7075Al/SiCp复合材料的热压缩变形流变应力和组织行为

采用圆柱试样在Gleeble-1500热模拟机上对喷射沉积7075Al/SiCp复合材料进行高温压缩变形实验,实验条件为:变形温度300～450℃,应变速率0.001～1s-1.结果表明:7075Al/SiCp复合材料的流变应力大小受到变形温度和应变速率的强烈影响,流变应力随应变的增加而逐渐增加,出现一峰值后逐渐下降;流变应力随变形温度的升高、应变速率的降低而降低.可用Zener-Hollomon参数的双曲正弦形式来描述7075Al/SiCp复合材料高温压缩变形流变应力.随着变形温度的升高和应变速率的降低,7075Al/SiCp复合材料热变形过程中SiCp的分布逐渐均匀化,有利其热加工性能的改善.     

3003铝合金动态再结晶实验研究

采用Gleeble-1500热模拟试验机对3003铝合金进行变形温度为300～500℃、应变速率为0.01～10.0s-1的高温等温压缩实验,由真应力-真应变曲线计算应变硬化速率,并采用截线法测量热压缩后平均晶粒尺寸,结果表明:3003铝合金动态再结晶临界应变εc随着Z参数的增大而提高,合金发生动态再结晶的临界条件为:...     

基于热加工图的7075铝合金热塑性变形工艺参数优化识别

在Gleeble-1500热模拟试验机上进行多组热压缩试验,得到7075铝合金在成形温度573～723K,应变速率0.01～10s-1下的真应力-应变数据,用此数据作为计算应变速率敏感指数（m值）、功率耗散因子（η值）、失稳判据（ξ（ε.）值）三重判据的基本模型。通过三重判据构建包含应变在内的7075铝合金热加工图,并观察试样变形后的微观组织来验证热加工图,最终判断该合金在试验范围内的最佳变形参数。结果表明7075铝合金热加工的安全区集中在高温低应变速率区,并随着应变的增加,η值逐渐增加;通过金相观察,稳定变形区,材料由于变形发生动态再结晶而使晶粒细化;不稳定变形区,裂纹伴随着流动位错带的产生而被发现,因此可以通过包含应变的热加工图所确定的最佳工艺参数来保证无缺陷的7075铝合金锻件。     

3003铝合金热变形流变应力及动态再结晶模型

在变形温度为300～500℃,应变速率为0.01～10.0s~(-1)的条件下,通过Gleeble-1500热模拟试验机对3003铝合金进行高温等温压缩实验。结果表明,该合金在热变形过程中的峰值流变应力可用双曲正弦本构方程来描述,由本构方程计算获得模型的流变应力预测值和实测值的相对误差在±7%范围以内。根据热力学不可逆原理确定动态再结晶临界应变,建立动态再结晶开始时间与变形温度关系的RTT(Recrystallization Start Time)图,研究表明:动态再结晶开始时间随着应变速率的减小与变形温度的降低而增大,由流变应力曲线计算动态再结晶体积比例,其大小随变形温度的升高和应变速率的减小而增大,并获得3003铝合金动态再结晶体积分数数学模型。     

5083铝合金的热变形组织演变及晶粒度模型

通过等温压缩实验、光学显微镜与透射电镜研究了变形温度300~450℃、应变速率0.01~1s-1、真应变0.36~1.2范围内变形条件对5083铝合金热变形组织演变的影响。结果表明:升高热变形温度或降低应变速率均可促进5083铝合金的动态再结晶发生,使变形后5083铝合金位错密度降低,再结晶晶粒尺寸增大;随着应变量的增加,变形后合金的位错密度降低,动态再结晶程度增大。根据唯象理论的指数模型,利用线性回归方法建立了5083铝合金动态再结晶晶粒度模型,模型计算值与实测值吻合良好,平均相对误差仅为4.6%。     

CuNi30Mn1Fe动态再结晶临界应变行为研究

借助热模拟试验机分别研究了变形温度为800℃、850℃、900℃、950℃、1 000℃,变形速率为10 s~(-1)、1 s~(-1)、 0.1 s~(-1)、 0.01 s~(-1)条件下CuNi30Mn1Fe的高温热压缩试验。基于加工硬化率方法,分析了CuNi30Mn1Fe在热压缩变形过程中的动态再结晶行为,并求得发生动态再结晶时所对应的临界应变值。结果表明:CuNi30Mn1Fe在热压缩变形时伴随着动态回复与再结晶的发生;临界应变随着温度的增加而减小,随着应变速率的增加而增加;再结晶峰值应变ε_p和临界应变ε_c的线性关系方程为ε_c=-1.03ε_p+1.36。     

