Al-Cu-Li合金多道次热变形过程中的力学行为与微观组织演化（英文）

对Al-2.5Cu-1.58Li-0.3Mn-0.12Zr-0.06Mg-0.05Ti(质量分数,%)合金进行连续、不连续、双道次和多道次热压缩,研究其力学行为和微观组织演化。采用Gleeble-1500试验机对合金进行热变形,变形温度为420℃,应变速率分别为0.001,0.1和10 s~(-1),对合金不同热变形阶段进行EBSD和TEM分析。双道次热压缩表明,道次间隔时间的延长有利于促进静态软化。通过改变变形过程中的应变速率,可控制合金的晶粒尺寸。多道次热变形过程中,道次间的静态软化促进动态软化,反之亦然。在多道次热变形过程中(T=420℃,ε=0.1 s~(-1))出现T_1和θ′相动态析出。变形初始阶段,应变诱导的位错为T_1和θ′相提供形核位置,促进它们的析出和粗化。随应变的增加,T_1和θ′相尺寸减小并趋于稳定,δ′相密度降低。试验合金多道次热变形过程中的流变应力受动态软化、静态软化和动态析出综合影响。     

铝合金多道次热变形过程的动态与静态软化

在Gleeble1500热力模拟机上，采用双道次间隙式等温热压缩试验，对1050、5182和7075铝合金多道次热变形过程中动态与静态软化特性进行研究，变形温度为300℃和400℃，应变速率为0．5s^-1，两道次间隙时间在30－120s内变化，每道次应变控制在0．4。结果表明，在400℃时，1050和7075铝合金流动应力由于结构软化而存在相当强的动态软化和奇异的静态软化，导致第二道次的起始流动应力比前一道次的起始流动应力低；对于所有合金，静态软化随着变形温度和道次间保温及停留时间的增加而增加，但是在同一变形条件下，5182铝合金的静态软化速率比1050和7075铝合金高。     

TA15钛合金双道次热压缩变形软化行为及等轴α相组织演变规律

对TA15钛合金进行了双道次热压缩实验,研究了该合金在变形温度910、940和970℃,应变速率0.01、0.1和1 s1及道次间隙保温时间600、1000、1400、1800和2200 s等不同变形参数下的软化行为,定量计算了相应的等轴0晶粒尺寸及其含量.结果 表明:TA15钛合金在双道次热压缩过程中,较高的变形温度和较小的应变速率会促使变形过程中的流动应力减小;在道次间隙保温过程中,材料呈现出了静态软化现象,其静态软化率随着变形温度的升高、应变速率的增大及道次间隙保温时间的延长而增加,且受应变速率的影响程度最大;此外,从合金的微观组织中观察到等轴d相晶粒在道次间隙保温过程中得到了明显的细化,且细化程度与其静态软化呈正相关性.     

3104铝合金高温热压缩过程的再结晶

在Gleeble-1500热模拟机上对3104铝合金进行双道次等温热压缩实验,变形温度为400和500 ℃,变形速率为0.01和0.1 s-1,道次的变形量均为0.4,道次间保温时间为30、60和120 s.结果表明:3104铝合金在400 ℃以上的双道次热变形过程中,发生动态与静态软化.道次间的软化率随着变形温度和应变速率的增加,以及道次间停留时间的延长和道次间保持温度的升高而增大.运用双道次软化率建立了3104铝合金热变形再结晶模型,其再结晶激活能为155 kJ/mol.     

工业纯钛TA1的双道次热压缩变形及软化行为

在Gleeble-3500热模拟试验机上对工业纯钛TA1进行单、双道次等温热压缩试验,变形温度为650~850 ℃,道次间隙时间为1~60 s,变形速率为10 s^-1,研究了工业纯钛TA1单、双道次热压缩过程中静态软化和动态软化行为。利用光学显微镜对变形后的微观组织进行观察,研究了工业纯钛TA1在不同变形条件下的微观组织演变。结果表明,工业纯钛TA1在单、双道次热压缩变形过程中表现出明显的硬化和软化行为,峰值应力前表现为加工硬化,峰值应力后表现为加工软化,最终达到动态软化和加工硬化的动态平衡。在道次间隙时间内发生静态软化,静态软化程度随着道次间隙时间的增加和温度的升高而增大。随着道次间隙时间的延长和温度的升高,道次间再结晶更加充分,第二道次变形后晶粒尺寸增加更明显,当发生完全再结晶时,软化程度达到最大。在热压缩变形期间,发生动态软化,650 ℃和750 ℃时以动态再结晶为主,850 ℃时以动态回复为主。     

Al-4.10Cu-1.42Mg-0.57Mn-0.12Zr合金热变形过程中显微组织动态演化的表征(英文)

