7A04铝合金时效强化的试验研究及其强度计算

以铝合金时效强化动力学理论为基础,研究了高温预热固溶处理后不同的时效工艺对7A04铝合金组织和性能的影响,得到了优化的双级时效工艺.在此基础上,建立了合金成分、析出相尺寸及其体积分数与合金屈服强度之间的计算模型,并利用该模型对7A04铝合金单级时效和双级时效后的屈服强度进行计算.该模型集成了固溶强化和弥散强化对合金屈服强度的贡献,在达到最大时效强度之前,计算结果和试验测量结果较为一致.此后,随着强化相体积分数计算偏差增加,计算强度与测量强度之间的误差也有所增大.     

Zn对Mg-3Sn-1.5Si合金组织和时效硬化效果的影响

利用X射线衍射仪、光学显微镜、扫描电镜和显微硬度计研究了Zn对Mg-3Sn-1.5Si合金相组成和组织的影响以及显微硬度随时效时间变化的关系。结果表明,铸态及其时效态合金第二相主要由Mg Zn、Mg2Sn和Mg2Si组成。当Zn由3%增加到8%时,共晶Mg Zn相逐渐增加。5%Zn扩大了Si在合金中的固溶极限,增加共晶Mg2Si析出的体积分数,并使部分Mg2Si转变成Mg2(Si,Sn)复合结构。而8%降低了Si的固溶极限,增加了初生Mg2Si析出的体积分数。当合金中Zn为8%时,能加速Mg2Sn的析出,使第二个硬度峰值出现的时间明显缩短。三种合金时效硬度峰值和对应的时效时间分别为67.9 HV/24 h,72.8 HV/48 h和84.5 HV/48 h。弥散分布的Mg+Mg Zn球化共晶相对基体具有强化作用,使合金整体硬度提高。     

深冷处理对7A99铝合金峰值时效析出相的影响

对7A99超高强铝合金反向挤压材采用T6峰值时效处理与冷热循环峰值时效热处理(简称T6-DCT),通过TEM、HRTEM与3DAP研究深冷处理对峰值时效析出相的种类、分布、尺寸以及析出密度的影响。结果表明,冷热循环峰值时效处理后晶粒内部析出相种类增多,由η'相变成η'相与η相共存;冷热循环峰值时效处理可以将析出相的平均等效半径由1.201nm减小为1.001 nm,将析出相的密度由4.53×10~(24)/m~3提升至7.55×10~(24)/m~3,实现弥散强化;深冷处理可以降低Zn、Mg元素的微观偏聚,提高析出相的分布均匀性。     

具有盘／片状，棒／针状析出相铝合金的时效—屈服强度变化模型

以析出热力学、长大动力学及强化理论为基础，研究了具有盘／片状、棒／针状析出相铝合金在时效过程中的析出相尺寸、体积分数变化及其对时效合金强化效果的影响，得到了合金成分、时效参数与组织参数、屈服强度间的解析关系式，进而从微观—宏观相结合的角度建立起了具有盘／片状、棒／针状析出相铝合金的时效工艺—屈服强度量化模型，并将该模型应用于6061合金和Al—Zn—Mg合金的时效性能预测，取得了较满意的结果。同时，详细讨论了析出相长径比对时效温度以及合金处理状况的依赖关系。     

铸造ZC62镁合金的时效行为

利用光学金相、X射线衍射、扫描电镜和透射电镜研究了ZC62镁合金铸态和固溶时效后的显微组织,初步确定了时效ZC62镁合金中主要合金相的种类和形态,ZC62镁合金铸态组织主要由初晶Mg基体和（Mg＋CuMgZn）共晶构成;固溶处理后,晶界大部分非平衡共晶组织溶解,固溶时效后析出相主要有三类：颗粒相CuMgZn（四方晶系）,尺寸大小约300nm;与颗粒相相连的曲线状“析出相”,长度约1μm;与颗粒相无关的平行、细针状相Mg（Zn,Cu）2（六方晶系）,长约200nm,同时与Mg基面（0001）垂直,并与基体保持某种取向关系．第二类（曲线状）“析出相”实际上是在位错线上形核的Mg（Zn,Cu）2;而第三类（细针状）析出相则是在Mg基体中均匀形核的Mg（Zn,Cu）2。     

