基于热加工图的TiNiNb合金高温塑性研究

采用热模拟压缩试验研究铸态TiNiNb合金在变形温度为700～1050℃、应变速率为0.01～10s-1条件下的热变形特征,基于试验结果建立了铸态TiNiNb合金的热变形本构方程.根据动态材料模型,计算并分析合金的热加工图.利用热加工图确定热变形的流变失稳区,并且获得了试验参数范围内热变形过程的最佳工艺参数,加热温度为750～880℃、应变速率为0.3～10s-1,或者加热温度为880～950℃、应变速率为0.01～0.5 s-1.     

TiB_2/7055Al原位合成铝基复合材料高温变形行为与热加工性能

采用Gleeble-1500热模拟机进行热压缩实验,研究变形温度为300～450℃、应变速率为0.01～10s-1时TiB2/7055Al原位合成铝基复合材料的热变形行为。结果表明:热变形过程流变应力可用双曲正弦本构方程来描述,平均变形激活能为158.3kJ/mol,根据材料动态模型,计算并分析TiB2/7055Al的加工图。利用加工图确定热变形的流变失稳区,获得试验参数范围内的热变形过程最佳工艺参数,其热加工温度范围在430～450℃,应变速率范围为10～3.16s-1和0.032～0.01s-1的两个区域。     

变形态Ti40合金高温变形行为

在GLEEBLE热模拟试验机上对变形态Ti40合金进行热压缩实验,采用基于Prasad准则的加工图技术,研究变形态Ti40合金在变形温度950℃～1100℃、应变速率0.001s-1～1.0s-1范围内的微观变形机制和流变失稳现象,并优化该合金的高温变形参数。结果表明,失稳区出现在低温、高应变速率区,当变形温度为950℃～1010℃、应变速率0.13s-1～1.0s-1时,失稳区会出现局部流动,在实际热加工时应尽量避开这一参数范围;变形温度950℃～1100℃、应变速率0.001s-1～0.01s-1为较佳的变形参数范围,其变形机制以动态再结晶为主,伴随动态回复,最佳的变形参数位于温度1050℃、应变速率0.001s-1附近,该区域发生了完全动态再结晶;除失稳区和较佳变形区以外的区域,变形机制以动态回复为主,伴随动态再结晶,是可加工的区域。     

2618铝合金的热变形和加工图

在Gleeble-1500D热模拟仪上进行热压缩实验,研究了变形温度为573～773 K、应变速率为0.01～10s-1时2618铝合金的热变形行为.热变形过程中的稳态流变应力可用双曲正弦本构关系式来描述,平均激活能为181 kJ/mol,大于其自扩散激活能.根据材料动态模型,计算并分析了2618铝合金的加工图.利用加工图确定了热变形的流变失稳区,并且获得了试验参数范围内的热变形过程的最佳工艺参数,其热加工温度为623～723 K,应变速率为0.01 s-1,温加工温度为573 K左右,应变速率为0.01 s-1.     

基于神经网络的7055铝合金流变应力模型和加工图

在Geeble-1500热模拟机上对7055铝合金进行热压缩试验,基于热压缩试验数据,建立流变应力的反向传播(BP)神经网络预测模型和加工图。结果表明:用人工神经网络能更精确地预测热压缩过程中的流变应力,预测精度明显高于线性经验公式的;通过预测模型可以获得样本数据值范围内的非样本数据变形条件下的流变应力,其预测结果充分反映该合金的高温变形特征;在本实验条件下,7055铝合金在高温变形时存在一个失稳区,即变形温度在实验温度范围内应变速率为0.025s-1以上的区域;在375～425℃的范围内,应变速率小于0.001s-1的区域,最大功率耗散系数为0.45;EBSD技术分析表明在安全区发生部分动态再结晶。利用加工图确定了热变形时的流变失稳区,并且获得了试验参数范围内热变形的最佳工艺参数,其热加工温度为350-430℃低应变速率区。     

