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.     

Influence of heat treatment regimes on microstructures and fracture characteristics of 7055Al alloy containing Ag

Tensile properties, fracture characteristics and microstructures of 7055 aluminum-based alloy containing Ag after T6, T73 and RRA treatment were investigated. The results show that RRA treatment retains strength of 7055-T6 with higher electrical conductivity close to that of 7055-T73 alloy, but its elongation decreases greatly.SEM fractographs reveal that intergranular cracking and shear-type transgranular cracking are both presented on the fracture appearance of 7055-T6 specimen. After T73 treatment, the fractographs mainly consist of dimple-type transgranular cracking with minor intergranular cracking. For 7055-RRA specimen, intergranular cracking domi-nates with minor dimples on the fracture surface. The type and size of precipitates, width of grain boundary and the ability of precipitates to impede dislocation motion vary with heat treatment regimes. Three frature models were built on the basis of microstructural analyses.     

热处理制度对含Ag的7055铝合金断裂特征的影响

研究了含Ag7055铝合金在T6，T73，RRA3种热处理状态下的力学性能、断裂特征及显微组织变化特征。实验结果表明，RRA处理可以在保持T6状态强度的同时，获得较高的电导率，然而试样的延伸率相对较低；断口SEM形貌观察表明，T6状态断裂机制为剪切型穿晶断裂和沿晶断裂同时并存，而T73处理后，主要呈韧窝型穿晶断裂，沿晶断裂部分减少，RRA试样断口则主要为沿晶断裂，并在晶界面上分布有韧窝型断裂特征；由于不同热处理状态下，强化相不同且其阻碍位错滑移能力也不同，同时晶界PFZ宽度也发生变化，这些因素的综合作用导致不同热处理状态下的断裂特征不同。     

7A41铝合金的力学性能和耐蚀性能

采用常温拉伸性能测试、应力腐蚀性能测试和盐雾腐蚀性能测试方法分别对双级时效态7A41铝合金的力学性能及耐蚀性能进行了测试。采用光学显微镜、扫描电镜(SEM)和透射电镜(TEM)对合金的显微组织、拉伸断口微观形貌进行了表征。结果表明,T6状态下合金的抗拉强度、屈服强度和伸长率分别为505 MPa、474 MPa和16.3%。耐应力腐蚀性能优异,应力腐蚀敏感系数为3.98%,合金的盐雾腐蚀速度为0.0914 mm/y。TEM观察分析表明,Tb态7A41铝合金晶内均匀弥散地分布着纳米级析出相,晶界上分布着大量的非连续析出相,析出相尺寸为20~50 nm,非连续析出相有效地阻碍了合金晶间腐蚀的路径,良好的组织特征保证了合金的综合性能。     

时效制度对Al-Zn-Mg-Cu铝合金应力腐蚀敏感性的影响

采用恒载荷拉伸应力腐蚀试样、恒变形C环应力腐蚀试样以及预裂纹双悬臂(DCB)试样,对不同时效制度处理的7B04预拉伸厚板的应力腐蚀性能进行测 定,并进行了扫描电镜断口形貌分析.研究表明,其抗应力腐蚀性能与时效制度密切相关,从峰值时效T6状态到过时效T74、T73状态,应力腐蚀敏感性依次降低.预拉伸厚板T6状态的应力腐蚀门槛值为120 MPa,而T74状态的应力腐蚀门槛值为300 MPa.T74状态的应力腐蚀开裂应力强度因子KISCC是T6的近2倍,且应力腐蚀裂纹扩展速率(da/dt)也明显降低.T6状态和T74状态的7B04铝合金应力腐蚀断裂为沿晶断裂,并有二次裂纹.而T73状态的断口形貌无典型的应力腐蚀沿晶断裂特征,为孔洞腐蚀特征,而且其KISCC几乎接近KIC.这说明T73状态的7B04铝合金几乎没有应力腐蚀敏感性.     