在Gleeble-1500热模拟机上对Al-4.10Cu-1.42Mg-0.57Mn-0.12Zr合金在变形温度300°C和应变速度10 s-1下进行热压缩变形,真应变分别为0.2、0.4、0.6和0.8。通过X射线衍射仪、扫描电镜和透射电镜研究合金变形过程中复杂的动态显微组织演变。结果表明:真应力随着应变的增加而迅速增大至峰值,之后随着应变的增加而趋于稳定,呈现动态软化特征。随着应变的增大,位错缠结成胞状与亚晶结构,表明变形过程中发生动态回复。动态析出相S相、θ相和Al3Zr相在变形过程中粗化速度加快。铝基体中析出连续的S相,并发现有不连续的S相在Al3Zr相附近和亚晶界处形核析出。Al3Zr相相对比较稳定,易于在位错和亚晶界处析出。流动软化机制是由于动态回复和动态析出导致位错密度减少而引起的。     

GH4720Li合金双道次热压缩变形过程的组织演变

对GH4720Li合金在1080~1180℃、应变速率为0.1s~(-1)条件下的双道次压缩过程的热变形行为进行研究。结果表明:动态再结晶是GH4720Li合金的主要软化机制。在双道次压缩间歇期内,合金发生亚动态再结晶、静态再结晶和晶粒长大;低于1120℃的变形间歇期,亚动态再结晶、静态再结晶和晶粒长大的速度缓慢;1120℃及以上温度的变形间歇期,亚动态再结晶、静态再结晶和晶粒长大的速度加快。随变形温度升高和第一道次变形量增大,道次间歇期的亚动态再结晶和静态再结晶速度加快。γ′相在热变形过程中发生协调变形,并发生细化。     

镍基耐蚀合金G3后动态再结晶行为研究

为了研究镍基耐蚀合金G3的后动态再结晶软化行为,在1100～1200℃,0.1～10s-1的变形条件范围内,进行了3种方式的热压缩:变形量为15%和60%单道次热压缩,15%+15%的双道次热压缩和15%热压缩并保温。得出以下结论:在变形温度范围内,15%变形量的第1道次压缩使G3合金发生动态再结晶,使其在后续保温过程中发生由亚动态和静态再结晶共同控制的后动态再结晶软化行为;并进一步得出G3合金的后动态再结晶动力学受应变速率影响,但最终的软化率只随温度而改变;通过15%压缩和保温获得的后动态再结晶组织均匀性低于压缩60%的动态再结晶组织。     

镁合金双道次热变形静态软化及残余应变研究

在变形温度250~450℃、变形速率0.005~5s-1和道次间隔时间15~240s下对AZ31B镁合金进行了双道次等温压缩试验,研究不同变形工艺条件对AZ31B镁合金道次间软化规律的影响,建立了AZ31B镁合金道次间软化率预测模型。根据轧制残余应变产生的原因提出了多道次轧制过程中残余应变率的计算方法。研究结果表明：随着变形温度和变形速率的提高,材料的静态软化率逐渐增大,道次间间隔时间越长材料软化程度越大。建立的道次间静态软化率计算模型能够很好地表征AZ31B镁合金道次间软化规律,平均相对误差为12.58%。进一步对残余应变率的精确计算能够为AZ31B镁合金多道次轧制过程中轧制力的求解提供理论支持。     

2195铝锂合金多道次热变形流变应力的模拟研究

采用G1eeble-1500热模拟实验机，对2195铝锂合金变形温度为360～520℃，应变速率为0．001-1．0s^-1的单道次热压缩及变形温度为320℃和360℃，应变速率为0．1s^-1，道次间隔时间30-180s的双道次热压缩的流变应力及静态软化规律进行了模拟研究。通过对幂指数应力函数中系数A和β与应变关系的分析，以及采用平均软化法考虑前一道次变形的残余应变对后一道次变形的影响，建立了2195铝锂合金多道次热变形的流变应力方程。     

Hot Deformation Behavior and Microstructural Characteristics of Ti–46Al–8Nb Alloy