A100超高强度钢的流变应力曲线修正与唯象本构关系

在Gleeble-3500型热模拟试验机上对A100超高强度钢进行热压缩实验,获得了在变形温度为850~1200℃,应变速率为0.001~10s -1 以及变形程度为60%条件下的流变应力曲线,分析热压缩过程中摩擦和温升效应对流变应力的影响,修正了流变应力曲线;并在Arrhenius双曲正弦函数方程的基础上引入应变量参数构建了基于应变量耦合的唯象本构模型。结果表明:随着变形温度的降低或应变速率的增加,摩擦和温升效应对流变应力的影响逐渐显著;所建立的本构模型预测值与实验值的绝对平均相对误差为4.902%,相关系数为0.99,能够用于准确预测不同应变下的流变应力。     

LD7铝合金热变形研究

在Gleeble-1500热模拟机上对LD7铝合金进行等温热变形实验,变形温度为300～500℃,应变速率为0.01～10s-1,研究其热变形的流变应力行为、显微组织及软化机制.结果表明LD7铝合金真应力-真应变曲线表现出动态回复特征,在应变速率ε=1.0s-1,变形温度高于420℃时,应力出现锯齿波动,表现出不连续动态再结晶特征.合金在压缩过程中主要软化机制为动态回复,同时也存在动态再结晶.变形后晶粒尺寸随变形温度升高而增大,随变形速率增加而减小.     

B30铜镍合金的高温热变形行为及加工图EI北大核心

在变形温度为750~1000℃、应变速率为0.01~10 s^(-1)条件下,对铸态BFe30-1-1铜镍合金进行了热压缩实验。综合分析摩擦和温升对合金流变应力的影响,利用修正后的流变应力曲线构建了BFe30-1-1铜镍合金的Arrhenius双曲正弦函数本构关系模型,基于动态材料模型构建合金的热加工图,研究合金热变形过程中的组织演变规律。结果表明:合金的峰值流变应力随着变形温度的降低或应变速率的增加而升高,摩擦和温升能够显著影响合金的真应力-真应变曲线,热变形过程中发生了动态再结晶,本研究构建的合金本构关系模型对峰值应力的预测值与修正后实验值的平均相对误差仅为3.77%,能够准确地预测合金在不同热变形条件下的流变应力。结合热加工图和微观组织分析,合金的较合理的热塑性变形工艺区间为变形温度900~1000℃、应变速率0.04~0.16 s^(-1),在该变形条件下热压缩后的样品可获得更多的动态再结晶组织。     

热挤压态Ni-Co-Cr基粉末高温合金热加工行为EI北大核心CSCD

利用Gleeble-3500D型热模拟实验机进行等温压缩实验,系统研究一种新型热挤压态Ni-Co-Cr基粉末高温合金在变形温度为1020~1110℃、应变速率为10-3~1 s-1条件下的热压缩变形行为,对获得的流变应力曲线进行摩擦修正,利用摩擦修正后的数据分别建立合金的热压缩本构关系方程和考虑应变补偿的流变应力模型;同时,构建热加工图,并结合显微组织分析,优化合金的热变形工艺参数。结果表明:合金在热压缩过程中发生了明显的动态再结晶现象,流变应力随应变速率的降低或变形温度的升高而降低。利用所建立的考虑应变补偿的合金流变应力模型进行流变应力的预测,其预测值与实验摩擦修正值吻合良好。根据构建的热加工图并结合微观组织分析,提出了合金较合理的热加工参数:变形温度约为1076~1103℃、应变速率约为10-3~10-2.77 s-1。     

Hot compressive deformation behavior of 7075 Al alloy under elevated temperature

The hot compression tests were conducted with wide strain rates and forming temperature ranges to study the high-temperature deformation behavior of 7075 Al alloy. The material flow behavior and microstructural evolution during hot-forming process are discussed. Based on the measured stress–strain data, a new constitutive model is proposed, considering the coupled effects of strain, strain rate, and forming temperature on the material flow behavior of 7075 Al alloy. In the proposed model, the material constants are presented as functions of forming temperature. The proposed constitutive model gives good correlations with the experimental results, which confirms that the proposed model can give an accurate and precise estimate of flow stress for 7075 Al alloy.     

