镁合金电镀锌工艺及其镀层性能研究

为了提高镁合金的耐蚀性能,采用特定前处理工艺,实现了在以硫酸锌为主盐、焦磷酸盐为配体的溶液体系中对AM60B镁合金进行电镀锌.通过电子探针(EDX)分析,扫描电镜(SEM)观察、电化学测试等手段研究了镀层性能.结果表明,镀层的自腐蚀电位接近-1.321 V(vs SCE),阳极极化曲线没有明显的钝化区.所得镀层为纯金属锌,镀层均匀致密,无明显缺陷,镀层与基体结合良好.     

镁合金化学镀镍层的性能研究

化学镀镍是镁合金保护的重要手段.为探讨化学镀镍对镁合金的保护效果,本文利用电化学极化曲线、X射线衍射和扫描电镜等手段研究了镁合金化学镀镍前处理方法及镀层性能.镁合金上化学镀镍层厚度达到15μm时已没有惯穿镀层的孔隙,200℃以上热处理可显著提高镀层结合力;由于镀层和镁合金间强烈的电偶腐蚀作用,在户外或潮湿环境中,化学镀镍对镁合金而言是一种有较大风险的防护方法.为获得更好的保护效果,多层化学镀或电镀与化学镀相结合是较好的选择.     

不同pH值模拟混凝土孔隙液中镀锌层的阳极特性逆转

在不同pH值的混凝土中镀锌层显示有阳极逆转现象,其对基体钢的保护作用出现变化。以回填海沙导致近海陆地混凝土建筑镀锌钢管的局部腐蚀为例,模拟其实际工况,将镀锌试样置于6种不同的模拟混凝土孔隙液中,将去锌层钢基置于3.5%NaCl中性溶液中浸泡24 h,用盐桥连接电解池,测定2种试样间的电位-时间曲线和电偶电流值,并与无预浸泡的相应值对比。结果表明:(1)当镀锌层在含有Cl-的中性溶液及pH=10.0,11.0的Ca(OH)2溶液中时,对钢基体起到了牺牲阳极的保护作用;(2)当镀锌层在pH=12.0的Ca(OH)2溶液中时,无论是否预浸泡其电位均出现逆转现象,且电偶电流值为正值,反而会促进钢基体的腐蚀;(3)在pH=12.5的Ca(OH)2溶液中,无预浸泡时镀锌层对去锌层钢基有保护作用,预浸泡24 h后初始阶段具有保护作用,1 650 s后时出现逆转,不仅已失去对钢基体的保护作用,反而会加速其腐蚀。     

镁及镁合金表面镀锌工艺

镁及镁合金基体上电镀锌是一种对其表面进行改性处理的新尝试，通过一定的新处理之后，再利用碱性光亮镀锌方法在镁表面获得锌镀层。分析了前处理、镀液成分、添加剂、电流密度、温度等工艺参数对镀层质量的影响，优化了工艺条件。利用显微硬度计和电子探针分析测定了镀层厚度、硬度、表面形貌和成分，结果表明，在优化的工艺条件下，所得镀层均匀且与基体的结合力良好，对基体具有一定的保护作用。     

压铸镁合金在防冻液中的电偶腐蚀规律研究

研究了压铸AZ91D镁合金分别与A3钢、H62黄铜、LF21铝合金及356号铸铝偶接后在80 ℃汽车防冻液中的电偶腐蚀行为及规律.自然腐蚀电位、电偶电位和电偶电流的测量结果表明,压铸AZ91D镁合金在与上述4种材料构成的电偶对中始终是阳极,且电偶腐蚀的阳极过程在该体系中受到较大的阻滞.电偶腐蚀效应的分析结果表明AZ91D与4种材料偶接后其阳极溶解速度较其未偶接前上升不超过1个数量级,且4种电偶对的电偶腐蚀效应存在如下相对关系:γ356号铸铝＜γLF21＜γH62＜γA3.     

化学镀镍磷层孔隙率的电化学评价

钢铁基体上的化学镀镍磷层属于阴极保护镀层,其孔隙率测定非常重要.为此,对化学镀镍磷层孔隙率电化学测定方法进行了探索.通过研究钢铁和化学镀镍磷层在不同介质中电化学行为的区别,选择了5%H2SO4作为测试介质,并研究了该介质中不同孔隙率镀镍磷层的电化学行为.结果表明:随镀层孔隙率的减少,镀层的自腐蚀电位逐渐从铁的自腐蚀电位向纯镍磷镀层的自腐蚀电位变化.而应用常规的孔隙率检测方法只能检测较大的孔隙.电化学方法与贴滤纸法孔隙率测试结果是一致的,说明该方法可行.     

