Synthesis,microstructure and mechanical properties of ZrB2 nano and microparticle reinforced copper matrix composite by in situ processings

Copper matrix composite reinforced with ZrB₂ particles was prepared by in situ reaction in two different ways: by mechanical alloying and subsequent hot pressing, i.e. mechanical alloying and followed by laser melting process. Microstructural changes during mechanical alloying, hot pressing and laser melting of Cu, Zr and B powder mixtures were studied using scanning electron microscopy and X-ray diffraction. In particular, changes in the Cu particle size, structural parameters of the powder mixtures and formation of new ZrB₂ and CuZr phases during hot pressing, i.e. laser melting were investigated. The mechanisms of in situ formation of reinforcement particles and hardening effects in the copper composite were also studied. Large supersaturation which is possible with laser melting process results in homogeneous nucleation of CuZr precipitates and the presence of finer CuZr precipitates and ZrB₂ reinforcements in the Cu matrix. This affected on significantly higher degree of Cu matrix hardening compared to composites obtained by mechanical alloying and hot pressing.     

Duplex-layered manganese phosphate conversion coating on AZ31 Mg alloy and its initial formation mechanism

A duplex-layered phosphate conversion coating was obtained on AZ31 Mg alloy by substituting NaF bath with a citric bath. The morphology, composition and corrosion resistance of the coating were investigated using SEM, EDS, SPM and electrochemical methods. A three-stage mechanism for initial formation of the coating was proposed: Dissolution of the loose oxide film and deposition of Mg₃(PO₄)₂ and AlPO₄, formation of a composite intermediate layer of Mg₃(PO₄)₂, AlPO₄ and Mg(OH)₂, and deposition of manganese phosphate nuclei followed by growth and lamination of the nuclei. The nuclei preferentially deposit at the Al–Mn phase surface and near the grain boundary.     

Layer-pillared metal-organic framework showing two-fold interpenetration and considerable solvent-accessible channels

Via solvothermal synthesis, the self-assembly of CuCl₂, 1,4-benzenedicarboxylic acid, and N,N′-bis(4-pyridylformamide)-1,4-benzene in DMF generated a layer-pillared metal-organic coordination polymer, which affords two-fold interpenetration and considerable solvent-accessible channels where the guest water molecules reside. Further, the TG and XRD researches disclose that such interpenetrating net stabilized by H-bonds can be maintained up to 350 °C even after the release of free water molecules, and through the calcination and immersion experiments, it is suggested that the guest water molecules in the channels are reversible, which is traced by XRD and IR studies.     

Key R&D activities for development of new types of wrought magnesium alloys in China

Many researchers in China are actively engaged in the development of new types of wrought magnesium alloys with low cost or with high-performances and novel plastic processing technologies. The research activities are funded primarily through four government-supported programs： the Key Technologies R＆D Program of China, the National Basic Research Program of China, the National High-tech R＆D Program of China, and the National Natural Science Foundation of China. The key R＆D activities for the development of new wrought magnesium alloys in China are reviewed, and typical properties of some new alloys are summarized. More attentions are paid to high-strength wrought magnesium alloys and high-plasticity wrought magnesium alloys. Some novel plastic processing technologies, emerging in recent years, which aim to control deformation texture and to improve plasticity and formability especially at room temperature, are also introduced.     

Microwave dielectric properties of LTCC materials consisting of glass–Ba2Ti9O20 composites

Interaction between Ba₂Ti₉O₂₀ microwave dielectric ceramics and BaBSiO glass materials was systematically investigated. BaTi(BO₃)₂ intermediate phase was induced and its proportion increased with firing temperature. Fortunately, the formed BaTi(BO₃)₂ phase does not result in marked degradation on the microwave dielectric properties of the Ba₂Ti₉O₂₀–BaBSiO composite materials. Good microwave dielectric properties (K=13.2, Q×F=1150) were obtained by firing the Ba₂Ti₉O₂₀–BaBSiO (50:50 vol.%) materials at 900 °C for 30 min. Precoating a thin layer of BaTi(BO₃)₂ materials on the Ba₂Ti₉O₂₀ powders prior to processing of the ceramic tapes can markedly suppress the interaction between the Ba₂Ti₉O₂₀ and BaBSiO glass, significantly improving the consistency of the microwave dielectric properties for the low temperature cofirable ceramic (LTCC) materials.     

镁合金表面铝涂层研究新进展

对镁合金表面沉积铝涂层这一镁合金表面处理的新技术进行了总结,分析了传统镁合金表面处理的优缺点以及在镁合金表面沉积铝涂层的优势.最新的在镁合金表面沉积铝涂层的工艺主要有铝粉埋覆扩散法、铝粉刷涂埋覆扩散法、火焰喷涂热扩散法、电弧喷涂热压法、动态金属喷镀法.在对以上沉积原理的分析和理解的基础上,详细阐述了镁合金表面铝涂层的耐蚀机理,并指出了该技术的应用前景和制约其发展的主要因素.     

聚合物熔体在压力振动场中的流变行为

在熔体的流动过程中叠加脉动的压力振幅,研究了压力振动场对聚合物熔体的流动性能的影响。表观黏度随着压力振幅、振频的增加而明显下降,当压力振幅为29.7 M Pa时,高密度聚乙烯(HDPE)、聚丙烯(PP)和丙烯腈-丁二烯-苯乙烯共聚物(ABS)表观黏度最大的降低幅度分别为99%、99%和94.3%;随着振频的增加,黏度迅速下降,当振频大于0.70 H z之后,增加振频对黏度的影响不大,HDPE、PP和ABS表观黏度随振频增加而降低,幅度分别为48.9%、82.9%、66.7%,可见压力振动场能明显地改善聚合物熔体的流动行为。     

基于FEA的加油口成形工艺优化设计

针对加油口成形工艺过程中可能出现的起皱、破裂和回弹现象,采用有限元分析软件Dynaform,对成形工艺参数进行分析,给出相应的拉深工艺优化和模具方案优化,最后通过实验生产出合格产品。     

同步带轮的FCF成形工艺与挤压模设计

针对同步带轮的特点,分析了FCF成形工艺方法,并进行了模具设计,结果显示在同步带轮的成形上,将板料成形与体积成形技术相结合,可以大大提高板料的应用范围,具有显著的技术经济效果。