Cu-Cr-Zr合金的高温热压缩变形行为

采用Gleeble-1500D热模拟试验机,对Cu-Cr-Zr合金在应变速率为0.001~10 s-1、变形温度为650~850℃的高温变形过程中的变形行为(流变应力和显微组织)进行研究。根据动态材料模型计算并分析该合金的热加工图,并结合变形显微组织观察确定该合金在实验条件下的高温变形机制及加工工艺。结果表明:流变应力随变形温度的升高而减小,随应变速率的提高而增大。从流变应力、应变速率和温度的相关性,得出该合金高温热压缩变形时的热变形激活能(Q)为392.5 kJ/mol,同时利用逐步回归的方法建立该合金的流变应力方程。利用热加工图确定热变形的流变失稳区,并且获得了实验参数范围内热变形过程的最佳工艺参数:温度范围为750~850℃,应变速率范围为0.001~0.1 s-1,并利用热加工图分析了该合金不同区域的高温变性特征以及组织变化。     

ZK31-1.5Y镁合金热变形行为及加工图

研究了ZK31-1.5Y镁合金在变形温度为250~450℃、应变速率为0.001~1 s-1条件下的热压缩变形特性,基于动态材料模型建立了热加工图,并结合真应力-真应变曲线确定了该合金在实验条件下的热变形机制及最佳工艺参数。结果表明:ZK31-1.5Y合金的真应力-真应变曲线主要以动态再结晶和动态回复软化机制为特征,峰值应力和稳态应力随变形温度的降低或应变速率的升高显著增加。合金功率耗散图和失稳图中分别包含了3个效率峰值区和1个马鞍形流变失稳区,峰区效率范围为38%~65%,叠加后形成的加工图给出了实验参数范围内热变形时的最优工艺参数,其热变形温度为350~450℃、应变速率为0.1~1 s-1。当应变量由0.1~0.6逐渐增大时对加工图分布规律影响不大。     

基于热加工图的Cu-Ni-Si-P合金的高温热变形行为

在Gleeble-1500D热模拟试验机上,通过高温等温压缩试验,对Cu-2.0Ni-0.5Si-0.03P合金在应变速率为0.01～5 s-1、变形温度为600～800℃的动态再结晶行为以及组织转变进行了研究。结果表明:在应变温度为750、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。同时从流变应力、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热变形激活能(Q)为485.6 kJ/mol和热变形本构方程。根据动态材料模型计算并分析了该合金的热加工图,利用热加工图确定热变形的流变失稳区,并且获得了试验参数范围内热变形过程的最佳工艺参数,温度为750～800℃,应变速率范围为0.01～0.1 s-1,并利用热加工图分析了该合金不同区域的高温变性特征以及组织变化。     

TiC颗粒增强钛基复合材料的热变形行为研究

在Gleeble-1500热模拟试验机上进行热压缩试验,研究了变形温度为900～1150 ℃,应变速率为0.001～10 s-1的TiC颗粒增强钛基复合材料的热变形行为.根据所得应力应变曲线分析了该合金的热变形特征,计算了α+β区域的平均变形激活能为799 kJ/mol,β区域平均变形激活能为105 kJ/mol.并根据动力学模型建立了加工图,分析了加工图中的高功率耗散区和流变失稳区,确定了不同区域的变形机制.观察了变形后的显微组织.结果表明:在温度范围为900～980 ℃,应变速率范围为0.001～0.1 s-1的低应变速率区域发生了超塑性和动态再结晶;在温度范围为1000～1100 ℃,应变速率范围为0.1～10 s-1的高应变速率区域变形机制主要是由亚晶界迁移扩散控制的动态再结晶.两个流变失稳区分别发生在温度为900～950℃,应变速率为0.1～10 s-1的区域和温度为1080～1130 ℃,应变速率为0.001～0.01 s-1区域.     