Hot deformation behavior,microstructural evolution and flow softening mechanism were investigated in Ti–46Al–8Nb alloy via isothermal compression approach.The true stress–strain curves exhibited typical work hardening and flow softening,in which the dependence of the peak stress on temperature and strain rate was obtained by hyperbolic sine equation with Zener–Hollomon(Z)parameter,and the activation energy was calculated to be 446.9 k J/mol.The microstructural analysis shows that the alternate dark and light deformed ribbons of Al-rich and Nb-rich regions appeared and were associated with local flow involving solute segregation.The Al segregation promoted flow softening mainly arising from the recrystallization of γ phase with low stacking fault energy.The coarse recrystallized γ and several massive γ phase were observed at grain boundaries.While in the case of Nb segregation,β/B2 phase harmonized bending of lamellae,combined with the growth of recrystallized γ grains and α+β+γ→α+γ transition under conditions of temperature and stress,leading to the breakdown of α_2/γ lamellar colony.During the hot compression process,gliding and dissociation of dislocations occurred in γ phase that acted as the main softening mechanism,leading to extensive c twins and cross twins in α/γ lamellae and at grain boundaries.In general,homogeneous microstructure during the hot deformation process can be obtained in Ti Al alloy with high Nb addition and low Al segregation.The deformation substructures intrinsically promote the formability of Ti–46Al–8Nb alloy.     

工具钢锻轧材退火软化机理

从减少位错运动的障碍物入手，分析了溶质原子，碳化物形态，数量，分布对硬度的影响，以及减少晶界，相界面积对降低硬度的作用；并以H13，S5，S7，X45CrNiMo4等工具钢锻轧材的退火新工艺研究为例，论述了工具钢退火软化机理，指出了在临界点A1稍下等温有利于软化，而对于X45CrNiMo4钢则以得到粗片状珠光体，才能有效降低轧锻材的退火硬度。     

20MnMoNiCr低合金钢恒温压缩动态软化及流变应力模型研究

本文利用高温压缩实验方法,对20MnMoNiCr低合金核电用钢进行了恒温压缩模拟,根据恒温流变应力曲线的特性, 研究了恒温压缩过程中的动态软化规律, 并通过非线性回归分析得到了20MnMoNiCr核电用钢的热流变方程及动态再结晶临界应变方程     

冷变形多晶Cu的疲劳软化行为及其门槛

对预变形多晶Cu,在不同载荷下进行拉压对称的恒应力循环试验,比较了不同预变形对其饱和行为及位错组态的影响。结果表明,低应力幅下循环饱和行为仍与历史相关,疲劳后的位错组态具有“继承”性。计算不同载荷下的软化量并外推出疲劳软化门槛,约为流变应力的0.43—0.45左右,其值与低碳钢的几乎相同。本文还描述了循环过程的三个阶段,并对其机理进行了探讨。     

FATIGUE SOFTENING BEHAVIOR AND ITS THRESHOLD OF COLD STRAINED POLYCRYSTALLINE Cu

The symmetrical push-pull fatigue tests in load control were carried out for prestrained polycrystalline Cu.The change in mechanical behaviour during cycling was recorded in detail and the effect of various degree of prestraining on saturated behavior and dislocation structure was compared.The results show that the cyclic saturation state is still history-dependent at low stress amplitude and the dislocation structure after fatigue exhibits an “inheritance” be- havior.The level of softening was calculated at various load amplitudes and a softening threshold of about 0.43 to 0.45 of the flow stress was obtained.This is the same as that of low carbon steel.Three stages of cyclic processes and their mechanism have been described.     

带钢轧制负荷的研究

本文在研究C Mn钢带钢热连轧再结晶软化程度的基础上 ,揭示其对实质应变及轧机负荷的影响 ,与传统的计算轧制压力方法相比 ,考虑奥氏体再结晶软化不充分的影响后预报和实测符合更好 ;对带钢热连轧的轧制压力计算 ,中轧阶段选用Sims式、精轧阶段采用才利柯夫式 ,对发生完全再结晶软化的道次偏差不大 ,但若发生部分再结晶 ,所得结果明显偏低     

Effects of superimposed high-frequency vibration on deformation of aluminum in micro/meso-scale upsetting

Micro/meso forming is an economically competitive process for the fabrication of miniature metallic parts. However, the size effects observed when scaling down the process leads to challenges such as tribological problems at the interface and premature tool wear due to localized stress concentration regions. In this study, a hybrid micro/meso forming assisted by high-frequency vibration and the contributing mechanisms of the high-frequency vibration were investigated. The effects of high-frequency vibration on the improvement of surface finish, decrease of the friction at the die-specimen interface, and reduction of forming stress were analyzed and discussed based on the vibration-assisted upsetting experiments. In addition, finite element analysis was conducted to help understand the significance of the vibration. Results show that a transverse vibration of 9.3 kHz led to surface roughness (Ra) reduction from 1.5 μm to 0.9 μm at the top surface, friction coefficient decrease from 0.14 to 0.07 at the punch/specimen interface, and nearly 50% reduction in the forming stress. The findings of this study confirmed the significant benefits of high-frequency vibration applied in micro/meso forming of metallic materials and provided a basis to understand the underlying mechanisms of vibration-assisted forming.