快速凝固Cu—Cr—Zr—Mg合金时效析出与再结晶的交互作用及其对性能？…

本文研究了快速凝固Ｃｕ－Ｃｒ－Ｚｒ－Ｍｇ合金在时效过程中，的出与再结晶的交互作用及其对显微硬度的影响。研究结果表明，形变使得快速凝固合金时效析出相更加细小弥散，析出过程先于再结晶过程，并对再结晶的形核和长大过程产生阻碍作用。使得冷变形后的合金在较高温度下时效，仍可达到较高的硬度，如冷变形４０％的合金在５００℃时效３０ｍｉｎ，其显微度值可达ＨＶ２００。     

热处理对铸造Ti15-3合金显微组织和力学性能的影响

借助光学显微分析、ＴＥＭ和ＳＥＭ分析手段研究了不同热处理工艺对Ｔｉ１５－３合金显微组织和力学性能的影响。结果表明：合金在铸态时的组织特征为粗大的β相,由于合金中没有析出相的弥散强化作用,因而合金的强度低,在不同温度时效处理后,在晶内和晶界析出α相,随着时效温度和时效时间的增加,析出相不断粗化,与铸态相比,合金时效后强度大幅度提高而处伸率大幅度下降,在变形过程中,合金中的位错在析出相周围形成缠结,合     

475℃ EMBRITTLEMENT DEVELOPMENT AND EMBRITTLING-INHIBITING MECHANISM BY YTTRIUM IN FeCrAl ALLOYS

经脆化动力学、内耗、ＴＥＭ和Ｍｏｓｓｂａｕｅｒ谱等研究表明：Ｆｅ－１５Ｃｒ－４Ａｌ和Ｆｅ－２５Ｃｒ－５Ａｌ合金的４７５℃脆化包括两种过程，碳化物在晶界析出损害界面结合，降低断裂应力、使塑性在时效０．２５ｈ后消失，时效温度从４００提高到６００℃时，发生过时效的时间从〉１０００ｈ缩短到约１ｈ，从α相均匀析出的富铬α‘相通过强化基体引起二次脆化，它与时效温度的关系有“Ｃ曲线”的特征，作用仅在４４０￣４７     

预温变形对2091Al－Li合金组织和性能的影响

用透射电镜和电子拉伸机研究了预温变形对２０９１Ａｌ－Ｌｉ合金组织和性能的影响。结果表明，经１８０℃温变形３０％和１９０℃时效５ｈ的合金具有最佳的强度和塑性配合，而且加速了时效动力学过程。其原因主要是１８０℃预温变形时产生均匀分布的位错亚结构，促进晶内ｓ’相细小均匀地析出以及减少或消除晶界沉淀相的析出等有关。     

预轧制变形电场时效对1420Al-Li合金组织与性能的影响

对预轧制变形的1420Al-Li合金进行了电场时效处理，并研究了预轧制变形电场时效对Al-Li合金力学性能的影响，利用透射电镜观察和分析了合金的显微组织。试验结果表明，经预轧制变形的1420Al-Li合金在时效时，随时效时，随时效时间的延长或提高时效温度，使δ‘析出相尺寸增大；随预轧制变形量的增加，合金中位错密度提高，但预轧制对析出的δ‘相数量及尺寸没有明显的影响；预轧制变形电场时效可以显著提高合金的强度，采用适当的变形量及电场时效工艺可获得良好的强塑性配合。     

微量Ag对CP276合金性能和组织的影响

研究添加不同含量的Ａｇ对ＣＰ２７６合金的拉伸性能和时效组织的影响。对拉伸强度、延伸率测试及透射电镜观察表明：０．１１ｗｔ％加入可促进Ｔ１相析出，使合金强度值升高；０．３５ｗｔ％Ａｇ的加入可在时效前期生成富Ａｇ、Ｍｇ的稳定的ＧＰ区，从而降低合金中Ｃｕ的固溶度，阻碍Ｔ１相析出，时效后期，ＧＰ区分解，生成大量Ｔ１相，使合金强度值显著升高。     

快速凝固Cu-Zr合金的析出特性及其对性能的影响

本文采用透射电镜对快速凝固Ｃｕ － Ｚｒ 合金析出过程中组织的变化进行了研究。分析了时效析出过程中组织和性能的变化规律。结果表明：快速凝固Ｃｕ － Ｚｒ 合金经适当的时效处理,可以在保持高的导电率的前提下,大幅度提高合金的显微硬度。合金经５５０ ℃时效２ｈ ,其导电率为８２ ％ ＩＡＣＳ,显微硬度可达ＨＶ２３０ ,时效析出相为球状的Ｃｕ５Ｚｒ ,在峰值状态时与母相保持共格关系。     

