合金元素对Al—Li合金组织结构和性能的影响

采用快速冷凝技术制备了四种不同合金系的AL-L i合金粉末,粉体经处理成形制成样品。研究了合金元素Cu、Mg、Zr对合金组织结构和力学性能的影响。讨论了合金元素的作用以及改善合金塑韧性的可能途径。

快速凝固Al—Li合金粉末的除气作用

本文研究了真空加热除气处理对快速凝固Al—Li合金粉末表面氧化层厚度和组成,以及对合金力学性能、断口形貌的影响。试验结果表明,由于Li的存在,除气过程中,Li不断向表面迁移,形成Li_2O,还原Al_2O_3,使表面氧化层厚度增加,组成和性质发生变化。除气处理后,虽然粉末颗粒界面结合状况有较大改善,但拉伸性能变化不大,延伸率略有提高,却很不明显。界面析出相Al_3Zr影响粉末界面结合强度。

Corrosion behavior of 2A97 Al-Cu-Li alloys in different thermomechanical conditions by quasi-in-situ analysis

As a promising material in the aircraft industry,2A97 Al-Cu-Li alloy exhibits high corrosion susceptibility that may limit its application.In the present work,to illustrate the influences of precipitate and grain-stored energy on localized corrosion evolution in 2A97 Al-Cu-Li alloy,cold working and artificial aging were carried out to produce 2A97 Al-Cu-Li alloys under different thermomechanical conditions.Quasi-in-situ analysis,traditional immersion test and electrochemical measurement were then conducted to examine the corrosion behavior of 2A97 alloys.It is revealed that precipitate significantly affects Cu enrichment at corrosion fronts,which determines corrosion susceptibility of alloys,whereas grain-stored energy distribution is closely associated with localized corrosion propagation.It is also indicated that quasi-in-situ analysis exhibits a consistent corrosion evolution with traditional immersion tests,which is regarded as a proper method to explore localized corrosion mechanisms by providing local microstructural information with enhanced time and spatial resolutions.

搅拌摩擦焊接Al-Li合金接头的微观组织及力学性能

采用锥形带螺纹搅拌头搅拌摩擦焊接5 mm厚的Al-Li合金轧制板材,并对接头组织、力学性能及断裂特性进行了研究。结果表明,焊核区组织发生动态再结晶,形成细小的等轴晶晶粒,在等轴晶的晶界处析出大量的偏析相。热影响区组织发生回复和粗化反应,形成粗大的棒状回复晶粒;热机影响区组织发生弯曲变形,但整体上仍保留带状组织形貌,前进侧热机影响区组织变形程度高于后退侧,该区同时还发生回复反应,且后退侧热机影响区内的回复晶粒数量多于前进侧。拉伸实验结果表明,焊接速度v=40 mm/min时,接头强度达到最大值,为345 MPa;v=60 mm/min时,接头延伸率达到最大值,为9.6％。硬度测试结果表明,搅拌摩擦焊接头发生软化,前进侧的软化区宽度大于后退侧。断口形貌分析表明,接头断裂模式为韧-脆混合型断裂。

预变形对含钪Al-Cu-Li合金组织与性能的影响

采用显微组织观察和室温拉伸试验等手段,研究了形变时效中预变形对含钪Al-3.5Cu-1.5Li-0.12Zr合金微观组织与拉伸性能的影响.结果表明:时效前的预变形能促进T1(Al2CuLi)相弥散细小析出,显著提高合金强度,使时效峰值提前.合金强度随预变形量和时效时间增加而增加,到峰值后,随预变形量增加和时效时间的延长,T1相长大粗化,合金强度和塑性降低.在本试验条件下该合金合宜的预变形量为3.5%～5.6%.

