7B50铝合金的热压缩变形行为

在变形温度为300-460℃、应变速率为0．001-1s^-1的条件下，采用Gleeble-1500型热模拟试验机对7850铝合金的热压缩变形行为进行了研究。结果表明：7850铝合金在热压缩变形中的流变应力随着温度的升高而减小，随着应变速率的提高而增大；该合金的热压缩变形流变应力可用Z参数公式来描述；在变形温度较高或应...     

新型抗热损伤车轮钢20CrSiMnMo的热变形行为

采用热力模拟试验研究了新型抗热损伤车轮钢20CrSiMnMo在温度为850-1250℃、应变速率为0．1～1s^-1条件下的热变形行为。结果表明：车轮钢在高温低应变速率下具有动态再结晶型流变曲线，低温高应变速率下其应力一应变曲线呈现硬化型；动力学分析得到该钢的热变形激活能Q=352．2725kJ／mol，应力指数n=5．56；组织观察和加工图表明，温度和应变速率参数选择在1000-1100℃，0．1～0．5s^-1或1250℃，1～0．25s^-1范围内变形，将获得细小的动态再结晶晶粒和转变组织。     

7N01铝合金热变形行为研究

采用Gleeble-3500热模拟机研究了7N01铝合金在变形温度为300℃~450℃、应变速率为0.01s~1s-1时的等温压缩热变形行为。结果表明:7N01铝合金的流变应力均在一个较小的应变时达到峰值,且随着应变速率的提高和变形温度的降低,流变应力峰值增加。在低应变速率(0.01s-1)时,7N01铝合金中出现了再结晶组织,随着变形温度的升高,再结晶晶粒数目增多且尺寸变大。7N01铝合金的显微硬度随着变形温度的升高和应变速率的增大而增大。     

Al-8.4Zn-2.2Mg-2.4Cu合金高温压缩变形的流变应力

在Gleeble-1500热模拟试验机上，采用高温等温压缩试验，研究了Al-8．4Zn-2．2Mg-2．4Cu铝合金在250～450℃温度范围及1．0～0．001s^-1应变速率范围内压缩变形的流变应力变化规律。结果表明，应变速率和变形温度的变化强烈地影响着合金的流变应力，流变应力随变形速率的提高而增大；随变形温度的提高而降低；其流变应力值可用Zener-Hollomon参数来描述。从流变应力、应变速率和温度的相关性，得出了该合金高温变形的四个特征常数。     

GH4169合金不同热变形条件下的流变应力研究

在Gleeble－3500型热加工模拟试验机上进行了GH4169镍基合金的高温压缩试验,变形温度为980℃～1100℃、应变速率为0,01s^-1、0,1s^-1、1s^-1、10s^-1,变形程度为50％。通过绘制真应力一真应变曲线,研究了GH4169镍基高温合金高温下的流变应力行为。结果表明：GH4169是应变速率和变形温度敏感型材料,变形温度升高和应变速率减小使流变应力显著减小;在变形的初始阶段,流变应力迅速增加,在到达峰值后,随着应变的增加,流变应力逐渐下降,并趋于一稳定值。采用简化后的双曲正弦模型Arrhenius方程,建立了GH4169高温条件下的本构方程,运用该方程计算出的峰值应力与试验测量值相比,拟合度达到了95.95％。     

CuNiSiP合金的动态再结晶行为

在Gleeble-1500D热模拟试验机上对CuNiSiP合金在高温压缩变形中的流变应力和组织变化进行了研究,分析了其再结晶行为。结果表明：应变速率和变形温度对合金的再结晶影响较大,在0．1,0．01s^-1应变速率下,650℃以上即可发生再结晶,而在1,5s^-1应变速率下,700℃以上才能发生再结晶;变形温度越高、应变速率越小,合金越容易发生再结晶;利用Arrhenius双曲正弦函数求得CuNiSiP合金的热变形激活能Q为485．6kJ·mol^-1。     

Cu-15Ni-8Sn(Zr)合金的高温压缩变形流动应力研究

在温度765～915℃、应变速率0．0011～0．33s^-1的试验条件下，测定了两种热处理状态的Cu-15Ni-8Sn(Zr)合金的高温压缩变形流动应力，并进行了分析。结果表明，应变速率和变形温度影响合金流动应力，流动应力随变形温度升高而降低，随应变速率提高而增大。在相同变形条件和变形程度下，固溶处理的试样要比未固溶处理试样的流动应力小。其它条件不变时，变形温度越高，或者应变速率越低，材料越容易发生动态回复和动态再结晶。     