时效处理对快速凝固AI—Li—Cu—Zr合金结构与性能的影响

通过拉伸和电镜观察等方法研究了时效处理对快速凝固的Ａ１２．４Ｌｉ－２．４Ｃｕ，Ａ１－２．４Ｌｉ－２．４Ｃｕ－０．３Ｚｒ和Ａ１－２．４Ｌｉ－２．４Ｃｕ－０．７Ｚｒ三种合金结构与性能的影响。实验结果表明，加入Ｚｒ元素和进行预变形可明显地提高Ａ１－ＬｉＣｕ合金的时效速度并提高合金的强度。但Ｚｒ含量超过０．３ｗｔ－％以后并不产生明显的强化效果。预变形产生的位错对Ｔ１强化相的均匀析出十分有利。     

二级时效形变对Cu-Cr-Zr-Mg合金组织与性能影响研究

采用力学性能和电导率测试及透射电子显微镜等方法,研究了不同时效工艺对Cu-0.45Cr-0.15Zr-0.05Mg合金硬度和电导率等性能的影响规律。结果表明:合金在一级时效工艺(950℃×1h固溶+70%冷变形+520℃×2.5h时效)下有很强的时效强化效应,合金的显微硬度和电导率分别为155HV和85%IACS;采用二级时效工艺(950℃×1h固溶+70%冷变形+520℃×2h时效+60%冷变形+450℃×2h时效),合金在保持较高的电导率的同时强度得到较大提高。显微硬度为190HV,比一级时效提高了22.5%,而电导率保持在80%左右。显微组织分析表明,高强度主要来源于冷变形引起的亚结构强化和弥散相的析出强化。二级时效工艺可促进析出相的析出,析出的弥散质点对基体的回复和再结晶阻碍作用强烈。析出相与冷变形过程中产生的位错交互作用使析出相不仅阻碍位错的运动而且沿密集且分布均匀的位错快速析出,促进合金强度提高。     

高温退火和时效处理对Ni47Ti44Nb9合金显微组织和马氏体相变的影响

本文用金相显微镜，电子探针和电阻率－温度曲线测试仪研究了高温退火和时效对Ｎｉ４７Ｔｉ４４Ｎｂｇ合金显微组织和马氏体相变的影响。结果表明，加热温度高于１０５０℃时，β－Ｎｂ相粒子聚集长大，但对马氏体相变并不产生明显影响。与富Ｎｉ的近等原子比Ｔｉ－Ｎｉ合金不同，Ｎｉ４７Ｔｉ４４Ｎｂｇ合金在时效过程中没有时效析出和时效硬化现象。Ｎｂ加入Ｔｉ－Ｎｉ合金中抑制了时效析出和Ｒ相变，从而降低了马氏体相变温度受热     

Al-Zn-Mg-Cu系超高强度铝合金的研究进展

Al-Zn-Mg-Cu系超高强度铝合金具有低密度、高比强度、高韧性和良好的抗腐蚀性能的特点,广泛应用于航空航天、交通运输和兵器领域。本文主要介绍近年来国内外Al-Zn-Mg-Cu系超高强度铝合金的最新研究进展。超高强度铝合金基体上分布着纳米级的晶内时效析出相、亚微米级的高温析出相、微米级的结晶析出相和晶界析出相,这些相的形态、数量、尺寸和分布对合金的综合力学性能和抗腐蚀性能有直接的影响;主元素成分含量对超高强度铝合金综合力学性能有影响,合金的综合力学性能随Zn/Mg和Cu/Mg比值的变化而变化;微量元素能够提高超高强度铝合金的综合力学性能。微量元素对铝合金的影响主要体现在提高沉淀相的过饱和度,改变沉淀析出过程,促进或抑制沉淀相的析出和促进新相的沉淀析出。新制备技术能够显著细化晶粒、抑制偏析、析出相均匀分布和提高各种元素的过饱和度,从而改善超高强度铝合金的综合力学性能。强化固溶处理能够提高时效析出程度,从而提高铝合金的力学性能。三级时效处理后的超高强度铝合金具有峰值时效T6态的强度和优异的抗腐蚀性能。     

Enhanced mechanical properties in an Al-Cu-Mg-Ag alloy by duplex aging

A type of duplex aging heat treatment was developed to improve the mechanical properties at room temperature and elevated temperatures in a pre-strained Al-Cu-Mg-Ag alloy. In contrast to the conventional T8 temper at 165 °C and 200 °C, the hardening response of the alloy to aging was increased by duplex aging treatment, the ultimate tensile strength and yield strength of duplex aging temper were improved by approximately 3-7%, which was attributed to the fact that the recovery of dislocations occurred and the precipitation of θ′ phase was restrained effectively at high aging temperature, and more Ω precipitates were formed during secondary aging.     