T6时效和T6I6时效对6005A铝合金微观组织和性能的影响

采用硬度测试、晶间腐蚀试验,透射电镜(TEM)和高分辨透射电子显微(HRTEM)分析研究6时效和T6I6时效工艺处理对6005A铝合金硬度和晶间腐蚀性能的影响。结果显示:6005A铝合金经T6峰时效175℃、12 h后,虽然硬度达到了120 HV,但存在严重的晶间腐蚀倾向,腐蚀深度约为100μm,同时,晶界上的析出相呈不连续分布,尺寸较小;经T6I6时效处理后,晶内生成细小的析出相,同时晶界的析出相呈不连续分布,但尺寸较大,此时合金可获得更高的峰值硬度(127 HV),而且其抗腐蚀能力得到显著提高,腐蚀深度约为30μm。     

时效制度对6156铝合金力学性能及腐蚀性能的影响

通过常规拉伸、慢应变速率拉伸和晶间腐蚀实验研究了T6及双级时效处理对6156铝合金力学性能与腐蚀性能的影响,并采用透射电镜(TEM)观察了析出相特征。结果表明:6156合金在T6欠时效状态下晶内析出相主要为GP区,晶界无明显析出相;T6峰时效晶内析出相主要为β″相,出现少量的Q′相,晶界析出物呈连续分布,合金虽然具有最高强度,但晶间腐蚀严重,应力腐蚀敏感性最大;随时效时间延长,Q′相增多并逐渐粗化,晶界析出物粗大非连续分布;T78时效态晶内析出大量的Q′相,晶界析出相球化且析出相之间的间距增大,呈断续分布,无沉淀析出带(PFZ)变宽,因此相比T6态而言T78状态合金强度损失不大而耐蚀性得到明显提高。     

Cr、Yb合金化对Al-Zn-Mg-Cu-Zr合金组织和断裂特征的影响

研究复合添加微量Cr、Yb、Zr对Al-Zn-Mg-Cu合金的显微组织和断裂特征的影响,分析其对合金韧化的作用机制.结果表明:在Al-Zn-Mg-Cu合金中复合添加Cr、Yb、Zr形成了含Cr、Yb、Zr的球形弥散相,这些均匀分布于基体上的弥散相能强烈钉扎位错和亚晶界,使基体保持形变回复组织,保持小角度晶界,抑制基体再结晶;T6态断裂机制主要为韧窝型穿晶断裂,与仅添加Zr相比,沿晶断裂抗力显著提高;晶界的无沉淀区(PFZs)较宽,且析出相在晶界呈明显不连续分布.     

时效处理对铝锂合金断裂行为的影响

通过拉伸试验机、扫描电镜、透射电镜等设备对不同时效工艺下铝锂合金厚板的拉伸性能、微观组织以及断裂特征进行了系统研究。结果表明:随人工时效时间延长,合金的高向强度迅速增加,同时延伸率快速降低,合金的断裂方式也由穿晶滑移剪切+沿晶混合断口转变为单纯的沿晶断口。时效过程中晶内析出了大量的T₁相,提高了晶内强度,抑制了拉伸过程中晶内的协调变形,降低了合金的塑性并导致合金沿晶开裂。     

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.     

热处理对7085铝合金应力腐蚀开裂、断裂韧性和强度的影响

采用慢应变速率拉伸应力腐蚀测试、Kahn撕裂实验和室温拉伸实验结合透射电子显微镜和扫描电子显微镜,研究热处理对7085铝合金应力腐蚀开裂、断裂韧性和强度的影响。结果表明：与T6时效相比,经T74时效处理的合金的断裂韧性提高22．9％,但屈服强度降低13．6％;经回归再时效（RRA）处理的合金屈服强度与T6的相当,断裂韧性提高14．2％。经两次回归再时效（DRRA）处理的合金断裂韧性与T74处理的相当,但屈服强度提高14．6％。合金的应力腐蚀开裂抗力依次为：T6〈RRA〈DRRA≈T74。热处理对合金应力腐蚀开裂和断裂韧性的影响主要与基体析出相和晶界析出相有关。     

