三级时效处理对7×××系铝合金组织与性能的影响

采用扫描电镜、透射电镜、硬度测试等手段研究了回归时间对试验铝合金的微观组织以及硬度、电导率、力学性能、断裂韧性等性能的影响.结果表明,三级时效态合金的强度峰值、硬度峰值、导电率和断裂韧性均超过了未回归时效态合金与T6态;回归的过程是晶内析出相GP区部分会先产生回溶,然后不断长大直至转变为η'相,晶界析出相逐渐粗化且不连...     

时效对新型Al-Zn-Mg-Cu合金力学及应力腐蚀性能的影响

通过力学性能和电导率测试、慢应变速率试验(SSRT)以及显微组织TEM分析,研究了不同时效制度对新型Al-7.5Zn-1.7Mg-1.4Cu-0.12Zr合金力学及应力腐蚀性能的影响。结果表明,合金的力学性能和应力腐蚀性能与时效制度密切相关。T6状态下,晶内析出相弥散细小,晶界析出相呈连续分布,合金的强度最高,抗应力腐蚀性能最差;经T7双级过时效处理后,晶界析出相粗化呈离散分布,出现明显宽化的晶间无析出带,合金的抗应力腐蚀性能得到明显提高,但其强度损失较多。经三级时效处理后,合金的组织综合了T6态和T7态的优点,使合金既有高的强度又有良好的抗应力腐蚀性能,合金的极限抗拉强度、屈服强度、伸长率和电导率分别达到580,570 MPa,16.7%和23.3 MS.m-1。     

2014合金的回归再时效

本文采用拉伸实验和透射电镜法,研究了2014铝合金的回归再时效(RRA)处理.结果表明:采用欠时效(100℃(2×2h)与适当回归处理(200×5min)配合的RRA处理,可同时提高2014合金的强度和塑性.适当的回归处理能使欠时效2014合金组织中部分GP区优先长大.随后再进行峰时效处理,不仅能改善晶界析出相的尺寸和分布,而且还能使基体析出相尺寸产生明显的差异.这种尺寸有明显差异的基体析出相协同强化有利于提高2014合金的强韧性.     

双级时效制度对7150铝合金微观组织和性能的影响

采用拉伸测试、电导率测试和透射电镜等手段研究了双级时效制度对7150铝合金的力学性能、电导率和微观组织的影响。结果表明:在本研究范围内,第一级时效制度对合金的力学性能和电导率影响不大;合金经过120℃/8h+160℃/6h,可以达到与单级峰时效处理相当的抗拉强度,并且电导率有明显提高;第二级时效温度为168℃时效时,相比在160℃进行第二级时效,合金在具有同等电导率水平时,损失的强度相对较多,但时效时间明显变短;120℃/8h+160℃/32h双级时效后,合金的抗拉强度为560MPa,屈服强度为520MPa,延伸率为11.5%,电导率22.7MS.m-1,晶内沉淀析出相以η′和η为主,晶界析出相完全断开。     

7×××系铝合金厚板表层局部"色差"缺陷原因分析

针对7×××系铝合金厚板在低倍检测过程中表层出现的"色差"缺陷问题,采用显微镜、扫描电镜、维氏硬度及电导率等多种检测方法对缺陷进行了定性分析,确定了7×××系铝合金厚板表层"色差"产生的根本原因及其对材料性能的影响机理。结果表明,当7×××系铝合金厚板表层局部淬火冷却不均匀时,合金中的过饱和固溶体将会发生脱溶析出现象,在合金晶界和晶内析出大量的粗大平衡相η。这些平衡相的析出消耗了大量的溶质原子,大大降低了合金固溶体的过饱和度,减少了时效过程中形成时效强化析出相的数量,从而导致合金硬度和强度的下降,电导率升高。可通过均匀控制淬火冷却方式来解决此问题。     

时效工艺对Al-Zn-Mg-Cu-Zr-Er铝合金组织与耐腐蚀性影响

采用剥落腐蚀、极化曲线、电导率、力学性能测试和TEM显微组织分析,研究T6、T74及RRA时效工艺对Al-Zn-Mg-Cu-Zr-Er铝合金的组织、力学性能与耐腐蚀性的影响.结果表明:①T6态合金的强韧性最高（σ_b:663.5 MPa、σ_0.2:625.4 MPa、δ:12.46 %）,但易腐蚀;与T6态合金相比,T74态合金（σ_b:640.2 MPa、σ_0.2:621.3 MPa、δ:11.34 %）的耐腐蚀性最好,但以牺牲强度为代价,而RRA态合金（σ_b:657.8 MPa、σ_0.2:628.8 MPa、δ:11.98 %）虽强韧性略低于T6态合金,但耐腐蚀性明显改善,综合性能优异.②合金的强度及耐腐蚀性分别与晶内η′析出相和晶界η析出相有关.晶内大量的η′析出相分布越均匀、弥散,尺寸越细小,合金的强度越高;晶界粗大的η析出相分布越离散,合金的耐腐蚀性越好.这与第一性原理计算的η′相与η相的理化性质相吻合.      

