工艺参数对7075铝合金带筋壁板时效成形回弹的影响

目的 研究7075航空高强度铝合金带筋壁板时效成形过程中工艺参数对零件回弹的影响,以提高筋板类零件的产品质量。方法 利用正交试验开展不同工艺参数组合下的带筋壁板时效成形试验,并对带筋壁板时效成形后的回弹率进行极差分析和规律曲线分析。结果 带筋壁板时效成形后的回弹同时受到时效参数和筋板结构参数的影响,各因素按对回弹的影响程度由大到小的顺序依次为时效时间、筋条厚度、筋条高度和时效温度,筋条结构参数对调节构件回弹有重要作用,并且回弹率实测值基本处于回弹率随工艺参数变化的拟合曲线附近。结论 回弹率随时效时间和筋条高度的增加表现为非线性下降趋势,随筋条厚度的增加呈现线性上升趋势。7075铝合金带筋壁板时效成形后的回弹行为可以用回弹率回归方程进行较为合理的描述。     

回归再时效中预时效温度对7050铝合金应力腐蚀性能的影响

采用硬度测试、电导率测试、慢应变速率拉伸、透射电镜和扫描电镜等方法,研究了回归再时效热处理工艺中预时效温度对7050铝合金微观组织和应力腐蚀性能的影响。结果表明:随着预时效温度升高,回归再时效后7050铝合金晶内析出相从以GP区为主转变为以η′相为主,晶界析出相逐渐粗化,晶界变得不连续分布,合金应力腐蚀敏感性降低;但晶界无沉淀析出带宽度增加,120℃时达到140nm,易导致应力集中和阳极溶解,合金抗应力腐蚀性能下降。预时效温度为80℃,即稍微欠时效时,7050铝合金抗应力腐蚀性能较好,在缓慢应变速率(10-6s-1)和3.5%NaCl溶液腐蚀介质下,合金抗拉强度为473.5MPa,伸长率为10.67%,应力腐蚀指数为0.05824。     

7050铝合金蠕变时效成形本构模型研究

为研究7050T451铝合金蠕变时效本构模型,在160℃、不同应力条件下进行单轴拉伸蠕变试验,分析了蠕变应变、屈服强度和微观组织随时间的变化规律.基于高强铝合金析出强化理论,建立了能描述蠕变时效成形宏观及微观变化的本构方程,并运用遗传算法对材料常数进行拟合优化.研究表明,该模型在不同应力水平下与试验结果吻合良好,能够用来模拟分析蠕变时效成形过程.     

Cu-Ni-Si合金时效早期动力学研究

通过对固溶态 Cu-Ni-Si合金时效时电阻变化规律的分析,研究了合金时效早期的析出行为,并借助透射电镜观察合金时效析出相的组织形态。根据Avrami 经验公式导出了合金在一定温度下时效的Avrami相变动力学经验方程,在此基础上计算出合金在不同温度下时效的相变开始时间。     

7050铝合金热压缩变形的流变应力本构方程

对7050铝合金在应变速率为0.01～10s-1、变形温度为250～450℃条件下的流变应力行为进行了实验研究.结果表明:7050铝合金热压缩变形中发生了明显的动态回复与动态再结晶,流变应力随应变速率的增加而增加,随温度的增加而降低;通过线性回归分析计算出7050材料的应变硬化指数n以及变形激活能Q,获得了7050铝合金高温条件下的流变应力本构方程.     

时效制度对7475和7050铝合金应力腐蚀及剥层腐蚀性能的影响

利用透射电子显微镜分析了7475和7050铝合金在各种时效状态下的显微组织。通过性能测试发现,先高温后低温的非常规双级时效制度能有效地提高合金应力腐蚀抗力,且不显著降低合金强度,合金经回归再时效处理后,具有最佳的抗剥层腐蚀能力。     