Effect of microstructure on tensile and fatigue properties of cast Mg–10Gd–2Y–0·5Zr alloy

Abstract

The microstructure and its effect on tensile properties and fatigue properties of a Mg–10Gd–2Y–0·5Zr (wt-%) cast alloy have been studied. The microstructures of as-cast, solution treated and T6 treated specimens were examined by optical and scanning electron microscopy (SEM). Tensile properties and fatigue properties of the specimens were determined and fractography was carried out. The SEM examination showed that the precipitates after T6 treatment were mainly distributed at grain boundaries, which accounts for the intergranular brittle fracture observed. The average grain size of the specimens measured after solution treatment varied from 87 to 128 μm. The mechanical tests showed that the tensile strength and low cycle fatigue strength increase with decreasing average grain size, whereas high fatigue strength is less sensitive to grain size. The fractography indicated that ductile and brittle fracture patterns coexist.     

Cu含量对一种新型Al-Mg-Si合金晶间腐蚀的影响

采用浸泡腐蚀实验和电化学实验研究了Cu含量变化和热处理条件对一种新型舰载飞机用Al-Mg-Si合金的耐腐蚀性能的影响.结果表明,添加Cu后,实验合金的 腐蚀方式由点蚀转变为晶间腐蚀,且腐蚀程度随Cu含量的增加而严重;与欠时效和过时效状态相比,T6态对晶间腐蚀较敏感,与晶界析出相的连续分布有关.电化学实验表明,所有实验合金均较快进入钝态;随Cu含量的增加,实验合金的自腐蚀电位向正向变化,腐蚀电流密度增加;随时效时间的延长,点蚀电位、晶间腐蚀的临界点位和自腐蚀电位逐渐向负向变化.而点蚀电位和自腐蚀电位随时效时间呈抛物线变化,晶间腐蚀的临界电位则呈直线变化.        

Corrosion Fatigue Behavior of 7A85 Aluminum Alloy Thick Plate in NaCl Solution

The S–N curves of 7A85-T7452 aluminum alloy in laboratory air and in neutral 3.5 wt% NaCl solution were obtained by axial fatigue tests. Results show that the detrimental effect of the aggressive solution was not noticeable at high-cyclic-stress regions, but the effect was significant at low-stress region. Corrosion fatigue mechanism was discussed by corrosion morphology analysis, fracture surface analysis and microstructure characterization. It was found that the corrosion fatigue crack commonly initialed at the localized intergranular corrosion site. TEM analysis showed that the microstructures of 7A85-T7452 aluminum alloy were characterized by fine and homogeneously distributed matrix precipitates, as well as continually distributed anodic grain boundary precipitates. The types of microstructures are the reason for its intergranular corrosion susceptibility. The corrosion fatigue process of 7A85 aluminum alloy in 3.5 wt% NaCl solution can be divided into four stages: the crack initiation stage, the stable growth stage with low and high growth rate and the final rupture stage. The sodium chloride solution mainly affected the crack initiation stage and the stable growth stage with low growth rate, and when the crack growth rate reached a threshold, the effect was reduced.     

On the Stress corrosion cracking behaviour of aluminium alloy sheet in an aqueous solution of 3% NaCl + 0.3% H2O2

The stress corrosion cracking (SCC) behaviour of aluminium alloy sheet was investigated in the long transverse direction using the slow strain rate testing technique. The synthetic environment used was an aqueous solution of 3% NaCl + 0.3% H₂O₂. No indications of SCC sensitivity are observed for the alloys 2024-T351, 8090-T81, and 2091 CPHK-T8X. The alloys 2091 T8X and 6061-T4 are found to be susceptible to intergranular stress corrosion cracking. At strain rates below 4 · 10^?7 s^?1, the slow strain rate testing technique indicates a slight SCC sensitivity with alloy 6013-T6. Fractography reveals transgranular stress corrosion cracking. Transgranular stress corrosion cracking is also observed with 6061-T4 specimens which are dynamically strained at strain rates below 5 · 10^?7 s^?1. Aqueous 3% NaCl solution with hydrogen peroxide addition promotes pitting and intergranular corrosion. The loss of ductility caused by these corrosion processes interferes with the evaluation of the results of the slow strain rate testing technique.     

