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     

7050铝合金热挤压成形过程的有限元模拟

针对传统工程机械用销轴数量多、重量大、工况差等不足,以7050高强轻质铝合金代替传统钢质材料,采用DEFORM-3D有限元分析软件,对7050铝合金热挤压成形过程进行有限元数值模拟,分析了挤压载荷、金属流动速率、等效应变、等效应力和温度场等参量的变化规律。结果表明,销轴的热挤压变形过程可分为4个阶段,即挤压填充阶段、开始挤出阶段、稳定挤压阶段和终了挤压阶段;工件内部等效应变分布横向均匀性较好,除了尾部变形不均匀外,其他部位应变分布基本一致;在挤压凹模模口处形成死区,工件内部等效应力达到最大值。     

A set of microstructure-based constitutive equations in hot forming of a titanium alloy

1. Introduction With the wide application of numerical simulation in metal forming, an accurate constitutive equation, which expresses a correlation between the deformation behavior and the process parameters, needs to be es- tablished. For many years, a …     

高纯铝晶粒尺寸与晶粒拓扑学参数定量关系研究

本文采用晶界渗镓剥离晶粒技术实现了三维晶粒尺寸及其拓扑学参数（晶粒界面数N2）的直接实验测量,利用回归分析,得出了晶粒尺寸与晶粒拓扑学参数定量关系;晶粒界面数N2与晶粒尺寸R^-间存在线性对应关系。     

时效处理对7050铝合金组织与性能的影响

对7050铝合金进行硬度测试、腐蚀性能测试和透射电子显微分析(TEM),研究了单级时效处理对合金组织与性能的影响。实验结果表明:7050铝合金具有较强的时效硬化效应。单级时效温度由120℃升高到160℃时,合金时效硬化速度显著加快,合金进入峰时效状态所需时间显著缩短,但合金的峰值点的硬度降低。时效处理后合金晶内析出了大量的尺寸细小的η'相,弥散分布在基体中。合金晶界处析出了粗大的平衡相,成分为MgZn_2,PFZ出现。随着时效温度的升高,合金晶间析出相连续且粗大,PFZ宽化,合金的抗晶间腐蚀性能持续下降。对于剥落腐蚀来说,合金的腐蚀程度不仅与晶界结构有关,还与晶界数量有关,温度上升,合金晶粒尺寸迅速增大,晶界数目显著减少,二者相互作用最终导致了合金的抗剥落腐蚀性能的提高。     

Sr Microalloying for Refining Grain Size of AZ91D Magnesium Alloy

The grain refining process of an AZ91D Mg alloy by Sr addition was studied and the heterogeneous nucleating particles of α-Mg were investigated by electron probe microanalysis （EPMA）. With 0.6 wt% Sr addition, the mean grain size of AZ91D alloy was refined from 235.4μm to 52.5 μm at the one-half radius of the ingot. The morphology of primary crystal changed from a sixford symmetrical shape to a petallike shape, Mg-Sr-Al-Fe-Mn heterogeneous nucleating particles were observed at the grain centers and Sr solute atoms presented segregation along the grain boundaries. Grain refinement was facilitated by both the Mg-Sr-Al- Fe-Mn nucleating particles and the Sr solute atoms, and the former played a dominate role in the process.     

Modeling on dynamic recrystallization of aluminium alloy 7050 during hot compression based on cellular automaton

The dynamic recrystallization(DRX) process of hot compressed aluminium alloy 7050 was predicted using cellular automaton(CA) combined with topology deformation. The hot deformatation characteristics of aluminium alloy 7050 were investigated by hot uniaxial compression tests in order to obtain the material parameters used in the CA model. The influences of process parameters(strain, strain rate and temperature) on the fraction of DRX and the average recrystallization grain(R-grain) size were investigated and discussed. It is found that larger stain, higher temperature and lower strain rate(less than 0.1 s~(–1)) are beneficial to the increasing fraction of DRX. And the deformation temperature affects the mean R-grain size much more greatly than other parameters. It is also noted that there is a critical strain for the occurrence of DRX which is related to strain rate and temperature. In addition, it is shown that the CA model with topology deformation is able to simulate the microstructural evolution and the flow behavior of aluminium alloy 7050 material under various deformation conditions.     