锌镁比对7085铝合金时效组织演变的影响

通过硬度和电导率测试,结合金相显微分析、透射电镜微观组织观察和DSC分析,研究了Zn/Mg比对7085铝合金120℃单级时效的影响.结果表明,120℃时效时,不同Zn/Mg比值的7085铝合金分别在4h和26 h到达GP区和(n)相强化的2个峰值,但Zn/Mg=7.27的合金两个时效峰值时间较Zn/Mg=5.84的合金略微提前.微观组织观察表明,时效4h后Zn/Mg=7.27的合金晶内已经有较多粗大的沉淀相(5～10 nm)析出,衍射斑点显示这些较大沉淀相为 η’相,而在Zn/Mg=5.84的合金内则较少发现.细小的GP区的减少以及较大 η’相的析出,降低了第二相粒子对合金的强化效果.DSC结果也表明,Zn/Mg=7.27的合金的GP区和η′相的析出温度都较Zn/Mg=5.84稍微降低.     

后时效对超细晶6061铝合金微观结构与力学性能的影响

采用TEM、XRD、显微硬度实验和拉伸实验，利用等通道转角挤压(ECAP)和后时效相结合制备出超细晶6061铝合金，对其微观结构和力学性能进行了对比研究。结果表明，经过两道次ECAP后，合金的平均晶粒尺寸细化到210 nm。两道次ECAP+80℃、20 min低温后时效，合金的平均晶粒尺寸为278 nm，基体中弥散分布细小的针状β’’、L相和Q’相纳米级析出物，拉伸强度和屈服强度分别达到514和483 MPa，并保持了15.1%的均匀伸长率。ECAP在基体中引入的大量位错促进了析出相的形核，加速了时效过程中的析出动力学；ECAP低温后时效，合金的高强度和高韧性与细晶强化、位错强化和纳米析出相强化有关。基于实验结果，分析了合金ECAP和后时效过程中时效相的演变过程。     

-180℃深冷处理对7A99铝合金峰值时效强韧性能与析出行为的影响

对7A99超高强铝合金反向挤压板材采用T6峰值时效处理与-180℃冷热循环时效热处理(简称T6-DCT),通过XRD、TEM、HRTEM与3DAP研究-180℃深冷处理对7A99铝合金反向挤压板材强韧性能以及析出行为的影响。结果表明,-180℃冷热循环时效处理使得铝基体的晶格常数由由0.40551 nm 增至0.40626 nm,起到了一定的固溶强化作用;-180℃冷热循环时效处理后晶粒内部生成大量与基体非共格的η相,晶界处η相呈现断续分布并形成晶界无析出带,降低材料的拉伸强度;-180℃冷热循环时效处理促进基体中Zn和Mg元素原子的微观偏聚,导致了Zn和Mg元素的非均匀析出;-180℃深冷处理可以减小时效终态析出相的平均等效半径与析出密度,将等效半径由1.2 nm减小至1.14 nm,将析出密度由4.53×10₂₄/m₃降低至3.87×10₂₄ /m₃,削弱析出强化效果; -180℃冷热循环时效处理后合金的强韧匹配性能得到显著改善,强度略有降低,韧性显著提高。     

时效处理对优质GH738合金组织及力学性能的影响

采用力学性能测试与组织观察相结合的方式研究了时效温度和保温时间对优质GH738合金组织及性能的影响规律。结果表明,时效温度和时间均会对γ′相的体积分数和尺寸产生影响。当时效温度在720~800 ℃时,随着时效温度升高,合金强度下降,一次和二次γ′相分别长大30 nm和8 nm,一次γ′相体积分数增加,二次γ′相体积分数减少,时效温度为800 ℃时一次γ′相体积分数达到峰值,约为8%。当保温时间为0~48 h时,随时效时间延长,合金强度先升高后降低,两类γ′相分别长大20 nm和6 nm,一次γ′相体积分数先增后减,二次γ′相体积分数则变化相反。当保温时间为8 h时,两类γ′相体积分数分别达到峰/谷值,含量约为8%和12%。γ′相尺寸和体积分数的变化,特别是体积分数的变化,导致位错的两种强化机制作用效果不同,致使强度发生变化。     

铝合金时效强化的实验研究及屈服强度计算

以铝合金时效强化动力学为理论基础,研究了时效处理工艺参数对7A04铝合金组织和性能的影响.得到了优化的分级时效工艺.在此基础上,建立了时效强化相类型、尺寸、体积分数与铝合金屈服强度关系的计算模型;给出了固溶强化、弥散强化对铝合金屈服强度影响的统一表达式;并利用该模型对7A04高强铝合金单级时效和二级时效处理后的屈服强度进行了预测.计算结果表明,在达到最大时效强度前,屈服强度计算结果与实验测量结果基本一致;此后,由于强化相体积分数计算偏差增加,屈服强度计算的准确度有所下降.     