INFLUENCE OF PRECIPITATES AND THEIR DISTRIBUTION ON SEAWATER CORROSION RESISTANCE OF Al-Mg ALLOY

ＩＮＦＬＵＥＮＣＥＯＦＰＲＥＣＩＰＩＴＡＴＥＳＡＮＤＴＨＥＩＲＤＩＳＴＲＩＢＵＴＩＯＮＯＮＳＥＡＷＡＴＥＲＣＯＲＲＯＳＩＯＮＲＥＳＩＳＴＡＮＣＥＯＦＡｌＭｇＡＬＬＯＹ①ＬｉｎＬｅｙｕｎ，ＺｈａｎｇＱｉｈａｉ，ＹａｎｇＺｈｉｍｉｎＢｅｉｊｉｎｇＧｅｎ...     

铜镍合金海水腐蚀的表面与界面特征研究

采用金相（ＯＭ）、俄歇（ＡＥＳ）、扫描电镜（ＳＥＭ）及透射电镜（ＴＥＭ）等技 术手段对实海暴露试样进行探测分析,揭示了表面膜缺陷（如碳膜）、晶界缺陷（晶界析出物）等加速该 合金腐蚀进程的试验现象和内在根据,特别指出影响该合金海水腐蚀产物膜稳定性的主要因素,分析了其中的沿晶扩散及应变诱生调峰分解与沿晶腐蚀、沿晶脆断的相互关系。     

淬火介质及工艺对Al-Zn-Mg-Cu合金腐蚀性能的影响

采用晶间腐蚀、剥落腐蚀、扫描电镜、透射电镜等方法,研究了不同的淬火方式对Al-6.5Zn-2.65Mg-2.2Cu-0.3Sc-0.13Zr锻造态铝合金的腐蚀性能及显微组织的影响.结果表明,空气中自然冷却淬火严重降低了T6时效态合金的抗腐蚀性能.而采用室温水淬的T6时效态合金比室温油淬的时效态合金具有更好的抗剥落腐蚀性能.当预先采用80 ℃×30 s水淬或80 ℃×30 s油淬再室温水淬时,相应T6时效态合金的抗腐蚀性能得到明显改善.预先80 ℃淬火能提高时效态合金的抗剥落腐蚀性能的主要原因是晶界析出相的大小与分布发生了明显的改变.     

非等温时效对7003铝合金组织和性能的影响

结合TEM与力学性能测试对7003铝合金在非等温时效过程中的析出行为和强化规律进行了研究,合金的抗腐蚀性能通过电导率、晶间腐蚀和电化学腐蚀的结果来评估。结果表明:以20 ℃/h升温至180 ℃时,合金的硬度和强度达到了113 HV0.5和367.8 MPa的峰值,与T6态标准相当。在降温阶段180~160 ℃范围内合金能够获得比T74更高的强度和相近的电导率。随着非等温时效的进行,合金的抗腐蚀性能不断提升。GP区和η′相在升温阶段为主要的析出相,到了降温阶段,晶内GP区逐渐消失,η′相不断粗化并有新的细小析出相形成。从升温开始到降温终止,晶界析出相的数量和尺寸越来越大,沿晶界呈断续链状分布,晶界无析出带的宽度也呈稳定增加的趋势。     

LC4高强铝合金的腐蚀性能研究

利用慢应变速率拉伸试验方法研究了LC4铝合金在空气和3．5％NaCl溶液中的应力腐蚀断裂行为；利用HB5455－90标准研究了LC4铝合金的剥蚀行为；利用HB5255－83标准研究了LC4铝合金的晶间腐蚀行为。结果表明：LC4铝合金具有应力腐蚀敏感性，应力腐蚀的断口形貌受应变速率ε的影响较大；LC4铝合金对剥蚀很敏感，对晶间腐蚀不是很敏感。