基于加工图的6082铝合金热成形性能

在Gleeble-1500热模拟试验机上对6082铝合金进行多组热压缩试验,得到6082铝合金在350~500℃和0.01~5 s-1条件下的流变应力数据。根据试验数据建立基于动态材料模型的6082铝合金热加工图,结合压缩变形后的微观组织观察分析,最终获得试验参数范围内6082铝合金热变形的最佳工艺参数。结果表明:保持较高功率耗散效率的加工安全区集中在变形温度430~490℃、应变速率0.1~0.3 s-1的区域,该区域成形时合金主要发生动态再结晶。根据热加工图及微观组织分析,建议在温度440~480℃、应变速率0.1~0.2 s-1范围内选择6082铝合金热成形的工艺参数。     

铝合金汽车中间轴螺塞半固态触变模锻研究

对Y112铝合金进行半固态触变模锻实验，确定了该试验最优的半固态二次加热工艺参数。研究表明，模锻后零件中的晶粒基本保持了半固态成形前坯料的颗粒状，说明在触变成形过程中坯料的流动方式是以液相包裹着同相颗粒的方式进行的。并将数值模拟数据与实验成形力曲线比较，结果二者数值和变化趋势基本吻合，说明数值模拟能够为分析整个锻造过程提供有效的依据，能够从结果中获得较为符合实际的材料流动规律和塑性行为。     

Conception of tooling adapted to thixoforging of high solid fraction hot-crack-sensitive aluminium alloys

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.7<?_s<1), which involves the processing of alloys in the semi-solid state. Tooling has to be adapted to this particular process to benefit shear thinning and thixotropic behaviour of such semi-solid material. Tooling parameters, such as the forming speed and tool temperature, have to be accurately controlled because of their influence on thermal exchanges between material flow and tool. These thermal exchanges influence the high-cracking tendency and the rheology of the semi-solid material during forming, which affects parts properties and therefore their quality. Extrusion tests show how thermal exchanges influence quality of thixoforged parts made of 7075 aluminium alloys at high solid fraction by modifying process parameters like forming speed, tool temperature and tool thermal protector. Thus an optimum in terms of thermal exchanges has to be found between surface quality and mechanical properties of the part. A direct application is the evaluation of surface quality of thixoforged thin wall parts made of 7075 aluminium alloy.     

Microstructural evolution during RAP process and deformation behavior of semi-solid SKD61 tool steel

Semi-solid forming technology has several advantages over the conventional metal forming process owing to the unique behavior and characteristic microstructure of metals in the semi-solid state. With the aim of establishing a shorter process chain for manufacturing the high-quality tools required for forming, the microstructural evolution and basic deformation mechanism of the hot-working tool steel SKD61 in the semi-solid-state were studied experimentally. The feasibility of the recrystallization and partial melting (RAP) process for the fabrication of SKD61 stock with a uniform spherical microstructure was validated. The effects of parameters in RAP processing, such as the predeformation temperature and predeformation ratio, on grain refinement were systematically clarified. Finally, the effects of semi-solid forming parameters, such as the forming temperature, forming ratio and strain rate, on the morphology of the microstructure and the flow stress were also investigated.     

半固态过共晶Al-Si合金的制备技术

论述了半固态过共晶Al-Si合金的制备技术,包括半固态搅拌、喷射沉积与触变成形、双重铸造、变质与等温处理等。这些技术可有效地改善初晶Si形态,细化初晶Si,获得一定量的球状α相,并控制浆料中的固相率,使合金具有预期的半固态组织。     

Deformation mechanism and forming properties of 6061Al alloys during compression in semi-solid state

The 6061 semi-solid aluminium alloy feedstocks prepared by near-liquidus casting were compressed in semi-solid state by means of Gleeble-3500 thermal-mechanical simulator. The relationship between the true stress and the true strain at different temperatures and strain rates was studied with the deformation degree of 70%. The microstructures during the deformation process were characterized. The deformation mechanism and thixo-forming properties of the semi-solid alloys were analyzed. The results show that the homogeneous and non-dendrite microstructures of semi-solid 6061Al alloy manufactured by near-liquidus casting technology could be transformed into semi-solid state with the microstructure suitable for thixo-forming which are composed of near-spherical grains and liquid phase with eutectic composition through reheating process. The deformation temperature and strain rate affect the peak stress significantly rather than steady flow stress. The resistance to deformation in semi-solid state decreases with the increase of the deformation temperature and decrease of the strain rate. At steady thixotropic deformation stage, the thixotropic property is uniform, and the main deformation mechanism is the rotating or sliding between the solid particles and the plastic deformation of the solid particles.     