7xxx系铝合金回归再时效的研究现状

7xxx系铝合金作为高强度铝合金的代表,以其较高的强度以及良好的韧性和耐蚀性等优异性能而广泛地应用于航空航天及交通运输领域.该类可热处理强化铝合金对微观组织结构敏感,其性能受合金内部析出相的形核、生长及分布情况的影响.采用三级时效工艺—回归再时效处理,通过预时效、回归、再时效3个过程的有效配合改变合金的析出相状态,可以...     

固溶时效处理对Al-6.6Zn-2.3Mg-2.1Cu-0.12Zr合金组织性能的影响

采用光学显微镜、扫描电镜、透射电镜、X射线衍射、硬度测试、电导率测试和室温拉伸性能测试等分析手段,研究了Al-6.6Zn-2.3Mg-2.1Cu-0.12Zr合金挤压板带固溶、单级时效和双级时效制度下的组织和性能。研究表明,Al-6.6Zn-2.3Mg-2.1Cu-0.12Zr合金挤压板带采用475℃/2 h的固溶处理制度,析出相回溶充分,无过烧现象;合金采用475℃/2 h+120℃/24 h的T6时效处理制度,晶内析出相细小弥散,晶界析出相连续分布;合金采用475℃/2 h+110℃/8 h+160℃/28 h的T74双级固溶时效处理制度,晶内析出相以η’和η为主,晶界析出物完全断开。     

7B04铝合金预拉伸厚板的微观组织与性能

研究了7B04铝合金材料在不同热处理状态下的微观组织和性能。结果表明,目前的单级固溶处理（470℃×80min）并未使合金内一次析出相充分回溶,经物相分析确定残留相为MgZn2,S（Al2CuMg）,T（Mg32（Al,Zn）49）及Al7Cu2Fe相等。T6状态下晶内析出相为细小GP区和η′相,晶界析出相为半连续状态,无明显的晶间无析出带（PFZ）存在,合金的抗拉强度达595MPa,电导率为31.7%IACS;在T7（115℃×7h＋160℃×12h）状态下,晶内的析出相为GP区、η′和η相,尺寸约为5～20nm,晶界有不连续的较为粗大相析出,有明显的PFZ存在,此时抗拉强度为532MPa,电导率为37.0%IACS;采用RRA处理可使合金获得较高强度和较高电导率,抗拉强度和电导率分别为575MPa和36.3%IACS,此时晶内析出相为η′和η相,晶界析出物粗大呈完全不连续分布,有明显PFZ存在。     

7050铝合金模锻件的热处理过程研究

将7050铝合金模锻件产品取样进行475℃×1 h固溶处理后,按照105℃×8 h、120℃×8 h、150℃×4 h、177℃×7 h依次叠加时效处理并于中间过程取样,采用透射电镜（TEM）、布氏硬度测试（HB）及能谱分析（EDS）等方法研究7050铝合金模锻件的固溶及四级时效热处理工艺过程中组织、化合物相和力学性能的演变规律。结果表明：固溶态合金中有含Fe、Ni、Ti、Si等杂质元素的未溶化合物以及少量的S相（Al2CuMg）;合金依次经4次时效处理后硬度逐渐升高;时效处理过程中,S相同时沿晶界和晶内析出,η相（MgZn2）呈颗粒状分布于Al基体上,尺寸约为40～50 nm。其中177℃时效处理后观察到的纳米级析出物η或η’相是7050合金的主要强化相。     

Atmospheric stress corrosion cracking of a superplastic 7475 aluminum alloy

The influence of different heat treatments upon the atmospheric stress corrosion cracking (SCC) of fine-grained 7475 Al-alloy plates has been investigated. The small size of the matrix precipitates and grain-boundary precipitates (GBPs) was found to be the main cause of atmospheric SCC suscepti-bility. Increasing the size of the matrix precipitates and GBPs by increasing the degree of aging could improve the atmospheric SCC resistance. The size of the matrix precipitates was the major factor affecting the atmospheric SCC resistance when GBPs were larger than a critical size that could nucleate hydrogen bubbles. However, if the size of the GBPs was smaller than this critical size, the improvement of atmospheric SCC resistance due to grain refinement, resulting from a more homo-geneous slip mode, could not be obtained because hydrogen embrittlement became serious. By meas-uring the electrical conductivity, the influence of matrix precipitates, but not that of GBPs, on SCC susceptibility could be obtained. Retrogression and reaging (RRA) treatment could effectively im-prove the atmospheric SCC resistance of T6 temper because RRA temper could produce larger sizes of both the matrix precipitates and GBPs than could T6 tempered condition.     