微量钪对高Cu/Mg比Al-Cu-Li-Mg合金组织与性能的影响

利用金相显微镜、透射电子显微镜和拉伸试验等手段,研究了微量Sc对高Cu/Mg比Al-3.5Cu-1.5Li-0.5Mg-0.12Zr合金组织和拉伸性能的影响.结果表明:在Al-3.5Cu-1.5Li-0.5Mg-0.12Zr合金中加入0.10%Sc消除了合金铸态枝晶组织,有效抑制合金再结晶,明显提高了合金的强度和塑性,但晶粒细化效果不明显;添加0.15%和0.25%Sc显著细化合金铸态晶粒组织,塑性随Sc增加而提高,但添加0.25%Sc促进合金再结晶,合金强度显著降低.

X射线衍射及散射方法研究Al-Li合金回火相变

采用X射线衍射(XRD)和小角散射(SAXS)技术研究了二元A l-2.70%(w)L i合金的回火相变。XRD结果发现合金190℃回火90、120 m in存在(100)有序化衍射峰;而同时SAXS结果发现回火沉淀相与基体之间有过渡区存在。表明该合金在回火初期存在有序化和调幅分解的共存现象。

快速冷凝Al-Li-Cu-Mg-Zr合金挤压工艺研究

通过对一种Al-Li-Cu-Mg-Zr合金在不同挤压工艺条件下力学性能和微观组织的检测,分析了挤压工艺参数对合金组织性能的影响规律,探讨了使合金获得较好强韧性配合的工艺参数范围。

Al-Li-Cu-Zr合金中T_1相结构、形核和长大机制研究

T_1(Al_2CuLi)相是Al-Li-Cu-Zr合金中的重要强化相。通过TEM在对T1相结构和形貌分析的基础上,构造了T1相的结构。T1相晶核以ABCBA的堆垛顺序,共由36个原子组成,其晶格常数a=0.495nm,c=0.933nm。与基体的位相关系为:狖0001狚T1∥狖111狚α,<1010>T1∥<110>α。合金中铜原子的偏聚降低了基体的层错能,从而为T1相依赖扩散层错形核提供了有利条件。T1相长大依赖于原子扩散和台阶滑移,是一种长程扩散控制的台阶机制。

微量Ag,Mg对Al-Cu-Li合金时效特性和显微组织的影响

研究了微量Ag,Mg对Al-Cu-Li合金显微组织和时效特性的影响。结果表明:单独加Ag对Al-Cu-Li系2197合金的固溶强化效果很小,但有较强的时效强化作用,Ag含量不同,时效强化效果也不同;Ag,Mg共同加入提高了T1相(Al2CuLi)的析出速率和析出密度,使合金具有较大的固溶强化效果及最强烈的时效响应和时效强化效果。Ag,Mg的添加对合金的不同影响可通过溶质原子与空位、溶质原子与溶质原子之间的相互作用来解释。

超轻Mg-Li-Al系变形镁合金冷轧及热处理后的组织和性能

研究了超轻变形镁合金Mg (5% ~ 22%)Li 2%Al冷轧性能,热处理特性以及机械性能。合金的密度为1.206~1.642g/cm3。在室温条件下β相合金(16%和22%(质量分数)Li)具有非常良好的延展性,压下极限可达到90%以上。研究了Mg Li Al 系变形镁合金铸锭经不同温度、时间均匀化退火后的组织性能。对均匀化后的合金锭进行了冷轧,轧后板材在不同温度下进行了退火,研究其再结晶行为及组织性能。结果表明, Mg 9Li 2Al 2Ca合金在573K温度均匀化退火12h后合金铸锭组织均匀,有利于冷轧开坯变形;而对于Mg 9Li 2Al 合金, 523K 温度均匀化退火24h后组织较好。冷轧合金板材在573K温度退火1h 可发生完全再结晶,生成细小均匀的等轴晶组织。

