Microstructure evolution and bio-corrosion behaviors of as-cast Mg-3Zn-0.4Zr-xY (x = 0, 1, 2, 3 and 4 wt.%) alloys were studied by using optical microscope, x-ray diffractometer, transmission electron microscopy, scanning electron microscope, immersion test and electrochemical measurement. Results indicated that yttrium addition led to significant grain refinement and to the formation of I-phase (Mg 3 YZn 6 ) and W-phase (Mg 3 Y 2 Zn 3 ). The volume fraction of I-phase is dramatically increased after 2 wt% yttrium addition, and the corrosion resistance is improved, while further addition reverses the effect, due to the rising W-phase, which increases the amount of cathodic sites and accelerates the galvanic corrosion process.

In power system, when a transmission line need to be tripped from the network for some reasons , it maybe lead to some other transmission lines being overload, especially for its associated lines. Overload of transmission lines are considered as one of the most important factors which result in further deterioration of the cascading failures in power systems. This paper introduces the breadth-first traversal principle firstly. The breadth-first traversal method is used to detect whether the island exist or not in the operating reliability assessment. Secondly, the transmission lines reliability model based on realtime operating conditions is built up. Finally, the reliability evaluation for IEEE 14-Bus test system under different operating states is conducted by using of the proposed algorithm. The calculation results illustrate that the indices can reflect the real time system state and provide operators with early warning information which points out the weakness of the power system.

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