Non-isothermal creep age forming of Al-Cu-Li alloy: Experiment and modelling

Non-isothermal Creep Age Forming (CAF), including loading, heating, holding, cooling and springback stages, is an advanced forming technique for manufacturing high performance large integral panels at short production period and low cost. However, the creep deformation and aging precipitation during heating stage is often neglected in experiments and modeling, leading to low forming precision. To achieve shape forming and property tailoring simultaneously, a deep understanding of the non-isothermal creep aging behavior and the establishment of predictive models are urgently required. A new five-stage creep feature of Al-Cu-Li alloy during the non-isothermal creep aging is observed. The microstructural interactions between the dislocations, solute atoms, Guinier Preston zones (GP zones) and T₁ precipitates are found to dominate the five-stage creep aging behavior. The physical-based model considering temperature evolution history is established to describe the five-stage creep feature. The springback and yield strength of non-isothermal creep age formed plates with different thicknesses are predicted and compared by non-isothermal CAF experiments and corresponding simulations. The CAF experiments show that the springback and yield strength of the non-isothermal creep age formed plate are 62.1% and 506 MPa, respectively. Simulation results are in good agreement with experimental results. The proposed model broadens the application of traditional CAF models that mainly focus on isothermal conditions.     

定向凝固钴基高温合金DZ40M的热处理研究

研究了热处理对新研制的定向凝固钴基高温合金DZ40M组织和性能的影响。结果表明 :12 80℃ / 4h固溶处理可完全溶解DZ40M合金中初生碳化物M7C3 和MC ,合金成为单相固溶体。95 0℃和 10 5 0℃时效处理可使DZ40M合金发生硬化 ,以 95 0℃时效硬化效果更为明显 ,相应的峰时效制度为 95 0℃ / 12h和 10 5 0℃ / 2 4h。时效处理引起M2 3 C6沉淀析出。 95 0℃ / 12h时效显著提高DZ40M合金室温强度和高温持久寿命 ,同时也减少了合金塑性 ,但合金仍保持一定的塑性。 10 5 0℃ / 2 4h虽然能增加室温拉伸性能 ,但削弱了高温持久性能     

新型Al-Zn-Mg-Cu合金双级时效制度研究

采用硬度法测定了一种新型Al-Zn-Mg-Cu合金挤压带板的GP区临界形核温度TV（GP区在此温度下形核不依靠空位浓度）和TC（GP区在此温度以上不能形核）。他们的温度区间分别为130～140℃和170～180℃。依据实验结果确定了合金的一级时效温度为120℃,二级时效温度为165℃。合金在120℃/4h+165℃/8h制度下热处理后,L向的抗拉强度、屈服强度、伸长率、断裂韧度和电导率分别为617MPa,590MPa,13.5%,41.6MPa m^1/2和39.1%IACS,是一种综合性能优良的双级时效600MPa级铝合金。     

Dependence of creep age formability on initial temper of an Al-Zn-Mg-Cu alloy

The initial temper of the material may directly affect the whole creep age forming(CAF)process. In terms of creep deformation and stress relaxation, using the constant-stress creep aging and constant-strain stress relaxation aging tests, the relationship between initial temper and CAF formability is investigated for an Al-Zn-Mg-Cu alloy at 165 °C for 18 h. Three tempers are selected as the initial tempers in CAF, viz., solution, retrogression and re-solution. The CAF formability of this alloy with initial temper of retrogression is the best, and the creep strain of the retrogression tempered specimen after creep aging of 18 h is about 1.21 and 1.34 times than that of the solution and the re-solution tempered specimens, respectively. The calculated stress exponents of this alloy with three initial tempers range from 7.3 to 9.5, indicating that the CAF of this alloy is mainly controlled by the dislocation creep. The various formability for three initial tempers are attributed to different inhibitions of the transgranular precipitates on the dislocation movement. For the retrogression temper, the initial fine and uniformly distributed precipitates are seriously coarsened after6 h of CAF, which minimally inhibit the dislocation movement. While, for the re-solution temper,the fine precipitates are re-precipitated in the matrix of the alloy, which observably hinder the dislocation movement and lead to the worst formability.     

