Superplastic behavior of TiAl based alloy at relatively low temperatures ranging from 800℃ to 1075℃

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GRAIN BOUNDARY CHARACTER DISTRIBUTION, TEXTURE AND SUPERPLASTIC DEFORMATION BEHAVIOR OF AN AI-Li ALLOY

The grain boundary character distribution and thetexture of 2091 Al-Li alloy recrystallized at different temperatures were measured by TEM and X-ray techniques respectively. The occurrence frequency of low-energy boundaries decreases with increasing recrystallization temperature, while the frequency of highenergy boundaries increases. The strongest component of recrystallization texture in the test temperature range is {011} <111>. The relative intensity of the texture tends to decrease with increasing recrystallization temperature. The material which contains a high frequency of low-energy boundaries exhibits lower deforming stress and high elongation.     

Calculation of free energy of Al-Cu-Li alloy under electric field

Based on Thomas-Fermi model, the interior potential boundary condition with the effect of electric field was defined, the calculation method of free energy for atom cluster under electric field was established. The change of free energy of Al-Cu-Li alloy under the effect of electric field was calculated quantitatively. It is shown that： near the zero electric field and the side of positive electric field, the free energy of Cu4LiAl7 compound at aging temperature 460 K is higher than that of free energy at solid solution temperature 725 K, but once the negative electric field increases to certain degree there will be opposite result. Under the effect of electric field, at 725 K the free energy of Cu4LiAl7 is higher than that of Al-1.0%Li-4.0%Cu, and at 460 K the free energy of compound is lower than that of solid solution. When the copper content in the Al-Li-Cu solid solution is below 5%, under the effect of electric field the free energy of solid solution increases gradually with the increasing of copper content, but the increasing amplitude reduces with the increasing of copper content. The free energy of binary solid solution increases with the addition of lithium, and with the increasing of electric field intensity the free energy margin of two kinds of solid solution becomes bigger.     

Superplastic characteristics of fine-grained 7475 aluminum alloy

A 7475-aluminum alloy was subjected to a thermomechanical heat treatment that resulted in a final recrystallized grain size on the order of 10 μm. Tensile specimens of dimensions 10 × 4 × 2.3 mm were machined such that the tensile axis was parallel to the rolling direction. Tensile tests were carried out at high temperatures in the range of 773 to 803 K at different cross-head speeds corresponding to initial strain rates in the range of 10⁻⁴ to 10⁻² s⁻¹. Elongations of several hundred percent were observed at strain rates of <10⁻³ s⁻¹. The correlation between flow stress and strain rate suggests that the strain rate sensitivity m is close to 0.5 at the lower strain rates. The value of m decreases to ≈0.2 at high strain rates. The decrease in m suggests a transition in the rate-controlling process from superplastic deformation (m ≈ 0.5) to dislocation creep (m ≈ 0.2) with increasing strain rate. The calculated activation energies in the two deformation regions are consistent with the suggested rate-controlling processes.     

工业态AZ31镁合金的超塑性变形行为

研究了工业态AZ31镁合金在温度 6 2 3～ 72 3K和应变速率 1× 10 -5～ 1× 10 -3 s-1范围内的超塑性变形行为。结果表明 ,工业态AZ31镁合金表现出良好的超塑性 ,其最高断裂延伸率达到 314%,应变速率敏感指数达 0 .4。显微组织观察和断口分析表明 ,工业态AZ31镁合金超塑变形主要由晶界滑动机制所控制 ,同时 ,动态再结晶也是合金超塑变形的一种协同机制。     

Al-Cu-Li合金电子束焊接头的耐蚀性能

研究了新型Al-Cu-Li合金电子束焊接头的晶间腐蚀和剥落腐蚀行为。利用金相显微镜观察分析接头不同区域的晶间腐蚀IGC(Intergranular Corrosion)及剥蚀EXCO(Exfoliation Corrosion)形貌,并测量其最大晶间腐蚀深度。结果表明,在IGC溶液中浸泡24 h后,母材发生严重孔蚀,腐蚀深度较深;焊缝区发生局部网络状晶间腐蚀;热影响区观察到少量的晶间腐蚀现象。在EXCO溶液中浸泡96 h后,母材发生了严重剥落腐蚀,热影响区发生轻微的剥蚀,焊缝未发生剥蚀。     

Zn-5Al共晶合金的恒载荷超塑性拉伸试验

用恒载荷法研究了Zn－5Al共晶合金的超塑变形特性，测定了应变速率敏感指数m值和超塑变形激活能Q。结果表明，Zn-5Al共晶合金在恒载荷条件下，不同的应变值对应不同的应变速率敏感指数m，随应变速率的增加m值半大，而超塑性流动的粘滞系数η值减小；超塑拉伸前对轧态试样进行保温处理将增加变形抗力和降低伸长率。这是由于合金在保温处理过程中通过回复和再结晶释放了储能，降低了超塑变形动力的缘故。     

