铝合金感应加热半固态重熔及复杂件触变成形

目的 研究铝合金半固态坯料在感应加热过程中的组织演变规律,并实现复杂构件近净成形。方法 对7075-T6铝合金挤压棒料进行感应加热条件下的半固态等温处理,观察其微观组织演变规律,并对其进行金相分析,研究晶粒粗化机制;随后采用梯度感应加热坯料进行触变-塑变复合成形试验。结果 晶粒随保温温度的升高,或保温时间的增加,尺寸逐渐增加;随保温时间的延长,晶粒圆整度逐渐增加。晶粒的长大主要以Ostwald熟化机制为主,合并长大为辅,且由于感应加热速率(5 ℃/s)较快,最终形成的晶粒较小。计算得出,晶粒在590, 600, 610, 620 ℃时的晶粒粗化速率分别为165, 226, 309, 497 μm3/s。采用梯度感应加热坯料,实现了某型铝合金尾翼构件的近净成形。结论 适用于7075铝合金触变成形的感应加热工艺参数为：在610~620 ℃下保温5~10 min。集成感应加热半固态重熔处理和触变-塑变复合成形技术,可实现复杂构件近净成形。     

杯形件温挤压成形工艺研究

对杯形件的生产进行了精密塑性成形方法的研究,并用有限元模拟软件对挤压过程进行了分析,结果表明,所设计的坯料尺寸及工艺方案是合理的,金属流动均匀,表面质量和尺寸精度都达到要求,大大提高了工件的强度和生产率,达到节省原材料、降低成本的目的。     

触变模锻成形工艺对镁合金成形件力学性能的影响

采用半固态等温热处理法、近液相线模锻法和等通道角挤压法制备AZ91D-Y镁合金半固态坯料。分别将3种状态的坯料加热到半固态温度区间进行二次重熔后,进行了触变模锻成形。结果表明,在半固态温度为560℃,模锻压力为200MPa的条件下,半固态等温热处理法、近液相线模锻法和等通道角挤压法制备坯料分别保温30,20,15min后触变模锻获得最佳力学性能;随着坯料加热温度的升高,触变模锻成形件力学性能呈现先上升后下降的趋势;增加成形压力有利于触变模锻成形件力学性能的提高;在相同成形条件下,等通道角挤压法制备坯料触变模锻后的力学性能最好,近液相线模锻法次之,半固态等温热处理法较差。     

铝合金半固态压铸技术的应用

在以前研究的基础上,简要概述了半固态成形技术的三道感应加热以及半固态坯料的触变成形,然后应用铝合金半固态压铸技术批量制备出形状复杂的汽车零件-后桥支承座,并对其进行性能测试以及疲劳台架试验.结果表明,应用半固态压铸技术可以制备出性能优异,且能满足厂家疲劳台架要求的复杂汽车零部件.     

ZL201合金的半固态成形组织和力学性能

制备ZL201合金半固态坯料、将其二次加热、触变模锻成形以及成形件热处理,研究了工艺条件对成形件的组织和力学性能的影响.结果表明:采用近液相线半连续铸造技术制备的ZL201合金半固态坯料微观组织为大量细小的等轴晶和少量短程枝晶;在适当的工艺条件(在640℃保温5 min,模具温度250～300℃,留模时间10～15 s)下可触变成形出表面光洁的ZL201合金成形件;经过T5处理后,ZL201合金的抗拉强度达到278 MPa,延伸率达到9%,大大高于压铸成形件的性能,其强化相为CuAl2和TiAl3.由于成形速度高,溶体高速充型,造成成形件气孔率高,使ZL201合金半固态压铸成形的组织致密度不如半固态模锻成形件,这是半固态压铸件强度低、模锻件强度高的主要原因.     

半固态7075 +1.7TiC铝合金二次加热工艺的研究

在不同的二次加热温度和保温时间条件下,对喷射沉积7075+1.7%(体积分数)TiC铝合金的二次加热工艺进行研究.采用扫描电镜观察合金的二次加热组织,利用平均截线法统计晶粒尺寸.结果表明,在580℃进行二次加热时其晶粒长大非常缓慢,温度提高到600℃后,晶粒长大速度有所提高.在580℃和600℃分别保温60min后,合金对应的平均晶粒尺寸为14μm 和20μm.二次加热温度超过610℃后晶粒长大速度显著提高,并出现明显的局部重熔现象.对应620℃保温30min的平均晶粒尺寸53μm.说明在上述条件下得到的半固态坯料仍保持细小等轴晶组织的特征,能够满足后续的触变成形工艺对合金组织的要求.     

圆管镦锻法兰成形的试验研究

通过对圆管镦锻法兰成形过程进行有限元数值模拟,分析了圆管坯料尺寸、摩擦等因素对圆管镦锻法兰成形过程中金属流动的影响及缺陷产生的原因。根据有限元数值模拟结果,进行了圆管镦锻法兰成形试验,数值模拟结果与试验结果具有较好的一致性。     

高频电磁感应加热成形热源模型建立及数值模拟研究

基于高频感应加热涡流分布及透入深度的特点,为模拟钢板高频电磁感应加热成形的温度场,提高数值模拟计算精度,结合电磁感应加热头的形状尺寸,建立了一种用于模拟电磁感应加热成形的热源模型。模型建立过程中,对其能量分布给出了明确的热流表达式,利用有限元方法分析了电磁感应加热成形的热源模型的有效性。结果表明,利用该热源模型分析的温度场结果与试验结果吻合良好。高频电磁感应加热的峰值温度位于感应加热头作用区域,随着输出功率或感应加热时间的增加,峰值温度增加。     

