Retrogression and re-aging treatment of Al-9.99%Zn-1.72%Cu-2.5%Mg-0.13%Zr aluminum alloy

The effect of retrogression and re-aging(RRA) heat treatment on the microstructure and mechanical properties of a low frequency electromagnetic casting alloy as Al-9.99%Zn-1.72%Cu-2.5%Mg-0.13%Zr was investigated by tensile properties test, Vickers hardness, electrical conductivity test, DSC analysis, SEM and TEM observation. The results show that RRA heat treatment can improve the stress corrosion cracking(SCC) properties with retention of the high strength of T6 level. After preaging at 100 ℃ for 24 h, retrogression at 200 ℃ for 7 min, and then re-aging at 100 ℃ for 24 h, the alloy obtains tensile strength up to 795 MPa, yield strength up to 767 MPa, maintains 9.1% elongation, and electric conductivity of 35.6%IACS. TEM observation shows that the re-dissolution of GP zone and η’ phase in the early stage of regression leads to the decrease of hardness, then the increase in the volume fraction of η’ and η phases leads to the increase again in the peak value, and finally the general coarsening of all particles results in a softening of the alloy. Meanwhile it is found that the conventional T6 heat treatment as the preaging and re-aging regime is not the optimum regime to the RRA treatment of the high-zinc content super-high strength aluminum alloy.

Microstructure and mechanical properties of Al-Zn-Cu-Mg-Sc-Zr alloy after retrogression and re-aging treatments

The mechanical properties and stress corrosion cracking (SCC) resistance of an Al-Zn-Cu-Mg-Sc-Zr alloy under different aging conditions were investigated. The dependence of microstructure and mechanical properties on aging parameters was evaluated by tensile test, hardness test and conductivity measurement. The results show that for the alloys with retrogression and re-aging treatment (RRA), the conductivity increases with the retrogression time and temperature, while the tensile strength decreases. The transmission electron microscopy (TEM) results show that the precipitates η(MgZn2) at grain boundary aggregate apparently with retrogression time and the precipitates inside the matrix exhibit the similar distribution to T6 temper, which comprises fine GP zones, large η′(MgZn2) and η(MgZn2) phases. According to the mechanical properties and microstructure observations, the optimal RRA regime is recommended to be 120 °C, 24 h + 180 °C, 30 min + 120 °C, 24 h. The strength level of the alloy after the optimum RRA treatment is similar to that in T6 condition and the SCC resistance is improved obviously in contrast to T6 condition.

Combined use of fly ash and silica to prevent the long-term strength retrogression of oil well cement set and cured at HPHT conditions

The long-term strength retrogression of silica-enriched oil well cement poses a significant threat to wellbore integrity in deep and ultra-deep wells, which is a major obstacle for deep petroleum and geothermal energy development. Previous attempts to address this problem has been unsatisfactory because they can only reduce the strength decline rate. This study presents a new solution to this problem by incorporating fly ash to the traditional silica-cement systems. The influences of fly ash and silica on the strength retrogression behavior of oil well cement systems directly set and cured under the condition of 200°C and 50 MPa are investigated. Test results indicate that the slurries containing only silica or fly ash experience severe strength retrogression from 2 to 30 d curing, while the slurries containing both fly ash and silica experience strength enhancement from 2 to 90 d. The strength test results are corroborated by further evidences from permeability tests as well as microstructure analysis of set cement. Composition of set cement evaluated by quantitative X-ray diffraction analyses with partial or no known crystal structure(PONKCS) method and thermogravimetry analyses revealed that the conversion of amorphous C-(A)-S-H to crystalline phases is the primary cause of long-term strength retrogression.The addition of fly ash can reduce the initial amount of C-(A)-S-H in the set cement, and its combined use with silica can prevent the crystallization of C-(A)-S-H, which is believed to be the working mechanism of this new admixture in improving long-term strength stability of oil well cement systems.

Various admixtures to mitigate the long-term strength retrogression of Portland cement cured under high pressure and high temperature conditions

In order to investigate the problem of long-term strength retrogression in oil well cement systems exposed to high pressure and high temperature(HPHT)curing conditions,various influencing factors,including cement sources,particle sizes of silica flour,and additions of silica fume,alumina,colloidal iron oxide and nano-graphene,were investigated.To simulate the environment of cementing geothermal wells and deep wells,cement slurries were directly cured at 50 MPa and 200?C.Mineral compositions(as determined by X-ray diffraction Rietveld refinement),water permeability,compressive strength and Young’s modulus were used to evaluate the qualities of the set cement.Short-term curing(2e30 d)test results indicated that the adoption of 6 m m ultrafine crystalline silica played the most important role in stabilizing the mechanical properties of oil well cement systems,while the addition of silica fume had a detrimental effect on strength stability.Long-term curing(2e180 d)test results indicated that nano-graphene could stabilize the Young’s modulus of oil well cement systems.However,none of the ad-mixtures studied here can completely prevent the strength retrogression phenomenon due to their inability to stop the conversion of amorphous to crystalline phases.