Effect of high-temperature pre-precipitation on mechanical properties and stress corrosion cracking of Al-Zn-Mg alloys

1　INTRODUCTIONMediumandhighstrengthAl Zn Mgseriesaluminumalloysarethe primaryweldingstructurematerialsofaerocrafts ,transportationvehiclesandmilitaryequipments[1,2 ] ,duetoitsbetterweldabilityandexcellenttechnologicalproperty .Buttheexten siveutilizationofthesealloysishamperedbyitspoorstresscorrosioncracking (SCC)resistance[3,4 ] .Ac cordingly ,manystudieshavebeenconcernedwithsuchaproblemashowtoimprovestresscorrosionre sistanceofAl Zn Mgalloyswithnon deterioratedstrength[3,58] .Atpres…     

喷射成形Al—Zn—Mg—Cu系高强铝合金的组织与性能

利用喷射成形工艺制备了Al-Zn-Mg-Cu系高强铝合金材料,研究了热挤压工艺与热处理工艺对材料微观组织与力学性能的影响,在峰时效的情况下材料表现出了高的力学性能指标,抗拉强度达到754MPa,屈服强度达到722ＭＰa,断裂延伸率达到8%,与采用传统铸造变形工艺制备的同类合金相比（σb≥610MPa,σ0.2≥580MPa,δ≥4%),性能有了明显的提高。合金性能的提高与其基体中呈弥散分布的Mg7Zn3相有很大的关系,合金的主要强化机制是沉淀强化。     

High-Strength Weldable Corrosion-Resistant Aluminum Alloy for Bearing Building Structures

A weldable corrosion-resistant alloy based on the Al - Zn - Mg system has been developed. The alloy has high strength characteristics (σ_r ≥ 500 MPa and σ_0.2 ≥ 450 MPa) and is well weldable (the factor of weld concavity is 0.8 – 0.95). The substrate metal and welded joints of this metal are characterized by high corrosion resistance, good ductility and fracture toughness, and high fatigue resistance. The alloys and the process of its production are based on known scientific achievements of the All-Russia Institute of Light Alloys (VILS) in the field of alloys of the Al - Zn - Mg system and in the field of alloying of aluminum alloys with scandium. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 30 – 35, August, 2005.     

复合添加Cr、Mn、Zr对Al-Zn-Mg合金组织和性能的影响

通过光学显微镜、扫描电镜、透射电镜观察以及拉伸试验等手段,研究Cr、Mn、Zr微合金元素对Al-Zn-Mg合金组织和性能的影响。结果表明:复合添加Zr、Mn、Cr在基体上析出大量不规则的、直径为10~20 nm与基体共格的(Al,Cr)₃Zr粒子。(Al,Cr)₃Zr粒子弥散相能强烈钉扎位错、阻碍位错和亚晶界迁移,显著抑制再结晶和晶粒长大。复合添加Zr、Mn、Cr的Al-Zn-Mg合金的抗拉强度和规定塑性延伸强度分别提高34 MPa、19 MPa,具有较好的加工性能和力学性能。     

Effect of trace rare earth element Er on Al-Zn-Mg alloy

1 Introduction Remarkable effects of rear-earth elements on aluminium alloys, such as eliminating impurities, purifying melt, refining as-cast structure, retarding recrystallization and refining precipitated phases, have been widely researched for a long…     

Influence of scandium on weldability of 7010 aluminium alloy

Abstract

The commercial 7000 series aluminium alloys are based on medium strength Al–Zn–Mg and high strength Al–Zn–Mg–Cu systems. The medium strength alloys are weldable, whereas the high strength alloys are non-weldable. This is because the amount of copper present in these alloys gives rise to hot cracking during solidification of welds. As a result, the high strength Al–Zn–Mg– Cu base alloys are not used for applications where joining of components by welding is an essential step. In the present study, using a combination of qualitative Houldcroft test and quantitative Varestraint test, it is shown that a small addition of scandium to the commercial 7010 alloy reduces the hot cracking susceptibility during solidification of welds produced by the gas tungsten arc welding process. The improvement in weldability is found to be the result of the considerable grain refinement in the weld structure following the scandium addition. The results of microhardness and tensile tests are further described within the context of the present work to demonstrate that the 7010+Sc welds also exhibit a combination of improved strength and ductility.     