Effect of prior cold work on age hardening of Cu-4Ti-1Cd alloy

This research is part of a project whose scope was to develop high strength ternary alloys based on Cu-Ti system with the primary aim of substituting them for toxic and expensive Cu-Be alloys. In this pursuit, age hardening behaviour of Cu-4Ti-1Cd alloy has already been investigated and the present paper reports the investigations on the influence of prior cold work by rolling of 50, 75 and 90% on the age hardening of a Cu-4Ti-1Cd alloy using hardness and tensile tests and optical as well as transmission electron microscopy. As a result of cold work followed by aging, hardness of the alloy increased from 237 Hv in solution treated condition to 425 Hv on 90% cold work and peak aging. Similarly, yield and tensile strengths of the alloy reached maxima of 1037 and 1252 MPa respectively on 90% deformation and peak aging. The microstructure of the deformed alloy exhibited elongated grains and deformation bands. The maximum strength on peak aging was obtained due to precipitation of ordered, metastable and coherent β^l, Cu₄Ti phase in addition to high dislocation density and deformation twins. Both hardness and strength of the alloy decreased on overaging due to the formation of incoherent and equilibrium β, Cu₃Ti phase. However, the morphology of the discontinuous precipitation was changed to globular shape due to large deformations and overaging.     

Effect of prior cold work on age hardening of Cu–3Ti–1Cr alloy

The influence of 50%, 75% and 90% cold work on the age hardening behavior of Cu–3Ti–1Cr alloy has been investigated by hardness and tensile tests, and light optical and transmission electron microscopy. Hardness increased from 118 Hv in the solution-treated condition to 373 Hv after 90% cold work and peak aging. Cold deformation reduced the peak aging time and temperature of the alloy. The yield strength and ultimate tensile strength reached a maximum of 1090 and 1110 MPa, respectively, following 90% deformation and peak aging. The microstructure of the deformed alloy exhibited elongated grains and deformation twins. The maximum strength on peak aging was obtained due to precipitation of the ordered, metastable and coherent β′-Cu₄Ti phase, in addition to high dislocation density and deformation twins. Over-aging resulted in decreases in hardness and strength due to the formation of incoherent and equilibrium β-Cu₃Ti phase in the form of a cellular structure. However, the morphology of the discontinuous precipitation changed to a globular form on high deformation. The mechanical properties of Cu–3Ti–1Cr alloy are superior to those of Cu–2.7Ti, Cu–3Ti–1Cd and the commercial Cu–0.5Be–2.5Co alloys in the cold-worked and peak-aged condition.     

Aging behavior of 359-type Al–9%Si–0.5%Mg casting alloys

The present study investigated the influences of aging temperature and time on the tensile properties and quality indices of 359-type Al–9%Si–0.5%Mg casting alloys. These alloys are still not widely used by most foundrymen in spite of the fact that they are extremely promising for several fields of engineering applications because of their superior strength. For the purposes of validating their use in industrial applications, a solid data base was created, based on the present study, correlating the tensile properties and the quality indices of these alloys with the aging parameters. Quality charts were used as an evaluation tool for selecting the optimum aging conditions for developing high strength and optimum quality in 359 casting alloy. Aging at a low temperature was observed to produce the greatest strength and optimum quality in the 359-type castings compared to aging at higher temperatures. The peak-strength for 359 alloy was observed to be attained after shorter aging times on condition that the aging temperature is increased. The aging times required for reaching peak-strength in 359 alloys are 32, 24, 1 h, 30, and 10 min when applying aging temperatures of 155, 170, 195, 220, and 245 °C, respectively. Aging treatment at higher temperatures is accompanied by a reduction in the tensile properties and quality index values of the castings; however, it also introduces the possibility of a significant economical strategy for minimizing the time and the cost of this treatment. Depending on the required level of tensile properties and based on the quality charts developed, it is possible to make a rigorous selection as to the most suitable aging parameters to be applied to the 359 alloy so as to obtain the best possible cost-effective compromise between alloy strength and quality.     

