供应状态LY12CZ硬铝合金的动态再结晶与超塑性研究

本文对供应状态LY12CZ硬铝合金在未经任何超细预处理的情况下进行了超塑性变形的力学特性、显微组织方面的研究。确认LY12CZ硬铝合金在等温压缩变形中发生了动态再结晶,动态再结晶会诱发超塑性,使用新研制的D润滑剂,使其能在快速成形时有较好的超塑性能,在实际生产中有推广应用价值。     

超硬铝 LC9的动态组织超塑性

采用简化的预处理工艺,使 LC9在较宽的温度和速率区间内产生超塑性效应。在最佳变形条件(693K,1.67×10~(-3)S~(-1))下,延伸率为220%,m 值为0.4,流动应力30MPa。LC9的超塑性效应是动态的组织超塑性,主要微观过程是动态再结晶诱发晶界滑移。预处理的简化原则是能够造成亚晶细化和强化相的弥散分布。     

供应状态铝合金LF6的超塑效应与动态再结晶

本文研究了经简单预处理的供应状态铝合金LF6热变形中动态再结晶及其导致的超塑效应。认为在一定温度下使合金的应变速率与动态再结晶速度相协调,可以提高合金的工艺塑性,降低变形抗力,获得超塑效应。本文包括下列内容:拉伸试验的超塑效应;压缩变形时温度、应变速率对合金的塑性和变形抗力,组织和性能影响的研究;利用偏振光显微镜和透射电子显微镜对再结晶组织的研究。     

碳化硅增强LY12铝基复合材料的超塑性

本文研究了以搅拌铸造法生产的碳化硅颗粒增强LY12铝基复合材料(SiCp/LY12)的超塑性预处理工艺及超塑性变形条件。经均匀化退火—热反挤压—温轧—再结晶预处理后,SiCp/LY12复合材料具有较好的超塑性。在T=793K、ε₀=6.4×10-4S-1的变形条件下,其最高延伸率达293%。并探讨了碳化硅颗粒在超塑性预处理及超塑性变形中的作用。     

超塑性形变中的晶界形变化及再结晶的作用

为了研究晶界形态及动态再结晶在超塑性形变中的作用，采用光学显微镜、扫描电镜，透射电镜，对硬铝ＬＹ１２的超塑性形过程进行了观察，分析，提出金属材料的超塑性主要依靠晶界流态化区的粘性变形来实现，动态再结晶不是超塑性的一种机制。     

超塑性形变中的晶界形态变化及再结晶的作用

为了研究晶界形态及动态再结晶在超塑性形变中的作用,采用光学显微镜、扫描电镜、透射电镜,对硬铝ＬＹ１２ 的超塑性形变过程进行了观察、分析．提出金属材料的超塑性主要依靠晶界流态化区的粘性变形来实现,动态再结晶不是超塑性的一种机制．     

超硬铝LC9超塑变形机理的研究

本文研究了超硬铝LC~9在超塑变形过程中变形机理的转化。热变形激活能Q值随应变量的增加而下降,应变速率敏感性指数m值随应变量的增加而上升,表明了变形机理由晶内滑移转变为晶界滑移为主。显微观察表明:)动态再结晶造成晶粒的微细化;)晶内位错密度相对减少,晶界附近位错密度相对增加,发生了以动态再结晶为主的软化过程,但该过程受到弥散分布的强化相质点的抑制,引起显微组织的等轴微细化,从而导致以晶界滑移为主的变形过程,即动态再结晶诱发微细晶粒超塑性。     

LF6防锈铝的再结晶诱发塑性

本文研究了 LF6防锈铝在预加弹性应力作用下,再结晶诱发塑性(RIP)现象,对 RIP 试验的δ-T 曲线的分析和特征点的 TEM 观察表明,该合金冷变形组织在弹性应力作用下加热过程中产生的宏观塑性流变,是再结晶诱发塑性的结果,初步探讨了该合金的高温拉伸性能和再结晶诱发塑性的机理。     

热轧态Al-Li合金的超塑性研究

本研究运用动态再结晶诱发超塑性的原理,对未经细化晶粒预处理的常规生产热轧态2091Al-Li合金直接进行高温拉伸,试验结果表明合金在470～530℃温度范围和2×10~(-4)～1×10~(-3)应变速率范围内具有超塑性,最大断裂延伸率达405％。根据光镜和电镜组织观察和真应力—真应变曲线的单一峰值和变形激活能随应变量增大而下降等特征,讨论了动态再结晶诱发超塑性的机制。     