18CrNiMo7-6齿轮钢的热压缩变形行为及显微组织演变

采用热模拟方法研究了18CrNiMo7-6齿轮钢在变形温度900～1 150℃、应变速率0.01～5 s^-1条件下的热压缩变形行为;建立了基于Arrhenius模型的全应变本构方程,采用该方程对流变应力曲线进行预测;根据动态材料模型绘制热加工图,并结合热加工图系统地研究显微组织演变特征。结果表明：试验钢的峰值应力随应变速率的增加或变形温度的降低而增大,动态回复和动态再结晶是热变形过程中的主要软化机制;采用建立的全应变本构方程预测得到流变应力曲线与试验结果基本吻合,预测真应力与试验结果的相对误差小于4.715%,说明该模型可以精确地模拟18CrNiMo7-6齿轮钢的热压缩变形行为。试验钢的适合热加工工艺参数为变形温度1 050～1 150℃、应变速率0.1～1 s^-1,此时组织为均匀细小的再结晶晶粒,晶粒尺寸在5～15μm。随着变形温度的升高或应变速率的降低,原始奥氏体晶粒不断被动态再结晶晶粒取代,且动态再结晶程度和再结晶晶粒尺寸增大。     

60Si2CrVAT高强度弹簧钢的热压缩变形本构方程

采用热模拟试验机对60Si2CrVAT高强度弹簧钢在不同温度(900,950,1 050,1 150℃)和应变速率下(0.1,1,5,10s~(-1))进行热压缩变形,研究了变形温度和应变速率对该钢热变形行为的影响规律;在此基础上,根据Arrhenius双曲正弦方程,建立了该钢的热压缩变形本构方程。结果表明:该钢的流变应力随着变形速率的增大而增大,随变形温度的升高而减小,动态再结晶在高变形温度和低应变速率下更容易发生;真应变为0.2时的变形激活能为372kJ·mol~(-1),流变应力的计算值与试验值之间的平均相对误差为4.89%,吻合得较好。     

HG700汽车大梁钢的热变形行为及 流变应力本构模型的建立

采用Gleeble 3500型热模拟试验机对HG700汽车大梁钢进行单道次压缩试验,研究了其在变形温度950～1 150℃和应变速率0.01～5.00s~(-1)条件下的流变应力行为;根据真应力-真应变曲线,采用线性回归方法建立该钢的流变应力本构模型,并进行了试验验证。结果表明:在高应变速率(1.00,5.00s~(-1))下,HG700汽车大梁钢的动态软化行为以动态回复为主,而在低应变速率(0.01,0.10s~(-1))下,HG700汽车大梁钢发生了明显的动态再结晶;变形温度的升高及应变速率的降低均会促进流变应力的降低,且会促进应力更早达到峰值;由构建的以变形温度、应变速率、真应变为变量的流变应力本构模型得到的预测结果与试验结果吻合良好,该模型可准确地预测HG700汽车大梁钢的流变应力。     

热变形参数对LC4铝合金流变应力的影响

在Gleeble-1500热模拟试验机上,以不同应变、应变速率和变形温度对LC4铝合金进行了高温压缩流变试验,得出了真实应力曲线,并采用神经网络的方法建立了该合金高温变形抗力与应变、应变速率和变形温度对应关系的预测模型。结果表明：变形温度和应变速率的变化强烈地影响合金流变应力的大小,流变应力随变形温度的升高而降低,随应变速率的提高而增大;神经网络能够比较精确地预测材料的流变应力。     

10B06冷镦钢连铸坯的热压缩流变行为

利用MMS-200型热力模拟试验机研究了10B06冷镦钢连铸坯在750～1 100℃、应变速率为0.01～20s-1条件下的热压缩流变行为,并且通过线性回归确定了该钢的应变硬化指数以及热激活能,获得了其在变形条件下的流变应力本构方程。结果表明:该钢在热压缩变形时的流变软化行为是动态再结晶、动态回复与加工硬化联合作用的结果;当变形温度较低、应变速率较小时,软化效应以动态再结晶为主;而当变形温度较高、应变速率较大时,软化效应是动态再结晶和动态回复共同作用的结果;该钢的流变应力可采用Zener-Hollomon参数的函数来描述,其热激活能为220.132 3kJ.mol-1。     

一种锌基合金热变形行为的试验模拟

采用热模拟试验机对一种自行研制的高强度易切削锌基合金进行了等温热压缩试验.结果表明:该锌合金热压缩变形流变应力随变形温度升高而减小,随应变速率增大而增大,变形材料内部的温升随应变速率的增大而加剧;可用包含变形温度、应变速率和变形程度的Zener-hollomon模型来真实描述该锌合金高温变形的流变行为.     

铸态42CrMo钢热压缩变形时的动态再结晶行为

基于Gleeble-1500型热模拟试验机进行热压缩试验,通过对试验数据进行线性回归分析推导出了铸态42CrMo钢热压缩变形的本构方程,同时探讨了热压缩变形参数对显微组织的影响。结果表明:在相同的变形温度(850～1 150℃)下,该钢变形后的显微组织随着应变速率的增大逐渐变细,在5s-1时达到最细;在相同的应变速率(0.1～5s-1)下,显微组织随着变形温度的升高逐渐变细后再粗化,在1 050℃时马氏体板条最细;在相同的应变速率(1～5s-1)和变形温度(900～1 050℃)下,随着变形量的增加,再结晶晶粒尺寸均得到了显著细化;在温度为1 050℃、应变速率为5s-1、应变为0.6时热压缩后晶粒的细化效果最为显著。     

AerMet100钢热压缩过程流变应力模型

用Gleeble-1500D型试验机研究了AerMet100钢热压缩变形过程流变应力的演变规律.结果表明:流变应力随变形温度的提高而降低,随应变速率和变形量的提高而增加.基于三因子的二次正交回归设计分析方法,建立了流变应力随变形量、应变速率和温度变化的数学模型并对流变应力进行了预测.该模型预测结果与实测结果基本吻合.     