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.

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

The redistribution and re-precipitation of solute atom during retrogression and reaging of three different Al-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

Effect of Pre-Aging, Over-Aging and Re-Aging on Exfoliation Corrosion and Electrochemical Corrosion Behavior of Al-Zn-Mg-Cu Alloys

By means of TEM, hardness, conductivity, tensile strength test, fracture toughness test, polarization curve and EIS, the Al-Zn-Mg-Cu alloys treated by a new multi-stage aging system, i.e. pre-aging, over-aging and re-aging (120°C/24h + 160°C/8h + 120°C/24h), were characterized. It is found that compared with the Al-Zn-Mg-Cu alloys treated by T76 (120°C/24h + 160°C/8h), the new multi-stage aging treatment can improve the tensile strength, fracture toughness, hardness and conductivity of the alloys at the same time. This is mainly due to the pre-aging, over-aging and re-aging process of super high strength aluminum alloys. Compared with the two-stage over aging process, the formation of multi-stage multi-phase precipitation structure can improve the strength, toughness and corrosion resistance of the alloys at the same time. The polarization curve is consistent with the conclusion. Therefore, we conducted this study to test how the comprehensive properties of the alloy can be improved.

Effect of Retrogression and Reaging on Stress Corrosion Cracking of Spray Formed Al Alloy

Stress corrosion cracking (SCC) resistance of a spray formed Al-Zn-Mg-Cu alloy underwent retrogression and reaging (RRA) was studied by slow strain rate tests in dry air and 3.5 wt% NaCl solution. The results showed that after RRA treatment, interrupted η phases at grain boundaries and slightly wide precipitate free zones could decrease SCC susceptibility of the alloy. Lots of reticular dislocations appeared in deformation process could prevent hydrogen induced cracking, and then SCC. Abundance transgranular dispersive η' phases separated out again promoted tensile strength to 759.4 MPa. The fracture ways of the specimens were dimple fracture in dry air and sub-cleavage fracture in 3.5% NaCl solution.

Retrogression characteristics of a novel Al-Cu-Li-X alloy

Retrogression characteristics of a novel Al-Cu-Li-X alloy of 2A97 were studied by hardness testing, transmission electron microscopy （TEM）, and differential scanning calorimetry （DSC）. The retrogression treatments of aging at 155°C for 12 h followed by aging at 220 and 240°C were chosen by determining the peak temperature of δ＇ precipitation at 230°C by DSC. The retrogression treatment at a lower temperature of 220°C causes the precipitation and coarsening of δ＇ and θ＇ phases in the matrix, resulting in an increase in hardness. Retrogression at a higher temperature of 240°C causes the dissolution and coarsening of δ＇ and θ＇ precipitates in the matrix and on the grain boundaries, resulting in a decrease in hardness. Microstructural changes upon retrogression including the appearance of equilibrium precipitates such as T1, T2, δ＇, and θ are confirmed by the selected area electron diffraction and the bright and dark field image analysis.

DIAGNOSTIC STUDY OF INTRASEASONAL ANOMALOUS PROGRESSION & RETROGRESSION OF SUBTROPICAL HIGH OVER WESTERN PACIFIC

Diagnostic study on two intraseasonal progressive and retrogressive progress of anomalous subtropical high in western Pacific is carried out with the aid of daily 2. 5°×2.5° grid point data of ECMWF inJuly and August of 1980 and 1983. It is revealed that the anomalous progression and retrosression ofthis high is intraseasonally teleconnected with that in the eastern Pacific, shown as low-ftequency wavespropagating westward along a latitudinal wave train across the northern Pacific i the same oscillatory displacement of eastern subtropical high is again triggered off by the variation of convergent sink of uppertropospheric divergent wind field in eastern Pacific, being resulted from anomalous heating from monsoon area in South Asia through trade wind zone in the Pacific Ocean.

<i>β</i>-HCG Level as a Predictive Marker of Pregnancy Progression or Retrogression

An ordered sequence of biologic events is precursors of the birth of a healthy baby. Hormonal interactions acting as a nexus between the fetus, placenta and mother that controls the establishment and progression of pregnancy and fetal development are very important. We examined the role of Beta-Human Chorionic Gonadotropin (β-HCG) as a predictive marker. Applying radioimmunoassay that utilizes anti-sera generated from specific β-submit of HCG we evaluated the serum β-HCG level in 60 pregnant women in the three trimesters. Results showed that there was consistent increase in concentration that drops gradually and maintained a plateau only to drop from the 40th week of pregnancy. 3 subjects (5%) that had a sudden sharp drop in β-HCG level resulted in complications. Inclusion of β-HCG level screening and monitoring in pregnancy will raise assurance of progress or retrogression in pregnancy. We provide data that can be used as a reference range for β-HCG using this method.

