Al-Zn-Mg-Cu-Zr合金型材的回归再时效析出行为研究

采用拉伸试验、硬度测试、电导率测试和透射电镜分析等方法研究了Al-Zn-Mg-Cu-Zr合金型材在180℃回归再时效阶段的析出行为。结果表明,合金在回归处理开始阶段,大部分的GPI区和部分尺寸细小的η’相迅速回溶到基体,合金的强度和硬度值降低至最小值;随着回归时间的延长,晶内析出了高温稳定性更好的η’相和GPII区,合金的强度和硬度值升高;进一步延长回归处理时间,合金中部分的η’相开始转变为η相,合金的强度和硬度值略有下降。再时效阶段,合金在较低的温度继续析出GPI区和较小尺寸的η’相,合金的强度和硬度值小幅增大。     

Al-Zn-Mg-Cu合金时效析出相的研究

采用硬度测试、电导率测量、透射电镜及三维原子探针对Al-Zn-Mg-Cu合金470℃固溶2h,然后120℃时效后的合金组织和相关性能进行分析.结果表明,试验合金在120℃时效6h后硬度值的变化比较小,此时的强化析出相为GPI区和η’相,GPI区是由Zn和Mg共同组成的团簇,η’相的化学成分不是固定的,Zn/Mg比的范围为1～1.6.合金的电导率在时效初期迅速升高,时效时间超过6h后合金的电导率上升的速度比时效初期的小.     

喷射沉积Al-Zn-Mg-Cu合金双级时效的微观组织和力学性能研究

采用喷射沉积技术制备了Al-12Zn-2.4Mg-1.1Cu合金。通过高分辨电子显微镜和硬度测试等手段,研究分析了双级时效处理对喷射沉积Al-Zn-Mg-Cu合金微观组织和力学性能的影响。结果表明:合金经120℃(14 h)时效后,硬度达到峰值,晶内主要强化相为η′亚稳相和少量的GPⅡ区,晶界析出相呈连续分布;合金经120℃(14 h)+160℃(0.5 h)、120℃(14 h)+160℃(16 h)、120℃(14 h)+160℃(24 h)双级时效后,硬度较峰时效相比,分别下降了5.92%、11.13%、15%,它们的晶内析出相依次是细小的η′相、粗大的η′相、粗大的η相,晶界析出相呈断续状分布,晶内和晶界的析出相明显长大,并且在120℃(14 h)+160℃(16 h)、120℃(14 h)+160℃(24 h)时效后,出现了晶界无沉淀析出带。通过对TEM图像的测量,可以得到η相和η′相的晶格参数分别为0.520、0.860 nm和0.490、1.402 nm;对η和η′相解卷处理,可以提高像的分辨率,然后用jems对η和η′相模拟,可以确定原子的基本位置。     

RRA处理对超高强铝合金微观组织与性能的影响

采用硬度、电导率测试、DSC热分析及TEM观察等手段,研究了回归再时效处理对一种新型低频电磁铸造超高强铝合金组织与性能的影响.研究发现:合金在120℃时效24 h后具有较高的硬度和强度水平.合金合宜的回归再时效处理工艺为120℃、24 h预时效,180、60 min回归,之后120℃、24 h再时效.在此条件下,合金的抗拉强度、屈服强度、延伸率和电导率(IACS)分别为721 MPa、700 MPa、8.1%和34.5%.TEM观察表明:回归再时效过程中合金性能的变化与其微观组织的演变密切相关;回归初期,GP区和η相的回溶导致合金硬度下降;随后,η和η相的析出使硬度重新上升至峰值;最后,η相转变成η、以及η相粗化引起硬度单调下降;再时效后析出的η相提高了合金的强度、硬度和电导率.     

