压损伤破裂预测、钛合金筒形件热强旋的微观组织性能演变特征等方面综述了相关研究工作,最后总结了钛合金筒形件热强旋成形仍面临的关键难题与挑战。本文对认识和发展钛合金薄壁筒形件精确成形成性一体化制造技术具有重要指导意义和参考价值。     

晶粒长大的蒙特卡罗模拟及其算法应用研究

概述了蒙特卡罗方法的基本思想和蒙特卡罗方法在模拟材料的微观组织结构演变的应用；并且较详细地介绍了蒙特卡罗在模拟材料微观组织演变时常用的几种算法：标准算法、改进算法和新近提出的一些其他算法．在此基础上，通过编程实现了该算法并进行了两个模拟算例．正常晶粒长大时和超塑性变形时，该算例验证了蒙特卡罗方法在模拟材料微观组织演变的有效性．     

Static recrystallization behavior of Inconel 718 alloy during thermal deformation

The softening behavior of Inconel 718 alloy at different temperatures was studied using twostage interrupted compression method on Gleeble1500D thermal stimulator, and the 2% offset method was applied to analyze the experimental dates. Finally, the static recrystallization fraction was obtained. At the same times, optical microscope(OM) and transmission electron microscopy(TEM) were employed to investigate the microstructure characteristic. The experimental results showed that the recrystallization was more sensitive to temperature than holding time. The recrystallization process finished quickly above 1 050 ℃, and significantly prolonged below 1 025 ℃. Additionally, the dynamical model of static recrystallization follows the Avrami equation. The nucleating mechanism was characterized by bulging at grain boundary and merging of sub-grain.     

热加工材料动态再结晶介观组织模拟模型的研究进展

通过计算机模拟技术可以有效模拟金属材料热变形过程中动态再结晶组织的演化过程, 从而达到预测材料性能的目的。介绍了目前材料动态再结晶过程介观组织模拟的两种模型--元胞自动机(cellular automaton, CA)模型和蒙特卡洛(monte carlo, MC)模型的模拟技术及其研究进展, 重点分析了现有动态再结晶介观组织MC模型存在的问题并且提出了解决思路。     

TP2铜管坯行星旋轧组织演变规律的研究

采用有限元技术与金相观测实验方法对TP2铜管坯行星旋轧组织演变进行研究.给出旋轧动态再结晶和晶粒长大模型,在此基础上,进行有限元模拟分析.研究结果发现:铜管坯在三辊行星旋轧过程中发生了动态再结晶,并在轧辊的集中变形区汇合,当轧制完成后,再结晶晶粒已经基本均匀分布,只保留有少量的加工流线组织.     

316LN热变形行为及动态再结晶晶粒的演变规律

采用热压缩试验研究了316LN不锈钢在温度1250℃-900℃,应变速率0．005s^-1～0．5s^-1,变形程度50％条件下的变形行为和组织演变;分析了变形参数对应力-应变曲线的影响规律,计算获得了该钢热变形应力指数和激活能;并通过动态再结晶晶粒演变规律的研究,建立了该钢热变形动态再结晶图,以及动态再结晶晶粒演变规律模型。研究结果可为316LN不锈钢锻造过程晶粒细匀化的控制提供科学的依据。     

Prediction of grain size for large-sized aluminium alloy 7050 forging during hot forming

A numerical approach for process optimization and microstructure evolution of lager-sized forging of aluminium alloy 7050 was proposed, which combined a commercial FEM code Deform 3D with empirical models. To obtain the parameters of empirical constitutive equation and dynamic recrystallization models for aluminium alloy 7050, the isothermal compression tests of 7050 samples were performed on Gleeble-1500 thermo-simulation machine in the temperature range of 250-450 ℃ and strain rate of 0.01-10 s-1, and the metallograph analysis of the samples were carried out on a Leica DMIRM image analyzer. The simulation results show that the dynamic recrystallization in the central area of the billet occurs more easily than that on the edge. Repetitious upsetting and stretching processes make the billet deform adequately. Among several forging processes e.g. upsetting, stretching, rounding and flatting, the stretching process is the most effective way to increase the effective strain and refine the microstructure of the billet. As the forging steps increase, the effective strain rises significantly and the average grain size reduces sharply. Recrystallized volume fractions in most parts of the final forging piece reach 100% and the average grain size reduces to 10 μm from initial value of 90 μm.     

热连轧403Nb棒材的组织结构与蠕变性能

为了获得403Nb钢更好的加工工艺及优异的高温蠕变性能,借助扫描电镜（SEM）、透射电镜（TEM）、x射线衍射仪（XRD）等分析手段,并通过蠕变性能测试,对热连轧403Nb钢蠕变前后的组织结构及行为进行了研究.结果表明：403Nb钢在热连轧期间发生了动态回复及动态再结晶,其组成相包括：α Fe、（Fe,Cr）23C6及（Fe,Cr,Nb）C,其中,（Fe,Cr）23C6多分布于晶界,（Fe,Cr,Nb）C主要分布于晶内.在实验条件下,热连轧403Nb钢具有极强的温度敏感性和应力敏感性,其蠕变激活能Q=287.5kJ/mol.蠕变期间发生了大量的交滑移,碳化物通过阻碍位错运动以及“钉扎”晶界起到提高蠕变抗力的作用.     

多道次轧制过程中超细晶粒控制

在高强度水平的基础上获得较高的韧性,控制热加工工艺实现晶粒尺寸超细化是最佳的途径之一。低碳管线钢的超细铁索体晶粒可以从相变前的超细奥氏体晶粒获得。通过优化轧制工艺使得奥氏体的动态再结晶发生在Z（Zeller-Hollomon）参数较大的工艺条件下,获得超细的奥氏体动态再结晶晶粒尺寸。然而,大的Z参数往往具有较大的动态再结晶临界应变。为了获得足够的应变积累来克服动态再结晶的临界应变,低温大变形量的变形是基本条件。提出了在多道次轧制过程中积累应变的条件以及避免混晶的技术路线,利用提出的模型对工业轧制工艺进行优化,模拟实验的结果得到了最终产品晶粒尺寸为1.5μm。     

Evolution of Grain Structure and Texture for 6082-T6 Aluminum Alloy during Friction Stir Welding

Stop-action technique was employed in order to study grain structure and texture evolution of thin 6082-T6 aluminum alloy sheets during friction stir welding(FSW). The evolutions of microstructure and texture were studied in different regions(ahead, behind, far behind the tool and base material as well) of the deformed samples. Materials ahead the tool experienced shear deformation were induced by rotation of the tool as well as the shoulder, which can pronounce copper and Goss texture. Grains behind the tool experienced dynamic recovery and recrystallization, exhibiting a characteristic of {110}001 recrystallization Goss texture. Materials far behind the tool probably experienced more thermal cycling. Recrystallization grains will grow and present {100}012 texture. In addition, the shoulder gave rise to a large shear stress that led to {111}110 shear texture.     

09CuPTiRE钢动态再结晶的热模拟实验与有限元模拟

以热模拟实验为基础，建立09CuPriRE钢的动态再结晶模型．应用有限元软件DEFORM模拟热压缩变形并提取模拟信息，编程实现动态再结晶体积百分数分布的可视化．模拟结果表明，增大变形量、提高变形温度以及减小变形速率，都能促进动态再结晶发生，其中变形量及变形温度影响显著．这与实验曲线反映的特征相符，从而证明了模型及模拟的有效性．