LD7铝合金淬火敏感性及相变动力学规律

通过分级淬火的方法,结合所测LD7铝合金淬火态电导率和时效态硬度拟合出合金的时间-温度-转化率(TTT)曲线和时间-温度-性能(TTP)曲线。利用透射电镜(TEM)和Johnson-Mehl-Avrami(JMA)方程研究了铝合金等温淬火过程中的组织变化和相变动力学规律。结果表明:LD7铝合金TTT和TTP曲线的鼻尖温度均为350℃,孕育期约为2s,淬火敏感区间为290~410℃;等温保温过程中过饱和固溶体析出第二相粒子,鼻尖温度附近析出速率最快;随保温时间的延长,第二相富集长大且粗化,无沉淀析出区域变宽,晶界第二相连续化,导致合金强化效果下降;根据相变动力学方程拟合出的S曲线,解释了合金在350℃附近淬火敏感性最大以及淬火敏感区间合金第二相主要以针状形态析出的规律。     

基于应力功恒等法的振动时效研究

振动时效主要用于消减构件的残余应力,本质上类似于应力松弛,应变变程恒定的情况下峰值应力随周期减小。材料发生应力松弛的部分为应力集中区,振动时效过程中产生局部塑性应变。针对如7075高强铝合金幂次硬化材料,可以采用基于等效线弹性模型的应力功恒等法近似计算材料的局部应力和应变变程,以弥补实验过程需要测量但不易获得的重要数据。计算得到的应力-应变曲线与流变塑性理论公式推导的结果及其它研究者通过模型仿真得到的结果相似,表明应力功恒等法应用于振动时效分析具有计算简单,准确实用的特点,对工程实践有一定的参考价值和指导作用。     

工艺参数对7075铝合金板材时效成形性的影响

为评价7075铝合金板材的可时效成形性并掌握最佳的时效成形工艺参数,基于机械加载时效成形试验工装,开展了时效温度和时间对7075铝合金板材时效成形后构件力学性能和物理性能影响的试验研究.结果表明:7075铝合金板材的时效成形性与工艺参数密切相关,随着时效温度和时间的增大,板材的电导率呈升高趋势,而其拉伸性能则呈降低趋势;且合金的拉伸断裂方式与时效状态有关,过时效初期以沿晶韧窝和穿晶韧窝混合型断裂为主,随着过时效进行主要为韧窝断裂.综合考虑构件时效成形后拉伸性能和电导率等情况,合金最佳时效温度为180℃,且保温时间不宜长于16 h.     

Cu—Cr—Zr合金等温时效动力学研究

本文通过测试Cu—Cr—Zr合金在等温时效过程中电阻率的变化研究了铜合金的等温时效动力学。试验中,在时效温度达到设定温度时,每lOs记录一个电压值,直到试验过程结束为止。通过分析曲线可知,Cu--Cr--Zr合金的时效曲线具有两个拐点,对应着时效析出的两个过程。最后,推导出了合金的时效动力学公式：ρ=ρmin（ρmax-ρmin）exp-（ktn）。通过对动力学公式二阶导数的分析,从数学上证明了合金等温时效两个析出过程的存在性。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Brainstorming for ISO Strategy 2016-2020

正Responding to ISO’s appeal for survey for the to-be-developed ISO Strategy Plan for 2016-2020,SAC hosted a special workshop over the needs and comments of various fi elds on June 8 in Beijing.The workshop was attended by ISO President-elect and Ansteel General Manager Zhang Xiaogang,SAC Vice-Administrator Yu Xinli,and 30 experts from     

CNAS Passes APLAC's PTP Review

正The review group of Asia Pacific Laboratory Accreditation Cooperation(APLAC)carried out a 4-day peer review of the proficiency testing provider(PTP)for China National Accreditation Service for Conformity Assessment(CNAS)from July 28 to 31,2014.CNAS passed the PTP review with excellent performance.Two senior peer reviewers of APLAC made a comprehensive,rigorous and detailed review of CNAS’s PTP accreditation activities,and made the on-spot inspection of the review groups in Shanghai and Shenzhen respectively.     

新闻(英文)

正China and Greece Sign the Standardization Cooperation Agreement Witnessed by Chinese Premier Li Keqiang and Greek Prime Minister Antonis Samaras,AQSIQ Minister Zhi Shuping and ELOT Chairman and Executive Director Angelos Tolkas signed the SAC-ELOT Standardization Cooperation Agreement.The Agreement is one of the critical cooperation documents signed during Li Keqiang’s visit in Greece,encouraging China and Greece to