热处理对激光增材制造TC4合金耐蚀性及室温压缩蠕变性能的影响

随着钛合金装备在航空、航天、航海等领域的使用逐渐增多,其服役环境日益严苛,对构件材料的抗腐蚀性能及室温应力蠕变性能提出了更高要求。针对钛合金耐蚀性及抗压缩蠕变的性能,分析了激光增材制造TC4合金不同热处理状态试样电化学及室温压缩蠕变性能,并结合蠕变曲线修正了蠕变第Ⅰ阶段本构方程的参数。结果表明,双重退火处理会显著减小增材制造TC4钛合金中α板条长径比与尺寸,而固溶时效可使α板条长径比增大、尺寸减小,导致了材料耐蚀性、屈服极限以及抗压缩蠕变性能的变化。沉积态合金经过固溶时效后自腐蚀电流降低64.92%,稳态蠕变应变率降低46.31%,蠕变应变降低50%。而经过双重退火后合金自腐蚀电流降低26.14%,稳态蠕变应变率提升111.20%,蠕变应变提升48.68%。相比于铸锻工艺制备TC4合金蠕变本构方程,修正后的拟合系数与蠕变曲线吻合度更高。     

TC1钛合金透射电镜组织研究

 用透射电镜研究TC 1 合金冷轧薄板在退火过程中精细组织的变化,揭示了位错组态与机械性能的关系。 试验用料为厚0.8mm的TC 1 钛合金冷轧板村,变形程度为33％,化学成分见表1。试验用退火温度见表2,退火保温时间为45min,采用普通电炉加热。退火后测定室温抗拉性能。     

Effects of RRA Treatments on Microstructures and Properties of a New High-strength Aluminum-Lithium Alloy-2A97

A new high strength 2A97 Al-Cu-Li-X alloy was subjected to triple-aging of retrogression and re-aging treatments (RRA). Transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and tensile tests were used to investigate the effects of RRA treatment on the microstructures and properties. DSC test reveals the reversion temperature range of the strengthening δ' (Al3Li)phase. The results show that the microstructure consists of δ' (Al3Li) phase, T1 (Al2CuLi) phase and θ"/θ'(Al2Cu) phase for 2A97 alloy treated by a triple-aging ora retrogression and re-aging treatment in the following order: (1) at 165 ℃×30 min, (2) at 220 ℃ or 240 ℃×15 min, (3) at 165 ℃×24 h. The plastic deformation, incorporated into the treatment after secondary high temperature aging, promotes the T1 precipitation during final re-aging. The tensile properties of the alloy treated by the retrogression and re-aging treatment reach the peak level of alloy single-aged at 165 ℃ in T6 temper.     

Influence of uniaxial tensile pre-strain on forming limit curve by using biaxial tensile test

This paper focused on the effect of pre-strain on forming limit curves (FLC) of 5754-O aluminum alloy sheet through utilizing biaxial tensile approach. Based on Swift model and Yld2000-2d yield criterion, the dimensions of cruciform specimen was optimized through applying finite element method for increasing the strain at specimen center. After that, with the recommended specimen size, the cruciform specimen was tested under various stroke ratios to experimentally characterize the limit strains under different pre-strain levels. Subsequently, the biaxial tensile tests were simulated by Abaqus to obtain the limit strains and validate the material models. It can be observed in both experiments and simulations that the pre-strained uniaxial tension followed by plane tension or equi-biaxial tension can improve the formability of sheet metals. Besides, the strain path change affects the trend of first derivative of strain rate difference between neighboring points with respect to time. An early increase occurred and then fell back to the stable value, the steady evolution continued until to a new increase reaching the critical value. The M–K prediction approach was simulated to verify the influence of pre-strain on FLC. It can be found that the early increase peaks of the major strain incremental ratio rose with the amplitude of pre-strain. Finally, the phenomenon of pseudolocalization caused by the strain path change was explained through evolution of stress state inside the groove.     