Manufacturing high-performance Mg alloy through hot extrusion

Mg-Gd-Y-Zr alloy is usually manufactured through method of combined homogenization, hot deformation and aging treatment and the obtained alloy usually exhibits low ductility. In this investigation, Mg-Gd-Y-Zr alloy possessing superior overall mechanical properties, both high ductility and strength, was obtained through a method of hot extrusion applied on the as cast alloy and a following T6 treatment involving a short solution and an aging. The coarse grains in the as cast alloy was severely refined during the extrusion processing, accompanied with the decomposition and dissolving of the eutectic structure generated during casting. After T6-treated, the alloy exhibits superior comprehensive mechanical properties of 293?MPa in yield strength and 9.4% in elongation. Compared with the alloy processed by extrusion and T5 treatment, which is usually used for wrought magnesium alloy, this alloy exhibits an increment of more than 90% in ductility with a sacrifice as low as 2% in yield strength. Meanwhile, the fabrication process is notably shortened. The improvement in mechanical property is attributed to the random texture, generated in the extrusion without a foregoing homogenization. This manufacturing method of combining extrusion and T6 treatment throws light on the application of extruded magnesium alloy through the significant improvement in ductility, notable shortening in fabrication process procedure and the sever reduction in energy consumption.     

形变量和时效对Al-Cu-Li合金组织性能的影响

为了改善铝合金的力学性能,利用形变和时效工艺提高Al-3.5Cu-1.5Li-0.12Zr合金的强度和塑性.采用TEM观察和室温拉伸试验等手段,研究了形变量和时效工艺对含钪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.合金强度随形变量和时效时间增加而增加,到峰值后,随形变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.该合金合宜的形变量和时效工艺为3.5%预变形和160℃/24 h时效.     

Influence of solution-aging treatment on damping and tensile properties of Ti-36Nb-2Ta-3Zr-0.3O alloy

High-damping alloys have been used in aerospace, automobile manufacturing and other fields due to its capacity to weaken vibration and noise. The damping and tensile properties of the Ti-36Nb-2Ta-3Zr-0.3O (wt-%) alloy were investigated by dynamic mechanical analysis and tensile tests. The results showed that aging treatment significantly improved the tensile strength. The Snoek-type relaxation was observed in the alloy with and without aging treatment, although the aging treatment exerted a negative influence on damping capacity, especially at high temperatures. This phenomenon could be related to the precipitation of the α phase and the segregation of oxygen in the α phase from the β phase during the aging process. As a result, the alloy aged at 713?K simultaneously presents excellent damping and tensile properties.     

Ca-modified Al–Mg–Sc alloy with high strength at elevated temperatures due to a hierarchical microstructure

Al-Mg alloys are normally prone to lose part of their yield and tensile strength at high temperatures due to insufficient thermal stability of the microstructure. Here, we present a Ca-modified Al–Mg–Sc alloy demonstrating high strength at elevated temperatures. The microstructure contains Al₄Ca phases distributed as a network along the grain boundary and Al₃(Sc,Zr) nano-particles dispersed within the grains. The microstructure evolution and age-hardening analysis indicate that the combination of an Al₄Ca network and Sc-rich nano-particles leads to excellent thermal stability even upon aging at 300 °C. The tensile strength of the alloy for temperatures up to 250 °C is significantly improved by an aging treatment and is comparable with the commercial heat-resistant aluminum alloys, i.e., A356 and A319. At a high temperature of 300 °C, the tensile strength is superior to the above-mentioned commercial alloys, even more so when expressed as the specific strength due to the low density of Ca-modified Al–Mg–Sc alloy. The excellent high-temperature strength results from a synergistic effect of solid solution strengthening, grain boundary strengthening and nanoparticle order strengthening.

     

Influence of Stress‐Aging Processing on Precipitates and Mechanical Properties of a 7075 Aluminum Alloy

Two‐step stress‐aging tests, as well as pre‐treatment plus stress‐aging experiments, are performed on a 7075 aluminum (Al–Zn–Mg–Cu) alloy. Influences of stress‐aging parameters on mechanical behavior and fracture mechanism are investigated through uniaxial tensile test and fracture morphology analysis. It is revealed that the stress‐aging dramatically influences the mechanical properties and fracture characteristics of the studied alloy, which is contributed to the sensitivity of microstructures to stress‐aging. When the alloy undergoes two‐step stress‐aging, the ultimate tensile strength and yield strength first increase and then decrease with the increased first step stress‐aging temperature, while the elongation first decreases and then increases. For the retrogression pre‐treated plus stress‐aged alloy, the yield strength first increases and then drops with the increased retrogression pre‐treatment time, while the ultimate tensile strength almost remains stable. Furthermore, the elongation continuously increases with the increased retrogression pre‐treatment time. The observation of fracture morphology indicates that the dimple‐type intergranular fracture is the main fracture mechanism for the two‐step stress‐aged and retrogression pre‐treated plus stress‐aged alloys.