Tumor： Life Retrogression？

癌症几千年以来一直伴随着人类的发展历史.似乎,在人类进化的同时,肿瘤也在不断进行着进化.为了解释和研宄肿瘤的进化机制,在这里我们提出一个新的假说,肿瘤是生命进化过程中的退化,是人体发育历史片段的重现.其依据为,肿瘤不是外来的疾病,而是通过利用人类固有的己经关闭的了发育基因而实现自我进展的.肿瘤的细胞与人类正常的干细胞的特征和生物学行为十分类似.那么,研宄人类进化的过程就可以推测并分析出肿瘤的发生发展规律.最新研宄表明,很多肿瘤治疗的新策略也正是利用了这一特点.不断深入分析并且利用人体内进化与发育的环境特点和内在规律,就可以产生出新的肿瘤预防与治疗方法.我们的假说首次提出利用进化的规律,扭转肿瘤的发展过程,比将肿瘤当作敌人完全杀灭效果更好.一些关于肿瘤诱导分化的新研宄也证明了该说所具有的临床意义.

High-resolution assessment of retrogressive thaw slump susceptibility in the Qinghai-Tibet Engineering Corridor

Under the rapidly warming climate in the Arctic and high mountain areas,permafrost is thawing,leading to various hazards at a global scale.One common permafrost hazard termed retrogressive thaw slump(RTS)occurs extensively in ice-rich permafrost areas.Understanding the spatial and temporal distributive features of RTSs in a changing climate is crucial to assessing the damage to infrastructure and decision-making.To this end,we used a machine learning-based model to investigate the environmental factors that could lead to RTS occurrence and create a susceptibility map for RTS along the Qinghai-Tibet Engineering Corridor(QTEC)at a local scale.The results indicate that extreme summer climate events(e.g.,maximum air temperature and rainfall)contributes the most to the RTS occurrence over the flat areas with fine-grained soils.The model predicts that 13%(ca.22,948 km^(2))of the QTEC falls into high to very high susceptibility categories under the current climate over the permafrost areas with mean annual ground temperature at 10 m depth ranging from-3 to-1℃.This study provides insights into the impacts of permafrost thaw on the stability of landscape,carbon stock,and infrastructure,and the results are of value for engineering planning and maintenance.

Impact of a retrogressive thaw slump on surrounding vegetation communities in the Fenghuoshan mountains,Qinghai-Tibet Plateau

Under global warming,permafrost around the world is experiencing degradation which is especially so on the Third Pole,the Qinghai-Tibet Plateau(QTP),China.Retrogressive thaw slump(RTS)is one of the thermokarst features caused by rapid degradation of ice rich permafrost,which transforms landforms and threatens infrastructures,and even affects the terrestrial carbon cycle.In this work,vegetation communities surrounding a RTS in the Fenghuoshan Mountains of the interior portion of the Qinghai-Tibet Plateau have been investigated to examine the impact from RTS.This investigation indicates that the occurrence of RTS influences the vegetation community by altering their habitats,especially the soil water content,which forces the vegetation community to evolve in order to adapt to the alterations.In the interior part of RTS where it has been disturbed tremendously,alterations have produced a wider niche and richer plant species.This favors species of a wet environment in a habitat where it was a relatively dry environment of alpine steppe prior to the occurrence of RTS.This study adds to limited observations regarding the impact of RTS to vegetation community on the QTP and helps us to reach a broader understanding of the effects of permafrost degradation as well as global warming.

回归温度和时间对深冷变形7A85铝合金显微组织、力学性能和腐蚀行为的影响

为了平衡合金的强度、塑性与耐蚀性,在不同回归温度和时间条件下对深冷变形7A85铝合金的显微组织和综合性能进行研究。结果表明,在较低回归温度和时间的回归再时效(RRA)制度和T6(120℃,24h)制度下,合金具有较高的强度,但耐蚀性较差。对于RRA,在一定范围内增加回归温度和时间会降低合金的强度,但合金的电导率和耐蚀性显著提高。然而,过度地增加回归温度和时间使合金的耐蚀性降低。相同的回归温度下,随着回归时间的延长,合金的伸长率先减小后增大。与三向深冷变形7A85铝合金的最佳匹配的制度为RRA180-0.5((120℃,24 h)+(180℃,0.5 h)+(120℃,24 h))。