时效制度对7150铝合金组织和性能的影响

通过室温力学性能和电导率测试以及显微组织的透射电镜分析,研究了时效制度对7150铝合金组织、性能和电导率的影响.结果表明,120℃×6 h+165℃×(6～12)h的二级时效使合金保持高的屈服强度(＞600MPa),同时具有较高的电导率(＞38%IACS).120℃单级时效后,析出相尺寸为1～5nm,分布均匀,主要为GP区和η′相.双级时效后,沉淀相主要为η′相和η相.双级时效制度保证合金具有较高强度的同时,提高了合金的电导率.     

Al-Zn-Mg-Cu合金时效沉淀相应变场研究

利用高分辨透射电子显微镜研究喷射成形Al12Zn2.4Mg1.1Cu合金不同时效时间析出的GPⅡ区和η′亚稳沉淀相,并结合几何相位分析软件计算了GPⅡ区和η′亚稳沉淀相的应变场。研究表明:该合金的时效硬度变化和主要析出相的变化密切相关。GPⅡ区大量弥散析出是造成合金硬度迅速上升的主要原因。η′是峰值时效状态下的主要析出强化相。析出相从GPⅡ区到η′的转变,是应变峰值较小的分散半共格应变场取代了应变峰值较大的集中共格应变场的过程。并对GPⅡ区和η′亚稳沉淀相的演变过程及强化机制进行了讨论。     

固溶-单级时效处理对7055铝合金力学和电学性能的影响

采用硬度测量、拉伸力学性能测试、电导率测定、显微组织结构分析方法，研究了不同固溶、单级时效处理条件下7055铝合金的力学性能、电学性能和显微组织结构。结果表明，7055合金有很强的时效强化效应，时效初期，合金硬度和强度迅速上升，时效4h即接近硬度和强度峰值，达到峰值后合金的硬度和强度仍维持在很高的水平；时效过程中，固溶体分解析出η′(MgZn2)相，随时效时间延长，析出相增加；7055合金适宜的固溶—单级时效处理工艺为480℃ 1h，水淬，120℃ 24h时效。在此条件下，合金的抗拉强度、屈服强度、伸长率、布氏硬度和电导率分别为513N／mm^2、462N／mm^2、9．5％、HB172和29％IACS。     

双级时效对7085铝合金组织和性能的影响

采用硬度、电导率、力学拉伸、慢应变速率拉伸试验及透射电镜等测试分析方法,研究双级时效对7085铝合金组织和性能的影响。结果表明:预时效热处理主要析出相为GP区和η′相,预时效时间对合金硬度和电导率的影响较小。随着第二级时效时间的延长,合金的抗拉强度和屈服强度先增大后减小,电导率和抗应力腐蚀性能提高,晶界析出相由连续分布变为非连续分布。第二级时效温度越高,合金强度随时效时间的延长,降低得越显著。采用(110℃,6 h)+(160℃,12 h)双级时效热处理,合金的抗拉强度、屈服强度、伸长率及电导率分别为515MPa、487MPa、11.7%、38%(IACS)。     

7B04铝合金的时效沉淀析出及强化行为

利用差示量热法(DSC)、透射电镜(TEM)、选区电子衍射(SAED)、常规力学性能测试等手段研究了7B04铝合金时效沉淀析出及强化行为。结果表明:该材料存在显著的自然时效现象,大量的GPⅠ区沉淀析出是自然时效强化的主要原因;合金在120℃进行人工时效的初期析出大量GP区,使材料的强度迅速提高,时效8 h后,其横向极限抗拉强度即可达到570 MPa,时效22 h时可达强度峰值点,此时GP区(包括GPⅠ和GPⅡ区)和η′相是主要强化相;峰值时效后继续延长时效时间,材料的强度无明显降低,极限抗拉强度保持在590 MPa左右。     