一种新型Al-Cu-Li合金性能研究

摘 要: 设计一种新型Al-Cu-Li-Mg-Ag合金,探索热处理制度对新合金拉伸性能及裂纹扩展性能的影响,利用光学显微镜、透射电镜和扫描电镜等手段研究合金微观组织及断口形貌。研究结果表明：该新型铝锂合金经过540℃固溶1小时,（12?AaRT（5d） 145℃（20h））双级时效热处理后获得良好的综合性能：抗拉强度σb =443Mpa,屈服强度σ0.2 =397Mpa,延伸率δ=16.5%,裂纹扩展速率da/dn≈1.34*10-3mm/cycle（△K=30 Mpa*m1/2）。双级时效态下析出大量细小均匀的T1相,在保证合金强度的同时,提高合金的抗疲劳裂纹扩展性能。T8态下析出相对粗大的T1相,θ′相和极少量的S′相,合金强度达到项目要求,抗疲劳裂纹扩展性能较差。T3态下析出相数量少,合金强度不满足项目指标。     

Effects of strain accumulation on the superplastic deformation behavior of 7075 Al alloy

The superplastic deformation behavior of a fine-grained 7075 Al alloy has been investigated within the framework of an internal variable theory for inelastic deformation. The theory takes the dislocation glide process within and across the grain boundaries (grain matrix deformation (GMD)) as the major accommodation mechanism for the grain boundary sliding (GBS). The flow curves were obtained by performing a series of load relaxation tests at the various prestrain values to examine the effects of accumulated strain on the superplastic deformation behavior. The most significant result obtained in this study is that the grain boundary characteristics change gradually with the strain accumulation from an initially Newtonian viscous flow signified with the power index value of M _g =1 to a non-Newtonian flow with the value of M _g =0.5 commonly observed in the various microduplex alloys such as Ti-6Al-4V. The variation of GBS characteristics with the prestrain is then examined by observing the microstructural evolution with the strain through the use of transmission electron microscopy (TEM).     

TA32钛合金超塑性变形行为及本构模型研究

通过单向拉伸实验研究了TA32钛合金在温度880~940 ℃、初始应变速率5×10-4~1×10-2 s-1条件下的超塑性变形行为和微观组织演变,构建了修正Johnson-Cook本构模型和BP神经网络本构模型。结果表明,TA32钛合金的流动应力与断后伸长率对温度和应变速率敏感,应变速率敏感性指数随应变量增加而减小,随温度升高而增大。温度升高和变形程度增大促进了α→β相转变和两相晶粒长大,应变速率降低使得两相晶粒有所长大。β相晶粒形貌随变形条件改变有显著变化,α相晶粒则保持等轴状。TA32钛合金的超塑性断裂模式为孔洞生长扩展导致的微孔聚集性断裂。相较于修正Johnson-Cook本构模型,BP神经网络本构模型在大范围变形条件下的预测精度更高。     

Continuous cooling transformation curve of a novel Al-Cu-Li alloy

1 Introduction Al-Li alloy is perspective for wide applications in aircraft industry. It has an attractive combination of medium strength with good plasticity, fracture toughness, corrosion resistance and weldability[1- 3]. Continuous cooling transformati…     

供应态LY12CZ铝合金在超塑性形变中晶界形态的研究

采用光学显微镜、扫描电镜和透射电镜对未经任何预处理、晶粒尺寸为19μm～21μm之间的供应态LYl2CZ铝合金超塑性形变中晶界形态进行了观察、分析。结果表明，此状态下的铝合金在超塑性变形过程中晶界宽度和形态会发生改变。在较大伸长率的条件下，晶界出现宽边化和圆弧化。在超塑性变形过程中形成的宽边晶界属于介稳状态的界面，在高温下短时间保温，宽边晶界会发生晶化，变成细小的普通晶界。试样在超塑性变形时产生的伸长率与晶界宽度有密切联系。在此次试验中超塑性伸长率大的试样其晶界宽度在2．1μm～2．7μm之间。     

Improvement of strength and ductility of Al-Cu-Li alloy through cryogenic rolling followed by aging

To develop an improved approach in achieving an excellent combination of high strength and ductility, the solutionized Al-Cu-Li plates were subjected to rolling at cryogenic and room temperatures, respectively, to a reduction of 83%, followed by aging treatment at 160 °C. The results indicate that Al-Cu-Li alloys through cryogenic rolling followed by aging treatment possess better mechanical properties. Rolling at cryogenic temperature produces a high density of dislocations because of the suppression of dynamic recovery, which in turn promotes the precipitation of T₁ (Al₂CuLi) precipitates during aging. Such high density of T₁ precipitates enable effective dislocation pinning, leading to an increase in strength and ductility. In contrast, room temperature rolled alloys after aging treatment exhibit lower strength and ductility due to low density of T₁ precipitates in the grain interior and high density of T₁ precipitates around subgrain boundaries.     

