新型Al-Zn-Mg-Cu合金型材回归再时效处理的组织与性能

采用拉伸、硬度、电导率测试和透射电镜分析等方法研究了不同回归处理工艺对Al-Zn-Mg-Cu合金型材组织与性能的影响。结果表明,采用120℃×24 h+180℃×45 min+120℃×24 h回归再时效处理后,合金的抗拉强度、屈服强度、伸长率和电导率分别为613.5 MPa、599 MPa、11.1%和39.2%IASC。与T6态相比,合金在抗拉强度和伸长率相当的情况下,屈服强度和电导率显著提高,合金的抗应力腐蚀性能明显改善。合金晶内为细小的η’相和η相,晶界沉淀相断续分布,伴有较窄的晶界无析出带。     

回归再时效7150铝合金的蠕变时效行为（英文）

通过蠕变时效实验、拉伸性能测试、电导率测试和透射电镜观察,系统研究回归再时效状态的7150铝合金的蠕变时效行为。蠕变时效实验结果表明,回归再时效状态7150铝合金的稳态蠕变主要是位错攀移机制(应力指数≈5.8),其稳态蠕变行为对晶内和晶界的析出相变化不敏感,但总的蠕变变形随着再时效时间的延长而增大。另外,在140°C蠕变时效16 h后,4种回归再时效样品的屈服强度和抗拉强度基本相同,但伸长率随着再时效时间的延长略有下降。而且回归再时效处理有利于提高7150铝合金的硬度和电导率。研究结果表明,蠕变时效前的回归再时效处理可以改善7150铝合金的晶内和晶界组织,提高合金的成形效率,改善合金的综合性能,包括力学性能和电导率。     

Al-6.8Zn-2.3Mg-2.0Cu-0.15Sc合金的高温回归再时效工艺

采用硬度计、数字涡流金属电导仪、透射电镜(TEM)、万能拉伸试验机、扫描电镜(SEM)等对Al-6.8Zn-2.3Mg-2.0Cu-0.15Sc合金在高温回归再时效(RRA)过程中的性能与组织演变规律进行研究。结果表明:合金在170 ℃回归时,具有较高硬度与优良的抗电化学腐蚀性能,合金170 ℃回归1 h时主相η′细小弥散数量众多,在形变过程中借助位错切过与Orowan机制强化合金,强度可达625.1 MPa,伸长率达9.6%,获得了优于单级时效(T6)G.P.区强化达到的强度592.4 MPa、伸长率6.5%,强度提高32.7 MPa,伸长率提高47.7%,拉伸断口形貌SEM显示为完全的韧性断裂特征。Al-6.8Zn-2.3Mg-2.0Cu-0.15Sc合金的优秀RRA工艺为140 ℃×24 h+170 ℃×1 h+160 ℃×24 h。     

Effects of retrogression heating rate on microstructures and mechanical properties of aluminum alloy 7050

The effects of the retrogression heating rate(340℃/min,57℃/min,4.3℃/min)on the microstructures and mechanical properties of aluminum alloy 7050 were investigated by means of hardness measurement,tensile properties testing,differential scanning calorimetry(DSC)and transmission electron microscopy(TEM).The results show that the retrogression heating rate significantly affects the microstructures and mechanical properties of the alloys treated by retrogression and re-aging(RRA)process, and it is found that the medium rate(57℃/min)leads to the highest mechanical properties.The strengthening phases in the matrix are mainly the fine dispersed η′precipitates and GP zones,and the grain boundary precipitates are coarse and discontinuous η phases.     

回归再时效处理对喷射成形7055铝合金挤压厚板组织与性能的影响

采用力学性能测试、抗剥落腐蚀性能测试、透射电镜(TEM)观察等方法,研究了回归再时效(RRA)处理对喷射成形7055铝合金挤压厚板微观组织与性能的影响。结果表明:厚板采用到温装炉的方式进行回归加热时,试样升温过程仍较长,提高回归加热温度有利于缩短试样在低温阶段的停留时间。试样经120 ℃×14 h预时效+(185 ℃×130 min、190 ℃×118 min)回归+120 ℃×24 h再时效两种RRA工艺处理后纵向屈服强度分别为649.3 MPa和652.6 MPa,高于T76试样的621.5 MPa;而抗剥落腐蚀性能与T76试样接近,达到EB级。试样经RRA处理后基体沉淀析出相主要为η′相+少量GP区,其尺寸为3~10 nm,晶界析出的η相呈断续分布。提高厚板试样在回归低温阶段的加热速率有利于提高试样再时效后的强度,而提高试样回归温度有利于提高RRA试样的抗剥落腐蚀性能。     