金属间化合物TiAl(W,Si)合金的蠕变行为和机制

 研究了 Ti-47Al-2 W-0.5 Si合金在 650～ 750℃区间的蠕变行为和变形机制。结果表明,合金 650℃蠕变寿命与施加应力之间符合线性的双对数关系,可用表达式 lg^t_f=10 lg^R+30来描述。蠕变寿命与最小蠕变速率之间满足 Monkman-Grant关系的修正式。合金的比蠕变强度与抗热腐蚀镍基高温合金 K438G相当。在700℃变载荷下蠕变时具有与恒载荷下蠕变相类似的特征。 800℃长期时效粗化合金组织,降低蠕变寿命。位错滑移和形变孪生是合金蠕变的主要变形机制。     

双峰时效对7075合金组织与性能的影响

采用洛氏硬度计、显微硬度计、光学显微镜(OM)、电子拉伸试验机等技术对7075铝合金时效行为、力学性能及显微组织进行了系统研究.结果表明,7075合金的硬度及强度都具有时效双峰特征.两个时效峰的硬度和强度相差很小,在较低温度下时效第二峰的强度、硬度、塑性、韧性较高.     

预处理对2219铝合金蠕变行为及力学性能的影响

为了研究不同预变形量对铝合金蠕变行为及力学性能的影响规律。以2219铝合金为研究对象,在温度为175℃,180 MPa应力条件下,研究0~8%的预变形量对2219铝合金蠕变行为及力学性能的影响。结果表明:预变形处理的引入,材料的蠕变变形量和力学性能大幅度增加。当预变形处理量为1%时,其蠕变变形量较未处理时试样蠕变变形量增加了118%。而随着预变形量的继续增加,试样的的力学性能呈现快速下降的变化趋势。综合考虑蠕变变形量与力学性能时,最利于构件的蠕变时效成形的2219铝合金的预变形处理量为3%。     

Creep Behaviors of FGH95 Powder Ni-Base Superalloy

This article makes an investigation into the creep behavior and deformation features of FGH95 powder Ni-base superalloy by means of creep curves and microstructural observation. Results show that this superalloy exposes obvious sensibility to the applied temperature and stresses in the experimental range. Microstructure of the alloy consists of γ′ phase of various sizes and dispersed carbide particles precipitated in the wider crystal boundaries between the powder particles. During the creep, the deformation of the alloy occurs in the form of single- or double-oriented slipping inside the grains, and some of the finer carbide particles are precipitated near the slipping traces. The wide grain boundaries might be broken into the finer grains due to severe deformation. The deformation mechanism of the alloy during creep is thought to be the activation of dislocations of double-oriented slipping, including (1/2)<110> dislocation inside the γ matrix phase and <110> super-dislocation inside the γ′ phase. The formation of the stacking faults and (1/3)<112> super-Shockleys partial dislocation configuration is attributed to the decomposition of <110> super-dislocation in the γ′ phase.     

时效工艺对冷变形多相紧固件GH350合金组织与性能的影响

 利用光学显微镜和扫描电镜(SEM)分析,研究了冷拔态GH350(AEREX350)合金中η-Ni₃Ti相的时效析出规律以及对合金高温拉伸性能的影响。研究发现,冷拔态GH350合金中η-Ni₃Ti相在780~1 060 ℃温度范围内析出,且呈两种形态。晶界片状η相在780~1 060 ℃温度范围内均可析出,但在850~1 060 ℃温度区间,除晶界η相外,在晶内沿(111)面呈魏氏体形态析出片状η相。冷变形GH350合金在980 ℃开始发生再结晶,1 010 ℃可完全再结晶。对二阶时效后冷变形GH350合金的高温拉伸实验表明,随着一阶时效温度的升高,合金的高温塑性增加,强度降低。     

时效处理对高强耐热镁合金等温模锻件组织与性能的影响

采用锻后直接时效处理的方法研究了时效处理工艺对高强耐热镁合金等温模锻件的组织与性能的影响,分析了其时效强化过程中第二相的形成及时效处理制度相关的断裂行为,得出了其时效强化的内在机理及优化的锻后时效制度.研究表明优化的时效处理制度为200℃×63 h.在该时效制度下,材料的室温抗拉强度达到了371MPa,屈服强度达到243 MPa,伸长率达4.1％     

Through-thickness heterogeneity in creep properties of friction stir welding 7B50-T7451 aluminum alloy thick plate joint: Experiments and modeling

Through-thickness heterogeneity in creep properties of 7B50-T7451 aluminum alloy Friction Stir Welding(FSW) joints was investigated. Creep tests for three slices of the FSW joint were conducted at the temperature of 150–200 °C and applied stress of 60–225 MPa. The theta projection method was used to predict creep curves and minimum creep rate. The results show that the minimum creep rate increases and creep rupture life decreases with the increase of creep temperature and applied stress. Creep p...     