Compressive Deformation of Semi-Solid AZ91D Magnesium Alloy

The compression tests of semi-solid AZ91D Mg alloy have been conducted on a parallel-plate viscometer. The results are as follows. With increasing the compression temperature, the deformation rate or the strain rate of the specimens rises, but the compressive stress continuously decreases; the deformation strain is obviously linear with the compressive stress and independent on compression temperature under a given compression load. In the wake of the compression load being added, the compressive strain increases but the compressive stress decreases clearly; the deformation strain is obviously linear with the compressive stress under different compression load. The mathematical apparent viscosity model about the semi-solid compressed AZ91D Mg alloy has been established, i.e. ηapp=2004.2exp(15.61fs)γ1.317fs-1.3511.     

Constitutive modeling of powder metallurgy processed Al–4%Cu preforms during compression at elevated temperature

In this study, a hot deformation constitutive base analysis has been conducted on powder metallurgy (P/M) processed Al–4%Cu preforms. The main objective is to evaluate the effect of initial relative density on the hot deformation behaviour and to establish the constitutive equation which considers the effect of initial relative density during hot compression test. This has been carried out by using the true stress–true strain curve data obtained from hot compression test of P/M processed Al–4%Cu preforms with different initial relative density of 0.84, 0.87 and 0.9 for various range of temperature 300–500 °C and strain rate range of 0.1–0.4 s⁻¹. It has been found that the flow stress is notably influenced by initial relative density, temperature and strain rate. The results show that the flow stress exhibits peak value at certain strain value, and then decreases showing flow softening until the flow stress remains constant at higher strain values. A constitutive equation that predicts the flow stress in hot compression of P/M processed Al–4%Cu preforms has been developed. The predicted flow stress values are in a good agreement with the experimental results and it is confirmed that the formulated constitutive equation is accurate and reliable to predict the flow stress of Al–4%Cu preforms during hot compression at elevated temperature.     

The influence of initial microstructure and temperature on the deformation behavior of AZ91 magnesium alloy

The deformation behavior of AZ91 magnesium alloy has been investigated using uniaxial compression tests at a temperature range of 100–300 °C. The different processing routes including homogenization treatment, hot rolling and annealing have been employed to study the effect of initial microstructure on the compressive mechanical response of the AZ91 alloy. The results show that the hot-rolled material presents an enhanced compressive workability at temperatures as low as 100 °C. The experimental alloy exhibit dynamic recrystallization during compression in any of the initial microstructures. The maximum and minimum DRX (dynamic recrystallization) fraction has been obtained in hot-rolled and homogenized conditions, respectively. The recrystallized fraction increases with raising the temperature. In addition the effect of initial microstructure on the peak stress diminishes with increasing temperature while its effect on the peak strain remains remarkable. The softening fraction has been increased with temperature, where a pronounced effect has been recorded in the case of homogenized (un-rolled) material.     

Mg-9Li-3Al-2.5Sr合金的热变形行为

使用Gleeble-1500D型热模拟试验机,对挤压态Mg-9Li-3A1-2.5Sr合金进行热力模拟实验(变形温度为200-350℃,应变速率为0.001-1 s^-1),分析了材料的流变应力与变形温度和应变速率的关系,建立了该合金热变形过程中的本构方程,计算了该合金的热加工图,并结合显微组织观察对加工图进行了分析.结果表明:材料的流变应力随着应变速率的增加而增加,随着温度的升高而下降;用双曲正弦函数关系式能很好地描述材料在热变形过程中的稳态流变应力;对热加工图的分析结果表明,在实验参数范围内材料的最佳理论热加工区为260-300℃和0.01-1 s^-1.材料的超塑性加工区为340-350℃和0.003-0.01 s^-1。     

Cu-2.32Ni-0.57Si-0.05P合金热压缩变形研究

在Gleeble-1500D热模拟试验机上,对Cu-2.32Ni-0.57Si-0.05P合金在应变速率为0.01～5s-1、变形温度为600～800℃、最大变形程度为60%条件下,进行恒温压缩模拟实验研究.分析了实验合金在高温变形时的流变应力、应变速率及变形温度之间的关系,研究了变形温度对合金显微组织的影响.计算了合金高温热压缩变形时的应力指数n、应力参数α、结构因子A以及平均热变形激活能Q.结果表明:合金的流变应力随变形温度升高而降低,随应变速率提高而增大.热变形过程的流变应力可用双曲正弦本构关系来描述.当变形温度高于750℃时,合金流变曲线呈现出明显的动态再结晶特征,合金显微组织为完全的动态再结晶组织.合金的热加工宜在应变速率为0.1～1s-1、温度为700～800℃范围内进行.     