Redistribution and re-precipitation of solute atom during retrogression and reaging of A1-Zn-Mg-Cu alloys

The redistribution and re-precipitation of solute atom during retrogression and reaging of three different A1-Zn-Mg-Cu aluminum alloys were investigated. The results of hardness and tensile strength test indicate that after pre-aging at 100 ℃ or 120 ℃ and retrogressing at 200 ℃ for various time and re-aging treatment, the hardness and strength of the alloys are all larger than those under pre-aging condition, some of them even exceed the value under peak aging（T6） condition. TEM observation shows that the PFZ formed during retrogressing in short time becomes narrow and even disappears after re-aging treatment. However, the PFZ formed during retrogressing for a long time does not narrow after re-aging treatment. It is suggested that the redistribution and re-precipitation of solute atom during re-aging treatment result in the narrowing and even disappearance of the PFZ formed during retrogression, which reinforces the grain-boundaries and presents the value of tensile strength exceeding peak-aging strength in the RRA condition, while the precipitates in the matrix of the alloys still keep or even exhibit a more dispersed distribution, and a greater effect of precipitation strengthening is obtained.     

回归再时效工艺对7055铝合金板材组织及性能的影响

通过TEM、SEM、DSC等分析及拉伸试验、电导率测试,对7055铝合金板材回归再时效后的显微组织、性能进行了系统研究。结果表明,随着回归时间的延长,回归再时效处理后的合金强度先升高后降低,导电率单调升高。与T6态相比,合金经回归再时效处理后,晶界析出相间距变大,呈断续分布,且晶内强化相的尺寸也发生了一定程度的粗化。当合金板材的回归再时效工艺为121℃×24 h+170℃×30 min+121℃×24 h时,7055铝合金板材的综合性能最优,抗拉强度达630.75 MPa,屈服强度达588.75 MPa,导电率达34.75%IACS,断裂机制为混合型断裂。     

回归再时效（RRA）处理对7050铝合金的影响

采用TEM和维氏硬度计研究了回归再时效 (RRA)处理对 70 5 0铝合金的影响 ,对处理后合金试样的强度和伸长率进行了测试 ,并对试样断口在SEM下进行了观察。研究发现 ,当回归温度为 45 3K ,在回归曲线上 ,随着回归时间的延长 ,硬度值下降 ,在 36 0 0s达到硬度最低值 ;继续延长回归时间 ,硬度值上升 ,在 72 0 0s硬度值达到最大值 ,随后硬度值下降 ;在RRA曲线上 ,随着回归时间的延长 ,硬度值上升 ,在 36 0 0s达到硬度峰 ,随后硬度值下降。当回归温度为 473K时 ,虽然与在 45 3K回归和再时效行为的趋势相同 ,但在回归曲线上 ,硬度的谷值和峰值时间都提前 ,并且硬度峰值稍微降低 ;在RRA曲线上 ,硬度峰提前。TEM研究结果表明 ,70 5 0铝合金在T6状态的硬化来自GP区。在回归处理过程中硬度谷值的产生与GP区的回溶有关 ,而峰值的产生与 η′和 η相的沉淀析出有关 ;在RRA处理过程中 ,峰值的产生与 η′和 η相的沉淀析出有关。回归温度对 70 5 0铝合金的影响与GP区、η′和 η相形核和时效沉淀动力学受回归温度影响有关。经过RRA(393K× 2 2h + 45 3K× 1h + 393K× 30h)处理后合金要比T745 1处理后的强度高 19% ,而伸长率稍微降低 ,经过RRA(393K× 2 2h + 473K× 5min + 393K× 30h)处理后合金要比T745 1处理后的强     

回归再时效处理对含Sc超高强Al-Zn-Mg-Cu-Zr合金组织与性能的影响

通过透射电镜分析、拉伸性能和电导率测试,研究回归再时效处理(RRA)工艺对含Sc超高强Al-Zn-Mg-Cu-Zr合金组织与性能的影响。结果表明：120 ℃,24 h预时效+180 ℃, 30 min回归+120 ℃, 24 h终时效的RRA处理,可以使合金保持接近T6态的强度和较高的电导率;晶内析出组织与T6态合金组织类似,而晶界析出相聚集、粗化,与双级过时效组织相似。     