Fe和Nb对TiNi形状记忆合金环双程记忆效应的影响

研究了预变形和热循环对Ti50.8Ni49.2及加入Fe和Nb后合金环的双程记忆应变影响。结果表明:在马氏体状态进行10.4%~13.8%的预变形,TiNi合金环随循环次数增加,双程记忆应变增大,在13.8%预变形和4次循环得到4.15%最大值;加入Fe和Nb后,在10.71%~15.18%的变形范围,合金环的双程记忆应变先增后降,其最大值分别为3.14%和2.56%。在变形量和循环次数相同时,TiNi合金环的记忆应变最高,当变形量和循环次数超过12.50%和2以后,TiNiFe合金环的双程记忆应变快速上升,其双程记忆应变超过TiNiNb合金环的。     

近α型钛合金长时高温暴露过程中显微组织演变及其对热稳定性的影响

研究了近α型钛合金TG6经α+β两相区热加工的盘锻件在600℃长时暴露过程中的显微组织演变及其对热稳定性的影响。结果表明:经600℃/100h和600℃/300h长时高温暴露后,TG6钛合金的室温拉伸强度略有提高,其增幅在5%左右,而其拉伸塑性显著降低,塑性保持率小于50%,拉伸断口趋于平直化,且存在梯田状台阶和二次裂纹等,表现为显著的解理断裂特征。在600℃高温长时暴露过程中,TG6钛合金中的显微组织变化主要有在基体组织中的共格有序α2相析出及硅化物析出。随着高温暴露时间的延长,TG6钛合金的显微组织逐渐趋于稳定,拉伸性能的变化也相应趋缓。α2相析出促进了拉伸变形时位错滑移的平面化及变形不均匀,是热稳定性下降的主要原因;而硅化物析出协同促进位错滑移集中化,是热稳定性下降的次要因素。     

少量Cu对喷射沉积Al-Li合金显微组织与性能的影响

用喷射沉积方法制备了Al-Li合金及其含0.5%Cu的改型合金,进行了挤压和时效处理,测定了不同状态下这两种合金的显微组织和室温拉伸性能。结果表明,喷射沉积状态的Al-3.8Li-1.0Mg-0.4Ge-0.2Zr合金具有等轴细晶组织,析出Al4Li9和δ AlLi相,时效后析出大量δ' AlLi相;添加0.5%Cu使屈服强度提高30～48MPa,拉伸强度提高44MPa,性能提高的原因是Cu的固溶强化和Li在基体固溶度减少导致δ'相含量增加。     

一种快速凝固铝锂合金的低温光滑和缺口拉伸性能

研究了快速凝固Ａｌ-４．７４Ｃｕ-１．３０Ｌｉ-０．３８Ｍｇ-０．４２Ａｇ-０．２１Ｚｒ合金在室温到液氦温度（７７Ｋ）范围内的光滑和缺口拉伸性能,并用扫描电镜观察了断口形貌,用透射电镜分析了合金组织及变形后的位错组态。结果发现,随着温度降低,合金强度线性升高,形变硬化能力增强,而延伸率的变化则取决于不同的时效态。尽管合金缺口强度随温度降低而减小,但７７Ｋ下该合金在欠时效态其缺口性能仍明显优于传统铝合金。     

重复固溶对Inconel 718合金组织性能的影响

以982℃固溶水冷状态的Inconel 718合金棒材为研究对象,分析该合金经重复固溶再时效处理后的组织性能,并与直接时效处理进行对比。结果表明:在941~1010℃范围内重复固溶,随着固溶温度的升高,晶粒无明显变化,但是δ相含量逐渐减少,主要强化相γ′′的析出量增多,使合金硬度、高温拉伸强度和高温持久寿命显著提高,高温拉伸塑性、高温持久塑性在982℃固溶时达到极大值。与直接进行时效处理相比,经982℃重复固溶再时效处理后的组织性能无明显变化,更低的重复固溶温度对性能不利,而更高的重复固溶温度则使性能提高。