FGH96合金热挤压棒材超塑性研究

对热挤压FGH96合金棒材超塑性进行了研究,结果表明:挤压FGH96合金在1050℃和1100℃的变形温度下具有良好的超塑性,在变形温度为1100℃初始应变速率为3.33×10-4s-1进行超塑拉伸时,伸长率可以达到405%,流变应力降低到32MPa。显微组织分析表明,FGH96合金经控制冷却速度的预热处理后,合金中γ′相尺寸及间距较大,能够促进合金在后续变形过程动态再结晶的发生,并阻碍晶粒快速长大。FGH96合金在挤压变形后发生了明显的动态再结晶,但由于再结晶进行的不充分,晶粒内部仍存在大量变形亚结构,这种亚稳态组织在超塑变形过程中通过进一步回复和再结晶,可以获得平均晶粒尺寸为10μm左右的等轴、均匀、稳定的细晶组织,使合金具有良好的超塑性。     

强电场对摩擦焊接头组织与性能的影响

为提高摩擦焊缝金属的变形能力，采用外加电场考察了摩擦焊缝金属的电塑性效应，利用金属组织观察、显微硬度测试及抗拉试验，定量分析了外加强电场对LY12铝合金摩擦焊缝组织与力学性能的影响，结果表明：外加强电场使焊缝金属组织轴向分布梯度减小，等轴性提高；不同焊接压力时，强电场使焊接接头的动态再结晶区宽度有不同程度的增大；在中等摩擦压力作用下，使近轴心线处的动态再结晶区宽度趋干均匀；此外，外加电场使接头焊合区硬度增加，并使焊接接头的硬度分布趋干均匀；采用强规范施焊时，外加电场提高了焊接接头的抗拉强度。     

挤压工艺对Mg-0.6Zr-0.5Y合金力学和阻尼性能的影响

系统地研究了挤压温度和挤压比对Mg-0.6Zr-0.5Y合金力学和阻尼性能的影响规律.采用光学金相显微镜、电子式万能试验机及动态机械分析仪(DMA)等手段分析合金显微组织、力学和阻尼性能的变化,并讨论了晶粒细化与合金力学和阻尼机理之间的内在联系.研究发现,合金在挤压过程中发生了动态再结晶,晶粒显著细化,使综合力学性能得...     

Mg-9Al-3Si-0.375Sr-0.78Y合金的热变形行为及本构模型

利用Gleeble-3500热模拟试验机对Mg-9Al-3Si-0.375Sr-0.78Y合金试样进行等温恒应变速率压缩实验,研究其在温度250~400℃、应变速率0.001~10s~(-1)条件下的热变形行为。结果表明:在热变形过程中,峰值应力随着应变速率的降低和温度的升高而减小,且峰值应力对应变速率的敏感性随着变形温度的下降而增强。建立了考虑应变的热变形Arrhenius本构模型,模型精度良好,在300,350℃及0.001~10s~(-1)范围内,模型的平均绝对误差分别为1.57%和1.76%;合金的平均变形激活能为183.58k J/mol,平均应变速率敏感指数为0.1616。热变形过程中,α-Mg相呈现明显的动态再结晶特征,β-Mg₁₇Al₁₂相尺寸减小且分布均匀,初生Mg_2Si相较小。在低温(250~300℃)变形时,动态再结晶仅发生在晶界处。在高温(350~400℃)变形时,初生α-Mg晶粒发生了明显的动态再结晶。随着温度的增加和应变速率的降低,再结晶程度提高,再结晶晶粒逐渐长大。     

霍普金森拉杆装置螺纹过渡段变形测量修正

基于经典三波法理论,提出了一种适用于分离式霍普金森拉杆实验装置的动态拉伸变形测量修正方法。该方法可有效避免入射杆、透射杆和试件之间的螺纹连接以及过渡段对拉伸试验结果造成的信号干扰。同时用LY12铝合金进行了霍普金森杆动态拉伸与压缩(SHTB/SHPB)试验,采用所提出的修正方法对LY12铝合金动态拉伸试验变形数据进行了修正;经过与压缩试验结果的比较分析验证了该文所提修正方法的合理性与适用性,并据此对拉伸试件外形给出了建议。     

Dynamic recrystallization behavior of a typical nickel-based superalloy during hot deformation