干热岩超高温防衰退水泥浆体系及应用

干热岩长期高温导致水泥石强度衰退,易造成套管挤毁或窜流,严重影响钻井的安全。针对200℃以上常规加砂水泥石强度衰退难题,基于硅铝键结合增强效应,通过优化水泥物相组成,开发了超高温增强材料SCKL,可以满足210~300℃下固井要求,不仅抑制了水泥石强度衰退,且促进了水泥石强度长期发育,300℃、48 h的抗压强度为18.2 MPa,30 d抗压强度高达23.2 MPa,探索了超高温增强材料对水泥石微观结构的影响,揭示了超高温水泥石微观作用机制。研选了温度广谱型缓凝剂,开发了大温差防衰退水泥浆体系,可以满足干热岩100℃温差下安全固井需求,并在青海共和盆地成功应用5口井,固井质量均为优质,为干热岩井筒水泥环密封完整性提供了安全保障。

福建省龙岩市新罗区牵引式滑坡稳定性分析及治理措施

牵引式滑坡是山区工程建设中一种常见的滑坡类型,往往是经历暴雨或人工开挖削坡后产生滑动,会首先在坡脚处滑移挤出,对工程场地的安全造成威胁。以福建省某工程滑坡为例,运用强度折减法和传递系数法两种方法,分别对滑坡天然和暴雨条件下不同工程阶段的工况进行稳定性分析,提出相应的治理措施并进行可行性研究。结果表明:滑坡在开挖后的暴雨工况下处于不稳定状态;综合治理措施在天然工况和暴雨工况下均处于稳定状态,满足安全要求。研究成果可为类似工程提供一定参考。

High- and Ultrahigh-pressure Metamorphism and Retrogressive Textures of Gneiss in the Donghai Area——Evidence from gneisses in drillhole ZK2304

In the gneisses from the drillhole ZK2304 of the Donghai area, there have been preserved high- and ultrahigh-pressure metamorphic mineral assemblages, a series of complicated retrogressive textures and relevant metamorphic reactions. In addition to garnet, jadeititic-clinopyroxene and rutile, other peak stage (M2) minerals in some gneisses include phengite, aragonite and coesite or quartz pseudomorphs after coesite. The typical peak-stage mineral assemblages in gneisses are characterized by garnet + jadeitic-clinopyroxene + rutile + coesite, garnet + jadeitic-clinopyroxene + phengite + rutile ± coesite and garnet + jadeitic-clinopyroxene + aragonite + rutile ± coesite. The grossular content (Gro) in garnet is high and may reach 50. 1 mol%. The SiO2 content of phengite ranges from 54.37% to 54.84% with 3.54-3.57 p.f.u. Quartz pseudomorphs after coesite occur as inclusions in garnet.The gneisses of the Donghai area have been subjected to multistage recrystallization and exhibit a closewise P-T evolutional path characterized by the near-isothermal decompression. The inclusion assemblage (Hb+Ep+Bi+Pl+Qz) within garnet and other minerals has recorded a pre-peak stage (Mi) epidote amphibole fades metamorphic event. High- and ultrahigh-pressure peak metamorphism (M2) took place at T=750-860℃ and P>2.7 GPa. The symplectitic assemblages after garnet, jadeitic-clinopyroxene and rutile imply a near-isothermal decompression metamorphism (M3, M4) during the rapid exhumation. Several lines of evidence of petrography and metamorphic reactions indicate that both gneisses and eclogites have experienced ultrahigh-pressure metamorphism in the Donghai area. This research may be of great significance for an in-depth study of the metamorphism and tectonic evolution in the Su-Lu ultrahigh-pressure metamorphic belt.

A Simplified Numerical Approach for the Prediction of Rainfall-Induced Retrogressive Landslides

Retrogressive landslides are common geological phenomena in mountainous areas and on onshore and offshore slopes. The impact of retrogressive landslides is different from that of other landslide types due to the phenomenon of retrogression. The hazards caused by retrogressive landslides may be increased because retrogressive landslides usually affect housing, facilities, and infrastructure located far from the original slopes. Additionally, substantial geomorphic evidence shows that the abundant supply of loose sediment in the source area of a debris flow is usually provided by retrogressive landslides that are triggered by the undercutting of water. Moreover, according to historic case studies, some large landslides are the evolution result of retrogressive landslides. Hence the ability to understand and predict the evolution of retrogressive landslides is crucial for the purpose of hazard mitigation. This paper discusses the phenomenon of a retrogressive landslide by using a model experiment and suggests a reasonably simplified numerical approach for the prediction of rainfall-induced retrogressive landslides. The simplified numerical approach, which combines the finite element method for seepage analysis, the shear strength reduction finite element method, and the analysis criterion for the retrogression and accumulation effect, is presented and used to predict the characteristics of a retrogressive landslide. The results show that this numerical approach is capable of reasonably predicting the characteristics of retrogressive landslides under rainfall infiltration, particularly the magnitude of each landslide, the position of the slip surface, and the development processes of the retrogressive landslide. Therefore, this approach is expected to be a practical method for the mitigation of damage caused by rainfall-induced retrogressive landslides.