建筑用AZ80Ti镁合金表面氯化胆碱类离子液体镀铝层的组织和耐蚀性

为了提高建筑用AZ80Ti镁合金的耐腐蚀性能,选择尿素与氯化胆碱共同组成一种新型的离子液体,以AZ80Ti镁合金为基体来完成Al的电沉积过程,并对沉积得到的铝层的微观组织结构及其在3.5％的NaCl溶液中的耐蚀性进行了表征.研究结果表明:经过镀铝得到的基体表面β组织已经完全消失,生成了部分块状结构.当增加电镀时间后,最初的片层组织不断长大变成了颗粒结构,不同颗粒发生扩散后形成了由颗粒与片状组织共同组成的镀层.经过镀铝处理后,镁合金获得了更高的自腐蚀电位,表现出更强的耐蚀性.经过3h电镀后,可以获得最优保护性能的铝镀层组织.对初始镁合金进行腐蚀测试后形成了粗糙的腐蚀表面,表面产生了大量的腐蚀脱落产物.经过3h电沉积后形成了颗粒与片层共存的表面组织结构,腐蚀破坏程度达到最低,形成了较为致密的片层组织.     

镁合金电偶腐蚀研究及其进展

研究了镁合金AM60与异种金属Q235碳钢、18-8不锈钢、LY12铝合金和纯铝之间的电偶腐蚀,介绍了镁合金电偶腐蚀的最新研究进展,重点探讨了影响镁合金电偶腐蚀的因素和减轻镁合金电偶腐蚀的措施,最后提出了镁合金电偶腐蚀研究中需要解决的科学问题.研究和讨论分析表明,为防止镁合金电偶腐蚀,应全面而系统地进行合理的结构设计、选择合适的匹配材料、在镁合金和异种金属表面分别涂装性能优良的耐碱性涂层体系.由于镁腐蚀发生碱化,所以防止电偶腐蚀的环境应避免选用含铝涂层体系.     

氯化胆碱-尿素离子液体中镁合金表面电沉积电流密度对镀锌层性能的影响

为了提高AM60B镁合金的耐腐蚀性能,以氯化胆碱-尿素(Reline)离子液体为电镀液,在AM60B镁合金表面脉冲电镀锌。利用扫描电镜、能谱仪、X射线衍射仪及涂层厚度测量仪研究了电沉积电流密度对镀锌层微观形貌及结构的影响;采用电化学极化曲线测试了不同电流密度下所得镀锌层的耐腐蚀性能。结果表明:随着电流密度的增加,镀锌层的晶粒逐渐变大,孔洞等缺陷减少,耐腐蚀性能先增强后减弱;当电流密度为5.0 mA/cm2时,镀锌层均匀致密、光亮、无明显缺陷、与基体结合力好、耐腐蚀性能最佳。     

AZ31B镁合金无氰脉冲镀锌层的结构与性能

镁合金耐腐蚀性差,氰化镀和化学镀虽能提高其耐蚀性,但分别存在许多问题,如污染环境、工艺复杂、与镀层结合力差、镀液寿命短等.为此,采用直流(DC)、脉冲电流(PC)方法在A231B镁合金表面电沉积锌层,以扫描电子显微镜(SEM)、X射线衍射(XRD)、极化曲线(Tafel)和电化学阻抗谱(EIS)等方法研究了沉积方式对镀层表面形貌、结构和耐蚀性的影响.结果表明:随时间的增加,镀层从初期疏松、多孔,逐渐趋于致密、平整;相同时间下,脉冲镀层更致密、孔隙更少;脉冲方式下晶面衍射峰强度较直流方式有所降低,半峰宽有变大趋势,晶粒有所细化,晶面取向由(101)择优取向变为随机取向;经直流和脉冲电镀锌后,镁合金表面腐蚀电势分别正向移动了0.42 V和0.48 V,腐蚀电流为80.4μA/cm2和34.57μA/cm2,脉冲条件下制备的镀层耐蚀性较直流制备的镀层有所提高.     

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.     

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.     

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.     

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)。