A study of the mechanism of hardness change of Al-Zn-Mg alloy during retrogression reaging treatments by small angle X-ray scattering (SAXS)

In this work, the changes in hardness of Al-Zn-Mg alloy during retrogression and reaging (RRA) treatments were detected and the mechanism of the hardness change was studied by Small Angle X-ray Scattering (SAXS). It was discovered that the hardness changes during RRA treatments are as follows. (1) Hardness decreases at the beginning of retrogression, achieves a minimum value at 90 seconds, and then increases and achieves the second maximum value at 6 minutes, and finally decreases simply. (2) Hardness of the reaged sample is higher than that of the retrogressed sample. The following conclusions were drawn from the experimental results of SAXS. (1) The drop in hardness for short retrogression time is attributed to the decrease of volume fraction of the precipitates and the growth of the particles; the drop in hardness with increasing retrogression time after the second maximum of hardness achieved is attributed to coarsening of the particles. 2. The increase in hardness during reaging is due to the occurrence of new precipitates and the increase of volume fraction of the precipitates.     

时效制度对7B04高强铝合金力学及腐蚀性能的影响

采用常规力学性能、标准紧凑拉伸、电导率、慢应变速率拉伸(SSRT)及剥落腐蚀测试等手段,研究了不同热处理状态下7B04铝合金预拉伸板的力学及腐蚀性能。结果表明,合金的强度、韧性和腐蚀性能与时效制度密切相关。单级峰时效(T6)状态下合金的强度最高,但是其抗应力腐蚀(SCC)性能及断裂韧性最低;双级过时效(T74和T73)状态下材料的断裂韧性和抗SCC性能明显提高,但是其强度牺牲较多;与T6相比,RRA时效处理可明显提高合金的抗SCC性能,且强度牺牲较少,仅下降2%左右,同时断裂韧性也有一定提高。     

回归再时效7150铝合金力学性能、剥蚀行为及微观组织研究

采用拉伸试验、剥蚀试验、硬度测试及透射电镜（TEM）观察研究了195℃回归时7150铝合金硬度变化及微观组织形祝,以及回归不同时间的RRA工艺对7150铝合金力学性能和剥蚀行为的影响,并与T6及T73进行了比较研究。结果表明,7150-T6铝合金强度高而剥蚀敏感性大;7150-T73铝合金强度降低而耐腐蚀性大幅度提高。195℃回归时,回归时间小于0．5h,7150-RRA铝合金强度高于7150-T6强度,而剥蚀敏感性未有效降低;当回归时间延长至1h,7150-RRA铝合金可保持7150-T6的高强度,而其剥蚀敏感性则大幅度降低。     

Effect of retrogression and reaging treatments on the microstructure of Ai-7075-T651

The effect of the retrogression and reaging treatments (RRA) on the microstructure of Al-7075 in the T651 temper, both in the matrix and on grain boundaries, was studied using transmission electron microscopy. The processes occurring in the matrix during the retrogression treatment are principally the dissolution of small particles of the η’ transition phase, transformation to η of the larger particles of η’, coarsening of the three commonly observed variants of the η phase precipitates (η₁, η₂, and η₄), and precipitation of new η phase particles, particularly the η₁ variant. The main process occurring during the reaging treatment is either growth of partially dissolved η’ particles or precipitation of the η’ phase. These lead to a microstructure containing many fine η’ precipitates and some larger η₁ and η₂ particles with a smaller amount of coarse η₄ particles, resulting in a broad particle size distribution. The high strength of the 7075 alloy in the RRA temper is believed to arise from the relatively high overall concentration of particles in this dispersion. The retrogression treatment produces rapid initial coarsening of the grain boundary particles, which are primarily η phase precipitates, resulting in an increase in their volume per unit grain boundary area,V _A . The beneficial effect of the RRA treatment on the susceptibility of 7075-T651 to SCC is believed to be due, at least partially, to the increased value ofV _A produced by the RRA treatment. Formerly Visiting Assistant Research Engineer in the Department of Materials Science and Engineering, University of California, Los Angeles, CA     