电磁搅拌对Mg-8Li-3Al合金显微组织和力学性能的影响

研究了不同强度的电磁搅拌对Mg-8Li-3Al合金显微组织和力学性能的影响。结果表明,电磁搅拌能改善凝固过程的传热传质,细化枝晶,提高合金的抗拉强度、伸长率和硬度。当施加的电磁场电压为100V时,Mg-8Li-3Al合金的显微组织细小均匀,室温抗拉强度、伸长率和硬度(HB)分别达到212.9MPa、10.5%和71.3,合金的组织和力学性能达到最佳。

High density dislocations enhance creep ageing response and mechanical properties in 2195 alloy sheet

The creep strain of conventionally treated 2195 alloy is very low,increasing the difficulty of manufacturing Al-Cu-Li alloy sheet parts by creep age forming.Therefore,finding a solution to improve the creep formability of Al-Cu-Li alloy is vital.A thorough comparison of the effects of cryo-deformation and ambient temperature large pre-deformation(LPD)on the creep ageing response in the 2195 alloy sheet at 160℃with different stresses has been made.The evolution of dislocations and precipitates during creep ageing of LPD alloys are revealed by X-ray diffraction and transmission electron microscopy.High-quality 2195 alloy sheet largely pre-deformed by 80%without edge-cracking is obtained by cryo-rolling at liquid nitrogen temperature,while severe edge-cracking occurs during room temperature rolling.The creep formability and strength of the 2195 alloy are both enhanced by introducing pre-existing dislocations with a density over 1.4×10^(15)m^(−2).At 160℃and 150 MPa,creep strain and creep-aged strength generally increases by 4−6 times and 30−50 MPa in the LPD sample,respectively,compared to conventional T3 alloy counterpart.The elongation of creep-aged LPD sample is low but remains relevant for application.The high-density dislocations,though existing in the form of dislocation tangles,promote the formation of refined T1 precipitates with a uniform dispersion.

Microstructural evolution of Mg, Ag and Zn micro-alloyed Al-Cu-Li alloy during homogenization

The microstructural evolution of a Mg, Ag and Zn micro-alloyed Al?3.8Cu?1.28Li (mass fraction, %) alloy ingot during two-step homogenization was examined in detail by optical microscopy (OM), differential scanning calorimetry (DSC), electron probe micro-analysis (EPMA) and X-ray diffraction (XRD) methods. The results show that severe dendritic segregation exists in the as-cast ingot. There are many secondary phases, includingTB(Al7Cu4Li),θ(Al2Cu),R(Al5CuLi3) andS(Al2CuMg) phases, and a small amount of (Mg+Ag+Zn)-containing and AlCuFeMn phases. The fractions of intermetallic phases decrease sharply after 2 h of second-step homogenization. By prolonging the second-step homogenization time, theTB,θ,R,S and (Mg+Ag+Zn)-containing phases completely dissolve into the matrix. The dendritic segregation is eliminated, and the homogenization kinetics can be described by a constitutive equation in exponential function. However, it seems that the AlCuFeMn phase is separated into Al7Cu2Fe and AlCuMn phases, and the size of Al7Cu2Fe phase exhibits nearly no change when the second-step homogenization time is longer than 2 h.

Grain structure and microtexture evolution during superplastic deformation of 5A90 Al-Li alloy

The microstructural evolution of banded 5A90 A1-Li alloy during superplastic deformation at 475℃ with an initial strain rate of 8× 10^-4 S^-1 was studied using EBSD technique. The results showed that, before deformation, the grain shape appeared to be banded, the most grain boundaries belonged to low-angle boundaries, and the initial sheet had a dominate of { 110}（112） brass texture. During deformation, there were grain growth, grain shape change, misorientation increasing and textural weakening. The fraction of high-angle boundaries increased rapidly once the flow stress reached the peak value. Corresponding deformation mechanism for various stages of deformation was suggested. Dislocation activity was the dominant mechanism in the first stage, then dynamic recrystallization occurred, and grain rotation was expected as an accommodation for grain boundary sliding （GBS）. At large strains, GBS was the main mechanism.