回归制度对7A20铝合金RRA过程中组织性能的影响

系统研究了RRA处理过程回归制度对7A20铝合金组织性能的影响,测试了力学性能和电导率,利用OM和TEM(HRTEM)表征了晶界和晶内的微观组织结构。结果表明:在160 ℃的回归温度下,随回归时间的延长,抗拉强度由630 MPa降低到525 MPa;经120 ℃保温12 h的再时效处理后,抗拉强度由645 MPa升高到710 MPa;回归时间越长,再时效引起的强度增量越大,80 min时达到最大值185 MPa。在200 ℃的回归温度下,回归时间为10 min时,便达到峰值强度715 MPa。随回归温度提高,导电率先升高后降低,与回归时间呈正相关关系。经160、200和240 ℃下峰值强度对应的回归处理后,基体晶粒尺寸分别为55、65和70 μm,相差不大。200 ℃×10 min的回归处理+再时效处理后,晶界处存在不连续的MgZn₂相,尺寸在10~20 nm,与基体呈非共格关系;晶内存在弥散分布的纳米级η′强化析出相,与基体呈共格或者半共格关系;晶界处存在45~55 nm宽度的PFZ(Precipitation free zone)区。     

Single-aging characteristics of 7055 aluminum alloy

The microstructures and properties of 7055 aluminum alloy were studied at different single-aging for up to 48 h using hardness test, tensile test, electrical conductivity measurement, XRD and TEM microstructure analysis. The results show that at the early stage of aging, the hardness and strength of the alloy increase rapidly, the peak hardness and strength are approached after 120 ℃ aging for 4 h, then maintained at a high level for a long time. The suitable single-aging treatment of 7055 alloy is 480 ℃, 1 h solution treatment and water quenching, then aging at 120 ℃ for 24 h. Under those condition, the tensile strength, yield strength, elongation and electrical conductivity of the studied alloy are 513 MPa, 462 MPa, 9.5% and 29%（IACS）, respectively. During aging, the solid solution decomposes and precipitation occurs. At the early aging stage of 120 ℃, GP zones form and then grow up gradually with increasing ageing time. η′ phase forms after ageing for 4 h and η phase starts to occur after 24 h aging.     

二次回归再时效对Al-Zn-Mg-Cu组织、强度及剥蚀性能的影响(英文)

采用硬度、拉伸和剥落腐蚀测试手段,结合透射电镜和扫描电镜观察以及能谱分析,研究二次回归再时效对组织、力学和剥蚀性能的影响。二次回归再时效处理保持了类似一次回归再时效处理的晶内析出相,得到比T76过时效更粗大且离散的晶界析出相。与T76相比,二次回归再时效处理的晶界析出相具有更高的铜含量和更低的锌含量。因此,二次回归再时效处理保持了一次回归再时效处理的强度,同时得到了比T76过时效处理更高的剥蚀抗力。     

Investigation on strength,toughness and microstructure of an Al–Zn–Mg–Cu alloy pre-stretched thick plates in various ageing tempers

The 7B04 Al alloy is a precipitation hardenable, plate and forging material, which is widely used in China for strength critical aerospace structural applications. In this paper, fracture toughness, electrical conductivity and tensile properties of the alloy were investigated, and their dependence on ageing treatment details was described. Varying the heat treatment details strongly influences the microstructure and properties of the alloy. The alloy is identified to respond well to retrogression and reageing (RRA) temper. The retrogressing treated material at 180 °C for 1 h and then reageing for 22 h at 120 °C can achieve tensile properties comparable to a T6 condition as well as excellent conductivity. The high strength associated with optimized RRA conditions tend to result in relatively low levels of fracture toughness, but still slightly higher than T651 condition treated material. A correlation has been made among such properties, microstructure and fracture behavior, as characterized using TEM and SEM observations, and the results are discussed in the light of this relationship.     

Effect of secondary aging on microstructure and properties of cast Al-Cu-Mg alloy

To obtain better comprehensive properties of cast Al-Cu-Mg alloys, the secondary aging (T6I6) process (including initial aging, interrupted aging and re-aging stages) was optimized by an orthogonal method. The microstructures of the optimized Al-Cu-Mg alloy were observed by means of scanning electron microscopy and transmission electron microscopy, and the properties were investigated by hardness measurements, tensile tests, exfoliation corrosion tests, and intergranular corrosion tests. Results show that the S phase and θ′ phase simultaneously exist in the T6I6 treated alloy. Appropriately increasing the temperature of the interrupted aging in the T6I6 process can improve the mechanical properties and corrosion resistance of Al-Cu-Mg alloy. The optimal comprehensive properties (tensile strength of 443.6 MPa, hardness of 161.6 HV) of the alloy are obtained by initial aging at 180 °C for 2 h, interrupted aging at 90 °C for 30 min, and re-aging at 170 °C for 4 h.