Optimization of Retrogression Parameters of AA7010 Alloy

The present work has been carried out on an AA7010 aluminium alloy so as to optimize the retrogression and re-aging (RRA) schedule that leads to the optimal combination of mechanical properties and stress corrosion cracking (SCC) resistance. The alloy is heat treated at different retrogression temperatures for varying retrogression time and subsequently the window for optimization of retrogression parameters of RRA schedule is established after re-aging. It is found that retrogression at 473 K for 35 min results into the best combination of the above properties. The enhancement in mechanical properties and SCC resistance is due to the formation of discontinuous and coarse precipitates along the grain boundaries and also the copper enrichment of the precipitates that occur during optimum RRA schedule. It is established that proper control of the process parameters is essential to control the final microstructure and thereby enhance the mechanical properties and SCC resistance of the alloys.     

Al-6.1Zn-2.6Mg-1.6Cu 铝合金的回归再时效热处理

The effects of the retrogression temperature and time of retrogression and re-aging heat treatment(RRA) on the hardness and electrical conductivity of Al-6.1Zn-2.6Mg-1.6Cu aluminum alloy were studied. Samples were pre-aged at 120℃ for 24h as the first-stage treatment. Then, retrogression was performed at a temperature range of 170～250℃ for times of between 1min and 180min, followed by re-aging at 120℃ for 24h. Hardness (H) and electrical conductivity (EC) measurements were used to characterize the samples after RRA treatment. Analysis of the results shows: (1)The re-aging treatment at 120℃ for 24 h increases both H and EC of the retrogressed alloy in the RRA process;(2) RRA with retrogression at higher than 200℃ result in EC higher than that of peak-aged, but H lower; The change of H and EC with respect to retrogression temperature (T) and time (t) can be seen as functions of H (t) = H0 A1e(-t/s) ,EC(t) =A(1-e(-k·(t-Xc)));(3) RRA treatments with retrogression at 190℃ for 4～30min result in H and EC which are both higher than those of the peak-aged temper, and retrogression at 190℃for 30min is the industrial application that yields H of 190 HV and EC of 33.5%IACS.     

Characterization of retrogression and reaging behavior of 8090 Al-Li-Cu-Mg-Zr alloy

An 8090 Al-Li-Cu-Mg-Zr alloy in the peak-aged (T8) temper was subjected to retrogression treatment at temperatures above and below the δ′ (Al₃Li) solvus line and immediately reaged to various tempers. Retrogression and reaging (RRA) behavior is characterized by hardness testing, tensile testing, transmission electron microscopy (TEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and electrochemical polarization studies. Retrogression of the T8 temper alloy causes dissolution primarily of δ′ (Al₃Li) precipitates into solid solution that results in a decrease of hardness and tensile strength and an increase of ductility of the alloy. Reaging of the retrogressed state causes reprecipitation of the δ′ precipitates in the matrix resulting in the restoration of strength and ductility properties. Retrogression and reaging to the peak-aged temper, designated at T77 temper, has been found to retain the strength of the conventional T8 temper, but with the gross aging time in the RRA temper almost twice that of the conventional T8 temper, the microstructure of the RRA temper approaches that of the overaged (T7) temper. Thus, RRA treatment contributes to an improvement of stress corrosion cracking (SCC) resistance over the conventional T8 temper while retaining the mechanical properties of T8 temper.     

Studies of retrogression and reaging behavior in a 1441 Al-Li-Cu-Mg-Zr alloy

A 1441 Al-Li-Cu-Mg-Zr alloy in the peak-aged T8 temper was subjected to retrogression treatment and immediately reaged to various tempers. Transmission electron microscopy (TEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), hardness measurements, tensile testing, scanning electron microscopy (SEM) fractography, and electrochemical polarization studies have been made to characterize the retrogression and the retrogression and reaging (RRA) behavior of the alloy. Retrogression of the T8 temper causes dissolution of δ′ (Al₃Li) precipitates into solid solution, resulting in a decrease of hardness and tensile strength and an increase of ductility. Reaging the retrogressed state causes restoration of strength and ductility properties because of the reprecipitation of the δ′ phase in the matrix, confirmed by TEM, XRD, and DSC studies and image analysis. The SEM fractographs revealed predominantly intergranular fracture in all the tempers due to strain localization at the grain boundaries. The gross aging time of the RRA tempers approaches that of the over-aged T7 temper, which would contribute to an improvement of the stress-corrosion cracking (SCC) resistance while maintaining the T8 temper mechanical properties.