The dynamic recrystallization (DRX) behavior of a typical nickel-based superalloy is investigated by the hot compression tests. Based on the conventional DRX kinetics model, the volume fractions of DRX are firstly estimated. Results show that there is an obvious deviation between the experimental and predicted volume fractions of DRX when the forming temperature is below 980 °C, which is induced by the slow dynamic recrystallization rate under low forming temperatures. Therefore, the segmented models are proposed to describe the kinetics of DRX for the studied superalloy. Comparisons between the experimental and predicted results indicate that the proposed segmented models can give an accurate and precise estimation of the volume fractions of DRX for the studied superalloy. In addition, the optical observation of the deformed microstructure confirms that the dynamically recrystallized grain size can be well characterized by a power function of Zener–Hollumon parameter.     

Effects of holding time and Zener-Hollomon parameters on deformation behavior of cast Mg-8Gd-3Y alloy during double-pass hot compression

Double-pass hot compression tests were carried out over a wide range of holding time (0–180?s) and Zener-Hollomon parameter (1.6E15–1.3E20) to study the deformation behavior of cast Mg-8Gd-3Y alloy. The flow curves show obvious work hardening and strain softening stages, leading to the peak stress of double-pass hot compression. Holding time and Zener-Hollomon parameter can significantly affect the second pass peak stress. It is found that increasing the holding time can cause a higher peak stress in the second pass deformation. The second pass stress reaches the peak stress of 71?MPa at Zener-Hollomom parameter of 1.6E15. When the parameter rises to 1.3E20, the second pass peak goes up to 237?MPa. In addition, the second pass peak stress is significantly higher than the unloading stress, which is opposite to the flow behavior of aluminum alloys. Residual stored deformation energy caused by the first pass deformation could be consumed by metadynamic recrystallization. Therefore, more strain energy is required for subsequent dynamic recrystallization, resulting in hardening behavior. A hardening fraction is defined to describe the deformation behavior quantitatively, which shows a positive correlation with the metadynamic recrystallization fraction. The metadynamic recrystallization leads to grain growth at the inter pass holding stage, diminishing dynamic recrystallization nucleation positions in the second pass deformation.     

Microstructural features of dynamic recrystallization in alloy 625 friction surfacing coatings

In friction surfacing (FS), material is deposited onto a substrate in the plasticized state, using frictional heat and shear stresses. The coating material remains in the solid state and undergoes severe plastic deformation (SPD) at high process temperatures (≈0.8 T_melt), followed by high cooling rates in the range of 30?K/s. Dynamic recrystallization and the thermal cycle determine the resulting microstructure. In this study, Ni-based alloy 625 was deposited onto 42CrMo4 substrate, suitable, for instance, for repair welding of corrosion protection layers. Alloy 625 is known to undergo discontinuous dynamic recrystallization under SPD, and the resulting grain size depends on the strain rate. The coating microstructure was studied by microscopy and electron backscatter diffraction (EBSD). The coatings exhibit a fully recrystallized microstructure with equiaxed grains (0.5–12?µm) and a low degree of grain average misorientation. Flow lines caused by a localized decrease in grain size and linear alignment of grain boundaries are visible. Grain nucleation and growth were found to be strongly affected by localized shear and nonuniform material flow, resulting in varying amounts of residual strain, twins and low-angle grain boundaries in different regions within a single coating layer’s cross section.

FS can be used to study dynamic recrystallization at high temperatures, strains and strain rates, while at the same time materials with a recrystallization grain size sensitive to the strain rate can be used to study the material flow during the process.     

一定条件下Al-Mg-Si-Ti合金动态再结晶的临界应变研究

在变形温度为350~510℃、应变速率为0.001~10s-1条件下,在Gleeble-3500热模拟实验机上对AlMg-Si-Ti合金进行等温热压缩实验,以实验所得数据为基础,结合变形微观组织,确定了Al-Mg-Si-Ti合金热变形时发生动态再结晶的条件,建立了Al-Mg-Si-Ti合金动态再结晶峰值应变模型。采用加工硬化率的方法,利用lnθ-ε曲线的拐点特征和-(lnθ)/ε-ε曲线的极小值判据对再结晶峰值应变与临界应变关系进行了研究。结果表明:AlMg-Si-Ti合金热变形时在变形温度430~510℃、应变速率0.001~0.1s-1发生动态再结晶。Al-Mg-Si-Ti合金发生动态再结晶时的临界应变随应变速率的增大而增加,随变形温度的升高而降低。临界应变与峰值应变满足关系:εc=0.88εp。