Thermo-plasticity of high-strength and high-ductility 7050 aluminum ingot

Thermo-plasticity of homogenized 7050 aluminum ingot was investigated by instantaneous tensile tests conducted at different temperatures. The results show that, with the increase of testing temperatures, the strength decreases, and the plasticity increases firstly and then decreases in homogenized 7050 ingot. When the studied alloy is deformed between 380 °C and 420 °C, the deformation resistance is lower and plasticity is better. And the actual heating temperature for ingot before hot extrusion should be controlled between 360 °C and 400 °C. At low tensile temperatures, the deformation structure is mainly composed of dislocation substructure. With the increase of testing temperatures, transgranular fracture transforms into intergranular fracture progressively during deformation. At high tensile temperatures, the grain boundaries are weakened, deformation is concentrated at the grain boundaries and the re-orientation of equilibrium phases at grain boundaries appears.     

单道激光熔覆Ni基合金涂层的组织与性能研究

采用10 kW高功率连续CO2横流激光器在Cr12MoV模具钢表面单道熔覆Ni60AA合金粉末,研究不同激光工艺参数对熔覆层组织和硬度的影响,利用光学显微镜观察熔覆层显微组织,并用自动转塔显微硬度计测量熔覆层显微硬度.结果表明：激光功率的大小对热影响区附近的显微硬度影响不大,扫描速度为400 mm/min时熔覆层次表层硬度可以达到856 HV0.2.熔覆层主要相组织是富Ni的γ-Ni奥氏体枝晶和多元共晶的混合组织,Cr,B等元素的碳化物硬质相弥散分布在基体上.     

MA-AA-AM三元共聚物的阻垢性能

以马来酸酐(MA)、丙烯酸(AA)和丙烯酰胺(AM)为原料,在水相中聚合制备三元共聚物PMAA,从因素效应方面综合研究其阻垢性能。实验表明,PMAA对温度有较宽的适应范围,在中酸性和弱碱性条件下能较好地发挥阻垢性能,在高浓缩倍数下亦有良好的阻垢效果。在水样pH=7,温度为80℃,阻垢剂PMAA质量浓度为6mg/L时,恒温10 h,对碳酸钙阻垢率为97.38%,对磷酸钙阻垢率为85.69%;PMAA质量浓度为12 mg/L,对碳酸钙阻垢率可达100%,对磷酸钙阻垢率亦能达96.5%以上。     

一种基于PMI的访问控制模型及其应用

为了加强大型分布式环境下访问控制的管理，该文介绍了一种基于PMI(Privilege Manager Infrdstructure)体系的访问控制模型，并阐述了该模型的特点及其在一类关键型业务系统中的应用。     

丙烯酸与丙烯酰胺共聚制备高吸水纤维的研究

采用溶液聚合法合成了丙烯酸／丙烯酰胺共聚物纺丝液，并纺制成纤维．研究了丙烯酰胺用量、中和度、引发剂用量、聚乙烯醇用量、交联时间等因素对纤维吸水倍率的影响，并用扫描电镜观察纤维的横截面和纵向表面，对制得的高吸水纤维进行SEM分析．     

稀醋酸酐冷凝器的振动分析

原子能工业与化工工艺过程中广泛应用的管壳式换热器、诸如冷凝器、蒸发器以及原子能蒸汽发生器，实际上一半以上都是在两相流状态下操作的。但是目前研究有关两相流诱发振动的资料仍然较少。持续的振动，由于疲劳与磨损将导致管子的破坏。根据两相流诱发振动的机理与有关文献中的实验数据，笔者推荐的振动分析方法可用来预测稀醋酸酐冷凝器的振动。     

时效处理对7050铝合金组织与性能的影响

对7050铝合金进行硬度测试、腐蚀性能测试和透射电子显微分析(TEM),研究了单级时效处理对合金组织与性能的影响。实验结果表明:7050铝合金具有较强的时效硬化效应。单级时效温度由120℃升高到160℃时,合金时效硬化速度显著加快,合金进入峰时效状态所需时间显著缩短,但合金的峰值点的硬度降低。时效处理后合金晶内析出了大量的尺寸细小的η'相,弥散分布在基体中。合金晶界处析出了粗大的平衡相,成分为MgZn_2,PFZ出现。随着时效温度的升高,合金晶间析出相连续且粗大,PFZ宽化,合金的抗晶间腐蚀性能持续下降。对于剥落腐蚀来说,合金的腐蚀程度不仅与晶界结构有关,还与晶界数量有关,温度上升,合金晶粒尺寸迅速增大,晶界数目显著减少,二者相互作用最终导致了合金的抗剥落腐蚀性能的提高。     

Numerical study of the solution heat treatment,forming, and in-die quenching (HFQ) process on AA5754

An FE model of the solution heat treatment, forming and in-die quenching (HFQ) process was developed. Good correlation with a deviation of less than 5% was achieved between the thickness distribution of the simulated and experimentally formed parts, verifying the model. Subsequently, the model was able to provide a more detailed understanding of the HFQ process, and was used to study the effects of forming temperature and speed on the thickness distribution of the HFQ formed part. It was found that a higher forming speed is beneficial for HFQ forming, as it led to less thinning and improved thickness homogeneity.     

Electrocatalytic behaviour of titanium implanted with nickel and molybdenum ions

Abstract

The electrocatalytic activity of titanium induced by ion implantation has been investigated. Ion implantation was carried out using a metal vapour vacuum arc source ion implanter at room temperature. Nickel ion implantation was followed by molybdenum ion implantation at doses ranging from 1 × 10¹⁶ to 1 × 10¹⁷ ions/cm² at the same average extracting voltage of 45 kV. The concentration profiles of Ni and Mo ions in the near surface were detected by electron probe microanalysis and X-ray photoelectron spectroscopy. The catalytic behaviour of implanted titanium was determined by an electrochemical method. Potential versus current density curves for the cathodic hydrogen evolution reaction indicated that Ni and Mo ions implanted into titanium electrodes resulted in a low hydrogen overvoltage of 110-180 mV (at a current density of 200-400 mA cm^-2 in 30 wt-%KOH at 25°C) and excellent stability. The electrocatalytic activity induced by ion implantation can be explained provisionally by interactions between Ni and Mo ions and the titanium substrate.     

Die quenching limit of AA2024 aluminum alloy billet on servo press

Die quenching of AA2024 aluminum alloy billets was carried out on a servo press with ram-motion control of WC-20 mass%Co dies directly after solution heat treatment (SHT). To clarify the dependence on billet size for die quenching, two billets with a height of h₀ = 8 mm or 16 mm and with the same diameter of 16 mm were prepared. The cylindrical billets were heated in an electric furnace at 823 K and transferred to the press. Then the billets were uniaxially compressed with a reduction in height (Δh/h₀) of 2% or 5%, and further held between the dies. The sandwiching duration by dies (t_d.q.) was varied from 0 to 8 s. Based a measured temperature change, hardness and TG–DTA analysis, it is found that die quenching is successfully carried out without precipitation hardening only in the case of the billet with a height of 8 mm and t_d.q. > 6 s. The reduction in height is limited less than 5% by intergranular fracture on side surface of billet during the die quenching process.