ZL116合金的半固态模锻成形组织与性能

采用300 t压力机,对半固态ZL116合金进行了模锻成形实验.结果表明 半固态模锻成形可以获得组织致密、轮廓清晰、充型完整的成形件;成形件微观组织主要为细小、分布均匀的近球状和蔷薇状非枝晶组织;同时由于成形静压力的作用引起局部组织发生塑性变形,使半固态模锻件的性能明显优于液态模锻件的性能.硬度可达65.7HB,高于液态模锻件20.5%,为半固态加工技术在战车上的应用奠定基础.     

基于数值模拟的粉末冶金TiAl合金叶片模锻工艺研究

采用Deform-3D有限元软件对粉末冶金Ti-47Al-2Cr-2Nb-0.2W(摩尔分数,%)合金叶片的模锻工艺进行数值模拟研究,分析预热温度和上模速度对TiAl合金叶片锻件的等效应变场和等效应力场分布以及上模载荷的影响。结果表明,随预热温度升高和上模速度减小,叶片锻件的等效应变场和等效应力场分布更均匀,有利于提高叶片组织的均匀性。随着模锻过程的进行,由于TiAl合金加工硬化以及锻坯与模具间的摩擦增大,导致上模载荷不断增大,而预热温度升高和上模速度减小均使上模载荷显著降低。粉末冶金TiAl合金叶片模锻变形的最佳工艺参数为预热温度1200℃、上模速度0.5 mm/s。     

我国将建世界最大模锻压机

等温模锻液压机是航空、航天、宇航及其他重要机械生产重要锻件的关键设备。大型模锻压机主要用于铝合金、钛合金、高温合金、粉末合金等难变形材料进行热模锻和等温超塑性成形。其锻造特点是通过大压力、长保压时间、慢变形速度改善变形材料的致密度，通过细化材料晶粒提高锻件的综合性能，提高整个锻件的变形均匀性，使难变形材料和复杂结构锻件通过等温锻造和超塑性变形来满足设计要求，并可节约材料40％。     

7A60铝合金杯形件等温压扭关键工艺参数分析

以7A60铝合金杯形件为研究对象,通过工艺实验和有限元模拟研究了杯形件在等温压扭成形过程中关键工艺参数对其成形性能的影响。结果表明:坯料高径比对累积变形量的影响主要在镦粗变形阶段,下模扭转速度增大,成形载荷降低,扭矩增加;但当下模转速太大时,压扭件盘面过渡圆角区域损伤值将大于1,边缘易于产生破裂缺陷;成形温度的变化对成形载荷和扭矩的影响较为显著;成形过程中对压扭件施加小于1圈的扭转剪切变形,合金的连续性不会遭到破坏,且合金强度相比传统挤压件有所提高。     

铜材接触线扩展挤压成形的三维有限元数值模拟

根据有限变形刚粘塑性有限元理论,基于DEFORM-3D软件平台,对接触线在模腔中扩展挤压成形过程进行了三维有限元数值模拟,获得了扩展挤压成形过程的应力场、应变场、温度场和速度场分布,并揭示了金属流动规律,从而为模具设计提供理论依据。     

中国大型铝合金等关键件模锻工艺取得重大进展

日前,作为"高档数控机床与基础制造装备"国家科技重大专项的重要内容之一,由中国第二重型机床集团公司承担的"大型关键件模锻工艺技术"课题研究取得了重大进展.该课题重点围绕大型航空模锻件热模锻近净成形技术,结合正在建设的800MN大型模锻压机,开发出复杂精密航空锻件的近净成形新技术,解决了大型模锻工艺基础共性技术和关键技术问题.突破了大型钛合金、铝合金锻件的整体成形技术,在航空用典型钛合金、铝合金、高强钢的基础数据测试,锻造成形过程的无网格法模拟技术研究,钛合金典型结     

一种板材小圆角胀压复合成形工艺解析

针对薄壁板材零件小圆角特征成形制造难的问题,提出了一种新型胀压复合成形工艺.其关键工艺参数为:预成形高度、预成形凹圆角大小和终成形胀形压力与背压凸模运行速度匹配关系.预成形高度决定了终成形小圆角的材料储备,预成形凹圆角的最佳值为充液拉深时凸模圆角可取的最小值,通过理论分析给出了预成形高度和预成形凹圆角的计算方法.建立了胀压复合成形过程力学模型,通过应力状态分析给出了不同胀形压力与背压凸模运行速度匹配关系下坯料圆角区变形状况.同时基于有限元模拟和工艺试验,研究了预成形高度和终成形胀形压力与背压匹配路径对试验件成形质量的影响,验证了理论分析的准确性,并证明了该新工艺的适用性.      