回归再时效处理对7050铝合金微观组织与性能的影响

采用拉伸试验、电导率测试和透射电镜分析等方法研究了7050厚板在185℃回归再时效过程中的析出行为,并与T6时效工艺进行了比较研究。结果表明,7050-T6的合金强度较高(屈服强度约为507 MPa),但其耐应力腐蚀性能较差,电导率仅为16.59 MS/m。经回归处理后,合金的力学性能呈上升后下降的趋势,电导率呈现总体上升的趋势。当回归处理1h时,7050-RRA合金的屈服强度提升至523 MPa,电导率达到20.07 MS/m,综合性能优异。TEM结果表明,T6处理后,基体强化相主要为GP(I)区和η′相;随着回归时效进行,GP(Ⅰ)区开始转变为GP(Ⅱ)区和η′相,η′相逐渐增多使强度上升至峰值;回归处理4h后,GP区基本消失,η′相开始转变成η相,合金强度下降。     

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.     

Microstructure and mechanical properties of forged Al-7.1Zn-1.1Mg-1.6Cu-0.14Zr alloy after two-step ageing treatment at 120 and 170℃

The tensile properties,electrical conductivity,and microstructure of the forged Al-7.1Zn-1.1Mg-1.6Cu-0.14Zr alloy were investigated after a two-step ageing treatment at 120 and 170℃.The results indicate that the strength of the alloy reaches the peak value at 170℃ for 1 h during the second step ageing and then decreases sharply.However,the electrical conductivity value increases continuously with the second ageing time increasing.The fracture mechanism of the alloy is intergranular fracture for 1 h and then changes to dimple transgranular fracture later,and the toughness of the alloy is improved significantly.The phases of η' and η are major precipitates in the alloy under the two-step ageing condition.Discontinuous grain boundary precipitates and precipitate-free zones along the grain boundary are clearly observed.     

Mg-4Zn-2Al-0.5Ca合金时效沉淀过程的相演变

利用高分辨透射电镜和扫描电镜分析了Mg-4Zn-2Al-0.5Ca合金时效沉淀过程中的相演变。结果表明:试验合金的时效硬化曲线呈现典型的时效硬化特征。试验合金在160℃时效达到峰值硬度时其沉淀相有:平行于(0001)Mg的圆盘状沉淀相、(梳齿状)块状沉淀相以及大量的亚稳过渡相。随时效时间的延长,生成长条状相,但基体中依然存在很多后析出的细小的弥散分布的粒状沉淀相。120℃×230 h时效处理后的微观组织中存在着蜂窝状组织,宽度为3～4 nm的长条状沉淀相,直径为5～7 nm的球状沉淀相;这些沉淀相的存在大大提高了合金的硬度。     

Effect of Different Ageing Processes on Microstructure and Mechanical Properties of Cast Al–3Li–2Cu–0.2Zr Alloy

The effect of different ageing processes on microstructure and mechanical properties of cast Al–3 Li–2 Cu–0.2 Zr alloy was investigated using transmission electron microscopy and tensile tests. The results showed that the mean size of δ′-Al_3 Li particles and the number density of Cu-rich precipitates both increased with increasing ageing temperature from 150 to 190 °C for 24 h, resulting in increasingly high strength. In contrast, the ductility deteriorated with the increase in ageing temperature as a result of the intensified planar slip. The duplex low-to-high ageing treatment(120 °C for 6 h followed by 160 °C for 24 h) was shown to be beneficial to the ductility compared with the corresponding single-stage ageing treatment(160 °C for 24 h). The reduced slip length induced by the precipitation of θ′-Al 2 Cu phases was found to be mainly responsible for this ductility improvement.     

Microstructure and mechanical properties of forged AI-7.1Zn-1.1Mg- 1.6Cu-0.14Zr alloy after two-step ageing treatment at 120 and 170℃

The tensile properties, electrical conductivity, and microstructure of the forged Al-7.1Zn-1.1Mg-1.6Cu-0.14Zr alloy were investigated after a two-step ageing treatment at 120 and 170°C. The results indicate that the strength of the alloy reaches the peak value at 170°C for 1 h during the second step ageing and then decreases sharply. However, the electrical conductivity value increases continuously with the second ageing time increasing. The fracture mechanism of the alloy is intergranular fracture for 1 h and then changes to dimple transgranular fracture later, and the toughness of the alloy is improved significantly. The phases of η′ and η are major precipitates in the alloy under the two-step ageing condition. Discontinuous grain boundary precipitates and precipitate-free zones along the grain boundary are clearly observed.     