Application of a novel multilayer spray forming technology in the preparation of large dimension aluminium alloy blanks

Ｓｐｒａｙｆｏｒｍｉｎｇｉｓａｎｏｖｅｌｒａｐｉｄｓｏｌｉｄｉｆｉｃａｔｉｏｎｔｅｃｈｎｏ ｌｏｇｙｆｏｒｔｈｅｐｒｅｐａｒａｔｉｏｎｏｆｍａｎｙｋｉｎｄｓｏｆａｄｖａｎｃｅｄｍｅｔａｌｓａｎｄｍｅｔａｌｍａｔｒｉｘｃｏｍｐｏｓｉｔｅｓ .Ｍｏｄｉｆｉｃａｔｉｏｎｓｔｏｔｈｅｔｅｃｈ ｎｏｌｏｇｙｏｒｉｇｉｎａｌｌｙｐｒｏｐｏｓｅｄｂｙＳｉｎｇｅｒ[1,2 ] ,ｈａｖｅｒｅｓｕｌｔｅｄｉｎｔｈｅｄｅｖｅｌｏｐｍｅｎｔｓｏｆｔｈｅＯｓｐｒｅｙｐｒｏｃｅｓｓ[3 ,4 ] ,ｃｏｎｔｒｏｌｌｅｄｓｐｒａｙｄｅｐｏｓｉ…     

2214铝合金上防扭臂故土温模锻工艺的研究

根据上防扭臂锻件技术条件要求 ,确定了等温模锻新工艺为解决锻件的粗晶问题的最佳成形工艺方案 .简要介绍了在 5× 10 4kN液压机上实现等温模锻新工艺时模具结构特性 .经工艺试验确定了最佳变形温度约为 45 0℃ ,应变速率为 9.6× 10 4～ 7.6× 10 - 3s- 1 及较佳的坯料形状、尺寸及润滑剂 .分析了该模锻件产生缺陷的原因和消除缺陷的方法 .用等温模锻新工艺研制的锻件冶金质量符合AIR3385、Z9-J冶 - 32 4、Z9-J冶 - 32 5技术条件要求 ,其力学性能、晶粒度、电导率、纤维流线和锻件内外表面质量均有所提高 ,满足了生产要求 .     

热轧螺纹钢筋连铸坯加热过程中奥氏体晶粒预测模型

利用有限元分析方法分析加热过程中螺纹钢连铸坯的温度分布随时间变化的规律。根据各节点温度与时间的关系,计算连铸坯各节点的加热速度,分析加热速度对奥氏体转变温度的影响规律。结果表明奥氏体化的温度与加热速度近似成线性关系。通过不同温度的中断淬火实验,研究奥氏体晶粒长大的动力学规律。结果表明,不同温度奥氏体晶粒长大激活能具有明显的差异。基于奥氏体晶粒长大和第二相粒子溶解之间的交互作用对不同温度奥氏体晶粒长大的动力学规律进行分析。     

4J29膨胀合金晶粒长大倾向的研究

针对在电子器件中常作为密封材料的4J29合金在生产时出现粗大晶粒造成工件开裂问题,采用热处理和单因素优选实验方法研究4J29合金的再结晶温度、预先变形率与晶粒度之间的关系。研究表明,4J29膨胀合金晶粒聚集长大是由大于70%预先变形率所造成。在实际生产中尽可能采用合理的预先变形率可以提高材料的再结晶温度和二次再结晶温度,可以防止合金晶粒聚集长大,从而保证了工件质量和使用性能。     

Effect of ultrasonic power and casting speed on solidification structure of 7050 aluminum alloy ingot in ultrasonic field

With the experiment and finite element simulation, the influences of power ultrasonic on the solidification structure of 7050 aluminum alloy ingot in semi-continuous casting were researched, and the effects of casting speed on solidification structure in ultrasonic field were also analyzed. The experiment and simulation results show that the solidification structure of the ingot is homogeneously distributed, and its grain size is obviously refined at ultrasonic power of 240 W. The average grain sizes, which can be seen from the Leica microscope, are less than 100 μm. When the casting speed is 45-50 mm/min, the best grain refinement is obtained.     

切削法构建铝合金Al7050-T7451材料流动应力本构模型

基于Oxley滑移线理论,采用正交切削实验的反求方法,构建了能够描述铝合金Al7050-T7451切削加工过程的Johnson-Cook流动应力本构模型。该模型的应变范围为0.61～1.12,应变率范围为10263～69941,温度范围为95～248;在与模型构建相同的切削实验参数区间内,采用该模型进行有限元仿真预测的切削力误差小于15％,切削热最大值误差小于11％。     

酸性镀液铝合金表面沉积Ni-Mo-P三元合金非晶镀层

采用酸性化学镀液在铝合金表面沉积Ni-Mo-P三元合金非晶镀层。利用透射电镜（TEM）、场发射扫描电镜（FESEM）、X射线衍射分析（XRD）、能谱（EDS）等现代分析手段,对镀层显微结构进行了表征,探讨了钼酸钠浓度和热处理对镀层纳米压痕硬度的影响。结果表明,镀态下,化学镀Ni-Mo-P三元合金镀层为致密非晶态镀层,镀层中Mo元素分布均匀,镀层与基体结合良好。热处理可促使非晶镀层晶化,产生Ni和Ni3P晶相,获得了纳米压痕硬度为15.12 GPa的最大值。     