计算机模拟成形技术在航空模锻件的应用研究

本文用基于有限元体积法的模拟成型分析软件模拟分析了机轮模锻件的成形过程，获得了工件变形全过程的流动速度、应力、应变场等信息。并将分析结果用于工艺优化和提高锻件质量及提高生产效率方面。     

钨合金丝材无模拉拔成形温度场及流动应力梯度

简述了目前钨合金丝材加工技术特点及变形过程存在的技术问题,分析了采用无模拉拔成形技术加工钨合金丝材的可行性及变形机制.通过实验研究,确定了钨合金丝材无模拉拔成形的温度场模型和流动应力模型,确定了钨合金丝材无模拉拔成形变形区温度梯度及流动应力梯度.研究结果表明,钨合金丝材尤模托拔成形时,当Z≤ZM时变形区温度场沿轴向呈线性分布;当ZZM时变形区温度场沿轴向呈非线性分布,温度梯度沿轴向呈线性分布;变形区流动应力场沿轴向接近线性分布,流动应力梯度接近于常数.     

C型钢的有限元模拟

以弹塑性大变形有限元理论为基础,对C型钢成型过程做出合理简化,建立分析模型.利用MARC软件对C型钢辊弯成型进行了三维有限元数值模拟,分析得出了C型钢在成形过程中变形区应力、应变的分布规律.     

加卸载下原煤力学特性及渗透演化规律

基于自主研发的煤岩热流固耦合试验系统,在考虑实际开采方式的条件下,进行轴压升高和围压降低的加卸载试验,分析研究不同加卸载速率下原煤的力学特性和渗透演化规律.结果表明:加卸载过程中,轴向应力的加载速率越大,峰值应力附近的曲线平台越长,峰值应力、轴向应变和环向应变也越大,体应变则越小.不同加卸载速率比下含瓦斯煤变形模量均先迅速减小后缓慢减小,到破坏时再迅速降低,而后逐渐保持稳定趋势;在相同轴向应变时,加卸载速率比越小,煤样的变形模量越大.加卸载过程中,煤样的偏应力、渗透率与应变的关系可分为三个阶段:初始压密与弹性阶段、屈服破坏阶段和破坏后阶段.加卸载速率比越小,煤样达到峰值应力时,含瓦斯煤的渗透率和体积变形越大.      

塑料模具钢镦粗过程内部空洞缺陷的有限元模拟

摘要：利用JmatPro软件模拟计算718类塑料模具钢（3Cr2MnNiMo）热物性参数。应用ABAQUS有限元模拟软件建立模具钢镦粗过程中孔洞模型，模拟不同压下率条件下孔洞的闭合规律。模拟结果表明：孔洞闭合分为开始闭合、闭合加速和闭合减速3个阶段；孔洞闭合的2个主要影响因素为孔洞表面等效应变εe、静水压力与等效应力之比σm/σe；随着孔洞所处位置不同，孔洞闭合度不同，根本原因为孔洞所处位置的等效应变不同。所得结果对于塑料模具钢实际锻造生产过程具有指导意义。     

7085铝合金的高温压缩流变应力及软化行为

对均匀化炉冷态7085铝合金进行高温压缩实验,研究该合金在变形温度为350~450℃、变形速率为0.001~0.1 s 1和应变量为0~0.6条件下的流变应力及软化行为。结果表明:流变应力在变形初期随着应变的增加而迅速增大,出现峰值后逐渐软化进入稳态流变;随着变形温度的升高和应变速率的降低,峰值流变应力降低。采用包含Zener-Hollomon参数的Arrhenius双曲正弦关系描述合金的流变行为。分析和建立了应变量与本构方程参数(激活能、应力指数和结构因子)的关系,研究发现本构方程参数随应变量的增加而减少。合金的流变行为差异与动态回复再结晶和第二相粒子相关。     

基于Deform-3D软件对AISI4340钢Φ600mm铸坯开坯工艺参数的模拟数值

利用Deform-3D软件对AISI4340钢Φ600 mm铸坯至300 mm × 300 mm坯的开坯过程工艺参数进行了数值模拟.通过对加热温度、轧制速度、压下率、2道次压下对铸坯心部变形和材料流动影响的研究,分析了开坯成形过程中心部等效应力和材料变形特点,获得了Φ600圆连铸坯开坯成300 mm方坯的成形规律.结果...     