Metadynamic recrystallization of the as-cast 42CrMo steel after normalizing and tempering during hot compression

The existing researches of hot ring rolling process are mainly based on forged billet. Compared with the existing process, the new ring casting-rolling compound forming process has significant advantages in saving materials and energy, reducing emission and reducing the production cost. The microstructure evolution of the casting materials during hot deformation is the basis of the research of the new process. However, the researches on the casting materials are rare. The metadynamic recrystallization of the as-cast 42CrMo steel after normalizing and tempering during the hot compression is investigated. The tests are performed on the Gleeble-1500 thermal-mechanical simulator. The influence rule of the deformation parameters on the metadynamic recrystallization is obtained by analyzing the experimental data. The kinetic model of the metadynamic recrystallization is deduced. The analysis results show that the metadynamic recrystallization fraction increases with the increase of the deformation temperature and the strain rate. The metallographic experiments are used to investigate the influence rule of the deformation parameters on the grain size of the metadynamic recrystallization. The experimental results show that the grain of the metadynamic recrystallization could be refined with the increase of the strain rate and the decrease of the deformation temperature during hot compression. The occurrence of the metadynamic recrystallization during the hot deformation is more difficult in as-cast 42CrMo steel than in forged 42CrMo steel. The research can provide the foundation for the further research of the hot deformation behaviors of the as-cast structure and theoretical support for the new ring casting-rolling compound process.     

Effect of silicon carbide volume fraction on the hot workability of 7075 aluminium-based metal–matrix composites

The hot deformation behaviour and microstructure evolution of stir cast 7075Al alloy and 7075Al alloy with 10, 15 and 20 % volume fraction of 20 μm SiCp composites have been studied by using the processing maps. The compression tests were conducted on both alloys and composites in the temperature range of 300–500 °C and the strain rate range of 0.001–1.0 s^?1 to establish the processing map. The dynamic recrystallization and instability zones were identified and validated through micrographs. The composites showed higher flow stress, efficiency and lower instability regimes than alloy. The 15 % volume fraction of SiCp composites achieved better hot workability due to grain refinement, hardening and strengthening of the material.     

The influence of heat treatment and hot deformation conditions on γ′ precipitate dissolution of Nimonic 115 superalloy

In precipitation hardenable materials, it is desirable to determine the precipitate dissolution temperature for homogenizing the microstructure by controlling the size and distribution of the precipitates. In this research, the influence of various heat treatment and hot deformation conditions on the kinetics of γ′ dissolution and its morphological evolution in Nimonic 115 was studied. In addition, hot deformation behavior of the material was investigated using hot compression experiments at varying temperature (between 1,050°C and 1,175°C) and strain rates (between 0.01 and 1 s^?1) up to a true strain of 0.8. The values obtained for the solvus temperature of γ′ precipitates by two methods are all in agreement indicating this temperature at approximately 1,165?±?5°C. Through examination of the influence of temperature and strain rate on the hot deformation behavior, it was determined that the experimental flow stress observations could be effectively related to the processing parameters using an Arrhenius relationship. The results indicate that dynamic recrystallization is the main softening mechanism during the high temperature deformation of Nimonic 115, and it can be effectively promoted by increasing the deformation temperature. By deformation at temperatures higher than 1,125°C, a completely recrystallized microstructure is obtained.     

热轧A36钢静态再结晶动力学模型

为了模拟A36钢轧制过程的微观结构演变,在Gleeble 1500热模拟试验机上进行了双道次热压缩实验。通过在不同变形工艺下的软化行为研究,建立了A36钢在轧制情况下的静态再结晶动力学模型。该模型综合考虑了不同变形温度、应变率、应变及初始奥氏体晶粒尺寸等参数对静态再结晶行为的影响,仿真结果和实验结果比较吻合。     

Study on the dynamic and static softening phenomena in Al–6Mg alloy during two-stage deformation through interrupted hot compression test

The dynamic and static softening phenomena in Al–6Mg alloy were studied through interrupted two-stage hot compression test performed isothermally at 480 °C and strain rate range of 0.001–0.1 s⁻¹. The interruptions of 29 and 90 s were considered when the true strain reached 0.5. It was concluded that the effect of static softening on the flow stress was not highlighted by extending the interruption at a constant strain rate. Also, it was exhibited that softening rate highly enhanced with the strain rate decrement at a constant time. Moreover, the static and dynamic recrystallization was revealed as the dominant softening mechanisms at low and high strain rates, respectively.