Effect of pre-deformation on aging creep of Al-Li-S4 alloy and its constitutive modeling

A set of uniaxial tensile creep tests at different pre-deformations, aging temperatures and stress levels were carried out for Al-Li-S4 alloy, and the creep behavior and the effects of pre-deformation on mechanical properties and microstructures were determined under basic thermodynamics conditions of aging forming. The results show that pre-deformation shortens the time of primary creep and raises the second steady-state creep rate. Then, the total creep strain is greater, but in the range of test parameters it is still smaller than that without pre-deformation. In addition, transmission electron microscopy（TEM） observation shows that pre-deformation promotes the formation of T1 phase and θ′ phase and makes them distribute more dispersively, while inhibits the generation of δ′ phase, which leads to the improvement of mechanical properties of the alloy. A unified constitutive model reflecting the effects of aging mechanism, stress levels and different pre-deformations was established. The fitting results agree with the experimental data well.

Microstructural evolution during homogenization of Al-Cu-Li-Mn-Zr-Ti alloy

The microstructure evolution of Al-Cu-Li-Mn-Zr-Ti alloy during homogenization was investigated by optical microscopy （OM）, scanning electron microscopy （SEM）, energy dispersive X-ray spectrometry （EDX）, and differential scanning calorimeter （DSC） methods. The results show that severe dendritic segregation exists in the experimental alloy ingot. Numerous eutectic phases can be observed in the grain boundary, and the distribution of the main elements along the interdendritic region varies periodically. The main secondary phase is Al2Cu. The overburnt temperature of the alloy is 520 °C. The second phases are gradually dissolved into the matrix, and the grain boundaries become spare and thin during homogenization with increasing temperature or prolonging holding time. Homogenization can be described by a constitutive equation in exponential function. The suitable homogenization treatment for the alloy is （510 °C, 18 h）, which agrees well with the results of homogenization kinetic analysis.

Influence of Li addition on mechanical property and aging precipitation behavior of A1-3.5Cu-1.5Mg alloy

The influence of Li addition on mechanical property and aging precipitation behavior of Al-3.5Cu-1.5Mg alloy was investigated by tensile test,scanning electron microscopy（SEM）,transmission electron microscopy（TEM） and high resolution transmission electron microscopy（HRTEM）.The results show that the tensile strength can be significantly improved with the slightly decreased ductility and the form of fracture morphology is converted from ductile fracture into ductile/britde mixed fracture by adding 1.0%Li.Besides,the peak aging time at 185 ℃ is delayed from 12 to 24 h and the main precipitation phase S（Al2CuMg） is converted into S＇（Al2CuMg）＋δ（Al3Li）,while the formation of S＇（Al2CuMg） is delayed.

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 of83%,followed by aging treatment at160°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 T1precipitates 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 T1precipitates in the grain interior and high density of T1precipitates around subgrain boundaries.

Effect of large strain cross rolling on microstructure and properties of Al-Li alloy plates with high magnesium content

Transmission electron microscopy(TEM),electron backscattered diffraction imaging(EBSD)and X-ray diffractometry were used to analyze the microstructure and texture characteristics of Al-9.8Mg-1.5Li-0.4Mn alloy cross-rolled and extruded plates,and the tensile properties and deep drawing performance were measured.The results show that the occurrence of dynamic recrystallization was promoted,the grains were refined and the preferred orientation of the recrystallized grains was improved by large strain cross rolling.Compared with CBA and CCB rolling methods,CBB rolling method significantly reduced the orientation density of the typical Brass texture{110}?112?in the extruded plates.The orientation densities of Copper texture{112}?111?and Brass texture{110}?112?on theβorientation line in the CBB rolled plates were the lowest,and there were no typical texture features in the plates.Meanwhile,better deep drawing could be gained in the CBB rolled plates,and the mechanical properties of the 0°,45°and 90°directions were basically the same.The tensile strength,yield strength and elongation at room temperature for the CBB rolled plates were 617 MPa,523 MPa and over 20.1%,respectively.The deviation of the mechanical properties at different directions was less than 3%.