Influence of deformation conditions and texture on the high temperature flow stress of magnesium AZ31

The evolution of hot working flow stress with strain is examined in torsion, uniaxial compression and channel die compression. The flow stress was found to be strongly dependent on texture and deformation mode. At low strains this dependency accounted for a difference in flow stress of up to a factor of two. At higher strains the influence of texture and deformation mode was less marked. The stresses corresponding to an equivalent strain of 0.5 were modelled using a power law expression with an activation energy of 147 kJ/mol and a strain rate exponent of 0.15. The influence of texture and deformation mode on flow stress is rationalised in terms of the influence of prismatic slip, twinning and dynamic recrystallisation on deformation stress and structure.     

Cyclic creep and cyclic deformation of high-strength spring steels and the evaluation of the sag effect: Part I. Cyclic plastic deformation behavior

The cyclic creep and cyclic plastic deformation behavior of two commercial suspension spring steels of high hardness levels, namely, SAE 9259 and SAE 5160, were studied under different testing conditions of cyclic peak stress and cyclic stress ratio. The experimental results indicate that both the cyclic stress ratio and cyclic peak stress have strong, but complicated, effects on the cyclic creep and cyclic plastic deformation behavior of these materials. It has also been found that the addition of silicon can increase the resistance of these steels to cyclic creep and cyclic plastic deformation, although the extent of this increase is also related to other cyclic deformation conditions. A transition in the relationship between the total plastic strain range and the cyclic stress ratio (R) has been detected at approximately R=0.5. The mechanism of such a transition is explained by the operation of cross-slip during the unloading process of cycling. Moreover, a cyclic softening behavior of these spring steels in the quench-tempered condition was also detected and is attributed to the activation and reorganization of obstacle dislocations introduced into the steels during the process of martensitic transformation. More importantly, this study has indicated that parameters such as the cyclic creep strain, the cyclic creep rate in the secondary creep stage, and the total cyclic plastic strain range can better reflect, and should be used to depict and characterize, the sag behavior of spring steels as well as other materials. Finally, the effect of silicon on sag behavior, in comparison with the results from the Bauschinger-effect test, has also been discussed through the influence of Si on carbide formation and distribution.     

Mathematical modeling of the extrusion of 6061/Al2O3/20p composite

An integrated approach, involving laboratory experiments, extrusion plant trials, and finite element modeling (FEM) has been adopted for the study of the extrusion of the metal matrix composite (MMC) 6061/Al₂O₃/20p. Gleeble compression tests were performed to develop the constitutive equation of the MMC under industrial extrusion process conditions. Extrusion plant trials were conducted to measure load and temperature and to obtain samples for microstructural analysis. Metal flow, with respect to particle behavior in the deformation zone, was examined microscopically. An FEM based on the commercial code DEFORM was adopted for the simulation of the extrusion of the MMC; the constitutive equation developed was incorporated into the model. Using an updated Lagrangian formulation, both the transient and steady-state regions of extrusion were modeled. Load and temperature predictions resulting from this model agree well with the measured values in the upsetting stage and in the steady-state region. Temperature predictions agree to within less than 3 pct of the measured values. The FEM predictions of temperature, stress, strain, and strain-rate distribution were correlated with the particle behavior and low-speed cracking during extrusion: large shear deformation promotes particle fracture in the deformation zone, and tensile stress generation in the die land zone of the billet leads to low-speed cracking of the MMC during extrusion. The latter occurs at low temperature in the front end of the billet at the beginning of the extrusion process due to heat loss to the cold die.     

冷拔六角钢一次成型的有限元分析

本文用弹塑性有限元法计算了由圆坯直接拔制六角钢的应力、应变分布。观察到在变形区的角部变形较小,但拉应力较大,而在模面变形中心附近压力最大,这些现象是六角钢角部裂纹和模面磨损不均的重要原因。     

316L不锈钢冷变形加工硬化机制及组织特征

通过对316L不锈钢的不同变形量的压缩试验,对其冷变形特性进行了研究.利用修正的Ludwik模型对流变应力数据进行非线性拟合,获得了316L不锈钢的真应力应变模型和加工硬化模型.试验结果表明:修正的Luiwik模型能较好的反映316L不锈钢真应力与应变关系;根据流变应力的变化规律,316L不锈钢冷变形流变应力可分为三个阶段,分别为真应变小于0.02的强加工硬化阶段,真应变在0.02与0.29之间的稳加工硬化阶段,以及真应变大于0.29的弱加工硬化阶段.电子显微技术研究表明316L不锈钢三个不同的变形阶段,其加工硬化机制、微观组织特征有所不同.