预轧制路径对ZK60镁合金力学性能的影响

采用低轧制压下量的预冷轧(<3%)来改善轧制ZK60板的力学性能。详细研究轧制路径对力学性能的影响。沿横向的预冷轧和沿法向的预冷轧均可提高屈服强度。但是,在改善综合力学性能方面,沿横向预冷轧比沿法向预冷轧更为有效。预冷轧3%的压下量后,沿横向轧制的样品和沿法向轧制的样品具有相近的拉伸屈服强度(〜270 MPa)。但是,前者比后者具有更高的压缩屈服强度、更低的屈服不对称性和更好的韧性。此外,预冷轧还可以增强沉淀硬化效果。但是,时效处理不能进一步提高预冷轧样品的屈服强度。最后,讨论相关的机理。

Dynamic compressive property and failure behavior of extruded Mg-Gd-Y alloy under high temperatures and high strain rates

For the purpose of investigating the dynamic deformational behavior and failure mechanisms of magnesium under high strain rates,the Split Hopkinson Pressure Bar(SHPB)was used for investigating dynamic mechanical properties of extruded Mg-Gd-Y Magnesium alloy at ambient temperature(300 K),200℃(473 K)and 300℃(573 K)temperature.The samples after compression were analyzed by scanning electron microscope(SEM)and metallographic microscope.Dynamic mechanical properties,crack performance and plastic deformation mechanism of extruded Mg-Gd-Y Magnesium alloy along the extrusion direction(ED)were discussed.The results show that,extruded Mg-Gd-Y Magnesium alloy has the largest dynamic compressive strength which is 535 MPa at ambient temperature(300 K)and strain rate of 2826 s^(−1).When temperature increases,dynamic compressive strength decreases,while ductility increases.The dynamic compression fracture mechanism of extruded Mg-Gd-Y Magnesium alloy is multi-crack propagation and intergranular quasi-cleavage fracture at both ambient temperature and high temperature.The dynamic compressive deformation mechanism of extruded Mg-Gd-Y Magnesium alloy is a combination of twinning,slipping and dynamic recrystallization at both ambient temperature and high temperature.

Dynamic tensile and compressive properties of vacuum and ordinary die-casting AT72 magnesium alloy at high strain rates

To investigate dynamic tensile and compressive properties of AT72 magnesium alloys under high strain rates,the Split Hopkinson tensile Bar(SHTB)and the Split Hopkinson Pressure Bar apparatus was used at ambient temperature.The specimens after dynamic tension and dynamic compression were analyzed by scanning electron microscope(SEM)and metallographic microscope.Dynamic mechanical properties and fracture mechanism were discussed in this paper.The results show that at approximate tensile strain rate,the dynamic tensile strength of ordinary die-casting AT72 and vacuum die-casting AT72 is very similar,but the dynamic failure strain is of great difference.AT72 magnesium alloys under dynamic compressive yield continuously,and have the slight positive strain rate effect.The dynamic compressive behaviors of ordinary die-casting AT72 and vacuum die-casting AT72 are nearly the same.The dynamic tensile fracture mechanism of both vacuum die-casting AT72 and ordinary die-casting AT72 is inter-granular fracture.The dynamic compressive fracture mechanism of both vacuum die-casting AT72 and ordinary die-casting AT72 is quasi-cleavage intra-crystalline failure.The pores have an important effect on dynamic properties of die casting magnesium alloys.

The LEGUE disk targets for LAMOST's pilot survey

We describe the target selection algorithm for the low latitude disk por- tion of the LAMOST Pilot Survey, which aims to test systems in preparation for the LAMOST spectroscopic survey. We use the PPMXL astrometric catalog, which provides positions, proper motions, B/R/I magnitudes （mostly） from USNO-B and d/H/Ks from the Two Micron All Sky Survey （2MASS） as well. We chose eight plates along the Galactic plane, in the region 0° 〈 α° 〈 67° and 42° 〈 δ 〈 59°, which cover 22 known open clusters with a range of ages. Adjacent plates may have some small overlapping area. Each plate covers an area of 2.5° in radius, with its cen- tral star （for the Shack-Hartmann guider） brighter than 8th magnitude. For each plate, we create an input catalog in the magnitude range 11.3 〈 Imag 〈 16.3 and Bmag available from PPMXL. The stars are selected to satisfy the requirements of the fiber positioning system and have a uniform distribution in the I vs. B - I color-magnitude diagram. Our final input catalog consists of 12 000 objects on each of eight plates that are observable during the winter observing season from the Xinglong Station of the National Astronomical Observatory of China.