     

多级热处理工艺对铝合金AA7049性能的影响(英文)

T6态高强7xxx系列铝合金对应力腐蚀开裂敏感。采用回归和再时效热处理(RRA)可以提高其抗应力腐蚀开裂性能而不降低其强度性能。研究了多级热处理工艺对7049铝合金性能和组织的影响。通过电导率测量、DSC分析和TEM组织观察,考察合金在不同热处理态的组织变化。DSC分析表明,RRA处理会导致合金的显微组织发生显著变化,RRA处理态合金的组织与T6和T73态合金的组织明显不同。RRA处理可以使合金保持在T6态的强度且获得T73态的热力学稳定性能。     

RRA过程中预时效时间对7A85铝合金组织性能的影响

系统研究了RRA处理过程预时效时间对7A85铝合金微观组织演变和性能的影响。利用Jmat-Pro软件计算了相变规律和TTT图,测试了硬度和拉伸性能指标,利用TEM表征了微观组织。结果表明,热力学平衡状态下,410 ℃开始析出MgZn₂相,体积分数达到9.5%左右;等温过程最先析出GP区,析出温度为室温~175 ℃,鼻尖温度在150 ℃左右;随着预时效时间的延长,硬度先升高后降低,20 h时达到峰值硬度192 HV;RRA处理过程,预时效时间为12 h时,屈服强度和抗拉强度达到峰值,分别为625 MPa和675 MPa;120 ℃保温20 h峰值时效状态下,η′-MgZn析出相尺寸在5~10 nm;预时效时间为12 h时,RRA处理后晶界处的Al-Zn-Mg-Cu四元相粒子呈不连续分布,尺寸在50~125 nm范围。     

Effect of aging temperature and of retrogression treatment time on the microstructure and mechanical properties of alloy AA 7075

Alloy AA 7075-T6 is studied after retrogression and re-aging. The retrogression heat treatment is performed at various temperatures and hold times, and subsequent aging is performed at 130°C for 12 h. The microstructure and mechanical properties of the alloy are studied depending on the temperature and the hold time of the retrogression heat treatment. Electron microscopic studies are preformed and mechanical characteristics are determined in tensile and impact tests. The HRB microhardness is measured.     

Effect of Retrogression Heat Treatment Time on Microstructure and Mechanical Properties of AA7010

The effect of retrogression time during retrogression and re-aging (RRA) treatment of AA7010 is evaluated by performing tensile tests and characterizing the microchemistry of the grain boundary precipitates (GBPs) using transmission electron microscope coupled with the energy-dispersive spectroscopy. Retrogression time is evaluated so that the ultimate tensile strength of the RRA-treated sample is equal to that of the T6-treated sample and the grain boundary microstructure similar to that of the over-aged (T7451) condition. The investigation reveals that the sample retrogressed at 200 °C for 20 min has UTS of 586 MPa which is equivalent to that of the T6 sample and 11.5% higher than that of the T7451 condition. The fracture toughness of the RRA-treated sample was 41 MPa√m. Microstructure of the RRA-treated sample is similar to T7451, along the grain boundaries and in the grain interior similar to that of the T6-treated sample. Energy-dispersive spectroscopy confirmed the increment of Cu content on the GBP’s with increase in the retrogression time, which is expected to improve the stress corrosion cracking resistance of the alloy.     

DSC AND TEM STUDY OF ULTRA HIGH STRENGTH ALUMINUM ALLOY

In this paper, the effect of RRA treatment on the microstructure evolution of a high strength aluminum alloy was investigated using DSC, TEM and SADP technology. The results show that the precipitation resulting from RRA is extremely fine and distributed homogeneously in the grains, being slightly coarser and more stable than that of T6 temper. While, the grain-boundary precipitation is very close to that of the alloy at T73 temper, being coarse and discontinuous. High retrogression temperature and long retrogression time leads to a more stable microstructure after re-aging.     

Effect of Retrogression and Re-Aging on Tensile Mechanical Properties in Transverse Direction of Extruded Rods from Aluminum Alloy AA7049

Metal Science and Heat Treatment - The effect retrogression and re-aging (RRA treatment) on the tensile properties in the transverse direction of extruded rods from aluminum alloy AA7049 is...