Hot deformation and processing map of an as-extruded Mg–Zn–Mn–Y alloy containing I and W phases

The hot deformation characteristics of an as-extruded ZM31 (Mg–Zn–Mn) magnesium alloy with an addition of 3.2 wt.% Y, namely ZM31 + 3.2Y, have been studied via isothermal compression testing in a temperature range of 300–400 °C and a strain rate range of 0.001–1 s^− 1. A constitutive model based on hyperbolic-sine equation along with processing maps was used to describe the dependence of flow stress on the strain, strain rate, and deformation temperature. The flow stress was observed to decrease with increasing deformation temperature and decreasing strain rate. The deformation activation energy of this alloy was obtained to be 241 kJ/mol. The processing maps at true strains of 0.1, 0.2, 0.3 and 0.4 were generated to determine the region of hot workability of the alloy, with the optimum hot working parameters being identified as deformation temperatures of 340–500 °C and strain rates of 0.001–0.03 s^− 1. EBSD examinations revealed that the dynamic recrystallization occurred more extensively and the volume fraction of dynamic recrystallization increased with increasing deformation temperature. The role of element Y and second-phase particles (I- and W-phases) during hot compressive deformation was discussed.     

Cu-Ni-Si合金冷变形及动态再结晶行为研究

研究了时效温度和时效时间对不同冷变形条件下Cu-2.0Ni-0.5Si合金性能的影响。在Gleeble-1500D热模拟试验机上,采用高温等温压缩试验,对Cu-2.0Ni-0.5Si合金在高温压缩变形中的流变应力行为进行了研究。结果表明,合金经900℃固溶,当变形量为40%,时效温度达到450℃时,其显微硬度达到201HV,导电率达到34%IACS。随变形温度升高,合金的流变应力下降,随应变速率提高,流变应力增大。在应变温度为700、800℃时,合金热压缩变形流变应力出现了明显的峰值应力,表现为连续动态再结晶特征。从流变应力、应变速率和温度的相关性,得出了该合金高温热压缩变形时的变形激活能Q。     

Microstructure evolution and mechanical properties of backward thixoextruded 7075 aluminum alloy

The present work deals with the microstructure evolution of 7075 aluminum alloy which has been backward thixoextruded in the temperature range of 550–600 °C using different ram diameters and ram displacement velocities. The recrystallization and partial melting (RAP) route has been used to obtain the semi-solid feedstocks for thixoforming. The results indicate that the back extruded microstructures mostly consist of semisolid grains which have been elongated along extrusion direction. The finest semisolid grain size has been obtained at lower deformation temperature and higher equivalent strain. This is attributed to the higher imposed shearing force on the liquid phase which could in turn fragment the grains. The current work also explores the room temperature mechanical properties of thixoformed work-pieces using shear punch testing method. It is found that the room temperature shear strength and ductility values have been substantially influenced by the deformation temperature, ram displacement velocity, and ram diameter.     

半固态AZ91D镁合金的压缩变形和显微组织

利用平行板触变压缩仪研究了电磁搅拌的半固态AZ91D合金试样的压缩变形和组织.结果表明:随着半固态压缩变形温度的升高,AZ91D镁合金试样变形的速度加快,即变形应变速度增大,但压缩应力不断下降;在某一载荷下,AZ91D镁合金试样压缩变形应力和应变呈明显的线性关系,与压缩温度的高低无关.随着半固态压缩载荷的提高,AZ91D镁合金试样变形的速度增加,应变速度增大,应力下降速度加快;在不同的压缩载荷下,AZ91D镁合金试样的压缩变形应力和应变都呈明显的线性关系.在实验中的各种半固态压缩变形条件下,初生α-Mg在压缩后AZ91D镁合金试样组织中的分布很均匀,几乎不存在组织偏析.当初生固相的形态呈球状结构,在相同的变形条件下,不同种类合金的半固态压缩变形规律非常相似.