Grain size distribution and topology in 3D grain growth simulation with large-scale Monte Carlo method

Three-dimensional normal grain growth was appropriately simulated using a Potts model Monte Carlo algorithm. The quasi-stationary grain size distribution obtained from simulation agreed well with the experimental result of pure iron. The Weibull function with a parameter β=2.77 and the Yu-Liu function with a parameter ν =2.71 fit the quasi-stationary grain size distribution well. The grain volume distribution is a function that decreased exponentially with increasing grain volume. The distribution of bounda...     

超微颗粒尺寸测量方法比较研究

应用x射线衍射线线宽法、透射电镜法、比表面积法和激光粒度分析法对自制的Ni(OH)2超微粉及标准颗粒度的样品进行比较分析,探讨了分析原理、颗粒形状等因素对粒径测试准确度的影响．实验结果表明：由球形颗粒组成的超微粉,透射电镜法和激光粒度分析法分析的结果均比较准确;4种方法对由不规则形状颗粒组成的超微粉分析结果相差悬殊,应采用不同的测试方法比较以得出可信的颗粒尺寸．实验证实,样品在分散介质中的分散程度对超微颗粒尺寸测量结果有较大影响,测量前对超微粉进行充分的分散是得出准确结果的前提．     

Influence of prior austenite grain size on the critical strain for completion of DEFT through hot compression test

A low carbon steel was used to determine the critical strain εc for completion of deformation enhanced ferrite transformation （DEFT） through a series of hot compression tests. In addition, the influence of prior austenite grain size （PAGS） on the critical strain was systematically investigated. Experimental results showed that the critical strain is affected by PAGS. When γ→α transformation completes, the smaller the PAGS is, the smaller the critical strain is. The ferrite grains obtained through DEFT can be refined to about 3 μm when the DEFT is completed.     

阳极氧化对压铸铝合金电解着黑色工艺的影响

选择压铸铝合金ADC12为研究对象,确定黑色为着色系,在确定的电解着色工艺下,重点探讨溶液种类、浓度和温度等阳极氧化工艺参数对黑色膜完整性、色泽度的影响。通过系列试验,优选工艺参数如下：以水磨、抛光、除油为前处理;在直流电压20V下,于20％H2SO4溶液中进行阳极氧化,温度为40℃。反应时间为40min,可获得黑度系数达0．9且膜色均匀的染色膜层。结合基体显微组织分析,认为要改善膜层着色效果,宜先通过有效的熔体处理,改善基体组织形态。     

Prevention of thinning at disc center during rotary forging

0　ＩＮＴＲＯＤＵＣＴＩＯＮＲｏｔａｒｙｆｏｒｇｉｎｇｈａｓｓｕｃｈａｄｖａｎｔａｇｅｓａｓｅｎｅｒｇｙｓａｖｉｎｇ ,ｈｉｇｈｐｒｅｃｉｓｉｏｎｗｏｒｋｐｉｅｃｅ ,ｌｏｗｅｒｌｅｖｅｌｓｏｆｎｏｉｓｅａｎｄｖｉｂｒａ ｔｉｏｎ .Ｔｈｅｒｏｔａｒｙｄｉｅｓｐｉｒａｌｌｙｃｏｍｐｒｅｓｓｅｓｐａｒｔｏｆｔｈｅｗｏｒｋ ｐｉｅｃｅｕｎｔｉｌｔｈｅｆｉｎａｌｓｈａｐｅｉｓｆｏｒｍｅｄ .Ｉｔｉｓｅｓｐｅｃｉａｌｌｙｓｕｉｔ ａｂｌｅｆｏｒｔｈｅｆｏｒｍｉｎｇｏｆａｘｉｓｙｍｍｅｔｒｉｃａｌｐａｒｔｓ[1] .Ｎｏ…     

深度还原工艺对铁颗粒粒度影响规律研究

采用深度还原技术处理浸染微细粒度的复杂难选铁矿石,控制铁颗粒粒度是分选出合格产品的关键.根据深度还原物料中铁颗粒的球形特征,通过测量铁颗粒二维截面参数,求取了其累计粒度特性曲线,定性地描述了不同深度还原工艺对铁颗粒粒度的影响规律.结果表明:适当的提高还原温度、延长还原时间、增大配碳系数,都有利于铁颗粒的长大,但还原温度过高、配碳系数过大将阻碍铁颗粒长大;适宜的工艺条件为:还原温度1 225℃,还原时间30min,配碳系数2.0,获得铁颗粒的d50为278.88μm.