回归时间对RRA处理超高强铝合金力学性能的影响

研究了回归时间对RRA处理后高Zn超高强度铝合金的组织和性能的影响.结果表明,以100℃/24 h为预时效和再时效参数,合金在200℃回归7 min的RRA(回归再时效)状态综合性能最好.其室温力学性能达到:σb=795 MPa,σ0.2=767 MPa,δ5=9.1%;抗应力腐蚀性能达到:在3.0%NaCl 0.5%H2O2腐蚀液环境及210 MPa拉伸应力下,断裂时间大于720 h.在200 ℃/7 min回归的RRA状态,其晶内的弥散粒子和再时效期间变窄的晶界无析出带保证了合金的超高强度.随着回归时间的延长,晶内粒子的弥散度下降,回归时形成的较宽的晶界无析出带不能再时效粒子填充而使强度大幅度降低.同时,处于该状态的合金具有优良的抗应力腐蚀性能,得益于晶界大尺寸,大间距粒子具有捕获氢原子、逸出氢气泡的作用,以及回归降低了晶界附近的位错密度、切断了氢原子向晶界迁移的通道.     

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。     

高速列车A7N01S-T5铝合金应力腐蚀行为研究

文章选取了我国某类型高速列车常用的A7N01S-T5铝合金材料,进行了恒载荷应力腐蚀试验,对A7N01S-T5材料的应力腐蚀机理、应力腐蚀强度因子K1SCC和裂纹生长机制进行了研究.结果表明,A7N01S-T5铝合金的应力腐蚀破坏敏感性很高,其临界应力场强度因子K1 SCC为5.2 MPa.m1/2,仅为断裂韧度K1 C的0.15,对应的临界应力门槛值б为123MPa,仅为拉伸强度бb0.27.裂纹断口面有明显的舌状凸起和凹坑的存在.A7N01S-T5铝合金的应力腐蚀裂纹以沿晶开裂为主,形貌呈树枝状,同时相邻二次裂纹之间有竞争生长的关系.     

7150铝合金型材三级时效热处理工艺研究

采用拉伸力学试验机、电导率测试仪、应力腐蚀测试和透射电子显微镜分析回归时效、回归时效升温速率和冷却方式对7150铝合金性能的影响。研究表明,回归时效采用185 ℃/100 min的RRA热处理工艺时,合金具有较高的电导率(36.7~37.4%IACS)和较少的强度损失(抗拉强度620~640 MPa,屈服强度590~610 MPa)。65 ℃/h升温至回归时效和回归时效风冷降温至120 ℃的RRA热处理可提高合金电导率,降低合金强度;预时效后空冷1 h再185 ℃回归时效和回归时效水冷的RRA热处理可提高合金强度,降低合金电导率;通过TEM明场像观察,回归时效采用185 ℃/100 min的RRA热处理工艺时7150合金晶内析出大量的GP区,晶界析出不连续的较粗大的η相,这种显微组织既保证了T6状态的强度又使合金具有较好的抗腐蚀性能。     

锰在7000系铝合金中的作用及机理

介绍了过渡族金属元素锰在铝中的固溶度变化特点及锰的存在形式;重点讨论了过渡族元素锰对7000系高强铝合金时效行为和力学性能(拉伸强度、延伸率、断裂韧性及抗应力腐蚀性能等)的有益作用及作用机理.铝合金中添加一定量的锰,不影响铝合金的时效动力学,但却明显提高铝合金的强度,对铝合金韧性(延伸率和断裂韧性)、抗应力腐蚀性能等有一定的作用.在现代高强铝合金的研发中,锰已成为一种重要的合金化元素.     

时效制度对7B04铝合金断裂韧性的影响

为研究不同时效制度对7B04铝合金断裂韧性的影响,测定了15种时效工艺的常规力学性能和断裂韧度,并利用扫描电镜对拉伸断口进行分析.通过比较不同时效工艺制度的性能指标和断口形貌,总结出时效制度对7B04铝合金断裂韧度的影响规律.结果表明:随着第二级时效温度的提高和时效时间的延长,7B04铝合金强度下降,断裂韧性提高,其中,温度对性能的影响更大;采用115℃×7 h 185℃×13 h双级时效工艺时,对应的强度和断裂韧度指标均比T73和T76工艺对应的指标高.     

喷射成形7055铝合金的应力腐蚀性能研究

以喷射成形7055铝合金为研究对象,通过室温拉伸、光学显微镜和扫描电镜等分析方法,研究了载荷应力和浸泡时间对7055铝合金腐蚀性能的影响。研究结果表明,随着应力载荷的提高、腐蚀时间的延长,试样的强度并未出现明显的下降,但材料的塑性明显降低。腐蚀应力越接近材料的屈服强度,塑性下降越明显,抗拉应变和延伸率均降低,在腐蚀液中,极化曲线测试也表现出同样趋势。试样表层部分区域有明显的点蚀和晶间腐蚀空洞。拉伸时,腐蚀缺口处会产生明显的应力集中成为起裂源,导致材料塑性下降,从拉伸断口分析可知,断口边缘被腐蚀区域为明显的沿晶断裂。     

多级时效热处理对7056铝合金析出组织与耐蚀性的影响

利用透射电子显微镜(TEM)、扫描电子显微镜(SEM)、力学性能测试、电导率测试以及剥落腐蚀、慢应变速率拉伸应力腐蚀(SSRT)、Tafel循环极化曲线等手段研究多级时效热处理对7056铝合金析出组织及耐蚀性的影响。结果表明:过时效再时效热处理后溶质原子二次析出,晶内析出相体积分数增大,晶界析出相粗化断开,无沉淀析出带宽化。与120℃/24h相比,采用120℃/6h预时效工艺有利于晶内细小析出相回溶和粗大相长大。再时效热处理可提高过时效合金的强度和电导率,与峰时效和回归再时效相比,合金的抗拉强度损失不大,电导率明显提升。过时效再时效热处理后,合金晶界处连续阳极溶解被有效避免,抗剥落腐蚀和抗应力腐蚀性能增强。     

7B04铝合金应力腐蚀敏感性研究

利用慢应变速率拉伸应力腐蚀实验方法研究7B04铝合金的应力腐蚀开裂敏感性。研究温度、腐蚀介质、电化学极化对应力腐蚀敏感性的影响,结果表明:随温度的升高7B04铝合金的应力腐蚀开裂敏感性增强;溶液的腐蚀性越强,7B04铝合金的应力腐蚀开裂敏感性越大;无论是阳极极化还是阴极极化都会增加7B04铝合金的应力腐蚀开裂敏感性。     

7B04铝合金厚板生产过程优化的数值分析

为了优化7B04铝合金厚板生产过程,对7B04铝合金厚板生产过程中淬火、压光、拉伸过程应力场的变化和分布情况进行了数值分析.结果表明:压光过程可以降低淬火应力并使淬火应力分布均匀化,但这种作用被后续的拉伸过程大大减弱,并且压光过程导致板材两端产生较大的应力集中区域;拉伸是降低铝板材应力和使应力均匀分布的关键环节;当纵向塑性延伸率为2.5%时,拉伸效果最好.     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。