Al-Zn-Mg-Cu合金多尺度第二相粒子与性能关系研究

介绍了Al-Zn-Mg-Cu合金多尺度第二相粒子与性能关系的研究。涉及的多尺度第二相粒子包括微米尺度的金属间化合物、亚微米尺度的弥散相、纳米尺度的晶内析出相和晶界析出相;涉及的相关性能为强度、断裂韧性以及腐蚀性能。结合相关文献与作者的研究工作,可以得出以下结论:金属间化合物会影响合金的断裂韧性和腐蚀抗力;弥散相通过抑制基体再结晶的方式影响合金的强度、断裂韧性以及腐蚀抗力;晶界析出相会影响合金的断裂韧性和腐蚀抗力;晶内析出相影响合金的强度和断裂韧性。     

均匀化对新型Al-Mg-Mn(Er)合金组织性能的影响

采用拉伸性能测试、光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)及能谱分析(EDS)研究了均匀化对低频电磁铸造Al-4.75Mg-0.7Mn-0.1Zr-0.1Ti-0.3Er合金的显微组织和力学性能的影响。在510℃/16h均匀化时,晶界残留相FeMnAl6/MnAl6的数量最少、而晶内弥散相的数量最多,且随后经热轧、冷轧和稳定化退火试样的强度最高;且在冷轧板拉伸变形组织中观察到了大量细小的胞状亚结构、100～500μm的FeMnAl6/MnAl6板条和10～30nm的ErAl3相;FeMnAl6/MnAl6相周围塞积了高密度的位错,ErAl3相易于在位错处析出并可有效地钉扎位错使变形更均匀。     

Reactive Milling and Mechanical Properties of NiAl Composite with HfC Dispersoids

A NiAl-based composite with HfB2 dispersed particles has been synthesized by mechanical alloying of Ni,Al,Hf and C powders.The formation mechanism of NiAl-HfC during milling can be attributed to two chemical reactions:Ni Al→NiAl ΔH;Hf C→HfC ΔH,induced by mechanical collision in a certain period of time,which results in an abrupt exothermic reaction.Hot pressing(HP) and hot isostatic pressing(HIP) have been used to make the NiAl-10HfC compacts near fully dense.Compressive testing from room temperature to 1000℃ indicated that the yield stress of NiAl-10HfC composite is 3-4 times higher than that of cast NiAl and correspond to the MA NiAl-10TiB2 composite.In the meantime,yield strength at high temperature is dependent on strain rate, and deformation is controlled by diffusion mechanism.     

微量Mn对A1-Mg-Si合金微观组织与拉伸性能的影响

研究了微量Mn对Al Mg Si合金的微观组织与拉伸性能的影响。结果表明 :微量Mn在Al Mg Si合金中主要以粒状α Al15(FeMn) 3 Si2 弥散相的形式存在 ,尺寸为 12～ 2 10nm ,均匀、弥散分布在基体中 ,有效地钉扎位错和亚晶界 ,抑制合金热挤压变形过程中的再结晶 ;均匀化处理过程中微量Mn可促进长针状 β Al9FeSi相向粒状α Al15(FeMn) 3 Si2 相转变 ,这种含Mn的α相弥散颗粒可作为合金时效强化相 β′(Mg2 Si)的非均匀成核位置 ,促进 β′相的析出 ,从而强化合金 ,使合金获得较好的强塑性配合     

Deformability enhancement in ultra-fine grained, Ar-contained W compacts by TiC additions up to 1.1%

Nano-sized Ar bubbles give negative influence on the fracture resistance and occurrence of superplasticity in ultra-fine grained (UFG) W–TiC compacts. In order to enhance deformability in UFG, Ar-contained W–TiC compacts, effects of TiC addition on the high-temperature deformation behavior were examined. W–TiC compacts with TiC additions of 0, 0.25, 0.5, 0.8 and 1.1 wt% were fabricated by mechanical alloying in a purified Ar atmosphere and hot isostatic pressing. Tensile tests were conducted at 1673–1973 K (0.45–0.54 T_m, T_m: melting point of W) at initial strain rates from 5 × 10⁻⁵ to 5 × 10⁻³ s⁻¹. It is found that as TiC addition increases, the elongation to fracture significantly increases, e.g., from 3 to 7% for W–0 and 0.25TiC/Ar to above 160% for W–1.1TiC/Ar when tested at 1873 and 1973 K at 5 × 10⁻⁴ s⁻¹. The flow stress takes a peak at 0.25%TiC and decreases to a nearly constant level at 0.5–1.1%TiC. The ranges of the strain rate sensitivity of flow stress, m, and the activation energy for deformation, Q, with TiC additions are 0.17–0.30 and 310–600 kJ/mol, respectively. The observed effects of the TiC additions on the tensile properties are discussed.     