Sn对镁合金显微组织和力学性能的影响

研究了Ｓｎ对镁合金显微组织和力学性能的影响。研究结果表明,纯镁中加入Ｓｎ后能使纯镁铸锭中粗大的柱状晶转化为均匀的等轴晶,并有效地细化晶粒,同时在显微组织中形成具有立方Ｃ１结构的Ｍｇ２Ｓｎ颗粒相。由于Ｍｇ２Ｓｎ颗粒相显微硬度和熔点高,热稳定性好,因而对基体具有有效的弥散强化作用,提高了ＭｇＳｎ二元合金的室温及高温强度。在Ｍｇ９Ａｌ０．８Ｚｎ基合金中加入少量的Ｓｎ便能有效地提高合金的耐热性,而加入过多的Ｓｎ反而会导致合金高温强度下降。     

Theoretical design and distribution control of precipitates and solute elements in Al−Zn−Mg−Cu alloys with heterostructure

In order to simultaneously improve strength and formability, an analytical model for the concentration distribution of precipitates and solute elements is established and used to theoretically design and control the heterogeneous microstructure of Al−Zn−Mg−Cu alloys. The results show that the dissolution of precipitates is mainly affected by particle size and heat treatment temperature, the heterogeneous distribution level of solute elements diffused in the alloy matrix mainly depends on the grain size, while the heat treatment temperature only has an obvious effect on the concentration distribution in the larger grains, and the experimental results of Al−Zn−Mg−Cu alloy are in good agreement with the theoretical model predictions of precipitates and solute element concentration distribution. Controlling the concentration distribution of precipitates and solute elements in Al−Zn−Mg−Cu alloys is the premise of accurately constructing heterogeneous microstructure in micro-domains, which can be used to significantly improve the formability of Al−Zn−Mg−Cu alloys with a heterostructure.     

Correlations among stress corrosion cracking,grain-boundary microchemistry,and Zn content in high Zn-containing Al–Zn–Mg–Cu alloys

The correlations among the corrosion behaviour, grain-boundary microchemistry, and Zn content in Al–Zn–Mg–Cu alloys were studied using stress corrosion cracking (SCC) and intergranular corrosion (IGC) tests, combined with scanning electron microscopy (SEM) and high-angle angular dark field scanning transmission electron microscopy (HAADF-STEM) microstructural examinations. The results showed that the tensile strength enhancement of high Zn-containing Al–Zn–Mg–Cu alloys was mainly attributed to the high density nano-scale matrix precipitates. The SCC plateau velocity for the alloy with 11.0 wt.% Zn was about an order of magnitude greater than that of the alloy with 7.9 wt.% Zn, which was mainly associated with Zn enrichment in grain boundary precipitates and wide precipitates-free zones. The SCC mechanisms of different Zn-containing alloys were discussed based on fracture features, grain-boundary microchemistry, and electrochemical properties.     

Effect of nano Al (Scx−1Zrx) precipitates on the mechanical and corrosion behavior of Al‐2.5 Mg alloys

Microanalytical, mechanical, and corrosion studies were undertaken to investigate the effect of nano‐precipitates of Al(Sc_x−1Zr_x) on the mechanical and corrosion characteristics of Al 2.5 alloy containing 0, 0.15, 0.3, 0.6, and 0.9 wt% of Sc with 0.15 wt% Zr. Addition of 0.3% Sc significantly increased the yield strength due to small precipitates sizes (5–19 nm) and the high coherency of the nano‐particles. Largest contributor to the strength was grain boundary strengthening caused by pinning of grain boundary precipitates. The alloys showed a good resistance to corrosion in 3.5 wt% neutral chloride solution. The alloy offered a high passivation tendency because of homogeneous coherent nano Al(Sc_x−1Zr_x) precipitates. The nano precipitates interfaces and homogeneously distributed Al₃Sc precipitates offer a high degree of corrosion resistance to Al 2.5 Mg Sc alloys compared to conventional aluminum alloys, such as Al 6061 and Al6013.