AA 7055铝合金时效析出强化模型

利用小角度X射线散射技术获得的系列定量信息,综合运用时效析出动力学理论和析出相切过、绕过强化机制,研究了AA 7055铝合金在120和160℃时效过程中的屈服强度演变模型。结果表明,在时效早期盘状析出相的盘面半径和半厚度均与t^1/2(t为时效时间)成线性关系;在时效后期,析出相尺寸则与t^1/3成线性关系。时效过程中析出相体积分数与t的变化关系遵循JMA (Johnson-Mehl-Avrami)型表达式。综合考虑了GPI区和η’相2类析出相对合金强度的贡献,并且分别考察了这2类析出相的模量强化机制和共格应变强化机制,最终建立了AA 7055铝合金在120和160℃时效过程中的屈服强度变化模型,确定了该合金时效过程中析出相与屈服强度之间的定量关系。     

Effects of the two-step ageing treatment on the microstructure and properties of 7B04 alloy pre-stretched thick plates

The effects of the two-step ageing parameters （temperature and time） on the mechanical properties and electrical conductivity of 7B04 （A1-Zn-Mg-Cu） pre-stretched thick plates were studied. The results reveal that the initial T1 ageing contributes a major increase of the tensile strength, and the 0.2% proof stress value reaches 482 MPa after ageing for 7 h at 115℃. Behavioral differences in the tensile properties of the alloy after the two-step ageing treatment were less with the first-step ageing at 115~C for different time periods （7, 14, and 21 h）. The effects of the second ageing parameters on the properties and microstructure of the 7B04 alloy were remarkable. TEM analysis of the samples aged at Temper I （7 h at 115℃ ＋ 12 h at 160℃） and Temper II （7 h at 115℃ ＋ 16 h at 165℃） indicates that two kinds of phases, i.e. 11＇ and 11 phases, precipitate from the matrix and efficiently improve the tensile strength of the alloy, and the grain boundary precipitates are coarse and discrete. There are obvious precipitate free zones （PFZs） along the grain boundary in the microstructure of the alloy after the two-step ageing treatment.     

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。     

直流电对7B04铝合金固溶与时效组织和性能的影响

本文采用拉伸试验、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等手段,研究了7B04铝合金在施加和不施加直流电条件下,经470℃固溶和100-140℃时效处理后的组织和力学性能。与传统的T6处理(470 oC/30 min+120 oC/24h)相比,固溶和/或时效处理时施加500A的电流,可显著提高GPII区的析出密度,进而提高峰时效状态下的拉伸强度和延伸率。固溶过程中施加直流电可将随后时效合金达到峰值强度的时间明显缩短12h。     

时效对超高强含Sc铝合金组织和性能的影响

采用维氏硬度测量、室温拉伸性能测试和显微组织结构分析,研究了不同时效制度下Al-Zn-Cu-Mg-Sc-Zr合金的力学性能、腐蚀性能和显微组织.结果表明,该合金具有显著的时效硬化效应,随时效温度的升高,合金达到时效硬度峰值的时间缩短.合金适宜的时效制度为120℃24h.此时,合金的抗拉强度、屈服强度、伸长率和维氏硬度分别为696N/mm2、654N/mm2、11.1％和211.2HV.合金中主要强化相为GP区和η'相,主要强化作用为沉淀强化及弥散强化.时效过程中Al3Sc和Al3(Sc,Zr)质点表现出较强的热稳定性;合金抗晶间腐蚀能力随时效时间的延长而增强.