Superior mechanical properties and strengthening mechanisms of lightweight AlxCrNbVMo refractory high-entropy alloys(x = 0, 0.5,1.0) fabricated by the powder metallurgy process

Light and strong AlxCrNbVMo(x=0,0.5,and 1.0) refractory high-entropy alloys(RHEAs) were designed and fabricated via a the powder metallurgical process.The microstructure of the AlxCrNbVMo alloys consisted of a single BCC crystalline structure with a sub-micron grain size of 2-3 μm,and small amounts(4 vol.%) of fine oxide dispersoids.This homogeneous microstructure,without chemical segregation or micropores was achieved via high-energy ball milling and spark-plasma sintering.The alloys exhibited superior mechanical properties at 25 and 1000℃ compared to those of other RHEAs.Here,CrNbVMo alloy showed a yield strength of 2743 MPa at room temperature.Surprisingly,the yield strength of the CrNbVMo alloy at 1000℃ was 1513 MPa.The specific yield strength of the CrNbVMo alloy was increased by 27 % and 87 % at 25 and 1000℃,respectively,compared to the AlMo_(0.5) NbTa_(0.5)TiZr RHEA,which exhibited so far the highest specific yield strength among the cast RHEAs.The addition of Al to CrNbVMo alloy was advantageous in reducing its reduce density to below 8.0 g/cm~3,while the elastic modulus decreased due to the much lower elastic modulus of Al compared to that of the CrNbVMo alloy.Quantitative analysis of the strengthening contributions,showed that the solid solution strengthening,arising from a large misfit effect due to the size and modulus,and the high shear modulus of matrix,was revealed to predominant strengthening mechanism,accounting for over 50 % of the yield strength of the AlxCrNbVMo RHEAs.     

Effect of Mn-Bearing Dispersoids on Tensile Properties and Recrystallization Resistance of Al-3Mg-0.8Mn Rolled Alloy

Herein, the precipitation behavior of Mn-bearing dispersoids in Al-3Mg-0.8Mn (AA5454) alloy subjected to different heat treatments is investigated. The effects of Mn-bearing dispersoids on the tensile properties and recrystallization resistance of the abovementioned alloy during hot/cold rolling and postrolling annealing are evaluated. The results show that a low-temperature three-step heat treatment (275 °C/12 h + 375 °C/48 h + 425 °C/12 h) generates a higher number density of Mn-bearing dispersoids with finer sizes compared with the typical high-temperature heat treatment (430 °C/2 h + 480 °C/2 h + 525 °C/2 h), thus resulting in significantly improved tensile strengths of hot/cold-rolled sheets. After annealing at 300 °C, the yield strength (YS) of the alloy reached 196 MPa after hot rolling and 237 MPa after cold rolling, showing an improvement of 30%–32% over samples subjected to high-temperature heat treatment. In addition, the low-temperature heat treatment provides a higher recrystallization resistance after hot and cold rolling owing to the higher number density of Mn-bearing dispersoids and the lower fraction of dispersoid-free zones. The YS contributions of various strengthening components after hot and cold rolling are discussed based on constitutive models. The predicted yield strengths agree well with the experimental values.     

SOME DEVELOPMENTS IN RAPIDLY SOLIDIFIED ALUMINUM ALLOYS FOR ELEVATED TEMPERATURE APPLICATIONS

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均匀化时间对7085铝合金淬火敏感性的影响

采用末端淬火实验、光学显微镜（0M）、扫捕电镜（SEM）和透射电镜（TEM）研究均匀化时间对7085铝合金淬火敏感性的影响。结果表明,均匀化时间从48h延长至384h,淬火敏感性有所增加,端淬试样经人工时效后硬度的最大差值从5．2％增加到6．9％。均匀化时间延长对晶粒组织没有影响,但促使丁相的溶解,增加Al3Zr弥散粒子的尺寸,减小其密度。慢速淬火时,在晶内的Al3Zr弥散粒子上能观察到一些尺寸较小的淬火析出η相,这降低了时效后的硬度。Al3Zr粒子特征的变化对淬火敏感性影响很小。     

The Oxidation of TiB2 Particle-Reinforced TiAl Intermetallic Composites

The oxidation kinetics of TiAl alloys with and without (3, 5, 10 wt.%) TiB₂ dispersoids were studied between 1073 and 1273 K in atmospheric air. The inert TiB₂ dispersoids effectively increased the oxidation resistance of TiAl alloys. The higher the TiB₂ dispersoids content, the more pronounced the effect. The oxide scale formed on TiAl–TiB₂ composites was triple-layered, consisting mainly of an outer TiO₂ layer, an intermediate Al₂O₃ layer, and an inner (TiO₂+Al₂O₃) mixed layer. No B₂O₃ was observed within the oxide scale because of its high vapor pressure. A thin Ti₃Al sublayer and discrete TiN particles were found at the oxide–substrate interface. During the oxidation of TiAl alloys with and without TiB₂ dispersoids, titanium ions diffused outwardly to form the outer TiO₂ layer, while oxygen ions transported inwardly to form the inner (TiO₂+Al₂O₃) mixed layer. The increased oxidation resistance by the addition of TiB₂ was attributed to the enhanced alumina-forming tendency and thin and dense scale formation.