Al-Cu-Li合金均匀化处理参数优化和微观组织演化

摘 要：对Al-Cu-Li铸态合金进行单级和双级均匀化处理,通过光学显微镜（OM）、扫描电镜（SEM）、能谱分析（EDS）、X衍射（XRD）和差热分析（DSC）研究合金元素分布和微观组织演化,结果表明：Al-Cu-Li合金铸态组织存在严重枝晶偏析,由晶内到晶界Cu元素分布十分不均匀,Mg、Zn、Mn和Ag变化不明显。晶界处存在大量的非平衡共晶相,主要包括Al2Cu、含有少量Mg元素的Al2Cu相,以及Al2CuMg相。经双级均匀化（495℃×24h 515℃×24h）处理后,大部分非平衡共晶相和部分第二相（Al2CuMg和Al2CuLi）溶解到合金基体,但仍有部分富-Fe和富-Mn相残留在晶界不能回溶。Al2CuMg相的熔点低于Al2Cu相,两者分别在495℃和515℃先后溶解。通过均匀化动力学分析,确定Al-Cu-Li铝锂合金最佳的均匀化制度为495℃×24h 515℃×24h,该双级均匀化制度与动力学分析结果一致。     

Al-Cu-Li合金搅拌摩擦焊接头的微观组织和力学性能

采用搅拌摩擦焊方法对2mm厚的Al-Cu-Li合金轧制板进行了焊接.接头内形成了焊核区、热机影响区和热影响区.焊核区由细等轴再结晶组织构成;热机影响区内的组织发生较大的弯曲变形,并在热循环的作用下发生了回复反应;热影响区形成了粗大的板条状组织.实验结果表明:在200mm/min的焊接速度下,接头的拉伸强度最高,达到393MPa,断裂形式为韧性和脆性的混合型断裂;在500mm/min的焊接速度下,接头强度为267.7MPa,断裂形式为脆性断裂.     

高温下Al3Zr颗粒对Al-Cu-Li基合金的热变形行为以及加工图的影响(英文)

采用等温平面压缩试验研究Al3Zr颗粒在不同温度(400⁵00°C)以及应变速率(0.01¹0s^-1)条件下对Al-Cu-Li基合金热压缩行为以及加工图的影响。通过金相观察(OM)、电子背散射衍射(EBSD)以及透射电镜(TEM)系统地表征不同变形条件下合金的显微组织。结果表明,在软化过程中相对于动态再结晶,动态回复起主导作用。在低温条件下,亚稳态Al₃Zr颗粒能够有效抑制动态回复以及动态再结晶的长大。当温度达到500°C时,晶界附近的Al₃Zr颗粒发生熔解,随Zr元素在晶界快速扩散,Al₃Zr颗粒在晶界再次析出,并呈链状分布。这些链状分布的Al₃Zr颗粒在热变形过程中导致宏观裂纹,在加工图中形成不安全区域(490⁵00°C,0.01 s^-1)。     

Zn-2.5Al合金超塑变形的研究

用恒载荷和恒速度蠕变法研究了 Zn- 2 .5Al合金的超塑变形特性 ,测定了 Zn- 2 .5Al合金的应变速率敏感指数 m值和超塑变形激活能 Q值。     

大晶粒FeAl合金超塑性变形的显微组织演变和变形激活能

本文对大晶粒ＦｅＡｌ金属间化合物塑性变形的微观组织演变进行了研究，并测定了其超塑性变形激活能，显微组织分析表明，合金的超塑性变形是一个晶粒变形，内部形成亚晶界，进而亚晶界向晶界转换，从而使晶粒得以细化的过程，Ｆｅ－３６．５Ａｌ，Ｆｅ－３６．５Ａｌ－１Ｔｉ和Ｆｅ－３６．５Ａｌ－２Ｔｉ合金变形激活能的测定值分别为３７０，２９０和２６０ｋＪ．ｍｏｌ＾－１大大低于其他的ＦｅＡｌ基合金蠕变激活能，表明超塑性     

Superplasticity in fine-grained AZ61 magnesium alloy

The effect of grain refinement on the superplasticity of ingot-processed magnesium alloy was investigated. From the AZ61 material with a linear intercept grain size of 5 μrn, which was obtained by the multi-rolling process at an elevated temperature, tensile elongation over 400% could be achieved at 10^-3s^-1 at 400°C with a maximum value of 560% at 2x10^-4s^-1 at the same temperature. It was found that grain boundary diffusion controlled grain boundary sliding and pipe diffusion controlled slip creep govern the plastic flow at low and high strain rate ranges, respectively. A deformation map for pure magnesium was constructed to examine the effect of grain size and flow stress on deformation behavior at elevated temperature. The superplastic formability of Mg alloys was demonstrated by forming an AZ61 sheet into a hemi-sphere.