On the microstructure formation in chromium steels rapidly cooled from the semi-solid state

Semi-solid metal forming requires precise knowledge concerning the microstructural parameters in the mushy state. For many light metals, the liquid and solid fraction and the size, shape and contiguity of the solid phase can be evaluated easily in the “quenched from the freezing range” condition. For iron-based alloys, however, determining them is more difficult or even impossible because steels may undergo different phase-transformations during cooling. Due to the high processing temperatures, diffusion during quenching is also of more importance. Here we describe the phase formation during rapid cooling from the semi-solid state of two different steel grades, tool steel X210CrW12 and bearing steel 100Cr6. For both of these steels the microstructure in the as-quenched state does not directly reflect the condition in the semi-solid state, and thus no metallographic evaluation of the microstructural parameters is possible. It is also shown here that the microstructure of semi-solid processed steels is completely different from that of the conventionally treated species.     

A356铝合金轮毂半固态挤压铸造成形数值模拟

通过建立A356铝合金的半固态表观粘度模型,采用计算机模拟方法对A356铝合金轮毂半固态挤压铸造成形工艺进行了研究.通过分析挤压速度、半固态浆料充填温度及模具预热温度对铝合金轮毂半固态成形性能的影响,探讨了不同条件下的金属流动特点和温度分布规律.结果表明,对该尺寸铝合金轮毂的最佳成形工艺:半固态浆料充填温度为600℃,模具预热温度为300℃,挤压速度为5 mm/s,保压时间为25 s.     

半固态材料成形评述

半固态加工与固态加工、液态加工同属金属加工领域,是金属材料热加工的新兴技术。主要介绍了半固态加工 的应用及未来发展趋势,以期推动其理论研究和工业发展。     

Hot Deformation Behavior of an Ultra-High-Strength Fe–Ni–Co-Based Maraging Steel

Hot processing behavior of an ultra-high-strength Fe–Ni–Co-based maraging steel was studied in temperature range of 900–1200 °C and strain rate range of 0.001–10 s~(-1). Deformation processing parameters and optimum hot working window were characterized via flow stress analysis, constitutive equation construction, hot processing map calculation and microstructure evolution, respectively. Critical strain value for dynamic recrystallization was determined through theoretical mathematical differential method: the inflection point of θ–σ and -αθ/ασ-σ curves. It was found that the flow stress increased with the decrease in deformation temperature and increase in the strain rate. The power dissipation maps in the strain range of 0.1–0.6 were entirely similar with the tendency of contour lines which implied that strain had no strong effect on the dissipation maps. Nevertheless, the instability maps showed obvious strain sensitivity with increasing strain, which was ascribed to the flow localization and instability. The optimized hot processing window of the experimental steel was obtained as 1100–1200 °C/0.001–1 s~(-1) and 1000–1100 °C/0.001–0.1 s~(-1), with the efficiency range of 20–40%. Owing to high Mo content in the experimental steel, high dynamic activation energy, Q = 439.311 kJ mol~(-1), was achieved, indicating that dynamic recrystallization was difficult to occur in the hot deformation process, which was proved via microstructure analysis under different hot deformation conditions.     

高固相率半固态镁合金触变成形数值模拟

对高固相率半固态镁合金触变成形过程进行数值模拟,分析了成形过程中的应力、应变分布和温度场,对比了半固态坯料与常规态坯料成形的特点.结果表明,半固态镁合金材料具有变形抗力小,应力、应变分布均匀的特点,材料流动性、充填性能优于常规坯料,能够一次成形复杂形状零件.数值模拟为半固态成形工艺参数的优化起到很好的参考作用.