梯度结构半固态9 Cr18不锈钢的制备与显微组织演变

基于Gleeble3500热模拟试验机设计了半固态触变锻造成形装置,通过触变锻造工艺制备了9Cr18不锈钢制件,研究其显微组织结构和演变特征.研究结果表明,半固态触变成形装置能够实现9Cr18半固态坯料成形.在触变锻造成形过程中,固相骨架破碎后,半固态坯料表现出触变特性,载荷随着变形的进行而下降.9Cr18触变制件变形区呈现梯度结构的显微组织特征.触变制件边部存在明显的液/固分界层.分界层外侧为液相凝固形成的共晶组织;分界层内侧主要为固相颗粒.9Cr18触变制件具有独特的组织演变规律,其内部主要为具有良好塑性变形能力的奥氏体组织,表层存在大量的M7 C3共晶碳化物,二者共同保证了9Cr18不锈钢触变制件具有"外硬内韧"的特征.     

高速铁路承轨台模板拉深成形工艺优化研究

通过Dynaform有限元模拟,制定了高速铁路承轨台模板两次拉深成形工艺方案.采用均匀设计法,选择出了预成形最佳压边力与坯料尺寸的组合.预成形实验结果与模拟结果符合较好,法兰外边缘宽度方向尺寸最大相对误差为1.22%,长度方向尺寸最大相对误差为4.86%.通过该拉深成形工艺方案获得了表面质量和尺寸均合格的高速铁路承轨台模板零件,并进行了小批量生产,已应用于工程实际.     

Gender differences in publication productivity in psychology in India

An analysis of gender differences in psychology in India provides quantitative and qualitative assessment of R&D output contributed by psychologists with the indication of the trend of growth, skewness, relatedness, co-authorship pattern of productivity.     

Metrology in Chemistry in Germany

The system for Metrology in Chemistry in Germany is described. At the national standards level, a network of high-level chemistry institutes coordinated by the national metrology institute, PTB, provides the primary references for chemical measurements. A dissemination mechanism employs chemical calibration laboratories accredited within the framework of the German Calibration Service (DKD). They act as “multipliers” between the national standards level and the user level by providing the user with calibration means which are traceable to the SI via national standards. Traceability structures in clinical chemistry, electrochemistry, elemental analysis and gas analysis are described     

Natural radioactivity in drinking water in private wells in Finland

Natural radioactivity in drinking water was determined in population-based random study of 472 private wells. The mean concentrations of (222)Rn, (226)Ra, (234)U, (238)U, (210)Pb and (210)Po in drilled wells were 460, 0.05, 0.35, 0.26, 0.04 and 0.05 Bq l(-1), and in wells dug in the soil were 50, 0.016, 0.02, 0.015, 0.013 and 0.007 Bq l(-1), respectively. Approximately 10% of the drilled wells exceeded a radon concentration of 1000 Bq l(-1) and 18% a uranium concentration of 15 microg l(-1). The mean annual effective dose from natural radionuclides for a drilled well user was 0.4 mSv and 0.05 mSv for a user of a well dug in the soil. The effective dose arising from (222)Rn was 75% of the total of all natural radionuclides for drilled well users. As regards long-lived radionuclides, (210)Po and (210)Pb caused the largest portion of the effective dose. The dose arising from (238)U, (234)U and (226)Ra was only 8% of the total of all natural radionuclides.     

Natural radioactivity in drinking water in private wells in Finland

Radiation Protection Dosimetry     

Radioactivity in building materials in Iraq

Activity concentrations of (226)Ra, (232)Th and (40)K in 45 samples of different building materials used in Iraq were measured using gamma-spectroscopy system based on high-purity germanium detector with an efficiency of 40 %. Radium equivalent activity, air-absorbed dose rate, annual effective dose, external and internal hazard indices and alpha index due to radon inhalation originating from building materials were measured to assess the potential radiological hazard associated with these building materials. The activity concentrations of the natural radionuclides (226)Ra, (232)Th and 40K were found to range from below detection limit (BDL) to 223.7 ± 9, BDL to 93.0 ± 3 and BDL to 343.1 ± 12, respectively. Values of average radium equivalent activity, air-absorbed dose rate, indoor and outdoor annual effective doses, external and internal hazard indices and alpha index ranged from 6.5 to 124.9, 16.2 to 89.5 (nGy h(-1)), 0.08 to 0.44 mSv, 0.02-0.11 mSv, 0.09 to 0.53, 0.13 to 0.69 and 0.03 to 0.62, respectively. These values indicate a low dose. Therefore, the building materials used in the current study are quite safe to be used as building materials.     

Optische in situ Schichtdickenmessung in Bedampfungsanlagen. Optical in situ film thickness monitoring in coating systems

Optical film thickness monitoring is more precise than crystal monitoring. The optical measurement makes use of the fact that the intensity of a monochromatic light beam which is reflected on a film will change periodically with increasing film thickness. The measurement is performed at an exchangeable test glass that is positioned beside the substrates and is therefore coated in the same way as the substrates. The accuracy of cut‐off is achieved by a “fit” of a theoretical curve shape to the measured values. Order filters are used to ensure that, at a certain wavelength, higher deflection orders do not influence the measurement when a monochromator grating is used.